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Gastrointestinal stromal tumour (GIST) arising in a colonic duplication cyst: case report

A 31-year-old woman presented with acute diffuse abdominal pain. Computerized tomography (CT) revealed an oedematous, slightly irregular 5.8 · 3.6 · 5.6 cm mass in the pelvis, behind the uterus, with a hypercaptating wall and inlying hypocaptating nodules. A differential diagnosis of pelvic inflammatory disease and ovarian torsion was considered. At laparoscopy, an inflamed mass, adherent to the jejunum and sigmoid, was seen in the right iliac fossa. The mass was removed by sigmoid resection. On gross examination, the lesion was 6 cm in diameter and showed a central cavity filled with blood. There was no communication between the lumen of the adherent sigmoid and the cavity in the mass. Microscopically (Fig. 1), the mass consisted of uniform, densely packed, diffuse sheets of spindle cells with little atypia and a mitotic count of < 5 ⁄ 50 high-power fields. The cells stained positively with antibodies directed against c-kit (CD 117), CD 34 and alpha-smooth muscle actin (alpha-SMA), but S-100 and desmin were negative. The diagnosis of a gastrointestinal stromal tumour (GIST) was made. Following the National Institute of Health Risk Stratification Categories [1], the GIST had an intermediate malignant potential: the tumour was 6 cm (intermediate) with a mitotic count of < 5 ⁄ 50 HPF (low). The inner surface of the macroscopically observed central cavity was lined by a colon-like mucosa with underlying remnants of smooth muscle. The final histopathological diagnosis was a GIST arising in a duplication cyst of the colon.