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The pathology and radiology of solitary benign bone tumors
The Pathology and Radiology of Solitary Benign Bone Tumors By JAMES R. STEWART, M.D., DAVID C. DAHLIN, M.D. AND DAVID G. PUGH, M.D.
T
HE LESIONS presented in this section are classified in Table 1 according to cellular origin. Not all of the entities classified are neoplasms in the strict sense. Nevertheless, a presentation of benign bone tumors would be incomplete without including these allied conditions. Space limitations prevent an all-inclusive classification, and some of the rarer or less related tumors and tumor-like conditions have been excluded. Notable among the exclusions are neurilemmomas, lipomas, and diverse and complicated angiomatous processes in bone. The role of the radiologist in the evaluation of a bone tumor includes locating the lesion, determining its extent, determining whether it is benign or malignant, and, ideally, specifically naming it. Determining whether a lesion is benign or malignant is the most important function of the radiologist (Table 2). Some are obviously benign and biopsy is unnecessary. Others are difficult to assess microscopically, even with adequate biopsy tissue, and experienced bone pathologists refuse to render an opinion without knowing more about the gross appearance of the lesion as seen radiographically. An accurate radiographic assessment, therefore, is an integral part of good management of patients with bone tumors, whether or not biopsy is necessary. To recognize specifically what type of bone tumor is present is of course the ultimate desire of the radiologist, but this is often not possible. Just as important is to know the limitations of the roentgenographic examination. When a difficult or unusual lesion is encountered, an approach that has proved helpful in our experience is to review the current classification of bone tumors, testing the unknown against those in the classification, taking into consideration the specific roentgenographic features, the location of the lesion, and the age of the patient. Often, by exclusion, only one logical diagnosis remains. A few general comments are in order with regard to our presentation of this subject. The relative sex incidence of the various bone lesions will not be mentioned since any difference is not sufficiently great to be of diagnostic value. Seldom shall we comment on the treatment or prognosis, as we do not feel well qualified, and there is insufficient data as well as much controversy in these areas. However, evidence is mounting that malignant transformation is more likely to occur if irradiation is employed, and it would seem wise to avoid this modality of treatment. From the Mayo Clinic and Mayo Foundation, Rochester, Minn. (Drs. Stewart and Pugh) and of Surgical Pathology (Dr. Dahlin).
Section of Roentgenology
SEMINARS IN ROENTGENOLOGY,VOL. 1, No. 3 (JULY), 1966
PATHOLOGY
AND RADIOLOGY
Table l.-Solitary
Benign Tumors and Tumor-like
FIBROGENIC:
ORIGIN
Table 2.-Roentgenographic
Internal architecture Periosteal reaction
Calcification or ossification Secondary signs
Location
UNKNOWN:
Giant cell tumor Aneurysmal bone cyst Simple bone cyst
Osteochondroma Enchondroma Benign chondroblastoma Chondromyxoid fibroma
Extent
of Bone
Osteoma Osteoid osteoma Benign osteoblastoma
CHONDROGENIC:
Margin
Lesions
OSTEOGENIC:
Cortical defect Nonosteogenic fibroma Fibrous rest Fibrous dysplasia
Feature
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Signs of Benignancy
Smooth, sclerotic or scalloped. Distinct Well circumscribed. Confined to medullary cavity or by cortex or periosteum
Organized, eroded, homogeneous or evenly trabeculated Sometimes present but seldom of degree or nature seen in malignant tumors. More striking in pathologic fracture. Organized. Focal or homogeneous distribution Evidence of chronicity; present on previous films with little change, or showing impairment of remodeling of bone Epiphyseal and small tubular bone tumors less likely to be malignant FIBFKIGENIC
and Malignancy Malignancy
Benignaney
Absent, ill-defined or sharply destructive Medullary involvement primarily. Extension along medullary cavity, or subperiosteally,or through cortex and periosteum. Unconfined soft-tissue mass Bizarre, mottled, or destroyed. Moth eaten Frequent, but may be absent. Irregular, interrupted, and more extensively layered, or with spiculation Disorganized, irregular. No pattern of distribution. May show streaking or whorling No evidence of chronicity. Acute osteoporosis suggesting active growth (if no fracture present) See text regarding chondrogenic group
TUMORS
Definition. Fibrogenic tumors (Table 1) are focal collections of nonspecific fibrous tissue located predominantly or entirely in the cortical portion of bone. Differing in several respects from true neoplasms, they are apparently related conditions resulting from local errors in osteogenesis. They differ from each other primarily in their biologic behavior and roentgenographic appearance. Cortical Defect Clinical Features. The term “cortical defect” has been popularized by Caffeyl in reference to the common, small, oval or round cortical lesion that originates in the metaphysis of the shaft of a long bone in normal children. In studies by Sontag and PylelO and by Caffey,l they were not seen before 18
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months of age but occurred in 40 to 50 per cent of normal children after 3 years of age. Cortical defects are most common in the metaphyses about the knee, particularly on the posterior medial aspect of the distal femur. Although they vary extremely in behavior, they most commonly diminish gradually in size and eventually disappear. Roentgenographic Features. The cortical defect appears as an oval or round rarefaction in or near the metaphysis (Fig. 1). Viewed tangentially, the defect is seen as a shallow concavity in the cortical wall. If oval, its long axis is parallel to that of the shaft. Cortical defects are usually 1 to 2 cm in diameter. The central rarefaction is either homogeneous throughout or partially compartmentalized. The inner margin of the defect is a smooth or slightly scalloped thin line of increased density. Occasionally, in the lower medial part of the femur it shows a loss of overlying cortex but the characteristic location and the age at which it occurs make its benign nature evident to those who are aware of this variation. The radiographic appearance of older lesions is variable and depends on their mode of resolution. Nonosteogenic Fibroma (nonossifying
fibroma)
Clinical Features. A much less frequent condition, first described by Jaffe and Lichtenstein’l is nonosteogenic fibroma. It is larger and more stable than the cortical defect, often trabeculated and characteristically located a few centimeters away from the metaphysis. Accurate figures on its true incidence are not available since it rarely produces symptoms and therefore is seldom radiographed. Nonosteogenic fibroma occurs predominantly, if not exclusively, in the long bones, especially those of the lower extremity. Most are seen in older children and young adults. Pathologic fractures are rare. Roentgen Features. Nonosteogenic fibromas appear similar to cortical defects but are larger, extend more deeply into the spongiosa, are further removed from the metaphysis, and characteristically have a thicker sclerotic shell (Fig. 2). The distinction between nonosteogenic fibroma, a large, older cortical defect, and monostotic fibrous dysplasia is of little importance. NO true bone tumor closely resembles this lesion unless its appearance is altered by a pathologic fracture. Fibrous Rest There still remains a hodge-podge of small fibrous defects that do not concisely fit into the above two categories. These common lesions are small and so innocuous in appearance that they are usually ignored by the radiologist. While the term fibrous rest seems to mean different things to different people, it most commonly is applied to these nondescript rarefactions. PATHOLOGIC FIBROUS
REST.
FEATURES
OF
CORTICAL
The tissue of cortical
DEFEa,
NONOSTEOGENIC
defects and fibroma
FIBROMA,
AND
is soft and often
PATHOLOGY
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Fig.
l.-Cortical
271
defect in lower part of tibia
of an 8 year old girl.
yellow, owing to its lipid content. Microscopically, there are interlacing fascicles of benign fibroblasts in collagenous tissue. Benign giant cells are present, usually in a somehat patchy distribution. Foam cells are often seen, sometimes in prominent clusters. The fibrous rests are zones of hypocellular, dense, fibrous tissue resembling a scar. Monostotic
Fibrous Dyspiksia
Definition. Even though the clinical stigmata are lacking in the monostotic form, this condition is considered a variant of generalized fibrous dysplasia. Clinical Features. Pain, particularly if the lesion is located in a weightbearing bone, is common. Pathologic fracture, swelling, deformity or incidental discovery accounts for detection of most of the remaining cases. At the time of discovery, nearly half the patients are adolescents, the remainder being fairly evenly distributed throughout life. Sites of predilection are the maxillofacial bones, skull, rib, femur, and tibia. The most common solitary benign lesion of a rib recorded in our pathologic files is monostotic fibrous dysplasia (Fig. 3). Roentgen Features. Monostotic fibrous dysplasia resembles the larger of the fibrous lesions just discussed. Basically, however, it is an intramedullary rather than a cortical rarefaction (Fig. 4). The distribution of monostotic fibrous dysplasia in the skeleton is also different, but when it does occur in the long tubular bones it lacks the striking affinity for the parametaphyseal region so characteristic of the other fibrous lesions. Of importance is the recognition of monostotic fibrous dysplasia in the facial bones, skull and ribs. The expanding,
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Fig. Z.-Nonosteogenic fibroma. Characteristic features are sclerotic margin, predominantly cortical location, large size, and slight separation from metaphysis.
deforming, obviously benign appearance is usually quite characteristic and few other conditions that occur in these areas resemble it. Pathologic Features. The dense collagenous tissue of fibrous dysplasia is characteristically gritty because of bony trabeculae which may be so abundant that the roentgen shadow is radiopaque. Myxoid degeneration and even extensive cyst formation may develop. Foci of metaplastic osteoid in the fibrous tissue distinguish fibrous dysplasia from the other fibrous processesin bone. CHONDROGENIC
TUMORS
Osteochondroma (0steocartiluginou.s Exostosis) Definition. Osteochondroma is a projection whose base consists of a continuation of the adjacent cortex and underlying spongiosa. It has a cartilaginous cap, which is the potentially neoplastic portion. Clinical Features. Solitary osteochondroma is a common benign bone tumor. It develops during the period of most active enchondral bone growth and is most often detected during the second decade of life. Any juxta-epiphyseal area may be involved but the most common locations are the femoral and tibia1 metaphyses near the knee. The patient usually notices a firm swelling or has pain from repeated trauma to the bony protrusion. Rarely, the tumor impinges on a major nerve or artery, or the stalk may fracture. Pelvic osteochondroma may cause dystocia. Roentgen Features. In the long bones, solitary osteochondroma presents typically in two common forms. One resembles a cauliflower, with a narrow stalk and a bulbous, somewhat irregular tip (Fig. 5) The other form is sessilr:
PATHOLOGY
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Fig. 3 (Top).-Solitary
OF
BONE
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TUMORS
lesion of fibrous dysplasia
in the posterior portion of the
right eighth rib of a 44 year old man. Fig. 4 (Bottom).-Solitary
lesion of fibrous dysplasia
in the left femoral neck.
with a broad base on the shaft and with a relatively smooth outer apex (Fig. 6). Osteochondroma of the pelvis may present as a large, popcorn-ball area of calcification resembling a calcified uterine fibroid, particularly if the site of attachment cannot be identified (Fig. 7).
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The finding of an osteochondroma should suggest the possibility of multiple familial cartilaginous excstoses. No other bone tumor closely resembles an osteochondroma. The radiologist’s contribution lies chiefly in recognizing signs suggestive of malignant transformation. These include (1) marked irregularity of the cartilaginous cap, (2) a soft-tissue mass projecting beyond the expected confines of the lesion, (3) flecks of calcification in the soft tissues beyond the lesion, and (4) rapid growth of the lesion revealed on serial films. Pnthologic Features. The cartilaginous cap merges with the underlying bony trabeculae. The cortex of the parent bone flares to become the cortex of the tumor, which encloses fatty or hematopoietic marrow. The cartilaginous portion tends to involute in adults. Enchondroma Definition. An enchondroma is a benign neoplasm arising in the medullary portion of the bone, composed chiefly of mature hyaline cartilage. It is probably the most common benign bone tumor, although few are proved by operation. Clinical Features. The age incidence of this neoplasm is fairly evenly distributed through the second to fifth decades. Any bone preformed in cartilage may house an enchondroma but those more frequently afflicted are the phalanges of the hands (50 per cent), metacarpals, phalanges of the feet, metatarsals, humerus and femur. A history of spontaneous swelling, or of pain and swelling following local trauma, is usually given by the patient with phalangeal, metacarpal, or metatarsal enchondroma. Local pain aggravated by motion accounts for detection of some enchondromas of the large bones. Still others are discovered as a result of pathologic fracture, or incidentally on roentgenographic examination obtained for other reasons. It is usually apparent from the roentgenogram that the tumor has been present for a much longer time than the clinical history indicates, since modeling of the bone is often altered. Roentgen Features. Typically, enchondromas are intramedullary tumors situated near the end of a diaphysis. In the small tubular bones, the entire shaft often undergoes lobulated expansion (Fig. 8). In spite of the moderately expansile nature of the tumor, the outer cortex is preserved as a distinct limiting shell. The cavity usually contains a variable quantity of coarse, flocculent calcification superimposed on a faintly translucent background. Another pattern, which, in our experience, occurs exclusively in the large tubular bones, is that of a conglomerate area of calcification without a lytic component (Fig. 9). The diagnosis of bone infarct is often suggested roentgenographically for lesions with this appearance, but the few we have subjected to biopsy have all shown histologic changes typical of enchondroma. A less common but characteristic location of a chondroma is immediately beneath the periosteum- the so-called subperiosteal chondroma (Fig. 10). In this location, there is, of course, no limiting cortical shell, but the tumor is sharply localized and does not invade the soft tissue. Calcification is also
PATHOLOGY
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Fig. 5 (Top left) .-Cauliflower-shaped osteochondroma Fi g. 6 (Top right) .-Broad-based
osteochondroma.
of humerus of an 8 yeaLr old
boy. Fi ig. 7 (Bottom).-Large
a 25 year old woman.
intrapelvic
osteochondroma
which caused dystoc:iaL in
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absent. As indicated, the location is a most characteristic feature, Subperiosteal chondroma often causes a fairly typical, smoothly scalloped erosion of the underlying cortex. Enchondroma is seldom difficult to differentiate from other benign tumors, Determining whether the neoplasm is potentially malignant or has already undergone transformation into a chondrosarcoma is a more important contribution. Fusiform widening of the shaft, especially if associated with cortical sclerosis, is an ominous feature, particularly if any degree of pain or ache is present. Pathologic Features. The cartilaginous tissue is often lobulated and may be slightly to heavily mineralized as a result of ossification or degenerative calcification. The chondrocytes have small and usually single nuclei. Differentiation from chondrosarcoma depends on nuclear abnormalities in conjunction with clinical and roentgen signs of aggressiveness. Treatment and Prognosis. Enchondromas of the large tubular bones that show flocculent calcification without a lytic element and enchondromas of the small tubular bones rarely become malignant. Thus, treatment is necessary only if the lesion is painful, prone to fracture, or causes mechanical difficulty. In contrast, fusiform, rarefied enchondromas of the large bones, particularly if generous in size, should be suspected of being malignant. Lesions of the acetabular region terminate as chondrosarcomas alarmingly often and should be treated accordingly. Benign Chondroblastoma Definition. Benign chondroblastoma is a tumor of bone thought to originate from primitive epiphyseal cartilage cells. First described by Ewing5 and Codman2 as a variant of giant cell tumor, this neoplasm was recognized as a distinct clinicopathologic entity in the early 1940’s.12 Clinical Features. Benign chondroblastoma is rare before 10 years of age and may be seen as late as the sixth decade of life. The majority are recognized in patients from 10 to 30 years of age, but usually before enchondral bone growth ceases. Benign chondroblastoma is an epiphyseal tumor. Although the flat bones of the axial skeleton are occasionally involved, the long bones are the most frequent site, especially the upper end of the humerus, the lower end of the femur, and the upper end of the tibia. Mild chronic local pain in the bone or adjacent joint, often historically related to incidental trauma, is the most common clinical feature. Roentgen Features. When encountered in a long bone, benign chondroblastoma is round or oval and its epiphyseal origin is obvious-an important observation since few other lesions arise from the epiphysis (Fig. 11). One should not exclude epiphyseal origin of a lesion confined to a tuberosity of the humerus or trochanter of the femur, since the tuberosity and the trochanter are each formed from an epiphysis (Fig. 12). After fusion of the epiphysis and the diaphysis, the tumor may extend into the latter but its epiphyseal origin USUally remains evident. The central portion of a benign chondroblastoma is not trabeculated and is
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Fig. 8 (Top left) .-Enchondroma
of proxi-
mal phalanx of a 24 year old woman. Fig. 9 (Bottom left) .-Enchondroma. The radiolucent component is not very obvious in this almost completely calcified variety. 10 (Bottom Fig. chondroma. Marginal
right).-Subperiosteal
reflections indicate an origin between periosteum and cortex. The cortex is eroded from without. The external limiting membrane is periosteum.
either uniformly rarefied or contains irregular patches of mottled calcification. Periosteal reaction may occur in larger lesions but is uncommon. Pathologic fracture is almost nonexistent. In flat bones the roentgen diagnosis is di5cult because the epiphyseal origin and characteristic roentgen features are not so evident. The tumors that most frequently resemble benign chondroblastoma are chondrosarcoma, enchondroma and giant cell tumor.
STEWART,
occupying Fig. 11 (Left).-Benign chondroblastoma epiphysis. Epiphysis and diaphysis have not fused.
DAHLIN,
most of right
PUGH
humeral
Fig. 12 (Right) .-Benign chondroblastoma arising from epiphysis of greater trochanter. The tumor was first discovered after enchondral bone growth had ceased.
It was not possible, therefore, to exclude giant cell tumor. (From Plum, G. E., and
Pugh, D. G.: Roentgenologic aspects of benign chondroblastoma of bone. Am. J. Roentgenol. 79:584-591,
1958. Reproduced with
permission of the publisher,
Charles C Thomas.) Pathologic Features. This soft, granular tumor may be grossly chondroid and partially calcified. Cellular zones very similar to those of giant cell tumor shade into the diagnostic chondroid islands which may show focal degeneration and calcification. We do not recognize a spontaneous malignant counterpart, but sarcoma has developed after irradiation of benign chondroblastoma. Chondromyxoid Fibroma Definition. Chondromyxoid fibroma, first described by Jaffe and LichtensteinI in 1948, is a benign tumor thought to originate from cartilage-forming connective tissue. Clinical Features. The frequency of recognition of chondromyxoid fibroma peaks in the second and third decades of life, a period in which approximately two thirds of these lesions are encountered. Eighty per cent of chondromyxoid fibromas occur in the long bones of the lower extremities. The flat bones and the long bones of the upper extremities account for most of the remaining cases. Because chondromyxoid fibroma is usually relatively small and eccentrically located, pathologic fracture seldom occurs. Pain is the most common presenting complaint.
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Roentgen Features. Since the majority are encountered in the long tubular bones and since, when we have encountered them elsewhere there were too few differential features to permit us to recognize them, the roentgen description will be confined to the appearance as seen in the shaft of a long bone. A chondromyxoid fibroma is an oval, eccentric lesion situated in the metaphyseal portion of the diaphysis, abutting the epiphyseal cartilage. The center is usually uniformly rarefied. The wall is sometimes smooth but more often scalloped. The cortex is characteristically expanded and is either very thin or no longer visible, even though the tumor is always restrained by the periosteum. In the majority of cases there is a definite thin sclerotic rim between the tumor and the adjacent normal medullary bonezl (Figs. 13 and 14). The differential diagnosis includes aneurysmal bone cyst, giant cell tumor, benign chondroblastoma, enchondroma, simple bone cyst and nonossifying fibroma. An important contribution of the radiologist in the roentgen evaluation of patients with chondromyxoid fibroma is to recognize that the lesion is benign and to alert the pathologist to the possibility of chondromyxoid fibroma, since histologically the lesion resembles chondrosarcoma. Pathologic Features. This lobulated tumor is grossly cartilaginous and sharply demarcated from adjacent bone. A histologically characteristic mixture of chondroid, myxoid, and fibromatoid elements makes’ up this lesion. Nuclear abnormalities mimic those of chondrosarcoma when viewed out of context or without the knowledge of the benign roentgen appearance: OSTEOGENIC
TUMORS
Osteoma Definition. Osteomas are benign tumors of osteoblastic mesenchyme and consist predominantly of dense, compact, mature bone. As defined, such conditions as unpneumatized compartments of sinuses, osseous reactions to various stimuli, bone islands, and ancient ossified bone tumors and cysts are excluded. Clinical Features. Osteomas occur later in life than most benign tumors, being more frequent in adults than in children. They are found almost exclusively in the paranasal sinuses (particularly the frontal sinus), calvarium and mandible. Sinus osteomas may obstruct drainage but, in our experience, this is uncommon and many are incidental roentgenographic observations. Being extremely hard tumors, those that arise from the external table of the skull or from the mandible are easily felt, even when they are small. Roentgen Features. Being well circumscribed and the most dense of all tumors, osteomas are seldom difficult to recognize (Fig. 15). Those that arise from the inner surface of the skull cannot be distinguished with certainty from a meningiomatous reaction. Fortunately, tangential views of the skull demonstrate that most osteomas arise from the outer table or its periosteum, with the bulk of the lesion projecting outward. Osteomas of the sinuses are sometimes less dense and more lobulated (Fig. 16). A non-pneumatized ossified compartment of the frontal sinus is usually
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Fig. 13 (Above, A and B.)-Chondromyxoid fibroma of upper tibia. There is marginal condensation along inner border of tumor, which is usually absent in aneurysmal bone cyst. (From Turcotte, B., Pugh, D. G., and Dahlin, D. C.: The roentgenologic aspects of chondromyxoid fibroma of bone. Am. J. Roentgenol. 87: 1085-1095, 1962. Reproduced with permission of the publisher, Charles C Thomas. ) Fig. 14 (Bottom left) .-Chondromyxoid fibroma of lower tibia. Lower margin abuts upon epiphyseal cartilage. A tiny satellite lesion can be seen above the primary site of involvement. (From Turcotte, B., Pugh, D. G., and Dahlin, D. C.: The roentgenologic aspects of chondromyxoid fibroma of bone. Am. J. Roentgenol. 87: 1085-1095, 1962. Reproduced with permission of the publisher, Charles C Thomas. )
distinguishable from a true osteoma since the corresponding segment of frontal bone that should be pneumatized is not. Rarely, a large osteoma will arise from a long tubular bone and resemble a parosteal osteogenic sarcoma, in which instance total removal is wise since the prognosis of such an atypical osteoma is unknown. Any osteoma in an unusual location raises the possibility of Gardner’s syndrome (polyposis of colon, soft tissue cysts or tumors, and osteomata). This applies especially to multiple
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Fig. I5 (TOP) .-Ivory osteoma of mandible, which had been present for 15 years. Fig. 16 (Bottom).- Osteoma of frontal sinus, somewhat lobulated. osteom as occurring
on the long tubular bones, but Gardner’s syndrome shol Ad also be suspected when osteoma of the mandible is seen. Path alogic Features. Osteomas are composed of dense bone con taini “g benign osteocytes. Sometimes a fibrous component is present and sug gest:s a relatior lship to fibrous ( fibro-osseous) dysplasia.
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Osteoid Osteoma Definition. Most observers regard osteoid osteoma as a true neoplasm of bone rather than an infection or foreign body reaction, in spite of its unusuai gross appearance and limited growth potential. Jaffe,a who coined the term “osteoid osteoma” in 1935, believed it arose from osteoblastic mesenchyme, which has the ability to produce large quantities of osteoid. These cells and their by-products make up what is commonly referred to as a nidus. The surrounding sclercsis, which may or may not be present and disappears when the nidus is removed, is a secondary reaction, Clinical Features. Osteoid osteoma has been observed in almost every bone in the body except the calvarium but is most common in the long tubular bones, especially the femur and tibia. It exhibits a peak incidence in the second decade of life and is distinctly uncommon after 35 years of age. Boring pain slowly but relentlessly becomes more intense, is often worse at night, and may dramatically be diminished by use of salicylates. Atrophy and weakness of an extremity, causing unstable gait or limp, may also be present and occasionally constitute the chief complaint. Fever, leukocytosis and elevation of the sedimentation rate are usually absent. Mild to moderate tenderness over the nidus is common but local warmth and swelling are infrequent. When the classic clinical features are present, the diagnosis seldom poses a problem, but in atypical cases the patients have frequently been labeled as malingerers or operated on for what was thought to be a herniated intervertebral disk. Roentgen Features. Most osteoid osteomas produce a typical roentgen appearance, that is, a small radiolucent or partially calcified nidus encoffined by osteosclerosis (Fig. 17). Periosteal reaction is present if the lesion is near a cortical surface. The sclerosis may be so intense that the nidus is obscured. The only lesion that has perfectly, though rarely, mimicked a typical osteoid osteoma in our cases has been focal osteomyelitis. Ewing’s tumor, histiocytosis X, and stress fracture produce sclerosis and periosteal reaction but the composite picture of each of these lesions is usually quite dissimilar. Intramedullary osteoid osteoma, unfortunately, often stimulates little or no osteosclerosis or periosteal reaction. Its nidus may be extremely difficult to see, particularly when located in coarse cancellous bone, and here its detection can be likened to finding a small bullet hole in the honeycomb of a bee hive! It is essential, in patients who clinically might have an osteoid osteoma, to obtain well-localized stereoscopic views and tomograms of the painful region when the routine films appear negative. The most insignificant-appearing alteration in trabecular pattern may prove to be a nidus at operation (Fig. 18). A group of our patients had clinical and roentgen findings compatible with or typical of osteoid osteoma but the resected sclerotic block of bone did not yield a nidus on careful microscopic examination. Yet there was dramatic and permanent relief of pain following excision. Although it is likely that the nidus is occasionally destroyed in removal or missed on sectioning, there are too many cases in this group to be accounted for in this manner and the explana-
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Fig. 17 (Left).-Osteoid osteoma. In the center of the rarefied nidus is a small calcific deposit. The usual intense reaction of cortical bone is present. Fig. 18 (Right).-Osteoid osteoma in spongiosa at base of coracoid process of scapula. There is no sclerosis. Patient was a 16 year old girl who had chronic shoulder pain. Only by correlation of the history and repeated films of the scapula was the correct diagnosis established.
tion must lie elsewhere. These are being re-evaluated and are the subject of a more detailed presentation to be published later. Pathologic Features. The nidus is usually discretely outlined in its sclerotic bed. Microscopically there is an interlacing network of more or less mineralized trabeculae mantled by benign osteoblasts. The intervening fibrovascular tissue usually contains a few benign giant cells. Benign Osteoblastoma (Giant Osteoid Osteoma) Definition. Benign osteoblastoma is a tumor composed of numerous osteoblasts and their products, osteoid and bone, deposited in a richly vascular connective tissue stroma. Proper designation of this lesion has been di5cult. Jaffe and Mayer,15 in 1932, used the descriptive name “an osteoblastic osteoid tissue-forming tumor.” In 1954, Dahlin and Johnson4 proposed the term giant osteoid osteoma to denote the histologic similarity to osteoid osteoma and yet set it apart from that lesion by one of its chief differences, its larger size. Benign osteoblastoma is the term most widely adopted and was offered independently by Lichtenstein16*” and by Jaffes in 1956.
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Clinical Features. Benign osteoblastoma occurs chiefly in the second and third decades of life and is an infrequent tumor. Approximately 50 per cent arise in the vertebral column and a few have been observed in the calvarium, a distribution that is in contrast to that of most benign bone tumors.l* The next most common location of benign osteoblastolma is in the long tubular bones. When the lesion is located in the vertebral column, symptoms referable to nerve root or cord compression have been common. In other locations, a dull aching pain usually directs attention to the tumor. Roentgen Features. Because of its relative rarity and variable appearance, benign osteoblastoma has proved to be a difficult tumor to diagnose roentgenographically. It has even been impossible to be certain that some of the more bizarre looking lesions were not malignant neoplasms. It most consistently appears to be an expanded, completely lytic defect or a lytic defect with a variable quantity of irregularly deposited mottled central calcification, often with a thin outer shell of periosteal new bone or marginal sclerosis. In some, an irregular internal architectural pattern may suggest malignancy, but, conversely, a sharply limited and distinct external margin indicates benignancy. This finding may prove to be characteristic of some benign osteoblastomas (Figs. 19 and 20). In a few of our cases the roentgen appearance has resembled that of osteoid osteoma, but in each instance the central radiolucency was considerably larger and more irregular. It is impossible to list a radiographic differential diagnosis until more experience is gained to formulate a better understanding of the variable manifestations of benign osteoblastoma. When one encounters a bizzare osseous lesion, particularly in the spine, which by virtue of its limited extent appears benign and which has some of the characteristics described, benign osteoblastoma should be considered. Pathologic Features. Osteoblastomas are bloody, firm, granular, circumscribed tumors, usually so lightly mineralized that they may be sectioned without decalcification. Sometimes the osteoblastic proliferation is so active that differentiation from osteosarcoma is a problem. Benign giant cells are often abundant and occasionally there are large blood-filled spaces, suggesting a kinship to aneurysmal bone cyst. BONE
TUMORS OF UNKNOWN
ORIGIN
Giant Cell Tumor Definition. The cellular origin of giant cell tumor is unknown and this neoplasm defies simple definition. Numerous other tumors of bone contain giant cells, and in the past many of these have been considered to be giant cell tumors or variants of them. Continued refinement of the clinical, roentgenologic, and pathologic features of this group of neoplasms with removal and recategorization of the nonconforming lesions has caused the evolution of this specific neoplasm as we now know it. To Jaffe, Lichtenstein and Portis14 must go much of the credit for our current concept of giant cell tumor.
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Fig. 19 (Left) .-Benign osteoblastoma showing the most characteristic location and features of this lesion. The tumor is expanding the transverse process and is
both rarefied and sclerotic. The architectural pattern is bizzare, yet the entire process is fairly well circumscribed. Fig. 20 (Right).-Benign osteoblastoma. This case illustrates one of the variations which cannot be distinguished from myeloma, metastatic lesion, or giant cell tumor. Clinical Features. The majority of giant cell tumors are encountered in persons beyond 20 years of age, that is, after fusion of the epiphysis and diaphysis. The peak incidence is in the third decade with a progressively diminishing incidence thereafter. Giant celI tumor is an epiphyseal tumor, but with prolonged growth it commonly extends into the diaphysis. More than half occur about the knee. Other less common but still frequent locations are the pelvis, ulna, radius, humerus and sacrum. Giant cell tumors are infrequent in the spine above the sacrum or in the small bones, skull or ribs. When small, giant cell tumors produce only mild symptoms, pain being the most frequent. With growth, pain and joint disability increase and local swelling and pathologic fractures occur. Roentgen Features. Giant cell tumor is entirely osteolytic, quite expanded and often very destructive. Arising in the epiphysis, it exhibits considerable inclination to encroach upon the articular cortex.? Since the epiphysis and diaphysis are usually fused, there is no barrier to extension into the shaft. The wall may be deeply scalloped which, when seen on the roentgenogram, erroneously suggests that the tumor is compartmentalized. There is no calcihcation within the tumor so that the central portion is rarefied. Osseous condensation is absent at the interface between the tumor and
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normal bone, and this margin, while abrupt, is indistinct. When a giant cell tumor becomes quite large, the cortex may be completely breached and no longer visible. Pathologic fracture with secondary periosteal reaction is common, but periosteal reaction without the presence of a fracture is distinctly uncommon (Fig. 21 and 22). In the long bones the roentgenographic features are fairly reliable. The differential diagnosis includes aneurysmal bone cyst, benign chondroblastoma and fibrosarcoma. The huge giant cell tumors that frequently were mistaken for malignant bone tumors in the past are seldom encountered today, as patients seek medical attention much sooner. Giant cell tumors are less common in flat bones, and when they occur there, the correct radiographic diagnosis can seldom be made with confidence ( Fig. 23). Pathologic Features. These tumors are soft and friable. Multinucleated cells are usually large and numerous. Their nuclei markedly resemble those of the adjacent stromal cells which, in diagnostic zones, are producing nothing but the giant cells. Foci of fibrogenesis or osteogenesis may be present, especially after fracture or therapy. Cytologic features of sarcoma are absent. We have been unable to grade giant cell tumors with the view of predicting ability to recur or to undergo subsequent malignant change. The malignant tumors that develop are fibrosarcoma and osteogenic sarcoma and have been observed in as many as 10 per cent of cases.” Aneurysmal
Bone Cyst
Definition. Aneurysmal bone cyst is a connective tissue-lined cyst of undetermined etiology, containing primarily an interconnecting network of cavernous spaces filled with blood. Because of the numerous giant cells present, aneurysmal bone cyst was originally classified as a variant of giant cell tumor. In 1942, Jaffe and Lichtenstein’O coined the term aneurysmal bone cyst for this lesion, which is now generally accepted as a distinct entity. Clinical Features. Aneurysmal bone cyst is most common in the second decade of life. Mild pain or a gradual awareness of swelling usually directs attention to the lesion. Because the tumor is characteristically located eccentrically, a sufficient amount of normal shaft is usually present so that pathologic fracture is uncommon. Patients with aneurysmal bone cyst of the vertebral column present with back pain and stiffness or with a neurologic deficit. The most frequently involved bones are the long tubular bones, vertebral column, pelvis, scapula, metacarpals, and metatarsals. In the long bones, the metaphyseal portion of the diaphysis is most often afflicted. Roentgen Features. Small aneurysmal bone cysts are radiolucent throughout and have smooth margins. In larger lesions, the periphery begins to show faint lobulation as the wall becomes more attenuated. Eventually, the cortex is completely eroded in areas so that the periosteum is the limiting membrane. Viewed tangentially, that portion of the cyst that projects beyond the bone at times shows a fine cobweb-like network of interlacing curved lines projecting through the lesion and along its periphery (Fig. 24). Periosteal reaction is common and frequently striking in aneurysmal cysts of
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Fig. 21 (Top left).-Giant cell tumor. The lesion extends downward close to the articular cortex. Fig. 22 (Top right).-Giant cell tumor of distal part of ulna showing how destructive this condition may be. The proximal margin is abrupt. Fig. 23 (Bottom left).-Giant cell tumor is relatively common in the sacrum and produces a more characteristic appearance than when it occurs in other flat bones. the long bones. This, along with a breached cortex, imparts a malignant appearance, but when judged in proper balance so far as the other features of the lesion are concerned, the mistaken diagnosis of malignant disease can usually be avoided. The junction between the cyst and spongiosa is sharp but usually lacks the fine zone of marginal condensation seen in chonclromyxoid fibroma. This sometimes is the only differential clue between these two lesions.
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Fig. 24 (Left).-Aneurysmal bone cyst. No marginal condensation at interface of tumor and normal bone. A fine trabecular lattice is evident throughout the cyst and there is periosteal reaction above and laterally. bone cyst ballooning out a considerable length Fig. 25 (Right) .-Aneurysmal of ischium.
tubular bones, an eccentric location is seldom recognizable, as the cyst soon enlarges to such a size that the entire circumference of the shaft is expanded. Aneurysmal bone cyst is rather effectively limited to the metaphysis unless the epiphysis and diaphysis have fused, in which event this barrier is no longer present to prevent epiphyseal extension. In the spinal column and flat bones, the expansile character of aneurysmal bone cyst is more prominent. The cyst tends to extend along the anatomic contour of the bone, progressively ballooning out the cortex (Fig. 25 and 26). More aggressive aneurysmal bone cysts, however, pay little respect to natural boundaries, and extension by erosion from one adjacent bone to another is a most conspicuous feature in the spine, where several contiguous vertebrae may be destroyed. The tumors which resemble aneurysmal bone cyst are giant cell tumor and chondromyxoid fibroma. Pathologic Features. This tumor may have solid zones that resemble osteo‘blastoma or even fibrous giant cell tumor. Demonstration of the spaces that in vivo contained blood and are often separated by fibrous septa is essential to diagnosis. Blood welling up into the surgical wound is characteristic, but there In smaller
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289
Fig. 26.-Aneurysmal bone cyst of body, pedicle, lamina and transverse process of third lumbar vertebra. Vertebra plana is occasionally produced by such aneurysma1 bone cyst but expansion of the transverse process excludes the possibility of histiocytosis X.
is evidence to suggest that in older aneurysmal bone cysts the blood may be replaced by a yellowish, clear fluid. Simple Bone Cyst ( Unicameral Bone Cyst) Definition. Simple bone cyst was first described by Virchow22 in 1876. It is not a neoplasm but a connective-tissue-lined cyst. The etiology has not been satisfactorily resolved. Clinical Features. Simple bone cyst usually develops in the first or early part of the second decade of life and enlarges rather rapidly initially and more slowly thereafter. Growth tends to cease at about the time of epiphyseal fusion. The site of origin is the diaphyseal side of the metaphysis and the tumor remains in this location during the period of most active bone growth. As cystic expansion becomes progressively less rapid relative to metaphyseal growth, the metaphysis interposes more and more normal bone between itself and the lesion, causing a relative displacement of the cyst toward the midportion of the shaft.6,20
If the cyst becomes large, the bone becomes structurally weak. This predisposes to pathologic fracture, which is usually what directs attention to the presence of these lesions.
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Fig. 27.-Old unicameral bone cyst displaced a considerable distance from metaphysis. The old fracture did not result in healing.
Simple bone cyst is predominantly a lesion of long tubular bones but occurs occasionally in flat bones and small round bones. Roentgen Features. The roentgenographic appearance of simple bone cyst is that of a homogeneously radiolucent, sharply demarcated defect in the metaphyseal or adjacent diaphyseal portion of a long bone. The central intramedullary origin predisposes to fairly equal expansion of the surrounding cortex in all directions. Although the cortex is often attenuated, it remains intact as a moderately thin, dense, and distinct limiting shell. An occasional feature is a multilocular appearance due to the deeply scalloped inner wall and incomplete, centrally oriented septal projections. It is not multilocular, however, but is one continuous cavity throughout. Periosteal reaction and cortical interruption are not present unless a pathologic fracture has occurred. Older, inactive cysts often elongate and become displaced a considerable
PATHOLOGY AND RADIOLOGY OF BONE TUMORS
291
distance down the shaft, refiecting a degree of passive conformity to normal bone contour and growth (Fig. 27). Simple bone cyst may be confused roentgenologically with monostotic fibrous dysplasia, giant cell tumor and aneurysmal bone cyst. The roentgen diagnosis is usually relatively easy in the long tubular bones but exceedingly difficult in the flat bones. Pathologic Features. After fracture, the cyst is usually filled with blood or an organizing hematoma. Unaltered cysts contain clear fluid or nothing at all. Occasionally, septa similar to those of aneurysmal bone cyst traverse the cavity. The cysts may have a giant cell-rich fibrous lining several millimeters thick, a thin fibrous lining, or no lining at all. SUMMARY
The more common solitary benign bone tumors have been classified as fibrogenic, chondrogenic, osteogenic, or of unknown origin. Although histopathologic characteristics determine the exact designation of each tumor, the roentgen reflection of the gross pathologic changes provides significant diagnostic evidence in all instances. The roentgenogram is often more revealing than an ill chosen or poorly interpreted microscopic specimen. From the therapeutic standpoint, irradiation is hazardous and is rarely indicated in the management of these processes. REFERENCES 1. Caffey, John: On fibrous defects in cortical walls of growing tubular bones: 7. Their radiologic appearance,structure, prevalence, natural course, and diagnostic significance. In Levine, S. Z.: Advances in Pediatrics, Vol. 7. Chi8. cage, Year Book Medical Publishers, Inc., 1955, pp. 13-51. 2. Codman, E. A.: Epiphyseal chondromatous giant cell tumors of the upper 9. end of the humerus. Surg., Gynec., Obstet. 52:543-548, 1931. 3. Dahhn, D. C.: Bone Tumors: General 10. Aspects and an Analysis of 2,276 Cases. Springfield, Illinois, Charles C Thomas, Publisher, 1957, pp. 73 ancl 169. 11. 4. Dahlin, D. C., and Johnson, E. W., Jr.: Giant osteoid osteoma. J, Bone Joint Surg. 36A:559-572, 1954. 12. 5. Ewing, James: The classification and treatment of bone sarcoma. In: Report of the International Conference on Cancer, London, 1928, Vol. I. Bristol, John Wright and Sons, Ltd., 1928, pp. 365-376. 13. 6. Garceau, G. J., and Gregory, C. F.: Sol-
itary unicameral bone cyst. J. Bone Joint Surg. 36A:267-280, 1954. Gee, V. ft., and Pugh, D. G.: Giant-cell tumor of bone. Radiology 70:33-44, 1958. Jaffe, H. L.: “Osteoid-osteoma”: A benign osteoblastic tumor composed of osteoid and atypical bone. Arch. Surg. 31:709-728, 1935. Jaffe, H. L.: Benign osteoblastoma. Bull. Hosp. Joint Dis. 17:141-151, 1956. Jaffe, H. L., and Lichtenstein, L.: Solitary unicameral bone cyst, with emphasis on the roentgen picture, pathologic appearance and pathogenesis. Arch. Surg. 44:1004-1025, 1942. Jaffe, H. L., and Lichtenstein, Louis: Non-osteogenic fibroma of bone. Amer. J. Path. l&205-215, 1942. .Jaffe, H. L., and Lichtenstein, Louis: Benign chondroblastoma of bone: A reinterpretation of the so-called calcifying or chondromatous giant cell tumor. Amer. J. Path. 18:969-983, 1942. Jaffe, H. L., and Lichtenstein, Louis: Chondromyxoid fibroma of bone: A
292 distinctive benign tumor likely to be mistaken especially for chondrosarcoma. Arch. Path. 45:541-551, 1948. 14. Jaffe, H. L., Lichtenstein, Louis, and Portis, R. B.: Giant cell tumor of bone: Its pathologic appearance, grading, supposed variants, and treatment. Arch. Path. 30:993-1031, 1940. 15. Jaffe, H. L., and Mayer, Leo: An osteoblastic osteoid tissue-forming tumor of a metacarpal bone. Arch. Surg. 24: 550-564,1932. 16. Lichtenstein, L.: Medical progress: Pathology; Diseases of bone. New Eng. J. Med. 255:427433, 1956. 17. Lichtenstein, Louis: Benign osteoblastoma: A category of osteoid- and boneforming tumors other than classical osteoid osteoma, which may be mistaken for giant-cell tumor or osteogenic sarcoma. Cancer 9:1044-1052, 1956. 18. Lichtenstein, Louis, and Sawyer, W. R.: Benign osteoblastoma: Further obser-
STEWART,
19.
20.
21.
22.
DAHLIN,
PUGH
vations and report of twenty additional cases. J. Bone Joint Surg. 46A: 755-765,1964. Sontag, L. W., and Pyle, S. Idell: The appearance and nature of cyst-like areas in the distal femoral metaphyses of children. Amer. J. Roentgen. 46: 185-188,194l. Stewart, M. J., and Hamel, H. A.: Solitary bone cyst. Southern Med. J. 43: 927-934,195o. Turcotte, Bernard, Pugh, D. G., and Dahlin, D. C.: The roentgenologic aspects of chondromyxoid fibroma of bone, Amer. J. Roentgen. 87:10851095,1962. Virchow: Quoted by Bloodgood, J. C.: Benign bone cysts, ostitis fibrosa, giantcell sarcoma and bone aneurism of the long pipe bones: A clinical and pathological study with the conclusion that conservative treatment is justifiable, Ann. Surg. 52:145-185, 1910.
T
HE LESIONS presented in this section are classified in Table 1 according to cellular origin. Not all of the entities classified are neoplasms in the strict sense. Nevertheless, a presentation of benign bone tumors would be incomplete without including these allied conditions. Space limitations prevent an all-inclusive classification, and some of the rarer or less related tumors and tumor-like conditions have been excluded. Notable among the exclusions are neurilemmomas, lipomas, and diverse and complicated angiomatous processes in bone. The role of the radiologist in the evaluation of a bone tumor includes locating the lesion, determining its extent, determining whether it is benign or malignant, and, ideally, specifically naming it. Determining whether a lesion is benign or malignant is the most important function of the radiologist (Table 2). Some are obviously benign and biopsy is unnecessary. Others are difficult to assess microscopically, even with adequate biopsy tissue, and experienced bone pathologists refuse to render an opinion without knowing more about the gross appearance of the lesion as seen radiographically. An accurate radiographic assessment, therefore, is an integral part of good management of patients with bone tumors, whether or not biopsy is necessary. To recognize specifically what type of bone tumor is present is of course the ultimate desire of the radiologist, but this is often not possible. Just as important is to know the limitations of the roentgenographic examination. When a difficult or unusual lesion is encountered, an approach that has proved helpful in our experience is to review the current classification of bone tumors, testing the unknown against those in the classification, taking into consideration the specific roentgenographic features, the location of the lesion, and the age of the patient. Often, by exclusion, only one logical diagnosis remains. A few general comments are in order with regard to our presentation of this subject. The relative sex incidence of the various bone lesions will not be mentioned since any difference is not sufficiently great to be of diagnostic value. Seldom shall we comment on the treatment or prognosis, as we do not feel well qualified, and there is insufficient data as well as much controversy in these areas. However, evidence is mounting that malignant transformation is more likely to occur if irradiation is employed, and it would seem wise to avoid this modality of treatment. From the Mayo Clinic and Mayo Foundation, Rochester, Minn. (Drs. Stewart and Pugh) and of Surgical Pathology (Dr. Dahlin).
Section of Roentgenology
SEMINARS IN ROENTGENOLOGY,VOL. 1, No. 3 (JULY), 1966
PATHOLOGY
AND RADIOLOGY
Table l.-Solitary
Benign Tumors and Tumor-like
FIBROGENIC:
ORIGIN
Table 2.-Roentgenographic
Internal architecture Periosteal reaction
Calcification or ossification Secondary signs
Location
UNKNOWN:
Giant cell tumor Aneurysmal bone cyst Simple bone cyst
Osteochondroma Enchondroma Benign chondroblastoma Chondromyxoid fibroma
Extent
of Bone
Osteoma Osteoid osteoma Benign osteoblastoma
CHONDROGENIC:
Margin
Lesions
OSTEOGENIC:
Cortical defect Nonosteogenic fibroma Fibrous rest Fibrous dysplasia
Feature
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OF BONE TUMORS
Signs of Benignancy
Smooth, sclerotic or scalloped. Distinct Well circumscribed. Confined to medullary cavity or by cortex or periosteum
Organized, eroded, homogeneous or evenly trabeculated Sometimes present but seldom of degree or nature seen in malignant tumors. More striking in pathologic fracture. Organized. Focal or homogeneous distribution Evidence of chronicity; present on previous films with little change, or showing impairment of remodeling of bone Epiphyseal and small tubular bone tumors less likely to be malignant FIBFKIGENIC
and Malignancy Malignancy
Benignaney
Absent, ill-defined or sharply destructive Medullary involvement primarily. Extension along medullary cavity, or subperiosteally,or through cortex and periosteum. Unconfined soft-tissue mass Bizarre, mottled, or destroyed. Moth eaten Frequent, but may be absent. Irregular, interrupted, and more extensively layered, or with spiculation Disorganized, irregular. No pattern of distribution. May show streaking or whorling No evidence of chronicity. Acute osteoporosis suggesting active growth (if no fracture present) See text regarding chondrogenic group
TUMORS
Definition. Fibrogenic tumors (Table 1) are focal collections of nonspecific fibrous tissue located predominantly or entirely in the cortical portion of bone. Differing in several respects from true neoplasms, they are apparently related conditions resulting from local errors in osteogenesis. They differ from each other primarily in their biologic behavior and roentgenographic appearance. Cortical Defect Clinical Features. The term “cortical defect” has been popularized by Caffeyl in reference to the common, small, oval or round cortical lesion that originates in the metaphysis of the shaft of a long bone in normal children. In studies by Sontag and PylelO and by Caffey,l they were not seen before 18
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months of age but occurred in 40 to 50 per cent of normal children after 3 years of age. Cortical defects are most common in the metaphyses about the knee, particularly on the posterior medial aspect of the distal femur. Although they vary extremely in behavior, they most commonly diminish gradually in size and eventually disappear. Roentgenographic Features. The cortical defect appears as an oval or round rarefaction in or near the metaphysis (Fig. 1). Viewed tangentially, the defect is seen as a shallow concavity in the cortical wall. If oval, its long axis is parallel to that of the shaft. Cortical defects are usually 1 to 2 cm in diameter. The central rarefaction is either homogeneous throughout or partially compartmentalized. The inner margin of the defect is a smooth or slightly scalloped thin line of increased density. Occasionally, in the lower medial part of the femur it shows a loss of overlying cortex but the characteristic location and the age at which it occurs make its benign nature evident to those who are aware of this variation. The radiographic appearance of older lesions is variable and depends on their mode of resolution. Nonosteogenic Fibroma (nonossifying
fibroma)
Clinical Features. A much less frequent condition, first described by Jaffe and Lichtenstein’l is nonosteogenic fibroma. It is larger and more stable than the cortical defect, often trabeculated and characteristically located a few centimeters away from the metaphysis. Accurate figures on its true incidence are not available since it rarely produces symptoms and therefore is seldom radiographed. Nonosteogenic fibroma occurs predominantly, if not exclusively, in the long bones, especially those of the lower extremity. Most are seen in older children and young adults. Pathologic fractures are rare. Roentgen Features. Nonosteogenic fibromas appear similar to cortical defects but are larger, extend more deeply into the spongiosa, are further removed from the metaphysis, and characteristically have a thicker sclerotic shell (Fig. 2). The distinction between nonosteogenic fibroma, a large, older cortical defect, and monostotic fibrous dysplasia is of little importance. NO true bone tumor closely resembles this lesion unless its appearance is altered by a pathologic fracture. Fibrous Rest There still remains a hodge-podge of small fibrous defects that do not concisely fit into the above two categories. These common lesions are small and so innocuous in appearance that they are usually ignored by the radiologist. While the term fibrous rest seems to mean different things to different people, it most commonly is applied to these nondescript rarefactions. PATHOLOGIC FIBROUS
REST.
FEATURES
OF
CORTICAL
The tissue of cortical
DEFEa,
NONOSTEOGENIC
defects and fibroma
FIBROMA,
AND
is soft and often
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Fig.
l.-Cortical
271
defect in lower part of tibia
of an 8 year old girl.
yellow, owing to its lipid content. Microscopically, there are interlacing fascicles of benign fibroblasts in collagenous tissue. Benign giant cells are present, usually in a somehat patchy distribution. Foam cells are often seen, sometimes in prominent clusters. The fibrous rests are zones of hypocellular, dense, fibrous tissue resembling a scar. Monostotic
Fibrous Dyspiksia
Definition. Even though the clinical stigmata are lacking in the monostotic form, this condition is considered a variant of generalized fibrous dysplasia. Clinical Features. Pain, particularly if the lesion is located in a weightbearing bone, is common. Pathologic fracture, swelling, deformity or incidental discovery accounts for detection of most of the remaining cases. At the time of discovery, nearly half the patients are adolescents, the remainder being fairly evenly distributed throughout life. Sites of predilection are the maxillofacial bones, skull, rib, femur, and tibia. The most common solitary benign lesion of a rib recorded in our pathologic files is monostotic fibrous dysplasia (Fig. 3). Roentgen Features. Monostotic fibrous dysplasia resembles the larger of the fibrous lesions just discussed. Basically, however, it is an intramedullary rather than a cortical rarefaction (Fig. 4). The distribution of monostotic fibrous dysplasia in the skeleton is also different, but when it does occur in the long tubular bones it lacks the striking affinity for the parametaphyseal region so characteristic of the other fibrous lesions. Of importance is the recognition of monostotic fibrous dysplasia in the facial bones, skull and ribs. The expanding,
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Fig. Z.-Nonosteogenic fibroma. Characteristic features are sclerotic margin, predominantly cortical location, large size, and slight separation from metaphysis.
deforming, obviously benign appearance is usually quite characteristic and few other conditions that occur in these areas resemble it. Pathologic Features. The dense collagenous tissue of fibrous dysplasia is characteristically gritty because of bony trabeculae which may be so abundant that the roentgen shadow is radiopaque. Myxoid degeneration and even extensive cyst formation may develop. Foci of metaplastic osteoid in the fibrous tissue distinguish fibrous dysplasia from the other fibrous processesin bone. CHONDROGENIC
TUMORS
Osteochondroma (0steocartiluginou.s Exostosis) Definition. Osteochondroma is a projection whose base consists of a continuation of the adjacent cortex and underlying spongiosa. It has a cartilaginous cap, which is the potentially neoplastic portion. Clinical Features. Solitary osteochondroma is a common benign bone tumor. It develops during the period of most active enchondral bone growth and is most often detected during the second decade of life. Any juxta-epiphyseal area may be involved but the most common locations are the femoral and tibia1 metaphyses near the knee. The patient usually notices a firm swelling or has pain from repeated trauma to the bony protrusion. Rarely, the tumor impinges on a major nerve or artery, or the stalk may fracture. Pelvic osteochondroma may cause dystocia. Roentgen Features. In the long bones, solitary osteochondroma presents typically in two common forms. One resembles a cauliflower, with a narrow stalk and a bulbous, somewhat irregular tip (Fig. 5) The other form is sessilr:
PATHOLOGY
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RADIOLOGY
Fig. 3 (Top).-Solitary
OF
BONE
273
TUMORS
lesion of fibrous dysplasia
in the posterior portion of the
right eighth rib of a 44 year old man. Fig. 4 (Bottom).-Solitary
lesion of fibrous dysplasia
in the left femoral neck.
with a broad base on the shaft and with a relatively smooth outer apex (Fig. 6). Osteochondroma of the pelvis may present as a large, popcorn-ball area of calcification resembling a calcified uterine fibroid, particularly if the site of attachment cannot be identified (Fig. 7).
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The finding of an osteochondroma should suggest the possibility of multiple familial cartilaginous excstoses. No other bone tumor closely resembles an osteochondroma. The radiologist’s contribution lies chiefly in recognizing signs suggestive of malignant transformation. These include (1) marked irregularity of the cartilaginous cap, (2) a soft-tissue mass projecting beyond the expected confines of the lesion, (3) flecks of calcification in the soft tissues beyond the lesion, and (4) rapid growth of the lesion revealed on serial films. Pnthologic Features. The cartilaginous cap merges with the underlying bony trabeculae. The cortex of the parent bone flares to become the cortex of the tumor, which encloses fatty or hematopoietic marrow. The cartilaginous portion tends to involute in adults. Enchondroma Definition. An enchondroma is a benign neoplasm arising in the medullary portion of the bone, composed chiefly of mature hyaline cartilage. It is probably the most common benign bone tumor, although few are proved by operation. Clinical Features. The age incidence of this neoplasm is fairly evenly distributed through the second to fifth decades. Any bone preformed in cartilage may house an enchondroma but those more frequently afflicted are the phalanges of the hands (50 per cent), metacarpals, phalanges of the feet, metatarsals, humerus and femur. A history of spontaneous swelling, or of pain and swelling following local trauma, is usually given by the patient with phalangeal, metacarpal, or metatarsal enchondroma. Local pain aggravated by motion accounts for detection of some enchondromas of the large bones. Still others are discovered as a result of pathologic fracture, or incidentally on roentgenographic examination obtained for other reasons. It is usually apparent from the roentgenogram that the tumor has been present for a much longer time than the clinical history indicates, since modeling of the bone is often altered. Roentgen Features. Typically, enchondromas are intramedullary tumors situated near the end of a diaphysis. In the small tubular bones, the entire shaft often undergoes lobulated expansion (Fig. 8). In spite of the moderately expansile nature of the tumor, the outer cortex is preserved as a distinct limiting shell. The cavity usually contains a variable quantity of coarse, flocculent calcification superimposed on a faintly translucent background. Another pattern, which, in our experience, occurs exclusively in the large tubular bones, is that of a conglomerate area of calcification without a lytic component (Fig. 9). The diagnosis of bone infarct is often suggested roentgenographically for lesions with this appearance, but the few we have subjected to biopsy have all shown histologic changes typical of enchondroma. A less common but characteristic location of a chondroma is immediately beneath the periosteum- the so-called subperiosteal chondroma (Fig. 10). In this location, there is, of course, no limiting cortical shell, but the tumor is sharply localized and does not invade the soft tissue. Calcification is also
PATHOLOGY
AND RADIOLOGY
OF BONE TUMORS
Fig. 5 (Top left) .-Cauliflower-shaped osteochondroma Fi g. 6 (Top right) .-Broad-based
osteochondroma.
of humerus of an 8 yeaLr old
boy. Fi ig. 7 (Bottom).-Large
a 25 year old woman.
intrapelvic
osteochondroma
which caused dystoc:iaL in
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STEWART,
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, PUGH
absent. As indicated, the location is a most characteristic feature, Subperiosteal chondroma often causes a fairly typical, smoothly scalloped erosion of the underlying cortex. Enchondroma is seldom difficult to differentiate from other benign tumors, Determining whether the neoplasm is potentially malignant or has already undergone transformation into a chondrosarcoma is a more important contribution. Fusiform widening of the shaft, especially if associated with cortical sclerosis, is an ominous feature, particularly if any degree of pain or ache is present. Pathologic Features. The cartilaginous tissue is often lobulated and may be slightly to heavily mineralized as a result of ossification or degenerative calcification. The chondrocytes have small and usually single nuclei. Differentiation from chondrosarcoma depends on nuclear abnormalities in conjunction with clinical and roentgen signs of aggressiveness. Treatment and Prognosis. Enchondromas of the large tubular bones that show flocculent calcification without a lytic element and enchondromas of the small tubular bones rarely become malignant. Thus, treatment is necessary only if the lesion is painful, prone to fracture, or causes mechanical difficulty. In contrast, fusiform, rarefied enchondromas of the large bones, particularly if generous in size, should be suspected of being malignant. Lesions of the acetabular region terminate as chondrosarcomas alarmingly often and should be treated accordingly. Benign Chondroblastoma Definition. Benign chondroblastoma is a tumor of bone thought to originate from primitive epiphyseal cartilage cells. First described by Ewing5 and Codman2 as a variant of giant cell tumor, this neoplasm was recognized as a distinct clinicopathologic entity in the early 1940’s.12 Clinical Features. Benign chondroblastoma is rare before 10 years of age and may be seen as late as the sixth decade of life. The majority are recognized in patients from 10 to 30 years of age, but usually before enchondral bone growth ceases. Benign chondroblastoma is an epiphyseal tumor. Although the flat bones of the axial skeleton are occasionally involved, the long bones are the most frequent site, especially the upper end of the humerus, the lower end of the femur, and the upper end of the tibia. Mild chronic local pain in the bone or adjacent joint, often historically related to incidental trauma, is the most common clinical feature. Roentgen Features. When encountered in a long bone, benign chondroblastoma is round or oval and its epiphyseal origin is obvious-an important observation since few other lesions arise from the epiphysis (Fig. 11). One should not exclude epiphyseal origin of a lesion confined to a tuberosity of the humerus or trochanter of the femur, since the tuberosity and the trochanter are each formed from an epiphysis (Fig. 12). After fusion of the epiphysis and the diaphysis, the tumor may extend into the latter but its epiphyseal origin USUally remains evident. The central portion of a benign chondroblastoma is not trabeculated and is
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TUMORS
Fig. 8 (Top left) .-Enchondroma
of proxi-
mal phalanx of a 24 year old woman. Fig. 9 (Bottom left) .-Enchondroma. The radiolucent component is not very obvious in this almost completely calcified variety. 10 (Bottom Fig. chondroma. Marginal
right).-Subperiosteal
reflections indicate an origin between periosteum and cortex. The cortex is eroded from without. The external limiting membrane is periosteum.
either uniformly rarefied or contains irregular patches of mottled calcification. Periosteal reaction may occur in larger lesions but is uncommon. Pathologic fracture is almost nonexistent. In flat bones the roentgen diagnosis is di5cult because the epiphyseal origin and characteristic roentgen features are not so evident. The tumors that most frequently resemble benign chondroblastoma are chondrosarcoma, enchondroma and giant cell tumor.
STEWART,
occupying Fig. 11 (Left).-Benign chondroblastoma epiphysis. Epiphysis and diaphysis have not fused.
DAHLIN,
most of right
PUGH
humeral
Fig. 12 (Right) .-Benign chondroblastoma arising from epiphysis of greater trochanter. The tumor was first discovered after enchondral bone growth had ceased.
It was not possible, therefore, to exclude giant cell tumor. (From Plum, G. E., and
Pugh, D. G.: Roentgenologic aspects of benign chondroblastoma of bone. Am. J. Roentgenol. 79:584-591,
1958. Reproduced with
permission of the publisher,
Charles C Thomas.) Pathologic Features. This soft, granular tumor may be grossly chondroid and partially calcified. Cellular zones very similar to those of giant cell tumor shade into the diagnostic chondroid islands which may show focal degeneration and calcification. We do not recognize a spontaneous malignant counterpart, but sarcoma has developed after irradiation of benign chondroblastoma. Chondromyxoid Fibroma Definition. Chondromyxoid fibroma, first described by Jaffe and LichtensteinI in 1948, is a benign tumor thought to originate from cartilage-forming connective tissue. Clinical Features. The frequency of recognition of chondromyxoid fibroma peaks in the second and third decades of life, a period in which approximately two thirds of these lesions are encountered. Eighty per cent of chondromyxoid fibromas occur in the long bones of the lower extremities. The flat bones and the long bones of the upper extremities account for most of the remaining cases. Because chondromyxoid fibroma is usually relatively small and eccentrically located, pathologic fracture seldom occurs. Pain is the most common presenting complaint.
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Roentgen Features. Since the majority are encountered in the long tubular bones and since, when we have encountered them elsewhere there were too few differential features to permit us to recognize them, the roentgen description will be confined to the appearance as seen in the shaft of a long bone. A chondromyxoid fibroma is an oval, eccentric lesion situated in the metaphyseal portion of the diaphysis, abutting the epiphyseal cartilage. The center is usually uniformly rarefied. The wall is sometimes smooth but more often scalloped. The cortex is characteristically expanded and is either very thin or no longer visible, even though the tumor is always restrained by the periosteum. In the majority of cases there is a definite thin sclerotic rim between the tumor and the adjacent normal medullary bonezl (Figs. 13 and 14). The differential diagnosis includes aneurysmal bone cyst, giant cell tumor, benign chondroblastoma, enchondroma, simple bone cyst and nonossifying fibroma. An important contribution of the radiologist in the roentgen evaluation of patients with chondromyxoid fibroma is to recognize that the lesion is benign and to alert the pathologist to the possibility of chondromyxoid fibroma, since histologically the lesion resembles chondrosarcoma. Pathologic Features. This lobulated tumor is grossly cartilaginous and sharply demarcated from adjacent bone. A histologically characteristic mixture of chondroid, myxoid, and fibromatoid elements makes’ up this lesion. Nuclear abnormalities mimic those of chondrosarcoma when viewed out of context or without the knowledge of the benign roentgen appearance: OSTEOGENIC
TUMORS
Osteoma Definition. Osteomas are benign tumors of osteoblastic mesenchyme and consist predominantly of dense, compact, mature bone. As defined, such conditions as unpneumatized compartments of sinuses, osseous reactions to various stimuli, bone islands, and ancient ossified bone tumors and cysts are excluded. Clinical Features. Osteomas occur later in life than most benign tumors, being more frequent in adults than in children. They are found almost exclusively in the paranasal sinuses (particularly the frontal sinus), calvarium and mandible. Sinus osteomas may obstruct drainage but, in our experience, this is uncommon and many are incidental roentgenographic observations. Being extremely hard tumors, those that arise from the external table of the skull or from the mandible are easily felt, even when they are small. Roentgen Features. Being well circumscribed and the most dense of all tumors, osteomas are seldom difficult to recognize (Fig. 15). Those that arise from the inner surface of the skull cannot be distinguished with certainty from a meningiomatous reaction. Fortunately, tangential views of the skull demonstrate that most osteomas arise from the outer table or its periosteum, with the bulk of the lesion projecting outward. Osteomas of the sinuses are sometimes less dense and more lobulated (Fig. 16). A non-pneumatized ossified compartment of the frontal sinus is usually
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Fig. 13 (Above, A and B.)-Chondromyxoid fibroma of upper tibia. There is marginal condensation along inner border of tumor, which is usually absent in aneurysmal bone cyst. (From Turcotte, B., Pugh, D. G., and Dahlin, D. C.: The roentgenologic aspects of chondromyxoid fibroma of bone. Am. J. Roentgenol. 87: 1085-1095, 1962. Reproduced with permission of the publisher, Charles C Thomas. ) Fig. 14 (Bottom left) .-Chondromyxoid fibroma of lower tibia. Lower margin abuts upon epiphyseal cartilage. A tiny satellite lesion can be seen above the primary site of involvement. (From Turcotte, B., Pugh, D. G., and Dahlin, D. C.: The roentgenologic aspects of chondromyxoid fibroma of bone. Am. J. Roentgenol. 87: 1085-1095, 1962. Reproduced with permission of the publisher, Charles C Thomas. )
distinguishable from a true osteoma since the corresponding segment of frontal bone that should be pneumatized is not. Rarely, a large osteoma will arise from a long tubular bone and resemble a parosteal osteogenic sarcoma, in which instance total removal is wise since the prognosis of such an atypical osteoma is unknown. Any osteoma in an unusual location raises the possibility of Gardner’s syndrome (polyposis of colon, soft tissue cysts or tumors, and osteomata). This applies especially to multiple
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Fig. I5 (TOP) .-Ivory osteoma of mandible, which had been present for 15 years. Fig. 16 (Bottom).- Osteoma of frontal sinus, somewhat lobulated. osteom as occurring
on the long tubular bones, but Gardner’s syndrome shol Ad also be suspected when osteoma of the mandible is seen. Path alogic Features. Osteomas are composed of dense bone con taini “g benign osteocytes. Sometimes a fibrous component is present and sug gest:s a relatior lship to fibrous ( fibro-osseous) dysplasia.
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Osteoid Osteoma Definition. Most observers regard osteoid osteoma as a true neoplasm of bone rather than an infection or foreign body reaction, in spite of its unusuai gross appearance and limited growth potential. Jaffe,a who coined the term “osteoid osteoma” in 1935, believed it arose from osteoblastic mesenchyme, which has the ability to produce large quantities of osteoid. These cells and their by-products make up what is commonly referred to as a nidus. The surrounding sclercsis, which may or may not be present and disappears when the nidus is removed, is a secondary reaction, Clinical Features. Osteoid osteoma has been observed in almost every bone in the body except the calvarium but is most common in the long tubular bones, especially the femur and tibia. It exhibits a peak incidence in the second decade of life and is distinctly uncommon after 35 years of age. Boring pain slowly but relentlessly becomes more intense, is often worse at night, and may dramatically be diminished by use of salicylates. Atrophy and weakness of an extremity, causing unstable gait or limp, may also be present and occasionally constitute the chief complaint. Fever, leukocytosis and elevation of the sedimentation rate are usually absent. Mild to moderate tenderness over the nidus is common but local warmth and swelling are infrequent. When the classic clinical features are present, the diagnosis seldom poses a problem, but in atypical cases the patients have frequently been labeled as malingerers or operated on for what was thought to be a herniated intervertebral disk. Roentgen Features. Most osteoid osteomas produce a typical roentgen appearance, that is, a small radiolucent or partially calcified nidus encoffined by osteosclerosis (Fig. 17). Periosteal reaction is present if the lesion is near a cortical surface. The sclerosis may be so intense that the nidus is obscured. The only lesion that has perfectly, though rarely, mimicked a typical osteoid osteoma in our cases has been focal osteomyelitis. Ewing’s tumor, histiocytosis X, and stress fracture produce sclerosis and periosteal reaction but the composite picture of each of these lesions is usually quite dissimilar. Intramedullary osteoid osteoma, unfortunately, often stimulates little or no osteosclerosis or periosteal reaction. Its nidus may be extremely difficult to see, particularly when located in coarse cancellous bone, and here its detection can be likened to finding a small bullet hole in the honeycomb of a bee hive! It is essential, in patients who clinically might have an osteoid osteoma, to obtain well-localized stereoscopic views and tomograms of the painful region when the routine films appear negative. The most insignificant-appearing alteration in trabecular pattern may prove to be a nidus at operation (Fig. 18). A group of our patients had clinical and roentgen findings compatible with or typical of osteoid osteoma but the resected sclerotic block of bone did not yield a nidus on careful microscopic examination. Yet there was dramatic and permanent relief of pain following excision. Although it is likely that the nidus is occasionally destroyed in removal or missed on sectioning, there are too many cases in this group to be accounted for in this manner and the explana-
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Fig. 17 (Left).-Osteoid osteoma. In the center of the rarefied nidus is a small calcific deposit. The usual intense reaction of cortical bone is present. Fig. 18 (Right).-Osteoid osteoma in spongiosa at base of coracoid process of scapula. There is no sclerosis. Patient was a 16 year old girl who had chronic shoulder pain. Only by correlation of the history and repeated films of the scapula was the correct diagnosis established.
tion must lie elsewhere. These are being re-evaluated and are the subject of a more detailed presentation to be published later. Pathologic Features. The nidus is usually discretely outlined in its sclerotic bed. Microscopically there is an interlacing network of more or less mineralized trabeculae mantled by benign osteoblasts. The intervening fibrovascular tissue usually contains a few benign giant cells. Benign Osteoblastoma (Giant Osteoid Osteoma) Definition. Benign osteoblastoma is a tumor composed of numerous osteoblasts and their products, osteoid and bone, deposited in a richly vascular connective tissue stroma. Proper designation of this lesion has been di5cult. Jaffe and Mayer,15 in 1932, used the descriptive name “an osteoblastic osteoid tissue-forming tumor.” In 1954, Dahlin and Johnson4 proposed the term giant osteoid osteoma to denote the histologic similarity to osteoid osteoma and yet set it apart from that lesion by one of its chief differences, its larger size. Benign osteoblastoma is the term most widely adopted and was offered independently by Lichtenstein16*” and by Jaffes in 1956.
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Clinical Features. Benign osteoblastoma occurs chiefly in the second and third decades of life and is an infrequent tumor. Approximately 50 per cent arise in the vertebral column and a few have been observed in the calvarium, a distribution that is in contrast to that of most benign bone tumors.l* The next most common location of benign osteoblastolma is in the long tubular bones. When the lesion is located in the vertebral column, symptoms referable to nerve root or cord compression have been common. In other locations, a dull aching pain usually directs attention to the tumor. Roentgen Features. Because of its relative rarity and variable appearance, benign osteoblastoma has proved to be a difficult tumor to diagnose roentgenographically. It has even been impossible to be certain that some of the more bizarre looking lesions were not malignant neoplasms. It most consistently appears to be an expanded, completely lytic defect or a lytic defect with a variable quantity of irregularly deposited mottled central calcification, often with a thin outer shell of periosteal new bone or marginal sclerosis. In some, an irregular internal architectural pattern may suggest malignancy, but, conversely, a sharply limited and distinct external margin indicates benignancy. This finding may prove to be characteristic of some benign osteoblastomas (Figs. 19 and 20). In a few of our cases the roentgen appearance has resembled that of osteoid osteoma, but in each instance the central radiolucency was considerably larger and more irregular. It is impossible to list a radiographic differential diagnosis until more experience is gained to formulate a better understanding of the variable manifestations of benign osteoblastoma. When one encounters a bizzare osseous lesion, particularly in the spine, which by virtue of its limited extent appears benign and which has some of the characteristics described, benign osteoblastoma should be considered. Pathologic Features. Osteoblastomas are bloody, firm, granular, circumscribed tumors, usually so lightly mineralized that they may be sectioned without decalcification. Sometimes the osteoblastic proliferation is so active that differentiation from osteosarcoma is a problem. Benign giant cells are often abundant and occasionally there are large blood-filled spaces, suggesting a kinship to aneurysmal bone cyst. BONE
TUMORS OF UNKNOWN
ORIGIN
Giant Cell Tumor Definition. The cellular origin of giant cell tumor is unknown and this neoplasm defies simple definition. Numerous other tumors of bone contain giant cells, and in the past many of these have been considered to be giant cell tumors or variants of them. Continued refinement of the clinical, roentgenologic, and pathologic features of this group of neoplasms with removal and recategorization of the nonconforming lesions has caused the evolution of this specific neoplasm as we now know it. To Jaffe, Lichtenstein and Portis14 must go much of the credit for our current concept of giant cell tumor.
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Fig. 19 (Left) .-Benign osteoblastoma showing the most characteristic location and features of this lesion. The tumor is expanding the transverse process and is
both rarefied and sclerotic. The architectural pattern is bizzare, yet the entire process is fairly well circumscribed. Fig. 20 (Right).-Benign osteoblastoma. This case illustrates one of the variations which cannot be distinguished from myeloma, metastatic lesion, or giant cell tumor. Clinical Features. The majority of giant cell tumors are encountered in persons beyond 20 years of age, that is, after fusion of the epiphysis and diaphysis. The peak incidence is in the third decade with a progressively diminishing incidence thereafter. Giant celI tumor is an epiphyseal tumor, but with prolonged growth it commonly extends into the diaphysis. More than half occur about the knee. Other less common but still frequent locations are the pelvis, ulna, radius, humerus and sacrum. Giant cell tumors are infrequent in the spine above the sacrum or in the small bones, skull or ribs. When small, giant cell tumors produce only mild symptoms, pain being the most frequent. With growth, pain and joint disability increase and local swelling and pathologic fractures occur. Roentgen Features. Giant cell tumor is entirely osteolytic, quite expanded and often very destructive. Arising in the epiphysis, it exhibits considerable inclination to encroach upon the articular cortex.? Since the epiphysis and diaphysis are usually fused, there is no barrier to extension into the shaft. The wall may be deeply scalloped which, when seen on the roentgenogram, erroneously suggests that the tumor is compartmentalized. There is no calcihcation within the tumor so that the central portion is rarefied. Osseous condensation is absent at the interface between the tumor and
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normal bone, and this margin, while abrupt, is indistinct. When a giant cell tumor becomes quite large, the cortex may be completely breached and no longer visible. Pathologic fracture with secondary periosteal reaction is common, but periosteal reaction without the presence of a fracture is distinctly uncommon (Fig. 21 and 22). In the long bones the roentgenographic features are fairly reliable. The differential diagnosis includes aneurysmal bone cyst, benign chondroblastoma and fibrosarcoma. The huge giant cell tumors that frequently were mistaken for malignant bone tumors in the past are seldom encountered today, as patients seek medical attention much sooner. Giant cell tumors are less common in flat bones, and when they occur there, the correct radiographic diagnosis can seldom be made with confidence ( Fig. 23). Pathologic Features. These tumors are soft and friable. Multinucleated cells are usually large and numerous. Their nuclei markedly resemble those of the adjacent stromal cells which, in diagnostic zones, are producing nothing but the giant cells. Foci of fibrogenesis or osteogenesis may be present, especially after fracture or therapy. Cytologic features of sarcoma are absent. We have been unable to grade giant cell tumors with the view of predicting ability to recur or to undergo subsequent malignant change. The malignant tumors that develop are fibrosarcoma and osteogenic sarcoma and have been observed in as many as 10 per cent of cases.” Aneurysmal
Bone Cyst
Definition. Aneurysmal bone cyst is a connective tissue-lined cyst of undetermined etiology, containing primarily an interconnecting network of cavernous spaces filled with blood. Because of the numerous giant cells present, aneurysmal bone cyst was originally classified as a variant of giant cell tumor. In 1942, Jaffe and Lichtenstein’O coined the term aneurysmal bone cyst for this lesion, which is now generally accepted as a distinct entity. Clinical Features. Aneurysmal bone cyst is most common in the second decade of life. Mild pain or a gradual awareness of swelling usually directs attention to the lesion. Because the tumor is characteristically located eccentrically, a sufficient amount of normal shaft is usually present so that pathologic fracture is uncommon. Patients with aneurysmal bone cyst of the vertebral column present with back pain and stiffness or with a neurologic deficit. The most frequently involved bones are the long tubular bones, vertebral column, pelvis, scapula, metacarpals, and metatarsals. In the long bones, the metaphyseal portion of the diaphysis is most often afflicted. Roentgen Features. Small aneurysmal bone cysts are radiolucent throughout and have smooth margins. In larger lesions, the periphery begins to show faint lobulation as the wall becomes more attenuated. Eventually, the cortex is completely eroded in areas so that the periosteum is the limiting membrane. Viewed tangentially, that portion of the cyst that projects beyond the bone at times shows a fine cobweb-like network of interlacing curved lines projecting through the lesion and along its periphery (Fig. 24). Periosteal reaction is common and frequently striking in aneurysmal cysts of
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Fig. 21 (Top left).-Giant cell tumor. The lesion extends downward close to the articular cortex. Fig. 22 (Top right).-Giant cell tumor of distal part of ulna showing how destructive this condition may be. The proximal margin is abrupt. Fig. 23 (Bottom left).-Giant cell tumor is relatively common in the sacrum and produces a more characteristic appearance than when it occurs in other flat bones. the long bones. This, along with a breached cortex, imparts a malignant appearance, but when judged in proper balance so far as the other features of the lesion are concerned, the mistaken diagnosis of malignant disease can usually be avoided. The junction between the cyst and spongiosa is sharp but usually lacks the fine zone of marginal condensation seen in chonclromyxoid fibroma. This sometimes is the only differential clue between these two lesions.
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Fig. 24 (Left).-Aneurysmal bone cyst. No marginal condensation at interface of tumor and normal bone. A fine trabecular lattice is evident throughout the cyst and there is periosteal reaction above and laterally. bone cyst ballooning out a considerable length Fig. 25 (Right) .-Aneurysmal of ischium.
tubular bones, an eccentric location is seldom recognizable, as the cyst soon enlarges to such a size that the entire circumference of the shaft is expanded. Aneurysmal bone cyst is rather effectively limited to the metaphysis unless the epiphysis and diaphysis have fused, in which event this barrier is no longer present to prevent epiphyseal extension. In the spinal column and flat bones, the expansile character of aneurysmal bone cyst is more prominent. The cyst tends to extend along the anatomic contour of the bone, progressively ballooning out the cortex (Fig. 25 and 26). More aggressive aneurysmal bone cysts, however, pay little respect to natural boundaries, and extension by erosion from one adjacent bone to another is a most conspicuous feature in the spine, where several contiguous vertebrae may be destroyed. The tumors which resemble aneurysmal bone cyst are giant cell tumor and chondromyxoid fibroma. Pathologic Features. This tumor may have solid zones that resemble osteo‘blastoma or even fibrous giant cell tumor. Demonstration of the spaces that in vivo contained blood and are often separated by fibrous septa is essential to diagnosis. Blood welling up into the surgical wound is characteristic, but there In smaller
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Fig. 26.-Aneurysmal bone cyst of body, pedicle, lamina and transverse process of third lumbar vertebra. Vertebra plana is occasionally produced by such aneurysma1 bone cyst but expansion of the transverse process excludes the possibility of histiocytosis X.
is evidence to suggest that in older aneurysmal bone cysts the blood may be replaced by a yellowish, clear fluid. Simple Bone Cyst ( Unicameral Bone Cyst) Definition. Simple bone cyst was first described by Virchow22 in 1876. It is not a neoplasm but a connective-tissue-lined cyst. The etiology has not been satisfactorily resolved. Clinical Features. Simple bone cyst usually develops in the first or early part of the second decade of life and enlarges rather rapidly initially and more slowly thereafter. Growth tends to cease at about the time of epiphyseal fusion. The site of origin is the diaphyseal side of the metaphysis and the tumor remains in this location during the period of most active bone growth. As cystic expansion becomes progressively less rapid relative to metaphyseal growth, the metaphysis interposes more and more normal bone between itself and the lesion, causing a relative displacement of the cyst toward the midportion of the shaft.6,20
If the cyst becomes large, the bone becomes structurally weak. This predisposes to pathologic fracture, which is usually what directs attention to the presence of these lesions.
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Fig. 27.-Old unicameral bone cyst displaced a considerable distance from metaphysis. The old fracture did not result in healing.
Simple bone cyst is predominantly a lesion of long tubular bones but occurs occasionally in flat bones and small round bones. Roentgen Features. The roentgenographic appearance of simple bone cyst is that of a homogeneously radiolucent, sharply demarcated defect in the metaphyseal or adjacent diaphyseal portion of a long bone. The central intramedullary origin predisposes to fairly equal expansion of the surrounding cortex in all directions. Although the cortex is often attenuated, it remains intact as a moderately thin, dense, and distinct limiting shell. An occasional feature is a multilocular appearance due to the deeply scalloped inner wall and incomplete, centrally oriented septal projections. It is not multilocular, however, but is one continuous cavity throughout. Periosteal reaction and cortical interruption are not present unless a pathologic fracture has occurred. Older, inactive cysts often elongate and become displaced a considerable
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distance down the shaft, refiecting a degree of passive conformity to normal bone contour and growth (Fig. 27). Simple bone cyst may be confused roentgenologically with monostotic fibrous dysplasia, giant cell tumor and aneurysmal bone cyst. The roentgen diagnosis is usually relatively easy in the long tubular bones but exceedingly difficult in the flat bones. Pathologic Features. After fracture, the cyst is usually filled with blood or an organizing hematoma. Unaltered cysts contain clear fluid or nothing at all. Occasionally, septa similar to those of aneurysmal bone cyst traverse the cavity. The cysts may have a giant cell-rich fibrous lining several millimeters thick, a thin fibrous lining, or no lining at all. SUMMARY
The more common solitary benign bone tumors have been classified as fibrogenic, chondrogenic, osteogenic, or of unknown origin. Although histopathologic characteristics determine the exact designation of each tumor, the roentgen reflection of the gross pathologic changes provides significant diagnostic evidence in all instances. The roentgenogram is often more revealing than an ill chosen or poorly interpreted microscopic specimen. From the therapeutic standpoint, irradiation is hazardous and is rarely indicated in the management of these processes. REFERENCES 1. Caffey, John: On fibrous defects in cortical walls of growing tubular bones: 7. Their radiologic appearance,structure, prevalence, natural course, and diagnostic significance. In Levine, S. Z.: Advances in Pediatrics, Vol. 7. Chi8. cage, Year Book Medical Publishers, Inc., 1955, pp. 13-51. 2. Codman, E. A.: Epiphyseal chondromatous giant cell tumors of the upper 9. end of the humerus. Surg., Gynec., Obstet. 52:543-548, 1931. 3. Dahhn, D. C.: Bone Tumors: General 10. Aspects and an Analysis of 2,276 Cases. Springfield, Illinois, Charles C Thomas, Publisher, 1957, pp. 73 ancl 169. 11. 4. Dahlin, D. C., and Johnson, E. W., Jr.: Giant osteoid osteoma. J, Bone Joint Surg. 36A:559-572, 1954. 12. 5. Ewing, James: The classification and treatment of bone sarcoma. In: Report of the International Conference on Cancer, London, 1928, Vol. I. Bristol, John Wright and Sons, Ltd., 1928, pp. 365-376. 13. 6. Garceau, G. J., and Gregory, C. F.: Sol-
itary unicameral bone cyst. J. Bone Joint Surg. 36A:267-280, 1954. Gee, V. ft., and Pugh, D. G.: Giant-cell tumor of bone. Radiology 70:33-44, 1958. Jaffe, H. L.: “Osteoid-osteoma”: A benign osteoblastic tumor composed of osteoid and atypical bone. Arch. Surg. 31:709-728, 1935. Jaffe, H. L.: Benign osteoblastoma. Bull. Hosp. Joint Dis. 17:141-151, 1956. Jaffe, H. L., and Lichtenstein, L.: Solitary unicameral bone cyst, with emphasis on the roentgen picture, pathologic appearance and pathogenesis. Arch. Surg. 44:1004-1025, 1942. Jaffe, H. L., and Lichtenstein, Louis: Non-osteogenic fibroma of bone. Amer. J. Path. l&205-215, 1942. .Jaffe, H. L., and Lichtenstein, Louis: Benign chondroblastoma of bone: A reinterpretation of the so-called calcifying or chondromatous giant cell tumor. Amer. J. Path. 18:969-983, 1942. Jaffe, H. L., and Lichtenstein, Louis: Chondromyxoid fibroma of bone: A
292 distinctive benign tumor likely to be mistaken especially for chondrosarcoma. Arch. Path. 45:541-551, 1948. 14. Jaffe, H. L., Lichtenstein, Louis, and Portis, R. B.: Giant cell tumor of bone: Its pathologic appearance, grading, supposed variants, and treatment. Arch. Path. 30:993-1031, 1940. 15. Jaffe, H. L., and Mayer, Leo: An osteoblastic osteoid tissue-forming tumor of a metacarpal bone. Arch. Surg. 24: 550-564,1932. 16. Lichtenstein, L.: Medical progress: Pathology; Diseases of bone. New Eng. J. Med. 255:427433, 1956. 17. Lichtenstein, Louis: Benign osteoblastoma: A category of osteoid- and boneforming tumors other than classical osteoid osteoma, which may be mistaken for giant-cell tumor or osteogenic sarcoma. Cancer 9:1044-1052, 1956. 18. Lichtenstein, Louis, and Sawyer, W. R.: Benign osteoblastoma: Further obser-
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vations and report of twenty additional cases. J. Bone Joint Surg. 46A: 755-765,1964. Sontag, L. W., and Pyle, S. Idell: The appearance and nature of cyst-like areas in the distal femoral metaphyses of children. Amer. J. Roentgen. 46: 185-188,194l. Stewart, M. J., and Hamel, H. A.: Solitary bone cyst. Southern Med. J. 43: 927-934,195o. Turcotte, Bernard, Pugh, D. G., and Dahlin, D. C.: The roentgenologic aspects of chondromyxoid fibroma of bone, Amer. J. Roentgen. 87:10851095,1962. Virchow: Quoted by Bloodgood, J. C.: Benign bone cysts, ostitis fibrosa, giantcell sarcoma and bone aneurism of the long pipe bones: A clinical and pathological study with the conclusion that conservative treatment is justifiable, Ann. Surg. 52:145-185, 1910.