Discussion
An axillary fossa mass may have a wide range of differential diagnosis from a reactive lymphadenopathy to malignant neo­plasms. While lymphadenopathy accounts for the vast majority of cases16,17, neural tumors can sometimes occur in this region. Schwannoma is the most common benign, slow-growing, peripheral nerve tumor in adults, originating from a single fascicle within the main nerve and displaces the nerve18. Malignant neural tumors are very uncommon developing from primitive, undifferentiated, small, round cells19.
pPNET is usually a large soft mass (>5 cm) with an undefined margin and local invasion to the surrounding tissue20-23. Clinical presentations of pPNET depend on the tumor site and mass effects. It can present as a rapidly growing mass causing swelling and pain24,25. Sometimes the metastatic disease can be the initial presentation24. The most probable sites of metastasis are the lungs, bone and bone marrow11,24,26,27. On the other hand a benign mass usually presents as a slow-growing mass taking several years to cause neurological symptoms28,29. In addition, the macroscopic features of pPNET seen during surgery were unlike those of schwannoma,lacking the well-formed capsule which is a very common and reassuring finding for the diagnosis30. Therefore, despite previous biopsy diagnosis, a frozen section study was requested upon surgery. The frozen section diagnosis was small round blue cell tumor.
In peripheral nerve tumors, MR neurography is a reliable technique for evaluation of anatomy and pathology of a nerve, regional muscle and functional assessment31. Although schwannomas have common MRI characteristics, radiologic diagnosis is not reliable on its own, especially when occurring in unusual sites32.
pPNET is associated with significant mortality rate33. Treatment should be individualized for each patient, based on the site and size of tumor, metastasis, age and health status, including total resection surgery with wide margins and chemotherapy. Radiotherapy may also be done34.
Only few well documented cases of pPNET arising from the peripheral nerves have been yet reported. Stout in 1918 first reported a case of a 42-year-old man with an ulnar tumor composed of small, round, blue cells forming rosettes but not confirmed by IHC or molecular studies35. Samuel et al. in 1982 reported a primitive neuroectodermal tumor in a 59-year-old man, arose from the ulnar nerve, but no confirmatory study was done neither36. Mohan et al. in 2011 reported 2 cases of intra-neural Ewing’s sarcoma/PNET of the upper limb (ulnar and radial nerve) confirmed by IHC staining and fluorescent in situ hybridization (FISH) study. Akeyson et al. in 1996 reported a median nerve PNET in an 80-year-old male, confirmed by pathological and cytogenetic studies38.