MR imaging findings of focal myositis: a pseudotumour that may mimic muscle neoplasm.

[focal myositis]

The authors describe magnetic resonance (MR ) findings in eight patients with histologically confirmed focal myositis .In each patient , axial TSE T 1 -weighted and fast short -tau inversion recovery (STIR ) images were obtained using a 1 .5 -T MR scanner . Three patients also underwent dynamic contrast-enhanced MR examination using a GE T 1 -weighted sequence . The following features were evaluated : anatomical distribution , extent of the involvement , signal intensity characteristics , dynamic enhancement pattern and outcome at follow-up examinations .Seven of eight lesions were located in the lower extremities , one of eight in the arm ; four of eight involved part of a muscle , two of eight diffusely involved a muscle and two of eight showed multifocal involvement of two or more muscles . All lesions were hyperintense on fast-STIR images : the hyperintensity was homogeneous in six of eight and inhomogeneous in two of eight . On T 1 -weighted unenhanced images , all lesions but two appeared isointense or slightly hypointense in comparison to normal muscles ; two lesions showed a slight hyperintensity . Dynamic enhancement pattern corresponded to the type usually seen in benign soft tissue lesions . All lesions disappeared .Focal myositis is an uncommon pseudotumour which should be considered in the differential diagnosis of muscular masses and myopathies .