Indian Journal of Cancer Medknow Publications on behalf of Indian Cancer Society ISSN: 0019-509X EISSN: 1998-4774 Vol. 48, Num. 1, 2011, pp. 135-137

Indian Journal of Cancer, Vol. 48, No. 1, January-March, 2011, pp. 135-137

Letter to Editor

CT findings of primary extra-intestinal gastrointestinal stromal tumor of greater omentum with extensive peritoneal and bilateral ovarian metastases

G Jindal, R Rastogi, S Kachhawa, GL Meena

Department of Radiodiagnosis, Sardar Patel Medical College, Bikaner, Rajasthan, India

Correspondence Address:
G Jindal
Department of Radiodiagnosis, Sardar Patel Medical College, Bikaner, Rajasthan
India
gauravjindal11@hotmail.com

Code Number: cn11035

Sir,

Extra-intestinal gastrointestinal stromal tumors (EGISTs) are rare mesenchymal tumors with immunohistochemical features suggestive of GISTs, but arising in the omentum, mesentery, and retroperitoneum. ^{[1],[2],[3],[4]} A case of primary malignant omental GIST with metastases to bilateral ovaries has not been reported previously.

A 45-year-old female presented with complaints of reduced appetite and vague lower abdominal pain of 3 months duration. Past history was unremarkable except hysterectomy done for fibroid uterus. A firm ill-defined mass was palpable in the left iliac fossa and in the hypogastrium.

Laboratory investigations including tumor markers (carcinoembryonic antigen and carbohydrate antigen) were within normal limits.

Contrast-enhanced abdominal CT scan revealed diffusely infiltrating, lobulated, enhancing soft tissue mass epicentered in greater omentum measuring approximately 6.2 × 5.3 × 5.2 cm [Figure - 1]. Multiple, similar-appearing round to ovoid masses of varying sizes were seen on the surface of small bowel loops, within the small bowel mesentery and in pelvis, on the surface of bilateral ovaries. [Figure - 2] and [Figure - 3]. There was no retroperitoneal lymphadenopathy or ascites. Upper GI endoscopy and chest radiograph were unremarkable. The provisional diagnosis of primary malignant omental, mesenteric, and peritoneal mass was suggested with ovarian metastases. The differential diagnosis include mesothelioma, metastases, and pseudomyxoma peritonei, but were unlikely because of the presence of enhancing soft tissue attenuating mass and absence of any ascites and lymphadenopathy.

Laparotomy revealed a large omental mass, studded with innumerable bulky nodules 0.5-5 cm in size, which on histopathology were found to comprise of epitheloid cells with high cellularity and frequency of mitotic figures, and central necrosis. Soft tissue nodules on the surface of ovaries, bowel, mesentery, and peritoneum revealed similar histopathology.

On pathological immunohistochemical analysis, tumor cells expressed c-kit and CD34 and were immunonegative for desmin, S100, and SMA. Immunoreactivity for c-KIT (CD117, a tyrosine kinase growth factor receptor) helps in differentiating GISTs from true leiomyomas, leiomyosarcomas, neurofibromas, and schwannomas. There was no continuity of the nodules with the bowel wall. Based on CT and pathological findings, a diagnosis of primary malignant omental GIST with metastases to the mesentery and bilateral ovaries was established. Post-operative recovery was uneventful. She was started on chemotherapy with imatinib mesylate and has been doing well on follow up since 9 months.

GISTs most frequently arise in the stomach (60%-70%), followed by the small intestine (20%-30%), colorectum (10%), and esophagus (< 5%). ^[2]

Five to seven percent of all GISTs occur as primary tumors outside the GI tract. Presence of frequent mitotic activity (>2/50 HPF), high cellularity, and the presence of necrosis indicate a potentially aggressive clinical course for EGIST, and presence of two or more of these three features have a poor outcome. ^[5],[6]

Extra-intestinal GISTs are rare mesenchymal tumors with immunohistochemical features suggestive of GISTs, arising primarily in the omentum, mesentery and retroperitoneum. ^[3],[4]

CT is the imaging modality of choice for detection, staging, surgical planning, and follow-up of patients with GIST. Omental GISTs appear as large, well circumscribed, heterogeneously enhancing, masses with regions of necrosis and hemorrhage.

CT features in malignant GISTs include lesion size exceeding 5 cm in diameter, irregular surface, indistinct margins, tissue invasion, heterogeneous contrast enhancement, hepatic metastasis, and peritoneal dissemination. ^[2],[3] Hepatic metastases were not seen in our case, though widespread peritoneal dissemination was evident. Lymph node enlargement is not a feature associated with malignant GISTs and ascites is only rarely seen.

The mainstay in treatment of a GIST is surgical resection. Imatinib mesylate has been found to be beneficial for both induction and adjuvant therapy. ^[1]

Bilateral ovarian metastases have not been previously described with EGIST in medical literature.

References

Copyright 2011 - Indian Journal of Cancer

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