[Primary malignant non-Hodgkin skeletal muscle lymphoma: a case report].

BACKGROUND: Malignant non-Hodgkin lymphoma (NHL) is rarely encountered in soft tissue. The differential diagnosis with other soft tissue tumors, particularly sarcoma, is difficult. CASE REPORT: A 70-year-old woman presented an increase in the volume of the right thigh. Ultrasonography visualized a hypoechogenic mass with irregular contours. At computed tomography, the mass measured 17x14x7 cm and was situated in the biceps femoris. Enhancement was heterogeneous after intravenous contrast injection with discrete infiltration of the subcutaneous fat. Tumor biopsy demonstrated diffuse malignant small B-cell lymphomatous-plasma cell proliferation. The diagnosis was primary NHL of the biceps femoris. Search for extension was negative. Wide resection was followed by chemotherapy. The patient was free of recurrence at 10 months follow-up. DISCUSSION: Primary NHL of skeletal muscle is usually observed in elderly subjects, principally in thigh muscles. Magnetic resonance imaging and computed tomography visualize characteristic features. Diagnosis is formally established by pathology.