Spindle cell lipoma: a clinicopathological study with some original observations.

Forty-one cases of spindle cell lipoma, an entity first described in 1975, are presented. Of these, 38 were identified in a systematic review of 2478 tumours of adipose tissue diagnosed and treated in one hospital over a 25 year period. This lesion, therefore, accounts for about 1.5% of adipocytic neoplasms and is outnumbered by conventional benign lipomas by approximately 60 to 1. The remaining three were referred cases. Seventy-five per cent of the lesions arose, as expected, on the back of the neck, upper back or shoulder, almost exclusively in males between 40 and 70 years of age. Ten lesions were identified at unusual sites: six in the limbs, three on the face and one on the trunk. One lesion arose within skeletal muscle, a previously unreported phenomenon, and this case showed both cartilaginous and osseous metaplasia. Only one of the 41 tumours has recurred locally. The range of histological features in spindle cell lipoma is described and the differential diagnosis is discussed.