Rare diagnosis of intraosseous lipoma in the scapula of a 15-year-old domestic shorthair cat

CASE SUMMARY: A 15-year-old male castrated domestic shorthair cat originally presented to its primary care veterinarian with a chief complaint of a multi-month history of decreased appetite, weight loss and mild weight-bearing lameness. On physical examination, over the right scapula there was mild-to-moderate muscle wasting and a palpable firm, bony mass measuring approximately 3.5 cm × 3 cm. A complete blood count, chemistry panel, urinalysis, urine culture and baseline thyroxine were clinically unremarkable. Further diagnostics included CT, which revealed a large, expansile, irregularly mineralized mass centered over the caudoventral scapula at the site of attachment of the infraspinatus muscle. Following wide surgical excision by means of complete scapulectomy the patient regained function of the limb and has been free of disease since. The clinical institution’s pathology service examined the resected scapula with associated mass and diagnosed an intraosseous lipoma. RELEVANCE AND NOVEL INFORMATION: Intraosseous lipoma is a rare form of bone neoplasia that has only been reported once in the small animal veterinary literature. Histopathology, clinical signs and radiographic changes were consistent with what is described in human literature. It is hypothesized that these tumors occur because of invasively growing adipose tissue within the medullary canal following trauma. Considering the rarity of primary bone tumors in cats, intraosseous lipomas should be considered as a differential diagnosis in future cases with similar signs and history.