Primary muscle lymphoma.

Primary muscle lymphoma is rare. Less than 50 cases have been described. The clinical and radiological features of muscle lymphoma are presented in this series of six cases. Most patients present with solitary or multiple masses which may be painful. Clinical presentation varies from the indolent to the rapidly progressive. Systemic symptoms occur in a minority. In most cases, ultrasound shows an ill-defined hypoechoic mass but apparent coarsening of fibroadipose septa and swelling of muscle bundles may occur. CT shows an iso/hypo dense mass. On MR the mass appears iso/minimally hyperintense to muscle on T1W and enhances, and hyperintense on T2W, proton density and fat suppression sequences. Infiltration of the subcutaneous fat is a striking feature in a majority of cases on CT and MR. The diagnosis can be established by ultrasound guided biopsy and should be performed urgently in HIV positive patients to exclude pyomyositis.