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Intraosseous lipoma of the calcaneus: A review and report of four cases
CASE REPORT
Intraosseous Lipoma of the Calcaneus: A Review and Report of Four Cases Glenn D. Weinfeld, DPM 1 , Gerard V. Yu, DPM, FACFAS,2 and James J. Good, DPM 3 Intraosseous lipomas have been reported as rare tumors in the lower extremity. They have been identified in the tibia, fibula, metatarsals, and calcaneus. They are frequently misdiagnosed as other tumors, especially unicameral bone cysts or aneurysmal bone cysts when found within the calcaneus. A detailed description of intraosseous calcaneal lipomas and their treatment is given. Surgical technique and four case reports are presented. One of the cases involved a pathologic calcaneal fracture, a finding to the authors' knowledge that has not been previously reported. (The Journal of Foot & Ankle Surgery 41 (6):398-411, 2002) Key words: benign bone tumors, calcaneus, intraosseous lipoma
Intraosseous lipomas of the calcaneus are uncommon. Because these lesions are benign and often asymptomatic, the true incidence is largely unknown. Much of the literature discusses isolated case reports. In 1955, Child published the first case to the authors' knowledge of an intraosseous lipoma involving the calcaneus (1). Dahlin's review of 8452 bone tumors from the Mayo clinic found only six intraosseous lipomas with an overall incidence less than I in 1000 (2). None of these cases involved the foot or ankle. A comprehensive review of the literature revealed only 28 cases of intraosseous lipomas involving the entire skeleton over a 100-year period (3). Six were found in the foot and ankle: three in the distal tibia, two in the distal fibula, and one in the anterior body of the calcaneus. More recently, Bakotic and Huvos reviewed 150 tumors specifically found in the small bones of the feet over a l5-year period from From St. Vincent Charity Hospital, Cleveland, OH. Address correspondence to: Glenn D. Weinfeld, DPM, 1215 Annapolis Rd., Suite 101, Odenton, MD 21113. E-mail: [email protected]. I Submitted during 2nd year of residency, St. Vincent Charity Podiatric Surgical Residency Program. 2 Diplomate, American Board of Podiatric Surgery; Director of Podiatric Medical Education, St. Vincent Charity Hospital; Faculty Member, The Podiatry Institute, Tucker, GA; private practice, Cleveland, OH ] Submitted during 3rd year of residency, St. Vincent Charity Podiatric Surgical Residency Program. Received for publication June 4, 2001; accepted in revised form for publication June 2, 2002. The Journal of Foot & Ankle Surgery 1067-2516/02/4106-0398$4.00/0 Copyright © 2002 by the American College of Foot and Ankle Surgeons
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1985 to 2000 (4). Although the calcaneus was the most common single bone involved in their study, there were no cases of an intraosseous calcaneal lipoma. The paucity of intraosseous lipomas may be explained by their classification as other entities such as unicameral or aneurysmal bone cysts (5). Recently, Greenspan et al. reviewed six osseous lesions in the calcaneus consistent with intraosseous lipomas (6). Three of the lesions were confirmed by histologic exam after undergoing surgical intervention. The remaining three lesions were asymptomatic and incidentally discovered while evaluating other musculoskeletal complaints. All of the lesions demonstrated a calcified nidus within a radiolucent lesion in the neutral triangle of the calcaneus, a feature that has been considered diagnostic (5, 7). The purpose of this article is to present four case reports of an intraosseous lipoma of the calcaneus and to provide a detailed description of the lesion. A detailed surgical protocol is also described. Case 1 A 27-year-old male patient was referred for evaluation and treatment of a symptomatic bone tumor in his left calcaneus. The patient stated that his heel had been painful for more than 5 years and became significantly more painful in the 2-3 preceding months. He had been seen by two other physicians and was treated for plantar fasciitis in a conventional manner. The pain was relieved overnight with rest; however, with weightbearing, a sharp,
FIGURE 1 Preoperative lateral x-ray demonstrating a large lytic lesion within the neutral triangle of the left calcaneus. Note the expansile appearance of this bone tumor and lack of intralesional calcification. An osseous septum is noted.
aching pain ensued which worsened over the course of the day. He had an antalgic gait, favoring the left foot by walking on his toes. He was extremely concerned about malignancy in light of a recent history of cancer in his family resulting in the loss of his mother. Examination revealed significant pain to palpation at the plantar aspect of his left heel and along the course of the plantar fascia. Palpation along the lateral wall of the calcaneus was also painful. Normal range of motion was present in the ankle, midtarsal, and metatarsophalangeal joints bilateral without pain or crepitation. There was aching and discomfort with active and passive range of motion of the left subtalar joint. Manual muscle testing revealed normal strength of the extrinsic musculature. A lateral radiograph revealed a large expansile lytic lesion within the neutral triangle of his left calcaneus (Fig. 1). There was no obvious cortical involvement of the subtalar or calcaneocuboid joints. Calcification was absent. Septations were evident within the lesion. Lateral and axial Tl- and T2-weighted magnetic resonance images were obtained. The T I-weighted images demonstrated heterogeneous signal intensities consistent with intralesional fat and hemorrhagic fluid (Fig. 2). A lateral incisional approach was employed. Surgical excision was performed through a lateral cortical window (Fig. 3). Curettage and drilling was performed leaving a large void within the body of the calcaneus (Fig. 4). The contents of the lesion consisted of yellow fatty tissue
with adherent pieces of tan bone and gray fibrous tissue measuring 2.3 x 2.2 x 1.4 cm. An additional 0.5 mL of hemorrhagic fluid was retrieved from the tumor area as well (Fig. 5). Pathologic examination was consistent with an intraosseous lipoma. Next, the void was packed with a combination of Osteosetf" bone pellets and Dynagraft™5 bone substitute (Fig. 6). A 4.0-mm cannulated screw was used to fixate the cortical window. The patient remained nonweightbearing for 7 weeks and gradually progressed to full weightbearing by 9 weeks postoperatively. Serial x-rays showed rapid incorporation of the synthetic graft (Fig. 7). No postoperative complications were encountered. The patient made a full functional recovery. Case 2 A 57-year-old Caucasian male presented with a lytic lesion within his right calcaneus that was first identified while he was being evaluated for metatarsalgia. He related a distinct history of an injury to the right heel 5 years prior when he kicked a sliding door. Initial radiographs revealed a large lucent lesion within the neutral triangle of the right calcaneus measuring approximately 3 em x 2 cm. The periphery of the lesion 4
5
Wright Medical Technology, Arlington. TN 38002. GenSci Regeneration Sciences Inc., Toronto, Canada.
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FIGURE 2 T1-weighted lateral (left image) and axial (right image) demonstrating the presence of a lipomatous lesion within the calcaneus. Multiple areas of hemorrhage are noted within the lesion.
FIGURE 3 Cortical window cut but not removed from the lateral wall of the calcaneus. The peroneal tendons have been reflected inferiorly. The extensor digitorum muscle is reflected dorsally and distally. A small area of the calcaneocuboid joint is visualized to ensure proper position and placement of the cortical window.
was well demarcated with an increase in sclerosis in some areas. Trabeculation was evident within the lesion. Further investigation of the lesion was recommended due to its unusually large size. 400
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A conventional bone scan revealed increase uptake of the lateral midfoot area. This finding was suggestive of degenerative changes of the midtarsal or intertarsal joints. Uptake specifically localized to the area of the tumor
FIGURE 4 Appearance of the cavity following removal of the window and excision of the contents of the tumor. Note the osseous septum , which correlates with the radiographic finding seen in Figure 1.
FIGURE 5 Appearance of the contents of the lesion. The recent hemorrhage has been collected in the syringe. The remaining portion of the tumor was consistent with intralesional lipomatous tissue.
was not seen. Furthermore, clinical exa mination failed to identify any symptoms in these areas. Magnetic reso nance imaging (MRI) of the righ t foot and ankle revealed a lobulated ex pansive lesion invol ving the entire anteri or and midp ortion of the body of the
ca lcaneus. Th e lesion extended from the superior to inferior cortex and from the medial to lateral cort ex as well . The lesion was sharply demarcated with low intensity central components, suggesting a central vascular supply. The predominant component of the lesion demon strated
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FIGURE 6 Appearance following compl ete curettage, drilling, and packing the deficit with a comb ination of osteoset'" pellets and Dynaqratt! bone substitute. Cortical window was then replaced and held in position with a small cortical bone screw.
FIGURE 7
Serial postoperative lateral x-rays of patient at 3 months (left) and 8 months (right). Note gradual incorporation of bone graft.
increased signal intensity on the T I-weighted image corresponding with decreased signal intensity on the T2weighted image , sugges ting a lipomatous lesion. The MRI esse ntially excluded the diagnosis of a unicamer al bone cys t, vascular lesion , or other lytic lesion and favored the diagnosis of an intraosseous lipomat ous tumo r. Due to the large expansive nature of the lesion and the concern for pathologic fracture in the future , surgical intervention was recommended. 402
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The patient underw ent complete excision of the tumor and packing of the deficit with autogenous and alloge neic cort icocancellous bone chips under general anesthesia. A lateral curvilinear incisional approach overlying the body of the calcaneus was employed. A " Z" -plasty transection of the peroneus brevis was performed. The peroneus longus was retracted inferiorly. Expansion of the lateral wall of the calcaneus was evident. The suspected tumor was localized with needl es and intraoperative radiographs.
A cortical window was created with the edges beveled inwardly to prevent inward migration of the window. Upon removal of the window, an abundance of lipomatous tissue was encountered. The resulting cavity measured 2.8 ern in depth, 3.5 em in length, and 3.0 em in height. The cortices and contiguous joints were not violated, although thinning of the cortex was appreciated. The wall of the entire lesion was gently curetted and irrigated. The defect was packed with autogenous iliac crest corticocancellous chips. Allogeneic cancellous chips were required to supplement the autogenous bone due to the large deficit. The cortical window was then replaced and secured with 2-0 absorbable suture and a single 2.0-mm cortical bone screw. Excellent stability was achieved. The peroneus brevis tendon was repaired with synthetic absorbable suture. Histologic examination confirmed the diagnosis of an intraosseous lipoma of bone. Mature adipose tissue was seen with some focal myxoid changes noted. Some bony spicules were observed within the fatty tissue itself. No evidence of malignancy was found. The histopathologic findings were consistent with the radiographs, MRI, and intraoperative findings. The postoperative course was unremarkable. Fourteen months postoperatively, the patient had full functional recovery with no limitations of activity. On a lateral x-ray 4 years postoperatively, there was no evidence of recurrence or degenerative changes in the contiguous joints.
Case 3 A 36-year-old female patient was seen in an emergency room for heel pain. Radiographs revealed a large lucency in the anterior one-third of the calcaneus. The patient was eventually referred for evaluation and treatment of a symptomatic bone tumor in her left calcaneus. The patient stated that her left heel had been painful for 7 months, and was increasing in severity over the preceding 4 months. The pain occurred during the night, disrupting her sleep, and during ambulation throughout the day. The pain was relieved with aspirin. Examination revealed tenderness while standing on the left heel and with direct palpation confined to a 3-cm area of the plantar lateral aspect of the calcaneus. Normal range of motion was present in the ankle, midtarsal, subtalar, and metatarsophalangeal joints bilateral without pain or crepitation. Manual muscle testing of the extrinsic muscles was normal. Lateral radiographs of the left calcaneus revealed a geographic lytic lesion with sclerotic borders within the anterior body of the calcaneus (Fig. 8). There was no apparent involvement of either the subtalar or calcaneocuboid joint. There was no periosteal reaction. lntralesional calcification was absent. A computed tomography (CT) scan revealed a large cystic lesion with a sclerotic rim involving the middle to distal two-thirds of the calcaneus and extending from
FIGURE 8 Preoperative lateral x-ray of left foot demonstrating large lytic lesion in the neutral triangle of the left calcaneus. There is no evidence of focal intralesional calcification.
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removed through a lateral cortical window with curettage. The contents of the lesion consisted of multiple shaggy fragments of yellow friable soft tissue measuring 2 x 1.5 x 0.4 em. The deficit was packed with autogenous iliac crest bone graft. The initial pathologic diagnosis was reported as fragments of unremarkable bone and fibrocollagenous and adipose tissue. After a complete review of the radiographs, CTs, intraoperative photographs, and discussion with the surgeon, the diagnosis was revised to that of an intraosseous lipoma. The patient's postoperative course was uneventful. At 7-year follow-up, radiographs showed complete graft incorporation (Fig. 10). Case 4
FIGURE 9 CT scan through the body of the calcaneus showing the extensive nature of the intraosseous lipoma. Note the preservation of the medial and lateral cortices.
medial to lateral cortices (Fig. 9). The attenuation values were consistent with intraosseous lipoma. The lesion was
FIGURE 10
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A 42-year-old male patient was referred for evaluation and treatment of a symptomatic bone tumor in his left calcaneus. He presented with severe pain and an antalgic gait pattern. He was treated in three different institutions for a severe flatfoot condition but the patient was unaware of the lesion. There was also a history of ankle sprain 2 years prior to presentation. The patient's past medical history was significant for multiple pituitary tumors requiring surgical excision, rheumatic fever, and Legionnaire's disease. He was taking 5 mg of prednisone daily. Neurologic examination revealed some nonspecific burning pain approximately 2-3 em posterior and superior to the left calcaneus. Orthopedic examination was consistent with a rigid flatfoot deformity. The left foot was severely abducted and left lower extremity externally rotated. Clinically there was no discernable movement of the subtalar joint. The peroneal
Seven-year postoperative lateral x-ray.
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FIGURE 11 sinus tarsi.
Lateral x-ray of left foot demonstrating geographic lesion in the neutral triangle. Note the increased sclerosis inferior to
tendon s were tight but not in severe spasm. Attempted manipulation of the subtalar joint was extremely painful with guarding. The midtarsal joint had limited range of motion . Original radiographs (Fig. II ) were reviewed along with CTs obtained 15 months follow ing the initial injury . A lytic lesion in the anterior body of the calcan eus extending proxim ally to the middle facet was seen with evidence of a healed pathologic fracture through the lesion (Fig. 12). The lesion did not appear to enter into the subtalar or calcaneocuboid joint complex. An MRI demonstrated irregular low linear signal in the anterior portion of the calcaneus surrounded by a focal zone of relatively increased signal within the marrow space on the T'I-weighted sequence. The T2 sequence showed persistent increased signal relative to the normal marrow signal. The increased signal was interpreted as being more con sistent with fat or hemorrhage probabl y secondary to the fracture. The diagno sis favored an intrao sseous lipoma rather than a bone cyst. The final diagno stic impression was consistent with a rigid spastic flatfoot deformity probably associated with the prior fracture in his left calcaneus. The patient elected to undergo excision and curettage of the lesion. packing the deficit autogenous iliac crest cancellous bone chips , and subtalar arthrode sis with autogenous iliac crest bone graft. The contents of the lesion were yellow-gray tissue measuring 1.9 x 1.2 x 0.3 em with bony fragments. Pathologic confirmation was obtained after a thorough review of the radiographs, CT, MRI, and clinical picture.
The patient was maintained nonweightbearing for 9 weeks and gradually progressed to full weightbearing at 12 weeks. A short cour se of physical therapy was completed. Serial x-rays were obtained and 7-year followup demonstrated consolidation of the subtalar fusion site and incorporation of the iliac crest cancellous bone chip s (Fig. 13). Discussion
The precise etiology of an intraosseous lipoma is unknown. Many authors believe that they arise as benign primary bone tumors consisting of mature adipose tissue (3, 6, 8, 9). Various theorie s have emphasized the uncertainty of its origin. Mueller and Robbins (8) hypothesized fatty degeneration or intramedullary callus formation following a tibial fracture 29 months earlier in a 14year-old male patient. Thi s view was supported by the following observation s: I) a lesion found at the location of a prior fracture , 2) a suggestive area of decreased density on x-ray 2 1h month s after the injury, and 3) no evidence of erosion or expansion of the cortex. Hart questioned whether intrao sseous lipomas are true tumor s of bone (3). He discussed the following pathologic entities as potential etiologies: fracture, chronic bone infarction, localized osteoporosis, and benign bone tumor. Ultimately, he supported the idea that they are true benign bone tumors based on the macro scopic appearance of the lesion as a distinct mas s within the bone and the frequent rate of bone expansion.
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FIGURE 12 CTscan demonstrating evidence of a healed calcaneal fracture through the bone tumor. Encroachment of the medial wall and floor of the sinus tarsi is present.
Intraosseous lipomas of the calcaneus are usually asymptomatic. Not uncommonly they are discovered as an incidental finding on roentgenographic exam (6, 10-12). However, symptoms in the presence of these lesions may be present in the heel and are usually nonspecific. Patients may relate a sensation of constant or intermittent aching heel pain most commonly on the plantar aspect, which is exacerbated by activity (1, 6, 12, 13). The duration of symptoms may vary from months to years and may lead to the misdiagnosis of plantar fasciitis (14). On physical exam, edema mayor may not be present. If present, it is usually not remarkable. Tenderness to palpation may be found in the region immediately surrounding the tumor. No prominences are found when examining the foot and the osseous architecture feels normal. Range of motion of the subtalar, midtarsal, and ankle joint is usually normal, but may be mildly painful and/or limited if the tumor is in close proximity to the joint. The patient may present with an antalgic gait pattern. Vibratory exam may elicit pain particularly if the tumor involves cortical or subchondral bone. 406
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Intraosseous lipomas usually present as lytic lesions in the metaphysis of long bones and, when isolated to the calcaneus, they have a geographic pattern. In general, intraosseous lipomas are small and most measure less than 6 em in diameter (15). In the calcaneus, these lesions are commonly located in the anterior portion of the body within the neutral triangle (6, 11, 16, 17). There is usually a well defined area of radiolucency with variable amounts of central calcifications (6, 7, 16-19). The calcifications, however, are not always present. When found in the calcaneus, this lesion usually has a well defined border (9, 12, 18, 20). Periosteal reactions are rare. To the authors' knowledge, there have been no known previous reported cases of pathologic fractures involving the calcaneus with these tumors. Bruni considered the radiographic appearance of intraosseous calcaneal lipomas to be diagnostic based on roentgenographic features, including the "cockade image" (7). This was described as an osteolytic zone with distinct margins and central calcification. While radiographic evaluation of intraosseous calcaneal lipomas is extremely helpful, the lytic findings are nonspecific. The features have sometimes led to misdiagnosis as unicameral bone cyst (UBC) or aneurysmal bone cyst (ABC) (6, 12, 13, 18) (Fig. 14). Intralesional calcification and cortical bone expansion are common findings of intraosseous calcaneal lipomas. In the absence of these findings, intraosseous calcaneal lipomas may closely resemble unicameral bone cysts (6). CT may be helpful in differentiating intraosseous lipomas from unicameral bone cysts of the calcaneus (Fig. 15) (12, 20-23). Keyter et al. found CT useful in making a preoperative differential diagnosis by measuring attenuation levels of the tissues within the lesion (22). Some consider CT identification of a calcific nidus confirmatory of an intraosseous lipoma of the calcaneus (24). However, the inaccuracy of CT evaluation by measuring attenuation levels of these tumors has been demonstrated in multiple studies, thus questioning the validity and benefit of its use (20, 21, 24). A poor interpretation may reflect the failure of the technician to localize the actual contents of the lesion. CT can be helpful with surgical planning by providing information such as anatomic location, size and extent of lesion, and pathologic fracture potential. Magnetic resonance imaging is more useful in defining the extent of bone marrow and soft-tissue involvement of bone tumors (25). The primary role of MRI is to visualize intralesional tissue that is consistent with fat, thus identifying the tumor as an intraosseous calcaneal lipoma (17, 26). On MRI, the margins of the intraosseous lipoma may be well demarcated or ill defined. Some consider MRI superior to CT when demonstrating the precise intraosseous expansion of lipomas of the calcaneus (27).
FIGURE 13 Long-term follow-up x-rays 7 years following surgical excision of the tumor and primary arthrodesis of the subtalar joint. Note complete consolidation of bone graft.
When the tumors are homogeneous on Tl-weighted images, anatomy, including adipose tissue, may be readily visualized. Increased signal intensity (51) within the lesion is consistent with intralesional fat. Occasionally, decreased 51 may be visualized centrally consistent with a central osseous nidus (28). On the T2-weighted image, the area consistent with intralesional fat will have decreased signal intensity. MRI often distinguishes UBCs from intraosseous calcaneal lipomas. UBCs are homogenous and will consistently demonstrate a decreased 51 within the entire lesion on Tl-weighted images. On T2-weighted images, the entire lesion shows increased 51 consistent with free fluid (Fig. 16). MRI may be very suggestive of aneurysmal bone cysts; however, it is not diagnostic (29). They may demonstrate expansile, multilocular fluid-filled cavities. Fluid-fluid levels from hemorrhage within the lesion and diverticulalike projections originating from the walls of the larger cyst are frequent findings (30). Fluid-fluid levels appear as a layered configuration of signal intensity within these septated Ioculations. At the periphery of the lesion, a well defined rim of low 51 on both Tl- and T2-weighted images is seen, indicating an inner wall of fibrous tissue (31). Misdiagnosis of intraosseous calcaneal lipomas can be attributed to the method by which the specimen was obtained, how the specimen was submitted, and/or lack of experience with this tumor. The tumor should be excised en toto for the best histopathologic analysis. The
pathologist must be aware that the specimen submitted represents the actual contents of the lesion. The main differential diagnosis is between intraosseous lipoma and normal fatty marrow. The histopathologic features are only meaningful in the context of radiographic and specialized imaging findings. Other less common differentials include bone infarct, enchondroma, chondromyxoid fibroma, giant cell tumor of bone, fibrous dysplasia, chondroblastoma, intraosseous ganglion, and Brodie's abscess of osteomyelitis (7, 11, 32-34). The histologic picture may vary for intraosseous lipomas. The specimen demonstrates atrophied bony trabeculae within mature adipose tissue. The presence of lamellar bone with no true capsular lining may also be seen (Fig. 17). Occasionally, osteocytes are found along with spicules of bone, but lack any osteoblastic activity. After reviewing the literature, there is still some inconsistency on conservative versus surgical treatment. When the patient is symptomatic and does not respond to standard conservative treatment, surgical intervention should be considered. Excision of the lesion with curettage and packing of the defect with bone graft is currently the treatment of choice. A biopsy may be indicated to establish the definitive diagnosis of questionable tumors prior to definitive treatment (34). To our knowledge, there have been no reported recurrences of intraosseous lipomas involving the foot or ankle after surgical excision.
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FIGURE 14 Lateral radiographs demonstrating radiographic appearance and location of an intraosseous calcaneal lipoma (A) and a unicameral cyst (B).
When the tumor is stable and the patient is asymptomatic, a "cautious, watch and wait" approach may be taken. Serial radiographs every 6 months, repeat MRls, and continued follow-up visits should be considered. Complications associated with these tumors, such as 408
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intra-articular or extra-articular calcaneal fracture should be discussed with the patient. The postoperative course may vary, depending upon the size, location, and extent of the lesion as well as involvement of the subtalar joint. It is recommended that
FIGURE 15 Axial CT scans demonstrating the similarity between an intraosseous lipoma (right image) and unicameral bone cyst within the calcaneus (left image).
FIGURE 16 MRI demonstrating a homogenous lesion with decreas ed signal intensity on an axial T1-weighted image qeft) with an increase in signal intensity on the corresponding T2- weighted image (right) . These find ings are cons istent with a unicameral bone cyst.
the pati ent remain non weightbearing for the first 6-8 weeks, followed by prote cted weig htbeari ng for an additional 2 weeks and a gradual return to full activities. Physical therapy and earl y range-of-motion exercises will help
increase strength and prevent stiffness. Serial radio graphs should be taken every 4-6 weeks to evaluate, monitor, and assess the incorporation of the graft within the calc aneu s and possible recurrence of the tumor.
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FIGURE 17
Photomicrograph (40x) of bony trabeculae within mature adipose tissue surrounded by a fibrous capsule.
Summary
A review of the literature, four new cases, and surgical technique associated with intraosseous calcaneal lipomas are presented. One of these tumors was associated with a pathologic fracture of the calcaneus, a finding that to our knowledge has not been previously reported in the literature. These tumors need to be investigated further when suspected. A combination of clinical, radiographic, and specialized imaging studies, along with a histopathologic examination, should be utilized to establish the final diagnosis. References 1. Child, P. L. Lipoma of the os calcis. Arne. J. Clini. Pathol. 25: 1050, 1955. 2. Dahlin, D. C. Bone Tumors: General Aspects and Data on 8,542 Cases, 4th ed., pp. 181-185, edited by Charles C Thomas, Springfield, IL, 1986. 3. Hart, J. Intraosseous lipoma. 1. Bone Joint Surg. 55-B:624-632, 1973. 4. Bakotic, B., Huvos, A. G. Tumors of the bones of the feet: the clinicopathologic features of 150 cases. 1. Foot Ankle Surg. 40(5):277-286,2001. 5. Resnick, D. Tumors and tumor-like lesions of bone: imaging and pathology of specific lesions, ch. 74. In Bone and Joint Imaging, 2nd ed., pp. 1037-1038, W.B. Saunders, Philadelphia, 1996. 6. Greenspan, A., Raiszadeh, K., Riley, G. M., Matthews, D. Intraosseous lipoma of the calcaneus. Foot Ankle Int. 18(1):53-56, 1997.
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7. Bruni, L. The "cockade" image: a diagnostic sign of calcaneum intraosseous lipoma. Rays 11(1):51-54, 1986. 8. Mueller, M., Robbins, J. Intramedullary lipoma of bone. J. Bone Joint Surg. 42-A:517, 1960. 9. Appenzeller, J., Weitzner, S. Intraosseous lipoma of the os calcis. Clin. Orthop. 101:171-175, 1974. 10. Niemi, W. J., Pressman, M. M., Patel, S. Y. Bilateral interosseous lipoma of the calcaneus. 1. Am. Podiatr. Med. Assoc. 87(4):189-191, 1997. 11. Poussa, M., Holstrom, T. Intraosseous lipoma of the calcaneus. Report of a case and a short review of the literature. Acta Orthop. Scand. 47(5):570-574, 1976. 12. Rhodes, R. D., Page, J. C Intraosseous lipoma of the os calcis. J. Am. Podiatr. Med. Assoc. 83(5):288-292, 1993. 13. Boylan, J. P., Springer, K. R., Halpern, F. P. Intraosseous lipoma of the calcaneus. A case report. 1. Am. Podiatr. Med. Assoc. 81(9):502-550, 1991. 14. Gonzalez, J. Y., Stuck, R. M., Streit, N. Intraosseous lipoma of the calcaneus: a clinicopathologic study of three cases. 1. Foot Ankle Surg. 36(4):306-310, 1997. 15. Mirra, J. M. Intraosseous lipoma. In Bone Tumors: Diagnosis and Treatment, 2nd ed., Lippincott Williams & Wilkins, Philadelphia, 1989. 16. Schatz, S. G., Dipaola, J. D., D' Agostino, H. R., Quinn, S. F. Intraosseous lipoma of the calcaneus. 1. Foot Surg. 31(4):381 - 384, 1992. 17. Lagier, R. Case report 128: lipoma of the calcaneus with bone infarct. Skeletal Radiol. 5(4):267-269, 1980. 18. Hodge, 1. C, Sundaram, M., Janney, C G. Clinics in diagnostic imaging (21). Intraosseous lipoma of the calcaneum. Singapore Med J. 38(1):41-43,1997. 19. Goldenhar, A. S., Maloney, 1. P., Helff,1. R. Negative bone scan in the diagnosis of calcaneal intraosseous lipoma. J. Am. Podiatr. Med. Assoc. 83(10):600-602, 1993.
20. Ramos, A, Castello, J., Sartoris, D. J., Greenway, G. D., Resnick, D., Haghighi, P. Osseous lipoma: CT appearance. Radiology 157:615-619, 1985. 21. Hall, F. M., Cohen, R. B., Grumach, X. Case report 377. Skeletal Radiol. 15:401-403, 1986. 22. Keyter, S, Brownstein, S, Cholankeril, J. CT diagnosis of intraosseous lipoma of the calcaneus. J. Comput. Assist. Tomogr. 7:546-547, 1983. 23. Reig-Boix, Y., Guinot-Tormot,1., Risent-Martinez, Aprisi-Rodriguez, 1., Ferrer-Jiminez, R. Computed tomography of intraosseous lipoma of os calcis. Clin. Orthop. 221:286-291,1987 24. Rosenblatt, E., Mollin, 1., Abdelwahab, I. Bilateral calcaneal intraosseous lipomas: a case report. Mt. Sinai J. Med. 57: 174- 176, 1990. 25. Cohen, M. D., Weetman, R. M., Provisor, D. J., et al. Efficacy of magnetic resonance imaging in 139 children with tumors. Arch. Surg. 121:522, 1986. 26. Zimmer, W. D., Berquist, T. H., Mcleod, R. A., Sim, F. H., Pritchard, D. J., Shives, T. c.. Wold, L. E., May, G. R. Bone tumors: magnetic resonance imaging versus computed tomography. Radiology. 155(3):709-718, 1985.
27. Levey, D. S., Sartoris, D. J., Resnick, D. Advanced diagnostic imaging techniques for pedal osseous neoplasms. Clin. Med. Surg. 10:655-682,1993. 28. Richardson, A. A, Erdmann, B. B., Beier-Hanratty, S., Lautz, D., Jacobs, P. M., Julsrud, M. E., Ringstom, J. B. Magnetic resonance imagery of a calcaneal lipoma. J. Am. Podiatr. Med. Assoc. 85(9):493-496, 1995. 29. Yu, G. Y., Roth, L. S., Sellers, C. S. Aneurysmal bone cyst of the fibula. J. Foot Ankle Surg. 37:426-436, 1998. 30. Hudson, T. M., Hamlin, J., Fitzsimmons, J. R. Magnetic resonance imaging of fluid levels in an aneurysmal bone cysts and in anticoagulated human blood. Skeletal Radiol. 13:267 - 270, 1985. 31. Munk, P. L., Helms, C. A, Holt, R. G., Johnston, 1., Steinbach, L., Neumann, C. MR imaging of aneurysmal bone cysts. AJR 153:99-101, 1989. 32. Milgram, J. W. Intraosseous lipomas: a clinicopathologic study of 66 cases. Clin. Orthop. 231 :277 - 302, 1988. 33. Leeson, M. C., Kay, D., Smith, B. S. Intraosseous lipoma. Clin. Orthop. 181:186-190, 1983. 34. Delee, J. C. Intraosseous lipoma of the proximal part of the femur. 1. Bone Joint Surg. 61-A:601-603, 1979.
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Intraosseous Lipoma of the Calcaneus: A Review and Report of Four Cases Glenn D. Weinfeld, DPM 1 , Gerard V. Yu, DPM, FACFAS,2 and James J. Good, DPM 3 Intraosseous lipomas have been reported as rare tumors in the lower extremity. They have been identified in the tibia, fibula, metatarsals, and calcaneus. They are frequently misdiagnosed as other tumors, especially unicameral bone cysts or aneurysmal bone cysts when found within the calcaneus. A detailed description of intraosseous calcaneal lipomas and their treatment is given. Surgical technique and four case reports are presented. One of the cases involved a pathologic calcaneal fracture, a finding to the authors' knowledge that has not been previously reported. (The Journal of Foot & Ankle Surgery 41 (6):398-411, 2002) Key words: benign bone tumors, calcaneus, intraosseous lipoma
Intraosseous lipomas of the calcaneus are uncommon. Because these lesions are benign and often asymptomatic, the true incidence is largely unknown. Much of the literature discusses isolated case reports. In 1955, Child published the first case to the authors' knowledge of an intraosseous lipoma involving the calcaneus (1). Dahlin's review of 8452 bone tumors from the Mayo clinic found only six intraosseous lipomas with an overall incidence less than I in 1000 (2). None of these cases involved the foot or ankle. A comprehensive review of the literature revealed only 28 cases of intraosseous lipomas involving the entire skeleton over a 100-year period (3). Six were found in the foot and ankle: three in the distal tibia, two in the distal fibula, and one in the anterior body of the calcaneus. More recently, Bakotic and Huvos reviewed 150 tumors specifically found in the small bones of the feet over a l5-year period from From St. Vincent Charity Hospital, Cleveland, OH. Address correspondence to: Glenn D. Weinfeld, DPM, 1215 Annapolis Rd., Suite 101, Odenton, MD 21113. E-mail: [email protected]. I Submitted during 2nd year of residency, St. Vincent Charity Podiatric Surgical Residency Program. 2 Diplomate, American Board of Podiatric Surgery; Director of Podiatric Medical Education, St. Vincent Charity Hospital; Faculty Member, The Podiatry Institute, Tucker, GA; private practice, Cleveland, OH ] Submitted during 3rd year of residency, St. Vincent Charity Podiatric Surgical Residency Program. Received for publication June 4, 2001; accepted in revised form for publication June 2, 2002. The Journal of Foot & Ankle Surgery 1067-2516/02/4106-0398$4.00/0 Copyright © 2002 by the American College of Foot and Ankle Surgeons
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1985 to 2000 (4). Although the calcaneus was the most common single bone involved in their study, there were no cases of an intraosseous calcaneal lipoma. The paucity of intraosseous lipomas may be explained by their classification as other entities such as unicameral or aneurysmal bone cysts (5). Recently, Greenspan et al. reviewed six osseous lesions in the calcaneus consistent with intraosseous lipomas (6). Three of the lesions were confirmed by histologic exam after undergoing surgical intervention. The remaining three lesions were asymptomatic and incidentally discovered while evaluating other musculoskeletal complaints. All of the lesions demonstrated a calcified nidus within a radiolucent lesion in the neutral triangle of the calcaneus, a feature that has been considered diagnostic (5, 7). The purpose of this article is to present four case reports of an intraosseous lipoma of the calcaneus and to provide a detailed description of the lesion. A detailed surgical protocol is also described. Case 1 A 27-year-old male patient was referred for evaluation and treatment of a symptomatic bone tumor in his left calcaneus. The patient stated that his heel had been painful for more than 5 years and became significantly more painful in the 2-3 preceding months. He had been seen by two other physicians and was treated for plantar fasciitis in a conventional manner. The pain was relieved overnight with rest; however, with weightbearing, a sharp,
FIGURE 1 Preoperative lateral x-ray demonstrating a large lytic lesion within the neutral triangle of the left calcaneus. Note the expansile appearance of this bone tumor and lack of intralesional calcification. An osseous septum is noted.
aching pain ensued which worsened over the course of the day. He had an antalgic gait, favoring the left foot by walking on his toes. He was extremely concerned about malignancy in light of a recent history of cancer in his family resulting in the loss of his mother. Examination revealed significant pain to palpation at the plantar aspect of his left heel and along the course of the plantar fascia. Palpation along the lateral wall of the calcaneus was also painful. Normal range of motion was present in the ankle, midtarsal, and metatarsophalangeal joints bilateral without pain or crepitation. There was aching and discomfort with active and passive range of motion of the left subtalar joint. Manual muscle testing revealed normal strength of the extrinsic musculature. A lateral radiograph revealed a large expansile lytic lesion within the neutral triangle of his left calcaneus (Fig. 1). There was no obvious cortical involvement of the subtalar or calcaneocuboid joints. Calcification was absent. Septations were evident within the lesion. Lateral and axial Tl- and T2-weighted magnetic resonance images were obtained. The T I-weighted images demonstrated heterogeneous signal intensities consistent with intralesional fat and hemorrhagic fluid (Fig. 2). A lateral incisional approach was employed. Surgical excision was performed through a lateral cortical window (Fig. 3). Curettage and drilling was performed leaving a large void within the body of the calcaneus (Fig. 4). The contents of the lesion consisted of yellow fatty tissue
with adherent pieces of tan bone and gray fibrous tissue measuring 2.3 x 2.2 x 1.4 cm. An additional 0.5 mL of hemorrhagic fluid was retrieved from the tumor area as well (Fig. 5). Pathologic examination was consistent with an intraosseous lipoma. Next, the void was packed with a combination of Osteosetf" bone pellets and Dynagraft™5 bone substitute (Fig. 6). A 4.0-mm cannulated screw was used to fixate the cortical window. The patient remained nonweightbearing for 7 weeks and gradually progressed to full weightbearing by 9 weeks postoperatively. Serial x-rays showed rapid incorporation of the synthetic graft (Fig. 7). No postoperative complications were encountered. The patient made a full functional recovery. Case 2 A 57-year-old Caucasian male presented with a lytic lesion within his right calcaneus that was first identified while he was being evaluated for metatarsalgia. He related a distinct history of an injury to the right heel 5 years prior when he kicked a sliding door. Initial radiographs revealed a large lucent lesion within the neutral triangle of the right calcaneus measuring approximately 3 em x 2 cm. The periphery of the lesion 4
5
Wright Medical Technology, Arlington. TN 38002. GenSci Regeneration Sciences Inc., Toronto, Canada.
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FIGURE 2 T1-weighted lateral (left image) and axial (right image) demonstrating the presence of a lipomatous lesion within the calcaneus. Multiple areas of hemorrhage are noted within the lesion.
FIGURE 3 Cortical window cut but not removed from the lateral wall of the calcaneus. The peroneal tendons have been reflected inferiorly. The extensor digitorum muscle is reflected dorsally and distally. A small area of the calcaneocuboid joint is visualized to ensure proper position and placement of the cortical window.
was well demarcated with an increase in sclerosis in some areas. Trabeculation was evident within the lesion. Further investigation of the lesion was recommended due to its unusually large size. 400
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A conventional bone scan revealed increase uptake of the lateral midfoot area. This finding was suggestive of degenerative changes of the midtarsal or intertarsal joints. Uptake specifically localized to the area of the tumor
FIGURE 4 Appearance of the cavity following removal of the window and excision of the contents of the tumor. Note the osseous septum , which correlates with the radiographic finding seen in Figure 1.
FIGURE 5 Appearance of the contents of the lesion. The recent hemorrhage has been collected in the syringe. The remaining portion of the tumor was consistent with intralesional lipomatous tissue.
was not seen. Furthermore, clinical exa mination failed to identify any symptoms in these areas. Magnetic reso nance imaging (MRI) of the righ t foot and ankle revealed a lobulated ex pansive lesion invol ving the entire anteri or and midp ortion of the body of the
ca lcaneus. Th e lesion extended from the superior to inferior cortex and from the medial to lateral cort ex as well . The lesion was sharply demarcated with low intensity central components, suggesting a central vascular supply. The predominant component of the lesion demon strated
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FIGURE 6 Appearance following compl ete curettage, drilling, and packing the deficit with a comb ination of osteoset'" pellets and Dynaqratt! bone substitute. Cortical window was then replaced and held in position with a small cortical bone screw.
FIGURE 7
Serial postoperative lateral x-rays of patient at 3 months (left) and 8 months (right). Note gradual incorporation of bone graft.
increased signal intensity on the T I-weighted image corresponding with decreased signal intensity on the T2weighted image , sugges ting a lipomatous lesion. The MRI esse ntially excluded the diagnosis of a unicamer al bone cys t, vascular lesion , or other lytic lesion and favored the diagnosis of an intraosseous lipomat ous tumo r. Due to the large expansive nature of the lesion and the concern for pathologic fracture in the future , surgical intervention was recommended. 402
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The patient underw ent complete excision of the tumor and packing of the deficit with autogenous and alloge neic cort icocancellous bone chips under general anesthesia. A lateral curvilinear incisional approach overlying the body of the calcaneus was employed. A " Z" -plasty transection of the peroneus brevis was performed. The peroneus longus was retracted inferiorly. Expansion of the lateral wall of the calcaneus was evident. The suspected tumor was localized with needl es and intraoperative radiographs.
A cortical window was created with the edges beveled inwardly to prevent inward migration of the window. Upon removal of the window, an abundance of lipomatous tissue was encountered. The resulting cavity measured 2.8 ern in depth, 3.5 em in length, and 3.0 em in height. The cortices and contiguous joints were not violated, although thinning of the cortex was appreciated. The wall of the entire lesion was gently curetted and irrigated. The defect was packed with autogenous iliac crest corticocancellous chips. Allogeneic cancellous chips were required to supplement the autogenous bone due to the large deficit. The cortical window was then replaced and secured with 2-0 absorbable suture and a single 2.0-mm cortical bone screw. Excellent stability was achieved. The peroneus brevis tendon was repaired with synthetic absorbable suture. Histologic examination confirmed the diagnosis of an intraosseous lipoma of bone. Mature adipose tissue was seen with some focal myxoid changes noted. Some bony spicules were observed within the fatty tissue itself. No evidence of malignancy was found. The histopathologic findings were consistent with the radiographs, MRI, and intraoperative findings. The postoperative course was unremarkable. Fourteen months postoperatively, the patient had full functional recovery with no limitations of activity. On a lateral x-ray 4 years postoperatively, there was no evidence of recurrence or degenerative changes in the contiguous joints.
Case 3 A 36-year-old female patient was seen in an emergency room for heel pain. Radiographs revealed a large lucency in the anterior one-third of the calcaneus. The patient was eventually referred for evaluation and treatment of a symptomatic bone tumor in her left calcaneus. The patient stated that her left heel had been painful for 7 months, and was increasing in severity over the preceding 4 months. The pain occurred during the night, disrupting her sleep, and during ambulation throughout the day. The pain was relieved with aspirin. Examination revealed tenderness while standing on the left heel and with direct palpation confined to a 3-cm area of the plantar lateral aspect of the calcaneus. Normal range of motion was present in the ankle, midtarsal, subtalar, and metatarsophalangeal joints bilateral without pain or crepitation. Manual muscle testing of the extrinsic muscles was normal. Lateral radiographs of the left calcaneus revealed a geographic lytic lesion with sclerotic borders within the anterior body of the calcaneus (Fig. 8). There was no apparent involvement of either the subtalar or calcaneocuboid joint. There was no periosteal reaction. lntralesional calcification was absent. A computed tomography (CT) scan revealed a large cystic lesion with a sclerotic rim involving the middle to distal two-thirds of the calcaneus and extending from
FIGURE 8 Preoperative lateral x-ray of left foot demonstrating large lytic lesion in the neutral triangle of the left calcaneus. There is no evidence of focal intralesional calcification.
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removed through a lateral cortical window with curettage. The contents of the lesion consisted of multiple shaggy fragments of yellow friable soft tissue measuring 2 x 1.5 x 0.4 em. The deficit was packed with autogenous iliac crest bone graft. The initial pathologic diagnosis was reported as fragments of unremarkable bone and fibrocollagenous and adipose tissue. After a complete review of the radiographs, CTs, intraoperative photographs, and discussion with the surgeon, the diagnosis was revised to that of an intraosseous lipoma. The patient's postoperative course was uneventful. At 7-year follow-up, radiographs showed complete graft incorporation (Fig. 10). Case 4
FIGURE 9 CT scan through the body of the calcaneus showing the extensive nature of the intraosseous lipoma. Note the preservation of the medial and lateral cortices.
medial to lateral cortices (Fig. 9). The attenuation values were consistent with intraosseous lipoma. The lesion was
FIGURE 10
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A 42-year-old male patient was referred for evaluation and treatment of a symptomatic bone tumor in his left calcaneus. He presented with severe pain and an antalgic gait pattern. He was treated in three different institutions for a severe flatfoot condition but the patient was unaware of the lesion. There was also a history of ankle sprain 2 years prior to presentation. The patient's past medical history was significant for multiple pituitary tumors requiring surgical excision, rheumatic fever, and Legionnaire's disease. He was taking 5 mg of prednisone daily. Neurologic examination revealed some nonspecific burning pain approximately 2-3 em posterior and superior to the left calcaneus. Orthopedic examination was consistent with a rigid flatfoot deformity. The left foot was severely abducted and left lower extremity externally rotated. Clinically there was no discernable movement of the subtalar joint. The peroneal
Seven-year postoperative lateral x-ray.
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FIGURE 11 sinus tarsi.
Lateral x-ray of left foot demonstrating geographic lesion in the neutral triangle. Note the increased sclerosis inferior to
tendon s were tight but not in severe spasm. Attempted manipulation of the subtalar joint was extremely painful with guarding. The midtarsal joint had limited range of motion . Original radiographs (Fig. II ) were reviewed along with CTs obtained 15 months follow ing the initial injury . A lytic lesion in the anterior body of the calcan eus extending proxim ally to the middle facet was seen with evidence of a healed pathologic fracture through the lesion (Fig. 12). The lesion did not appear to enter into the subtalar or calcaneocuboid joint complex. An MRI demonstrated irregular low linear signal in the anterior portion of the calcaneus surrounded by a focal zone of relatively increased signal within the marrow space on the T'I-weighted sequence. The T2 sequence showed persistent increased signal relative to the normal marrow signal. The increased signal was interpreted as being more con sistent with fat or hemorrhage probabl y secondary to the fracture. The diagno sis favored an intrao sseous lipoma rather than a bone cyst. The final diagno stic impression was consistent with a rigid spastic flatfoot deformity probably associated with the prior fracture in his left calcaneus. The patient elected to undergo excision and curettage of the lesion. packing the deficit autogenous iliac crest cancellous bone chips , and subtalar arthrode sis with autogenous iliac crest bone graft. The contents of the lesion were yellow-gray tissue measuring 1.9 x 1.2 x 0.3 em with bony fragments. Pathologic confirmation was obtained after a thorough review of the radiographs, CT, MRI, and clinical picture.
The patient was maintained nonweightbearing for 9 weeks and gradually progressed to full weightbearing at 12 weeks. A short cour se of physical therapy was completed. Serial x-rays were obtained and 7-year followup demonstrated consolidation of the subtalar fusion site and incorporation of the iliac crest cancellous bone chip s (Fig. 13). Discussion
The precise etiology of an intraosseous lipoma is unknown. Many authors believe that they arise as benign primary bone tumors consisting of mature adipose tissue (3, 6, 8, 9). Various theorie s have emphasized the uncertainty of its origin. Mueller and Robbins (8) hypothesized fatty degeneration or intramedullary callus formation following a tibial fracture 29 months earlier in a 14year-old male patient. Thi s view was supported by the following observation s: I) a lesion found at the location of a prior fracture , 2) a suggestive area of decreased density on x-ray 2 1h month s after the injury, and 3) no evidence of erosion or expansion of the cortex. Hart questioned whether intrao sseous lipomas are true tumor s of bone (3). He discussed the following pathologic entities as potential etiologies: fracture, chronic bone infarction, localized osteoporosis, and benign bone tumor. Ultimately, he supported the idea that they are true benign bone tumors based on the macro scopic appearance of the lesion as a distinct mas s within the bone and the frequent rate of bone expansion.
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FIGURE 12 CTscan demonstrating evidence of a healed calcaneal fracture through the bone tumor. Encroachment of the medial wall and floor of the sinus tarsi is present.
Intraosseous lipomas of the calcaneus are usually asymptomatic. Not uncommonly they are discovered as an incidental finding on roentgenographic exam (6, 10-12). However, symptoms in the presence of these lesions may be present in the heel and are usually nonspecific. Patients may relate a sensation of constant or intermittent aching heel pain most commonly on the plantar aspect, which is exacerbated by activity (1, 6, 12, 13). The duration of symptoms may vary from months to years and may lead to the misdiagnosis of plantar fasciitis (14). On physical exam, edema mayor may not be present. If present, it is usually not remarkable. Tenderness to palpation may be found in the region immediately surrounding the tumor. No prominences are found when examining the foot and the osseous architecture feels normal. Range of motion of the subtalar, midtarsal, and ankle joint is usually normal, but may be mildly painful and/or limited if the tumor is in close proximity to the joint. The patient may present with an antalgic gait pattern. Vibratory exam may elicit pain particularly if the tumor involves cortical or subchondral bone. 406
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Intraosseous lipomas usually present as lytic lesions in the metaphysis of long bones and, when isolated to the calcaneus, they have a geographic pattern. In general, intraosseous lipomas are small and most measure less than 6 em in diameter (15). In the calcaneus, these lesions are commonly located in the anterior portion of the body within the neutral triangle (6, 11, 16, 17). There is usually a well defined area of radiolucency with variable amounts of central calcifications (6, 7, 16-19). The calcifications, however, are not always present. When found in the calcaneus, this lesion usually has a well defined border (9, 12, 18, 20). Periosteal reactions are rare. To the authors' knowledge, there have been no known previous reported cases of pathologic fractures involving the calcaneus with these tumors. Bruni considered the radiographic appearance of intraosseous calcaneal lipomas to be diagnostic based on roentgenographic features, including the "cockade image" (7). This was described as an osteolytic zone with distinct margins and central calcification. While radiographic evaluation of intraosseous calcaneal lipomas is extremely helpful, the lytic findings are nonspecific. The features have sometimes led to misdiagnosis as unicameral bone cyst (UBC) or aneurysmal bone cyst (ABC) (6, 12, 13, 18) (Fig. 14). Intralesional calcification and cortical bone expansion are common findings of intraosseous calcaneal lipomas. In the absence of these findings, intraosseous calcaneal lipomas may closely resemble unicameral bone cysts (6). CT may be helpful in differentiating intraosseous lipomas from unicameral bone cysts of the calcaneus (Fig. 15) (12, 20-23). Keyter et al. found CT useful in making a preoperative differential diagnosis by measuring attenuation levels of the tissues within the lesion (22). Some consider CT identification of a calcific nidus confirmatory of an intraosseous lipoma of the calcaneus (24). However, the inaccuracy of CT evaluation by measuring attenuation levels of these tumors has been demonstrated in multiple studies, thus questioning the validity and benefit of its use (20, 21, 24). A poor interpretation may reflect the failure of the technician to localize the actual contents of the lesion. CT can be helpful with surgical planning by providing information such as anatomic location, size and extent of lesion, and pathologic fracture potential. Magnetic resonance imaging is more useful in defining the extent of bone marrow and soft-tissue involvement of bone tumors (25). The primary role of MRI is to visualize intralesional tissue that is consistent with fat, thus identifying the tumor as an intraosseous calcaneal lipoma (17, 26). On MRI, the margins of the intraosseous lipoma may be well demarcated or ill defined. Some consider MRI superior to CT when demonstrating the precise intraosseous expansion of lipomas of the calcaneus (27).
FIGURE 13 Long-term follow-up x-rays 7 years following surgical excision of the tumor and primary arthrodesis of the subtalar joint. Note complete consolidation of bone graft.
When the tumors are homogeneous on Tl-weighted images, anatomy, including adipose tissue, may be readily visualized. Increased signal intensity (51) within the lesion is consistent with intralesional fat. Occasionally, decreased 51 may be visualized centrally consistent with a central osseous nidus (28). On the T2-weighted image, the area consistent with intralesional fat will have decreased signal intensity. MRI often distinguishes UBCs from intraosseous calcaneal lipomas. UBCs are homogenous and will consistently demonstrate a decreased 51 within the entire lesion on Tl-weighted images. On T2-weighted images, the entire lesion shows increased 51 consistent with free fluid (Fig. 16). MRI may be very suggestive of aneurysmal bone cysts; however, it is not diagnostic (29). They may demonstrate expansile, multilocular fluid-filled cavities. Fluid-fluid levels from hemorrhage within the lesion and diverticulalike projections originating from the walls of the larger cyst are frequent findings (30). Fluid-fluid levels appear as a layered configuration of signal intensity within these septated Ioculations. At the periphery of the lesion, a well defined rim of low 51 on both Tl- and T2-weighted images is seen, indicating an inner wall of fibrous tissue (31). Misdiagnosis of intraosseous calcaneal lipomas can be attributed to the method by which the specimen was obtained, how the specimen was submitted, and/or lack of experience with this tumor. The tumor should be excised en toto for the best histopathologic analysis. The
pathologist must be aware that the specimen submitted represents the actual contents of the lesion. The main differential diagnosis is between intraosseous lipoma and normal fatty marrow. The histopathologic features are only meaningful in the context of radiographic and specialized imaging findings. Other less common differentials include bone infarct, enchondroma, chondromyxoid fibroma, giant cell tumor of bone, fibrous dysplasia, chondroblastoma, intraosseous ganglion, and Brodie's abscess of osteomyelitis (7, 11, 32-34). The histologic picture may vary for intraosseous lipomas. The specimen demonstrates atrophied bony trabeculae within mature adipose tissue. The presence of lamellar bone with no true capsular lining may also be seen (Fig. 17). Occasionally, osteocytes are found along with spicules of bone, but lack any osteoblastic activity. After reviewing the literature, there is still some inconsistency on conservative versus surgical treatment. When the patient is symptomatic and does not respond to standard conservative treatment, surgical intervention should be considered. Excision of the lesion with curettage and packing of the defect with bone graft is currently the treatment of choice. A biopsy may be indicated to establish the definitive diagnosis of questionable tumors prior to definitive treatment (34). To our knowledge, there have been no reported recurrences of intraosseous lipomas involving the foot or ankle after surgical excision.
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FIGURE 14 Lateral radiographs demonstrating radiographic appearance and location of an intraosseous calcaneal lipoma (A) and a unicameral cyst (B).
When the tumor is stable and the patient is asymptomatic, a "cautious, watch and wait" approach may be taken. Serial radiographs every 6 months, repeat MRls, and continued follow-up visits should be considered. Complications associated with these tumors, such as 408
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intra-articular or extra-articular calcaneal fracture should be discussed with the patient. The postoperative course may vary, depending upon the size, location, and extent of the lesion as well as involvement of the subtalar joint. It is recommended that
FIGURE 15 Axial CT scans demonstrating the similarity between an intraosseous lipoma (right image) and unicameral bone cyst within the calcaneus (left image).
FIGURE 16 MRI demonstrating a homogenous lesion with decreas ed signal intensity on an axial T1-weighted image qeft) with an increase in signal intensity on the corresponding T2- weighted image (right) . These find ings are cons istent with a unicameral bone cyst.
the pati ent remain non weightbearing for the first 6-8 weeks, followed by prote cted weig htbeari ng for an additional 2 weeks and a gradual return to full activities. Physical therapy and earl y range-of-motion exercises will help
increase strength and prevent stiffness. Serial radio graphs should be taken every 4-6 weeks to evaluate, monitor, and assess the incorporation of the graft within the calc aneu s and possible recurrence of the tumor.
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FIGURE 17
Photomicrograph (40x) of bony trabeculae within mature adipose tissue surrounded by a fibrous capsule.
Summary
A review of the literature, four new cases, and surgical technique associated with intraosseous calcaneal lipomas are presented. One of these tumors was associated with a pathologic fracture of the calcaneus, a finding that to our knowledge has not been previously reported in the literature. These tumors need to be investigated further when suspected. A combination of clinical, radiographic, and specialized imaging studies, along with a histopathologic examination, should be utilized to establish the final diagnosis. References 1. Child, P. L. Lipoma of the os calcis. Arne. J. Clini. Pathol. 25: 1050, 1955. 2. Dahlin, D. C. Bone Tumors: General Aspects and Data on 8,542 Cases, 4th ed., pp. 181-185, edited by Charles C Thomas, Springfield, IL, 1986. 3. Hart, J. Intraosseous lipoma. 1. Bone Joint Surg. 55-B:624-632, 1973. 4. Bakotic, B., Huvos, A. G. Tumors of the bones of the feet: the clinicopathologic features of 150 cases. 1. Foot Ankle Surg. 40(5):277-286,2001. 5. Resnick, D. Tumors and tumor-like lesions of bone: imaging and pathology of specific lesions, ch. 74. In Bone and Joint Imaging, 2nd ed., pp. 1037-1038, W.B. Saunders, Philadelphia, 1996. 6. Greenspan, A., Raiszadeh, K., Riley, G. M., Matthews, D. Intraosseous lipoma of the calcaneus. Foot Ankle Int. 18(1):53-56, 1997.
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7. Bruni, L. The "cockade" image: a diagnostic sign of calcaneum intraosseous lipoma. Rays 11(1):51-54, 1986. 8. Mueller, M., Robbins, J. Intramedullary lipoma of bone. J. Bone Joint Surg. 42-A:517, 1960. 9. Appenzeller, J., Weitzner, S. Intraosseous lipoma of the os calcis. Clin. Orthop. 101:171-175, 1974. 10. Niemi, W. J., Pressman, M. M., Patel, S. Y. Bilateral interosseous lipoma of the calcaneus. 1. Am. Podiatr. Med. Assoc. 87(4):189-191, 1997. 11. Poussa, M., Holstrom, T. Intraosseous lipoma of the calcaneus. Report of a case and a short review of the literature. Acta Orthop. Scand. 47(5):570-574, 1976. 12. Rhodes, R. D., Page, J. C Intraosseous lipoma of the os calcis. J. Am. Podiatr. Med. Assoc. 83(5):288-292, 1993. 13. Boylan, J. P., Springer, K. R., Halpern, F. P. Intraosseous lipoma of the calcaneus. A case report. 1. Am. Podiatr. Med. Assoc. 81(9):502-550, 1991. 14. Gonzalez, J. Y., Stuck, R. M., Streit, N. Intraosseous lipoma of the calcaneus: a clinicopathologic study of three cases. 1. Foot Ankle Surg. 36(4):306-310, 1997. 15. Mirra, J. M. Intraosseous lipoma. In Bone Tumors: Diagnosis and Treatment, 2nd ed., Lippincott Williams & Wilkins, Philadelphia, 1989. 16. Schatz, S. G., Dipaola, J. D., D' Agostino, H. R., Quinn, S. F. Intraosseous lipoma of the calcaneus. 1. Foot Surg. 31(4):381 - 384, 1992. 17. Lagier, R. Case report 128: lipoma of the calcaneus with bone infarct. Skeletal Radiol. 5(4):267-269, 1980. 18. Hodge, 1. C, Sundaram, M., Janney, C G. Clinics in diagnostic imaging (21). Intraosseous lipoma of the calcaneum. Singapore Med J. 38(1):41-43,1997. 19. Goldenhar, A. S., Maloney, 1. P., Helff,1. R. Negative bone scan in the diagnosis of calcaneal intraosseous lipoma. J. Am. Podiatr. Med. Assoc. 83(10):600-602, 1993.
20. Ramos, A, Castello, J., Sartoris, D. J., Greenway, G. D., Resnick, D., Haghighi, P. Osseous lipoma: CT appearance. Radiology 157:615-619, 1985. 21. Hall, F. M., Cohen, R. B., Grumach, X. Case report 377. Skeletal Radiol. 15:401-403, 1986. 22. Keyter, S, Brownstein, S, Cholankeril, J. CT diagnosis of intraosseous lipoma of the calcaneus. J. Comput. Assist. Tomogr. 7:546-547, 1983. 23. Reig-Boix, Y., Guinot-Tormot,1., Risent-Martinez, Aprisi-Rodriguez, 1., Ferrer-Jiminez, R. Computed tomography of intraosseous lipoma of os calcis. Clin. Orthop. 221:286-291,1987 24. Rosenblatt, E., Mollin, 1., Abdelwahab, I. Bilateral calcaneal intraosseous lipomas: a case report. Mt. Sinai J. Med. 57: 174- 176, 1990. 25. Cohen, M. D., Weetman, R. M., Provisor, D. J., et al. Efficacy of magnetic resonance imaging in 139 children with tumors. Arch. Surg. 121:522, 1986. 26. Zimmer, W. D., Berquist, T. H., Mcleod, R. A., Sim, F. H., Pritchard, D. J., Shives, T. c.. Wold, L. E., May, G. R. Bone tumors: magnetic resonance imaging versus computed tomography. Radiology. 155(3):709-718, 1985.
27. Levey, D. S., Sartoris, D. J., Resnick, D. Advanced diagnostic imaging techniques for pedal osseous neoplasms. Clin. Med. Surg. 10:655-682,1993. 28. Richardson, A. A, Erdmann, B. B., Beier-Hanratty, S., Lautz, D., Jacobs, P. M., Julsrud, M. E., Ringstom, J. B. Magnetic resonance imagery of a calcaneal lipoma. J. Am. Podiatr. Med. Assoc. 85(9):493-496, 1995. 29. Yu, G. Y., Roth, L. S., Sellers, C. S. Aneurysmal bone cyst of the fibula. J. Foot Ankle Surg. 37:426-436, 1998. 30. Hudson, T. M., Hamlin, J., Fitzsimmons, J. R. Magnetic resonance imaging of fluid levels in an aneurysmal bone cysts and in anticoagulated human blood. Skeletal Radiol. 13:267 - 270, 1985. 31. Munk, P. L., Helms, C. A, Holt, R. G., Johnston, 1., Steinbach, L., Neumann, C. MR imaging of aneurysmal bone cysts. AJR 153:99-101, 1989. 32. Milgram, J. W. Intraosseous lipomas: a clinicopathologic study of 66 cases. Clin. Orthop. 231 :277 - 302, 1988. 33. Leeson, M. C., Kay, D., Smith, B. S. Intraosseous lipoma. Clin. Orthop. 181:186-190, 1983. 34. Delee, J. C. Intraosseous lipoma of the proximal part of the femur. 1. Bone Joint Surg. 61-A:601-603, 1979.
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