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Calcaneal Intraosseous Lipoma: A Case Report and Review of the Literature
The Journal of Foot & Ankle Surgery 50 (2011) 216–220
Contents lists available at ScienceDirect
The Journal of Foot & Ankle Surgery journal homepage: www.jfas.org
Case Reports
Calcaneal Intraosseous Lipoma: A Case Report and Review of the Literature Sagar Narang, MS 1, Mimi Gangopadhyay, MD 2 1 2
Assistant Professor, Department of Orthopaedics, North Bengal Medical College and Hospital, Darjeeling, India Assistant Professor, Department of Pathology, North Bengal Medical College and Hospital, Darjeeling, India
a r t i c l e i n f o
a b s t r a c t
Level of Clinical Evidence: 4 Keywords: bone fat foot heel neoplasm surgery tumor
Intraosseous lipomas are rare benign bone tumors. This benign neoplasm has been reported to occur in the calcaneus as well as the proximal femur. In the past, the relative absence of symptoms and radiographic similarity to a bone cyst has accounted for underdiagnosis of intraosseous lipoma. The case presented in this article was diagnosed with the help of computerized tomography and histopathologic analysis, after which the patient was treated by means of curettage and packing with calcium phosphate bone graft substitute. The purpose of this article is to increase awareness among clinicians of the existence of this unusual lesion. Ó 2011 by the American College of Foot and Ankle Surgeons. All rights reserved.
The list of differential diagnoses for heel pain is long and varied, and includes such common culprits as plantar fasciitis, retrocalcaneal bursitis, gout, and stress fracture. This article describes a case of heel pain caused by an intraosseous lipoma (IOL), which is a rare benign bone tumor. IOL does not usually present as an expansive mass within bone, with the exception of the parosteal variant of IOL (1). The calcaneus is now recognized as the most common site of involvement for IOL, followed by the subtrochanteric region of the femur (2, 3).
Case Report A 38-year-old male army recruit presented with the complaint of a dull, aching pain in his left heel of 3 months’ duration. The pain was noted to increase after strenuous walking or other rigorous activities involving the left foot, and had been increasing steadily over the 3-month period, although there was no associated swelling observed in the foot. The patient’s primary care physician at the army base hospital managed him initially with rest and analgesics (aceclofenac, 100 mg twice a day, for 1 week), which afforded temporary relief. The clinician also obtained blood laboratory tests, including an erythrocyte sedimentation rate, and measurement of the uric acid and C-reactive protein level, and no abnormalities were found. Plain radiographs revealed the presence of a radiolucent lesion interspersed with trabeculations in the anteroinferior portion of the left Financial Disclosure: None reported. Conflict of Interest: None reported. Address correspondence to: Sagar Narang, MS, Department of Orthopaedics, North Bengal Medical College and Hospital, Gokul Apartments, Block A, Flat 1A, Panjabipara, Siliguri-734001, India. E-mail address: [email protected] (S. Narang).
Fig. 1. Preoperative radiograph (lateral view) of the left heel showing presence of intraosseous lipoma.
1067-2516/$ - see front matter Ó 2011 by the American College of Foot and Ankle Surgeons. All rights reserved. doi:10.1053/j.jfas.2010.12.004
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Fig. 2. (A) CT scan of sagittal section showing calcaneal intraosseous lipoma. (B) CT scan of axial section showing calcaneal intraosseous lipoma.
calcaneus underlying the subtalar joint (Figure 1). It was at this point that the patient was referred to our surgical service. Upon gross examination, we noted that the patient walked with an antalgic limp, and preferred to walk on his left toes to avoid left heel contact with the ground. There were no obvious soft tissue masses, scars, sinuses or venous prominences overlying the affected area, and the ankle and subtalar joint motions were normal, and the left heel was tender to palpation. There was no past medical history that would increase the likelihood of bone infarction, such as corticosteroid use, infection, previous irradiation, lipid storage disease, collagen-vascular disease, or lymphoproliferative disorder. A computerized tomography (CT) scan of the left foot revealed the presence of a cyst in the anteroinferior portion of the calcaneus, with expansion of the inferior cortex. The cyst was subjacent to the subtalar joint and displayed soft tissue density without cortical breach (Figure 2), whereas the calcaneocuboid and talocalcaneal joints appeared normal. The report of the radiologist described a benign bone cyst of the calcaneus and advised further correlation. Based on the clinical and diagnostic image findings, IOL was diagnosed and operative decompression of the cyst was subsequently undertaken. The calcaneus was approached from the lateral aspect through an incision overlying its long axis, after which the cortex overlying the cyst was exposed on the inferior and lateral aspects.
When the cyst was decorticated, a greasy, yellow intraosseous lipoma-like “syrup” was identified and evacuated from the osseous cavity (Figure 3). The soft tissue contents of the intraosseous cyst were removed along with the greasy fluid (Figure 4), and the entire specimen was sent for histopathologic diagnosis. The cavity of the calcaneus was lavaged with normal saline before injection of calcium phosphate bone graft substitute (chronOs Inject, Synthes, West Chester, PA) to back-fill the resultant void (Figure 5). After filling the cavity, the wound was closed in anatomic layers and a sterile dressing applied, followed by application of a below-the-knee plaster splint for use during the initial postoperative period of non–weight-bearing ambulation. Subsequent histopathologic analysis revealed areas of mature lipocytes with the presence of medullary trabecular bone, interspersed with areas of hemorrhage (Figure 6). There was no cellular atypia or abnormal mitosis. These findings were consistent with the diagnosis of IOL. The patient’s heel pain subsided almost immediately after the operation, with the exception of surgical wound pain, which subsided in a normal fashion. Superficial breakdown of the surgical wound was noted at a dressing change on the fifth day postoperative, and this was treated with cleansing and secondary suturing that healed without incident by 2 weeks following the evacuation and packing of the calcaneus. Two weeks following suture removal, the plaster splint was
Fig. 3. Intraoperative photograph of the left calcaneus showing the cavity following removal of the intraosseous lipoma.
Fig. 4. Intraoperative photograph of the intraosseous lipoma after removal from the calcaneus.
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Fig. 5. (A) Injection of bone graft substitute under image intensifier guidance. (B) Postoperative radiograph of the left foot after injection of bone graft substitute.
removed, and ankle range of motion exercises and toe-touch weight bearing were initiated. At 1 month postoperative, the patient was ambulating full weight bearing using a stick for added support. He subsequently gave up use of the cane, and resumed his regular weight-bearing activities. At the time of the 12-month follow-up evaluation, the patient was free of pain and ambulating unaided. Radiographs (not shown) taken at that visit displayed partial osseous integration of the calcium phosphate bone graft substitute without evidence of recurrence of the cyst. Discussion Intraosseous lipoma was first reported in 1880 (4), and its etiology is still a matter of debate. It is generally accepted that IOL accounts for fewer than 0.1% of primary bone tumors; however, higher prevalences have been reported (5). Males and females are affected in equal proportion (6), as opposed to its soft tissue counterpart, namely, soft tissue lipoma, which shows a female preponderance (2). The mean age at presentation is 40 to 43 (range 4–85) years. The paucity of symptoms associated with IOL often results in delayed diagnosis, and it is reported as an incidental finding in 30% of cases. In 70% of cases, pain is the presenting feature (7–9). Microfractures in the trabecular network of the calcaneus following minor trauma may be responsible for the pain at presentation (2). The lower limb is involved in 71% of cases, and upper limb involvement accounts for 7% of cases; and, when the axial skeleton is involved, the following prevalences have
been reported: skull (4%), mandible (3%), spine (4%), sacrum (2%), pelvis (5%), and ribs (2.5%) (2). Furthermore, the most common site of involvement in the lower limb is the calcaneus (32%), followed by the subtrochanteric region of the femur, the distal femur, and the proximal or distal fibula (2). Pathologic fracture of the calcaneus has also been reported in association with IOL (10–12). Small cysts that are not located in the pressure-bearing trabecular area of the calcaneus are usually asymptomatic and can be treated conservatively (13). A “critical-size cyst” has been defined as an IOL extending the full breadth of the calcaneus laterally to medially in the coronal plane, and occupying at least 30% of the length of the calcaneus anteroposteriorly. Because the presence of a pathological fracture through a calcaneal cyst makes the operative procedure more complex and healing less predictable, the authors believe that large symptomatic calcaneal cysts should be managed surgically to reduce morbidity (14). The decision to operate on a calcaneal cyst should be based on its size and location, the provisional diagnosis, associated symptoms, and the activity level and health of the patient (3, 15). Although IOL is a benign lesion, Milgram (16) described 4 cases of IOL that underwent malignant transformation, and liposarcoma and malignant fibrous histiocytoma have also been found adjacent to benign lipomas. It is also interesting to note that each and every case of calcaneal IOL reported in the biomedical literature localized to the “neutral triangle,” an area devoid of the trabecular network crossing the calcaneus and sometimes referred to as the “pseudotumor” or “pseudocyst” in standard radiographs (17). The neutral triangle is
Fig. 6. (A) Histological specimen showing viable lipocytes (black arrow) and bony trabeculae (red arrow) (hematoxylin and eosin, 250). (B) High-power view showing lipocytes, bone, and hemorrhage.
S. Narang, M. Gangopadhyay / The Journal of Foot & Ankle Surgery 50 (2011) 216–220
Fig. 7. Radiograph of the neutral triangle of calcaneum with intraosseous lipoma.
a normal radiographic finding that is formed between the traction trabeculae radiating from the inferior cortex of the calcaneus and the compression trabeculae converging to support the posterior and anterior articular facets (Figure 7). IOLs are classified according to their location or histopathologic and radiographic characteristics. Based on location, osseous lipomas are classified as intramedullary, intracortical, subperiosteal, or parosteal (3). Milgram (8), using histopathology and radiographs, classified IOLs into 3 groups depending on the degree of involution. Stage I lesions are purely radiolucent; contain viable lipocytes and thin, bony trabeculae; and do not display necrosis. Stage II lesions are partially radiolucent with some calcification, and display an admixture of necrosed and viable lipocytes. Stage III tumors have larger areas of central and peripheral calcification, no bony trabeculae, and the fat component is fully necrotic (8). The gross appearance of an IOL is that of soft yellow tissue. Free oil (fluid lipid) has been reported to be present during surgery, possibly owing to the breakdown of fatty tissue-forming intralesional cysts (18), and this was the case in the patient described in this article. Histologically, the lesion is well circumscribed and consists of mature lipocytes surrounding bony trabeculae with no cellular atypia (19). Areas of fat necrosis may also be present, as well as foamy histiocytes, cholesterol clefts, and reactive bone formation (2). The histologic findings may be difficult to distinguish from those of liposarcoma, chondrosarcoma, pseudocyst of rheumatoid arthritis, localized osteoporosis, hyperlipoproteinemia, and chronic tuberculosis (3). Radiographically, IOL appears as an osteolytic, well-circumscribed lesion with a thin sclerotic rim. Lesions may be expansive, particularly in the fibula, and internal septations and nidus/mineralization may be present, depending on the stage. Owing to the indolent course of the tumor, there is an absence of cortical destruction and periosteal reaction. The radiographic appearance is not unique, making it difficult to distinguish IOL from nonossifying fibroma, simple bone cyst, aneurysmal bone cyst, giant-cell tumor, fibrous dysplasia, bone infarct, chondroid tumor (2), or a fungal infection of bone (3). Peripheral calcification may be seen in lesions localized outside of the calcaneus. The CT appearance of calcaneal cysts demonstrates attenuation values equivalent to that of fat, and Milgram stage III tumors
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displaying massive calcification and other dystrophic changes on CT and magnetic resonance image (MRI) scans may present a diagnostic challenge (20). In addition, IOLs may be confused with bone infarcts, because the latter also contain fat and have a low signal intensity rim when imaged with CT or MRI. However, unlike bone infarcts, calcaneal IOLs are expansile lesions that remodel cancellous and cortical bone. MRI images best display the presence of fat inside the tumor on T1-weighted and T2 fat-suppressed images (21). Whether IOLs are true benign adipose tumors is a matter of debate owing to the difficulty of distinguishing neoplastic from nonneoplastic lipocytes (8). Some have described IOLs as overshoot phenomena of the normal remodelling process from hematopoietic to fatty marrow, or as a maturational continuum between a bone cyst and an IOL. Simple cysts of the calcaneus occur in the same location and, like IOLs, do not possess an epithelial lining, suggesting a common etiology. Lipomas have also been postulated to be an involutional stage of simple bone cysts. Conversely, some authors argue that calcaneal cysts arise from degeneration of preexisting IOLs (22). Bone infarcts can give rise to IOLs, as can the final stages of an inflammatory process (23). Trauma has been postulated as a cause, whereby a fracture callus undergoes fatty degeneration and infarction (24, 25). Increased intravenous pressure in the intraosseous compartment has also been proposed as a possible cause of IOL, based on the treatment success obtained with continuous cavitary decompression, which has gained a foothold as a treatment option. IOL has also been found to be associated with a group of lesions called liposclerosing myxofibrous tumors (LSMFT) (26). Treatment of IOL is based on the site, size, and symptomatology of the lesion. Small, asymptomatic cysts in non–weight-bearing areas of bone can be observed for progression. Symptomatic, “critical-size cysts” require surgical intervention, as a general rule. Treatment options include steroid injection, curettage without grafting, curettage plus augmentation with bone graft or bone graft substitute, or continuous decompression in conjunction with the use of a cannulated cancellous titanium screw (13, 27). Steroid injections yield unpredictable results, whereas curettage with bone-grafting or calcium phosphate bone cement augmentation have been shown to be effective more often than not. Furthermore, calcium phosphate bone graft substitute is advantageous in comparison with autograft, because donor site morbidity is no longer a concern. The purpose of this article and the accompanying literature review is to increase clinicians’ awareness of intraosseous lipoma and the usefulness of CT scans in establishing the diagnosis, and to provide an overview of treatment modalities that highlight the use of calcium phosphate bone graft substitute as an osteoconductive scaffold in the management of this benign bone defect when it occurs in the calcaneus. References 1. Ramos A, Castello J, Sartoris DJ, Greenway GD, Resnick D, Haghighi P. Osseous lipoma: CT appearance. Radiology 157:615–619, 1985. 2. Campbell RSD, Grainger AJ, Mangham DC, Beggs I, Teh J, Davies AM. Intraosseous lipoma: report of 35 new cases and a review of the literature. Skeletal Radiol 32:209–222, 2003. 3. Kapukaya A, Subasi M, Dabak N, Ozkul E. Osseous lipoma: eleven new cases and review of the literature. Acta Orthop Belg 72:603–614, 2006. 4. Reig-Boix V, Guinot-Tormo J, Risent-Martinez F, Aparisi-Rodriguez F, FerrerJimenez R. Computed tomography of intraosseous lipoma of os calcis. Clin Orthop 221:286–291, 1987. 5. Chow LT, Lee KC. Intraosseous lipoma. A clinicopathologic study of nine cases. Am J Surg Pathol 16:401–410, 1992. 6. Oztekin O, Argin M, Oktay A, Arkun R. Intraosseous lipoma: radiological findings. Radiol Bras 41(2):81–86, 2008. 7. Levin MF, Vellet AD, Munk PL, McLean CA. Intraosseous lipoma of the distal femur: MRI appearance. Skeletal Radiol 25:82–84, 1996. 8. Milgram JW. Intraosseous lipomas. A clinicopathologic study of 66 cases. Clin Orthop 231:277–302, 1988.
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9. Gonzalez JV, Stuck RM, Streit N. Intraosseous lipoma of the calcaneus: a clinicopathologic study of three cases. J Foot Ankle Surg 36:306–310, 1997. discussion 329. 10. Csizy M, Buckley RE, Fennell C. Benign calcaneal bone cyst and pathological fracture: surgical treatment with injectable calcium-phosphate bone cement (NorianÒ): a case report. Foot Ankle Int 2:507–510, 2001. 11. Epstein J, Wertheim SJ. Unicameral bone cyst of the calcaneus. Literature review and case studies. J Am Podiatr Med Assoc 74:76–79, 1984. 12. Grumbine NA, Clark GD. Unicameral bone cyst in the calcaneus with pathologic fracture. J Am Podiatr Med Assoc 76:96–99, 1986. 13. Saraph V, Zwick E-B, Maizen C, Schneider F, Linhart WE. Treatment of unicameral calcaneal bone cysts in children: review of literature and results using a cannulated screw for continuous decompression of the cyst. J Pediatr Orthop 24:568–573, 2004. 14. Pogoda P, Matthias P, Wolfgang L, Alexander S, Gerhard A, Joachim W, Johannes R, Michael A. Clinical relevance of calcaneal bone cysts: a study of 50 cysts in 47 patients. Clin Orthop Relat Res 424:202–210, 2004. 15. Sim E, Haid CH. Einkammrige Fersenbeinzysten: Operationsindikation, biomechanische Berechnungen und Nachuntersuchungsergebnisse. Z Orthop 128:623– 631, 1990. 16. Milgram JW. Malignant transformation in bone lipomas. Skeletal Radiol 19:347– 352, 1990. 17. Sanders R. Current concepts review: displaced intra-articular fractures of the calcaneus. J Bone Joint Surg Am 82:225–250, 2000.
18. Dickson AB, Ayres WW, Mason MW, Miller WR. Lipoma of bone of intra-osseous origin. J Bone Joint Surg Am 33:257–259, 1951. 19. Huvos AG. Miscellaneous tumors of soft tissue and bone. In Bone Tumors: Diagnosis, Treatment, and Prognosis, ed 2, pp 745–766, edited by AG Huvos, Philadelphia, WB Saunders Company, 1991. 20. Goto T, Kojima T, Iijima T, Yokokura S, Motoi T, Kawano H, Yamamoto A, Matsuda K. Intraosseous lipoma a clinical study of 12 patients. J Orthop Sci 7:274–280, 2002. 21. Templeton KJ. A 29-year-old man with buttock pain. Clin Orthop Relat Res 413:316–322, 2003. 22. Lagier R. Case report 128: lipoma of the calcaneus with bone infarct. Skeletal Radiol 5:267–269, 1980. 23. Barker GR, Sloan P. Intraosseous lipomas: clinical features of a mandibular case with possible aetiology. Br J Oral Maxillofac Surg 24:459–463, 1986. 24. Poussa M, Holmstrom T. Intraosseous lipoma of the calcaneus. Report of a case and a short review of the literature. Acta Orthop Scand 47:570–574, 1976. 25. Mueller MC, Robbins JL. Intramedullary lipoma of bone. J Bone Joint Surg Am 42:517–520, 1960. 26. Ragsdale BD. Polymorphic fibroosseous lesions of bone: an almost site specific diagnostic problem of the proximal femur. Hum Pathol 24:505–512, 1993. 27. Hong J, Andersson J, Ekdahl KN, Elgue G, Axen N, Larsson R, Nilsson B. Titanium is a highly thrombogenic biomaterial: possible implications for osteogenesis. Thromb Haemost 82:58–64, 1999.
Contents lists available at ScienceDirect
The Journal of Foot & Ankle Surgery journal homepage: www.jfas.org
Case Reports
Calcaneal Intraosseous Lipoma: A Case Report and Review of the Literature Sagar Narang, MS 1, Mimi Gangopadhyay, MD 2 1 2
Assistant Professor, Department of Orthopaedics, North Bengal Medical College and Hospital, Darjeeling, India Assistant Professor, Department of Pathology, North Bengal Medical College and Hospital, Darjeeling, India
a r t i c l e i n f o
a b s t r a c t
Level of Clinical Evidence: 4 Keywords: bone fat foot heel neoplasm surgery tumor
Intraosseous lipomas are rare benign bone tumors. This benign neoplasm has been reported to occur in the calcaneus as well as the proximal femur. In the past, the relative absence of symptoms and radiographic similarity to a bone cyst has accounted for underdiagnosis of intraosseous lipoma. The case presented in this article was diagnosed with the help of computerized tomography and histopathologic analysis, after which the patient was treated by means of curettage and packing with calcium phosphate bone graft substitute. The purpose of this article is to increase awareness among clinicians of the existence of this unusual lesion. Ó 2011 by the American College of Foot and Ankle Surgeons. All rights reserved.
The list of differential diagnoses for heel pain is long and varied, and includes such common culprits as plantar fasciitis, retrocalcaneal bursitis, gout, and stress fracture. This article describes a case of heel pain caused by an intraosseous lipoma (IOL), which is a rare benign bone tumor. IOL does not usually present as an expansive mass within bone, with the exception of the parosteal variant of IOL (1). The calcaneus is now recognized as the most common site of involvement for IOL, followed by the subtrochanteric region of the femur (2, 3).
Case Report A 38-year-old male army recruit presented with the complaint of a dull, aching pain in his left heel of 3 months’ duration. The pain was noted to increase after strenuous walking or other rigorous activities involving the left foot, and had been increasing steadily over the 3-month period, although there was no associated swelling observed in the foot. The patient’s primary care physician at the army base hospital managed him initially with rest and analgesics (aceclofenac, 100 mg twice a day, for 1 week), which afforded temporary relief. The clinician also obtained blood laboratory tests, including an erythrocyte sedimentation rate, and measurement of the uric acid and C-reactive protein level, and no abnormalities were found. Plain radiographs revealed the presence of a radiolucent lesion interspersed with trabeculations in the anteroinferior portion of the left Financial Disclosure: None reported. Conflict of Interest: None reported. Address correspondence to: Sagar Narang, MS, Department of Orthopaedics, North Bengal Medical College and Hospital, Gokul Apartments, Block A, Flat 1A, Panjabipara, Siliguri-734001, India. E-mail address: [email protected] (S. Narang).
Fig. 1. Preoperative radiograph (lateral view) of the left heel showing presence of intraosseous lipoma.
1067-2516/$ - see front matter Ó 2011 by the American College of Foot and Ankle Surgeons. All rights reserved. doi:10.1053/j.jfas.2010.12.004
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Fig. 2. (A) CT scan of sagittal section showing calcaneal intraosseous lipoma. (B) CT scan of axial section showing calcaneal intraosseous lipoma.
calcaneus underlying the subtalar joint (Figure 1). It was at this point that the patient was referred to our surgical service. Upon gross examination, we noted that the patient walked with an antalgic limp, and preferred to walk on his left toes to avoid left heel contact with the ground. There were no obvious soft tissue masses, scars, sinuses or venous prominences overlying the affected area, and the ankle and subtalar joint motions were normal, and the left heel was tender to palpation. There was no past medical history that would increase the likelihood of bone infarction, such as corticosteroid use, infection, previous irradiation, lipid storage disease, collagen-vascular disease, or lymphoproliferative disorder. A computerized tomography (CT) scan of the left foot revealed the presence of a cyst in the anteroinferior portion of the calcaneus, with expansion of the inferior cortex. The cyst was subjacent to the subtalar joint and displayed soft tissue density without cortical breach (Figure 2), whereas the calcaneocuboid and talocalcaneal joints appeared normal. The report of the radiologist described a benign bone cyst of the calcaneus and advised further correlation. Based on the clinical and diagnostic image findings, IOL was diagnosed and operative decompression of the cyst was subsequently undertaken. The calcaneus was approached from the lateral aspect through an incision overlying its long axis, after which the cortex overlying the cyst was exposed on the inferior and lateral aspects.
When the cyst was decorticated, a greasy, yellow intraosseous lipoma-like “syrup” was identified and evacuated from the osseous cavity (Figure 3). The soft tissue contents of the intraosseous cyst were removed along with the greasy fluid (Figure 4), and the entire specimen was sent for histopathologic diagnosis. The cavity of the calcaneus was lavaged with normal saline before injection of calcium phosphate bone graft substitute (chronOs Inject, Synthes, West Chester, PA) to back-fill the resultant void (Figure 5). After filling the cavity, the wound was closed in anatomic layers and a sterile dressing applied, followed by application of a below-the-knee plaster splint for use during the initial postoperative period of non–weight-bearing ambulation. Subsequent histopathologic analysis revealed areas of mature lipocytes with the presence of medullary trabecular bone, interspersed with areas of hemorrhage (Figure 6). There was no cellular atypia or abnormal mitosis. These findings were consistent with the diagnosis of IOL. The patient’s heel pain subsided almost immediately after the operation, with the exception of surgical wound pain, which subsided in a normal fashion. Superficial breakdown of the surgical wound was noted at a dressing change on the fifth day postoperative, and this was treated with cleansing and secondary suturing that healed without incident by 2 weeks following the evacuation and packing of the calcaneus. Two weeks following suture removal, the plaster splint was
Fig. 3. Intraoperative photograph of the left calcaneus showing the cavity following removal of the intraosseous lipoma.
Fig. 4. Intraoperative photograph of the intraosseous lipoma after removal from the calcaneus.
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Fig. 5. (A) Injection of bone graft substitute under image intensifier guidance. (B) Postoperative radiograph of the left foot after injection of bone graft substitute.
removed, and ankle range of motion exercises and toe-touch weight bearing were initiated. At 1 month postoperative, the patient was ambulating full weight bearing using a stick for added support. He subsequently gave up use of the cane, and resumed his regular weight-bearing activities. At the time of the 12-month follow-up evaluation, the patient was free of pain and ambulating unaided. Radiographs (not shown) taken at that visit displayed partial osseous integration of the calcium phosphate bone graft substitute without evidence of recurrence of the cyst. Discussion Intraosseous lipoma was first reported in 1880 (4), and its etiology is still a matter of debate. It is generally accepted that IOL accounts for fewer than 0.1% of primary bone tumors; however, higher prevalences have been reported (5). Males and females are affected in equal proportion (6), as opposed to its soft tissue counterpart, namely, soft tissue lipoma, which shows a female preponderance (2). The mean age at presentation is 40 to 43 (range 4–85) years. The paucity of symptoms associated with IOL often results in delayed diagnosis, and it is reported as an incidental finding in 30% of cases. In 70% of cases, pain is the presenting feature (7–9). Microfractures in the trabecular network of the calcaneus following minor trauma may be responsible for the pain at presentation (2). The lower limb is involved in 71% of cases, and upper limb involvement accounts for 7% of cases; and, when the axial skeleton is involved, the following prevalences have
been reported: skull (4%), mandible (3%), spine (4%), sacrum (2%), pelvis (5%), and ribs (2.5%) (2). Furthermore, the most common site of involvement in the lower limb is the calcaneus (32%), followed by the subtrochanteric region of the femur, the distal femur, and the proximal or distal fibula (2). Pathologic fracture of the calcaneus has also been reported in association with IOL (10–12). Small cysts that are not located in the pressure-bearing trabecular area of the calcaneus are usually asymptomatic and can be treated conservatively (13). A “critical-size cyst” has been defined as an IOL extending the full breadth of the calcaneus laterally to medially in the coronal plane, and occupying at least 30% of the length of the calcaneus anteroposteriorly. Because the presence of a pathological fracture through a calcaneal cyst makes the operative procedure more complex and healing less predictable, the authors believe that large symptomatic calcaneal cysts should be managed surgically to reduce morbidity (14). The decision to operate on a calcaneal cyst should be based on its size and location, the provisional diagnosis, associated symptoms, and the activity level and health of the patient (3, 15). Although IOL is a benign lesion, Milgram (16) described 4 cases of IOL that underwent malignant transformation, and liposarcoma and malignant fibrous histiocytoma have also been found adjacent to benign lipomas. It is also interesting to note that each and every case of calcaneal IOL reported in the biomedical literature localized to the “neutral triangle,” an area devoid of the trabecular network crossing the calcaneus and sometimes referred to as the “pseudotumor” or “pseudocyst” in standard radiographs (17). The neutral triangle is
Fig. 6. (A) Histological specimen showing viable lipocytes (black arrow) and bony trabeculae (red arrow) (hematoxylin and eosin, 250). (B) High-power view showing lipocytes, bone, and hemorrhage.
S. Narang, M. Gangopadhyay / The Journal of Foot & Ankle Surgery 50 (2011) 216–220
Fig. 7. Radiograph of the neutral triangle of calcaneum with intraosseous lipoma.
a normal radiographic finding that is formed between the traction trabeculae radiating from the inferior cortex of the calcaneus and the compression trabeculae converging to support the posterior and anterior articular facets (Figure 7). IOLs are classified according to their location or histopathologic and radiographic characteristics. Based on location, osseous lipomas are classified as intramedullary, intracortical, subperiosteal, or parosteal (3). Milgram (8), using histopathology and radiographs, classified IOLs into 3 groups depending on the degree of involution. Stage I lesions are purely radiolucent; contain viable lipocytes and thin, bony trabeculae; and do not display necrosis. Stage II lesions are partially radiolucent with some calcification, and display an admixture of necrosed and viable lipocytes. Stage III tumors have larger areas of central and peripheral calcification, no bony trabeculae, and the fat component is fully necrotic (8). The gross appearance of an IOL is that of soft yellow tissue. Free oil (fluid lipid) has been reported to be present during surgery, possibly owing to the breakdown of fatty tissue-forming intralesional cysts (18), and this was the case in the patient described in this article. Histologically, the lesion is well circumscribed and consists of mature lipocytes surrounding bony trabeculae with no cellular atypia (19). Areas of fat necrosis may also be present, as well as foamy histiocytes, cholesterol clefts, and reactive bone formation (2). The histologic findings may be difficult to distinguish from those of liposarcoma, chondrosarcoma, pseudocyst of rheumatoid arthritis, localized osteoporosis, hyperlipoproteinemia, and chronic tuberculosis (3). Radiographically, IOL appears as an osteolytic, well-circumscribed lesion with a thin sclerotic rim. Lesions may be expansive, particularly in the fibula, and internal septations and nidus/mineralization may be present, depending on the stage. Owing to the indolent course of the tumor, there is an absence of cortical destruction and periosteal reaction. The radiographic appearance is not unique, making it difficult to distinguish IOL from nonossifying fibroma, simple bone cyst, aneurysmal bone cyst, giant-cell tumor, fibrous dysplasia, bone infarct, chondroid tumor (2), or a fungal infection of bone (3). Peripheral calcification may be seen in lesions localized outside of the calcaneus. The CT appearance of calcaneal cysts demonstrates attenuation values equivalent to that of fat, and Milgram stage III tumors
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displaying massive calcification and other dystrophic changes on CT and magnetic resonance image (MRI) scans may present a diagnostic challenge (20). In addition, IOLs may be confused with bone infarcts, because the latter also contain fat and have a low signal intensity rim when imaged with CT or MRI. However, unlike bone infarcts, calcaneal IOLs are expansile lesions that remodel cancellous and cortical bone. MRI images best display the presence of fat inside the tumor on T1-weighted and T2 fat-suppressed images (21). Whether IOLs are true benign adipose tumors is a matter of debate owing to the difficulty of distinguishing neoplastic from nonneoplastic lipocytes (8). Some have described IOLs as overshoot phenomena of the normal remodelling process from hematopoietic to fatty marrow, or as a maturational continuum between a bone cyst and an IOL. Simple cysts of the calcaneus occur in the same location and, like IOLs, do not possess an epithelial lining, suggesting a common etiology. Lipomas have also been postulated to be an involutional stage of simple bone cysts. Conversely, some authors argue that calcaneal cysts arise from degeneration of preexisting IOLs (22). Bone infarcts can give rise to IOLs, as can the final stages of an inflammatory process (23). Trauma has been postulated as a cause, whereby a fracture callus undergoes fatty degeneration and infarction (24, 25). Increased intravenous pressure in the intraosseous compartment has also been proposed as a possible cause of IOL, based on the treatment success obtained with continuous cavitary decompression, which has gained a foothold as a treatment option. IOL has also been found to be associated with a group of lesions called liposclerosing myxofibrous tumors (LSMFT) (26). Treatment of IOL is based on the site, size, and symptomatology of the lesion. Small, asymptomatic cysts in non–weight-bearing areas of bone can be observed for progression. Symptomatic, “critical-size cysts” require surgical intervention, as a general rule. Treatment options include steroid injection, curettage without grafting, curettage plus augmentation with bone graft or bone graft substitute, or continuous decompression in conjunction with the use of a cannulated cancellous titanium screw (13, 27). Steroid injections yield unpredictable results, whereas curettage with bone-grafting or calcium phosphate bone cement augmentation have been shown to be effective more often than not. Furthermore, calcium phosphate bone graft substitute is advantageous in comparison with autograft, because donor site morbidity is no longer a concern. The purpose of this article and the accompanying literature review is to increase clinicians’ awareness of intraosseous lipoma and the usefulness of CT scans in establishing the diagnosis, and to provide an overview of treatment modalities that highlight the use of calcium phosphate bone graft substitute as an osteoconductive scaffold in the management of this benign bone defect when it occurs in the calcaneus. References 1. Ramos A, Castello J, Sartoris DJ, Greenway GD, Resnick D, Haghighi P. Osseous lipoma: CT appearance. Radiology 157:615–619, 1985. 2. Campbell RSD, Grainger AJ, Mangham DC, Beggs I, Teh J, Davies AM. Intraosseous lipoma: report of 35 new cases and a review of the literature. Skeletal Radiol 32:209–222, 2003. 3. Kapukaya A, Subasi M, Dabak N, Ozkul E. Osseous lipoma: eleven new cases and review of the literature. Acta Orthop Belg 72:603–614, 2006. 4. Reig-Boix V, Guinot-Tormo J, Risent-Martinez F, Aparisi-Rodriguez F, FerrerJimenez R. Computed tomography of intraosseous lipoma of os calcis. Clin Orthop 221:286–291, 1987. 5. Chow LT, Lee KC. Intraosseous lipoma. A clinicopathologic study of nine cases. Am J Surg Pathol 16:401–410, 1992. 6. Oztekin O, Argin M, Oktay A, Arkun R. Intraosseous lipoma: radiological findings. Radiol Bras 41(2):81–86, 2008. 7. Levin MF, Vellet AD, Munk PL, McLean CA. Intraosseous lipoma of the distal femur: MRI appearance. Skeletal Radiol 25:82–84, 1996. 8. Milgram JW. Intraosseous lipomas. A clinicopathologic study of 66 cases. Clin Orthop 231:277–302, 1988.
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