Clinical History: A 63-year old woman presents with an asymptomatic mass inferior to the right inguinal area for 10 days

Diagnosis: Proliferative myositis

MR Technique:

Imaging of the right lower extremity was performed on a 3T MR system (Siemens Skyra). (A) Coronal T2-weighted TIRM (TR/TE 3000/38ms) and (B) axial T2-weighted TSE with fat suppression (TR/TE 3022/90) were acquired in combination with subsequent Gd-enhanced T1-weighted TSE (TR/TE 700/11ms) images with Dixon fat suppression (C-E).

Imaging Findings:

An ill-defined mass (2.5 x 2.2 x 10.1 cm) is noted in the belly of the right adductor longus muscle. The lesion has slightly inhomogeneous high signal intensity on fat-saturated T2-weighted images, as compared with the normal musculature. After contrast injection, imaging reveals near homogenous enhancement of the mass. It is noteworthy that the muscle fibers within the lesion are preserved without disruption, helping to distinguish it from the other aggressive malignant diseases.