PMC4748208_01
MRI of the pelvis showing a large mass occupying the left ischiorectal fossa.
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F1
Pelvic magnetic resonance imaging (MRI) showed a 16 x 10-cm mass in the left ischiorectal fossa, extending from the left levator ani muscle, which appeared displaced cranially, to the subcutaneous fat of the left buttock (Figure 1). MRI is the imaging modality of choice, accurately identifying these lesions based on peculiar radiological features suggestive of fibrosis, predominantly at the core of the lesion (Figure 1).
(A) Operating room setup with the patient in the prone jack-knife position. A large mass is evident bulging through the left buttock (arrows) (B) Intraoperative view of the mass almost completely mobilized with intact capsule.
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F2
A surgical resection of the mass was performed through a longitudinal left gluteal incision, with blunt dissection of the mass from the rectal wall, whose integrity was preserved (Figure 2).
(A) Patternless architecture of the tumor with spindle-shaped cells mixed in hypocellular (right) and hypercellular (left) areas, surrounding branching hemangiopericytoma-like vessels (H-E, x10 magnification) (B) Tumor cells and vessel walls showing intense CD34 immunoreactivity (CD34, x10 magnification).
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F3
The tumor showed intense immunohistochemical positivity for vimentin and CD34 (Figure 3).