Clinical Presentation
A 30-year-old male presented with a one-year history of right little finger progressive paresthesia and a non-tender palpable enlarging mass in the right axillary fossa.
MR neurography revealed a 30×25×24 mm heterogeneous, high-signal, round mass within the right axillary fossa in proximity to the medial aspect of brachial plexus branches. The mass showed high-signal intensity on T1 image, a very high T2 signal intensity and no signal drop on fat-saturated sequence with the fluid-fluid level (Figure 1), indicating a hemorrhage in the tumor. On operation a well-circumscribed ovoid, solid, dark-blue tumor, originating from the ulnar nerve covered by the nerve sheath was seen. Some nerve bundles were encased in the tumor with no extra-neural invasion (Figure 2).
Frozen-section study revealed a small, round, blue cell tumor. Since all motor functions of the ulnar nerve were intact, total tumor resection with a wide margin of the surrounding soft tissue was done.
Histomorphological study (Figure 3) and IHC staining (Figure 4) revealed a malignant, small, round, blue cell tumor, consistent with primitive neuroectodermal tumor.