Peripheral Primitive Neuroectodermal Tumor with Osseous Component of the Small Bowel Mesentery: A Case Study
A 23-year-old man was referred to Inha University Hospital due to severe abdominal pain. Computed tomography revealed an ovoid solid and cystic tumor in the pelvic cavity, measuring 11.0×6.0 cm. Emergency surgery was performed, and a large ruptured mass was found in the jejunal mesentery, 1 cm from the ligament of Treitz. The tumor involved the jejunal wall, and another mass the size of a thumb was detected within the porta hepatis. Disseminated miliary nodules were present in the greater omentum, the right colonic gutter, and the pelvic peritoneum. Segmental resection of the small intestine and omentectomy were performed. Postoperative laboratory examination revealed normal levels of serum lactate dehydrogenase, cancer antigen 125, and carcinoembryonic antigen, and postoperative positron emission tomography computed tomography was normal. After operation, chemotherapy (vincristine, ifosfamide, etoposide, and doxorubicin) was performed. One year after the operation, a 10 cm, locally recurrent mesenteric mass was resected.\nMacroscopically, a tumor measuring 12.0×8.0×7.5 cm was located in the mesentery of jejunum. Rupture was seen in the surface of tumor. The tumor showed a whitish-pink solid cut surface with foci of hemorrhage, extensive necrosis, and myxoid change. The jejunal wall was involved directly by the tumor and contained focal mucosal ulceration. The cut surface was white-gray and dense ().\nMicroscopically, the entire wall of the jejunum contained tumor cells which also proliferated within the mesentery. The mucosa of the jejunum was involved by the tumor with surface erosion (). Small round cells containing uniform vesicular, round or oval nuclei, scanty clear, or eosinophilic cytoplasms and indistinct cytoplasmic borders comprised the tumor in sheet or lobule formation (). Often, intermingled spindle-shaped cells were found. Though some cells had a single prominent nucleolus, most cells had indistinct nucleoli. Well-formed Homer-Wright rosettes were frequently observed (). Flexner-Wintersteiner rosettes did not exist, but perivascular pseudorosettes were occasionally seen. The tumor contained concentrated mild desmoplastic stromal changes. Mitotic figures were present in approximately 35 per 10 high-powered fields. Areas of production of osseous matrix with calcification and partly well-formed bony trabeculae were observed (). The osteogenic area was not more than 1% of the tumor. Although cytologically malignant cells were admixed with this osteogenic area, benign metaplastic bone formation was suspected, because the atypical cells were present only in the peripheral portion of the osteoid () and positive for CD99. The osteogenic area, in contrast, was CD99 negative. The pathologic findings of the metastatic lesions of the omental mass were identical to those of the primary mesenteric mass. Cytoplasmic glycogen was undetected in the tumor cells when pretreated with and without diastase in periodic acid-Schiff reactions. No cytoplasmic reactivity was found with Grimelius and Masson-Fontana staining.\nPositive CD99 (MIC2), CD57, and neuron-specific enolase identified many tumor cells immunohistochemically (), whereas positive vimentin and neurofilament results were also present in some cells. Synaptophysin, chromogranin, desmin, cytokeratin, S-100, CD117, and leukocyte common antigen were all absent in the tumor cells.\nUsing dual color break-apart Ewing's sarcoma probing, fluorescence in situ hybridization (FISH) was performed on sections of the tissues that were formalin-fixed and paraffin embedded (Vysis, Downers Grove, IL, USA) with a mixture of 2 FISH DNA probes. The first was a 500-kb probe, labeled in the spectrum orange, and flanking the 5' side of the Ewing sarcoma breakpoint region 1 (EWSR1) gene. The second probe, which flanked the 3' end of the EWSR1 gene, was a 1,100-kb probe, utilizing a spectrum green label. Introns 7 through 10, used as restrictions within the EWSR1 gene, were the known break points. FISH showed a split signal pattern (one green and one orange) in interphase nuclei which was indicative of a EWSR1 gene rearrangement (). A pPNET of the small bowel mesentery diagnosis was ascribed to the lesion, given these results.\nThe recurrent tumor resected one year after surgery, revealed similar histologic features: a typical small round cell tumor with rosette formation and metaplastic bone formation (). The bony islands were more mature than the primary tumor.