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.