Features of small bowel obstruction secondary to ileoileal intussusception. At surgery, a leading point mass of 3 cm was identified.

MICROSCOPIC DESCRIPTION: The nodule is dumbell shaped and bulges under the mucosa and under the serosa. The constriction lies in the muscularis propria. The overlying mucosa is ulcerated and the lesion is covered by acute inflammatory exudate. It is composed of intersecting bundles of spindle cells with fibrillary cytoplasm and elongated oval nuclei with even chromatin and rounded ends. There is a light infiltrate of lymphocytes, plasma cells, histiocytes and a few eosinophils and mast cells. There are no mitoses in 90 high power fields (0/5mm2). No necrosis is present. The lesion extends up to the serosa but the mesothelium appears to be intact. The mucosa at the edges of the lesion shows villous stunting and crypt distortion with active chronic inflammation but no epithelial dysplasia. There is transmural edema with a light mixed inflammatory cell infiltrate. The resection margins pass through normal small bowel wall. In immunostains, the cells are CD34+ (weak, patchy), DOG-1+, CD99+, c-kit+, smA+ (weak), desmin-, S100-. About 2% of the cells are Ki67+.

DIAGNOSIS: Small bowel: Gastrointestinal stromal tumor (GIST) 32mm in diameter with 0 mitoses/5mm2, associated with intussusception; clear of specimen margins.