Case 538 -- A 57-year-old male with a pelvic mass

Contributed by M. Dvorakova, M.D. and A. Palekar, M.D.


The patient was a 57-year-old gentleman with a 2 week history of nausea, vomiting, abdominal pain and distention who presented with fever, chills, and sharp pain radiating to both groins. The initial CT scan showed a large heterogeneous pelvic soft tissue mass partially encasing bilateral common iliac vessels, rectum, anus, and sigmoid colon with deviation of the urinary bladder but no evidence of colonic obstruction.

His past medical history was significant for hypertension, hypercholesterolemia, coronary artery disease and inferior wall myocardial infarction in 1998.

A resection of the mass was attempted.


The specimen consisted of a large, poorly circumscribed, irregular grey tan rubbery soft tissue mass. The majority of the tumor was soft, with myxoid and gelatinous areas, pink and rubbery with focal hemorrhage. Portions of the tumor had a more fibrous, firm, tan-to-yellow appearance. No overt necrosis was present. Grossly, the tumor extended to soft tissue margins with entrapment of the normal-appearing adipose tissue.


The histologic sections demonstrated an infiltrative, relatively paucicellular lesion with prominent variably sized, thin and thick walled vascular channels and areas of hemorrhage. Several foci of smooth muscle differentiation around and in between the blood vessels were observed. The tumor was composed of widely scattered spindle and stellate- shaped cells with scant cytoplasm, uniform oval nuclei and delicate nucleoli in a background of edematous fine collagen fibers. No mitoses were seen. The neoplasm showed an infiltrative growth pattern but no invasion into the intestinal or urinary bladder wall. Immunohistochemically, the neoplastic cells were positive for CD34 and estrogen receptor. Areas of perivascular smooth muscle proliferation were positive for desmin and smooth muscle actin. Calponin staining was observed in less than 1% of neoplastic cells. Ki-67 proliferation index was <3%. Negative stains included S-100, pankeratin, CD68, androgen receptor, PSA and CD31.


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