Involvement of muscle by malignant lymphoma: MR and CT appearances

The purpose of this study is to investigate the CT and MR findings of muscular involvement by malignant lymphoma and identify the CT and MR features that may assist in their diagnosis.

Magnetic resonance imaging was performed on four patients (five lesions) with pathologically proven non-Hodgkin lymphoma using a 1.5 T unit (Cases 1, 2, and 4) and a 0.5 T scanner (Case 3). Computed tomography scans were carried out on three patients (Cases 1, 3, and 4).

The lesions that extended along muscle fascicles with preserved fat planes looking like swelling of the muscle were of slightly hyper- to isointensity relative to uninvolved muscles on T1-weighted images, of hyperintensity on T2-weighted images, and of low or isodensity on CT. Microscopically, lymphoma cells were seen clustering among normal and atrophic muscle fibers in a biopsy specimen of one patient. The lesions enhanced relatively homogeneously after Gd-DTPA injection. In three cases, vessels were coursing through the lesion on MRI and in two cases on enhanced CT.

Magnetic resonance imaging proved useful to show the extension of involvement of muscular lymphoma compared with CT. The diagnosis of infiltration of muscle by lymphoma is entertained when a lesion of relatively homogeneous intensity and density extends along the muscle fascisles without obliteration of the fat planes and especially when vessels are identified within the lesion.