|Year : 1989 | Volume
| Issue : 1 | Page : 54-6
Ossifying lipoma of the thigh (a case report).
HG Pandit, PB Bhosale, SS Khubchandani
H G Pandit
The term ossifying lipoma is used to describe a rare case of lipoma when its mature adipose tissue shows foci of chondrification and ossification. We are presenting here, a case report of a large sized ossifying lipoma in the anteromedial compartment of the left thigh of a 55 year old farmer.
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Pandit H G, Bhosale P B, Khubchandani S S. Ossifying lipoma of the thigh (a case report). J Postgrad Med 1989;35:54-6
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Pandit H G, Bhosale P B, Khubchandani S S. Ossifying lipoma of the thigh (a case report). J Postgrad Med [serial online] 1989 [cited 2023 Mar 30 ];35:54-6
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Lipoma is a common benign tumour. But unlike other connective tissues, it's mature adipose tissue rarely shows cartilagenous or osseous metaplasia. We are presenting here, a rare case of lipoma showing areas of both cartilage and bone formation.
A 55 year old farmer was admitted to the S.D.B. Orthopaedic Centre and Research Institute, K.E.M. Hospital, Bombay on 23-2-1988, with a large painless swelling over the anteromedial aspect of his left thigh [Fig. 1]. He was apparently alright till one and a half years back when he noticed a small swelling on the medial aspect of the thigh. It gradually increased to the present size. It apparently had started spontaneously without any association to injury or symptoms of infection. Apart from its size, it did not give any problem. On examination, the swelling was firm, lobulated and non tender. It's border were well defined and was 25 cm x 20 cm x 20 cm in size . It extended proximally upto the obturator foramen and occupied almost fully the antero-medial aspect of the proximal half of the thigh. There were no signs of inflammation. The overlying skin was freely mobile and did not show any venous engorgement. The tumour was mobile only in transverse plane but was fixed longitudinally. On contracting the adductor muscle, the tumour became more fixed and appeared less prominent. The femoral arterial pulsations were deviated laterally along the lateral border of the tumour. A clinical diagnosis of large neurofibroma or lipoma with possible sarcomatous changes was made. The radiological examination revealed on the antero-medial aspect of the left thigh, a large radiolucent tumour with central zone of irregular specules of calcification and ossification [Fig, 2]. His pelvic bones and femur were normal. With these findings a possibility of various soft tissue sarcoma like synovial sarcoma, liposarcoma and rhabdomyosarcoma was considered. Needle biopsy failed to reveal the identity of the tumour. As the tumour was still mobile an excisional biopsy appeared feasible and probably the only logical cause. On 16-3-1988, the tumour was exposed through a long 'S' shaped incision. The adductor longus muscle was detached from its origin at the pubic bone and a plane was developed so as to excise the tumour with its capsule in toto [Fig. 3]. The tumour showed lobulated extensions in various tissue planes and was fixed to the periosteum of the anterior surface of the proximal third of the femoral shaft. It was engulfing most of the branches of the obturator nerve and the profunda femoris vessels which were sacrificed along with parts of the adductor brevis, adductor magnus and vastus medialis muscles to facilitate total excision of the tumour. The tumour was relatively avascular and the intraoperative bleeding was only 200 ml. After proper hemostasis, the wound was closed with a drainage tube. Wound healed and patient returned to farming in two weeks' time without any complications.
Gross examination of the tumour revealed a large tumour mass 20 cm x 14 cm x 11 cm in size. It was soft, well circumscribed, and thinly encapsulated. At one end, the mass had a rounded border but the other borders were irregular. On cut section, it was pale yellow and had a uniform greasy surface. Focal areas of discoloration were seen, resembling areas of hemorrhage. Most of the tumour was soft but a few firm to hard areas could be palpated, irregularly distributed amongst the tumour. Microscopy of the tumour revealed a lesion composed entirely of mature fat cells. The cells were varying in size and shape and did not reveal nuclear atypia. Frozen section stained with Sudan III was positive for lipid. Sections from the inner areas revealed presence of other mesenchymal elements namely cartilage and bone. [Fig. 4]. The cartilagenous metaplasia was mainly hyaline in nature and showed enchondral ossification. The bony specules were mainly of lamellar bone but no definite marrow elements were seen. The tissues examined did not show any evidence of malignant changes. Hence taking the gross and varied microscopic appearance into consideration a diagnosis of ossifying lipoma was made.
Chondrification and ossification are known to occur in non-fatty connective tissues with or without undergoing an intermediate process of necrosis as in the walls of arteriosclerotic arteries, myositis ossificans, tubercle, in the lesion of skin and urinary mucosa and stroma of various adenocarcinomatas. It is rather surprising that they do not occur as frequently in the preexisting fibrofatty tissues. The process of chondrification and ossification in adipose tissue is believed to be metaplastic in nature. The process is probably activated by the pressure variant created by foci of differential growth inside an encapsulated mass. However, a significant number of lipomatous lesions like angiolipoma, angiomyolipoma and ossifying lipoma which have various mesenchymal element in addition to fatty tissue might have their origin as hamartoma.
Ossifying lipoma is usually dull yellowish in colour due to mature adipose tissue. On section, it shows lobulated arrangement with a well formed fibrous capsule. Whitish nodules of cartilagenous and bony tissues are seen scattered more often centrally than peripherally in the tumour. On microscopic examination, the adipose, tissues contain mature fat cells. The cartilagenous and bony foci are usually surrounded by fibrous perichondrium and periosteum. Cartilage nodules are hyaline in nature and not infrequently associated with enchondral ossification. Bony islands consist of cancellous and/or lamellar bone encircling adipose and non-haemopoeitic bone marrow. Our present case of ossifying lipoma had developed in the adductor compartment of the thigh, one of the commonest sites of its occurrance. Although it was well encapsulated, it had many lobular processes and extensions, and was fixed to the periosteum of the femur. It had also engulfed the profunda femoris vessels and the branches of obturator nerve, which were sacrificed to excise the tumour in toto.
The case is being presented as a rare but interesting case and having clinico-radiological features suggestive of soft tissue sarcomas, from which it could be carefully differentiated.
We thank the Dean of K. E. M. Hospital and Seth G. S. Medical College for allowing us to publish this case.
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