The patient went on to have a resection. 

Histology
 
Sections show multiple small biopsies,  some of which include skeletal muscle and adipose tissue.   The biopsies contain a "small round blue cell tumor". The neoplastic cells form loosely cohesive sheets.  One or two possible rosettes are present.  The neoplastic cells have small round to slightly oval nuclei, fine chromatin and an indistinct nucleolus. There is a moderate amount of variably eosinophilic or vacuolated cytoplasm. Occasional mitoses are seen.  There is no tumor necrosis.   The tumor surrounds vessels and infiltrates into skeletal muscle and into adipose tissue. A PAS stain highlights cytoplasmic glycogen.
 
Immunohistochemistry:   The neoplastic cells are strongly and diffusely positive for CD99 and Vimentin.  CD99 shows membranous staining.  NSE is equivocal.  The cells are negative for chromogranin, synaptophysin, desmin, S100, CD20, CD3 and AE1/3.
 

FINAL DIAGNOSIS: Ewings sarcoma.