Bizarre parosteal osteochondroma in the foot (a case report).SS Hemmadi, BR Patel
Department of Orthopedics, Seth G.S. Medical College, Parel, Bombay.
A rare case of a bizarre parosteal osteochondroma in the foot is presented. The tumour first described in 1983 by Nore et al is rare in any location and has to be differentiated from a juxta-cortical osteosarcoma and a benign osteosarcoma. Its differentiating characteristics are discussed.
Keywords: Bone Neoplasms, pathology,surgery,Case Report, Child, Human, Male, Metatarsophalangeal Joint, pathology,surgery,Neoplasm Recurrence, Local, pathology,surgery,Osteochondroma, pathology,surgery,Reoperation,
"Bizzare" in the term bizzare parosteal osteochondroma coined by Nora et al refers to its microscopic histopathological picture, and hence has to be differentiated from a juxtacortical osteosarcoma.
This tumour grossly resembles an osteochondroma, however, its characteristic location, radiological and microscopic features differ from the above.
In 1947, an 8 yr old boy complained of a painless swelling around the right great toe, which was gradually increasing in size. The swelling was excised. The wound healed without any problems. Histopathology report was not available. In 1962 the swelling recurred; it was again painless and was excised. No details available. In 1990 the patient, now a 60 yr old tailor, came back with a swelling on the right great toe extending over the metacarpo-phalangeal joint. It had gradually increased in size and following trauma a small ulcer had developed on the most prominent part of the swelling.
All laboratory investigations were within normal limits.
On examination there was 6 cm x 4 cm hard non-tender swelling with a healing ulcer 1 cm in diameter on the most prominent part of the swelling. The swelling was not fixed to skin. It was mainly overlying the first metatarso-phalangeal joint.
An excision biopsy was done. The swelling was found to be a smooth, cartilagenous capped osseous outgrowth 3cm x 3cm x 2cm attached to the proximal phalanx but not involving the metatarso- phalangeal joint. (See [Figure:1]) No connection was found with the medullary cavity. The remaining part of the external swelling was contributed to by the overlying fat.
Post-operatively the wound healed uneventful.
Gross : The lesion resembled an osteochondroma having a cartilagenous cap.
This diferred from an osteochondroma in having (i) the cartilagenous portion of the tissue was less orderly than that of an exostosis (ii) the lesion was discrete and had irregular islands of both cartilagenous and osseous tissue. It was surrounded by moderately cellular fibrous tissue in which there were stellate and spindle cells. Calcified cartilagenous tissue was also present.
Osteochondroma are the most common of the benign bone tumours. However, the rarely occur in the hand  or foot. In Dahlin's series  only 14 out of 516 osteochondroma occurred in hand or foot.
A bizzare parosteal osteochondroma is a rare tumour in any location. It was first described in 1983 by Nora et al.
These lesions have been confused in the past with juxtacortical osteosarcomas. They usually occur in the proximal phalanges metacarpals and metatarsals. Radiologically they differ from osteochondromas in the following aspects. 1. The tumor appears to arise from the surface of the cortex directly. 2. There is no continpity between the central part of the tumour and the medullar of the underlying bone. 3. There is no flaring of the cortex of the underlying bone.
These tumours have a high rate of recurrence after excision as compared to those of a benign osteochondroma. Nora et al reported a 51 % initial recurrence, 22% second recurrence.
This patient probably had a second recurrence.