Intramuscular spindle cell lipoma: Case report and review of the literature.

Spindle cell lipoma (SCL) is a relatively rare adipocytic neoplasm and is histologically characterized by a mixture of uniform spindle cells and mature fat cells. It occurs predominantly in male patients aged 45-65 years, and in most cases it arises in the subcutaneous tissue of the neck or shoulder. Although the neoplasm sometimes affects unusual sites, only three cases have been reported in which the lesion was intramuscular. Here we present a case of SCL arising in skeletal muscle; to our knowledge, the first report in 10 years. The tumor occurred in the neck of a 50-year-old male patient. Magnetic resonance imaging (MRI) revealed a lipomatous tumor within the right trapezius muscle. The tumor was localized beneath the fascia and was excised completely at surgery. Histologically, the tumor was typical of a spindle cell lipoma with no evidence of malignancy. An immunohistochemical study revealed all spindle cells were strongly positive for CD34. Differential diagnosis is discussed with a review of the literature.