Intratendinous Lipoma of Biceps Long Head: A Case Report and Current Concepts Review of Musculoskeletal Lipomas.

Introduction: Lipomas arising from the muscle and bone are uncommon and remain unnoticed till giant size. Major concern is to differentiate from atypical lipomatous tumors (ALTs) which have propensity to recur or differentiate to liposarcomas. Through this case report, we review the intramuscular lipomas involving muscles of shoulder girdle and the current concepts in imaging and histopathological examination to differentiate deeply seated lipomas from ALTs. Case Report: A 47-year-old female was evaluated for a painless swelling that gradually increased in size in the right shoulder and upper arm for 8 months. Magnetic resonance imaging (MRI) showed lipomatous lesions in the biceps tendon of size 7 × 5 cm but expressed heterogeneous fat signals on suppression sequence. The biopsy revealed mature adipocytes with occasional fibrous septa that contained mixed inflammatory cells. Due to equivocal findings with ALT, immunohistochemical staining for murine double minute 2 (MDM2) homolog expression was performed but negative. There was no recurrence of the lesion and patient had no functional impairment. Conclusion: Intramuscular lipomas that grow to giant size can exhibit heterogeneous fat signals in MRI and need to be looked for ALTs or well-differentiated liposarcoma through histopathological examination. Staining for MDM2 homolog and cyclin-dependent kinase-4 expression that are typical for ALTs is necessary when histopathological findings are indeterminate.