Clinical History: 49-year old woman with an asymptomatic pelvic mass for 10 years (an incidental finding on routine physical examination)

Diagnosis: Pelvic schwannoma

MR Technique:

Pelvic MR imaging was performed on a 3T system (Skyra, Siemens). (A) Coronal T2-weighted TIRM (TR/TE 4000/78ms), (B) sagittal T2-weighted TIRM (TR/TE 4000/70), (C) axial T1-weighted TSE (TR/TE 450/18) and (D) axial T2-weighted TSE with spectral fat suppression (TR/TE 2500/84) were acquired as pre-contrast scans. Then, contrast-enhanced T1-weighted TSE (TR/TE 550-700/11ms) images were acquired following IV gadolinium chelate administration in three orthogonal planes, using a VIBE sequence (E-G).

Imaging Findings:

There is a well-encapsulated, oval lesion located anterior to the right sacrum. It is 4.2×2.8×3.5 cm in size. The lesion has nearly homogeneous isointense signal similar to the skeletal muscles on T1WI, and high signal intensity on T2WI in the majority of the lesion. After contrast injection, the lesion appears inhomogeneous with predominantly peripheral enhancement. The small areas with low signal intensity on both T1WI and T2WI, and without enhancement on post-contrast images, likely represent a combination of non-viable tissue and dense calcification, consistent with degeneration of the lesion over a long time period. Displacement of structures adjacent to the lesion, such as the internal iliac artery, are also noted. The pathological exam revealed a degenerative schwannoma after surgery.