Answer: Intramuscular myxoma

Histology: The current tumor is composed of cytologically bland stellate- bipolar fibroblasts in a background of abundant extracellular myxoid matrix. Intramuscular myxoma (IM) may contain areas of ‘reactive” hypercellularity and vascularity that could raise the differential diagnosis of a low grade sarcoma (eg. myxofibrosarcoma, low-grade fibromyxoid sarcoma, and myxoid liposarcoma). The absence of cytologic atypia, mitotic activity, or necrosis in association with the hypercellular ity help establish the benign nature of an IM and avoid its misinterpretation as a sarcoma.

Discussion: Myxoid morphology can be encountered in a variety of benign and malignant soft tissue neoplasms. IM are benign deep seated neoplasms confined to skeletal muscle. IM are almost always cured after surgical excision. Recurrence is exceptionally rare, even after incomplete or marginal resection. IM most commonly affect middle-aged occurring in the quadriceps and gluteal muscles of the lower extremity region. Multiple intramuscular myxomas are rare occurrence and are usually associated with monostotic or polyostotic fibrous dysplasia and Albright’s syndrome. Similar neoplasms affecting periarticular tendons, ligaments, joint capsules are termed “Juxta-articular myxoma” and have been reported to have local recurrence in one third of cases. Superficial “cutaneous myxoma” have also been associated with similar rate of local recurrence but there have been no metastases reported. Multiple cutaneous myxoma can be a part of Carney complex.

Reference(s):
– Silver WP, Harrelson JM, Scully SP. Intramuscular myxoma: a clinicopathologic study of 17 patients. Clin Orthop Relat Res. 2002 ;(403):191-7.
– Allen PW. Myxoma is not a single entity: a review of the concept of myxoma. Ann Diagn Pathol. 2000 ;4(2):99-123.
– Nielsen GP, O’Connell JX, Rosenberg AE. Intramuscular myxoma: a clinicopathologic study of 51 cases with emphasis on hypercellular and hypervascular variants. Am J Surg Pathol. 1998 ;22(10):1222-7.