Primary Extragastrointestinal Stromal Tumor of the Dorsolateral Anorectum Resected via a Posterior Approach: A Case...

Gastrointestinal stromal tumors (GISTs) can arise anywhere along the gastrointestinal tract. When they originate outside the gastrointestinal tract, they are referred to as extragastrointestinal stromal tumors (EGISTs), which are rare. In particular, EGISTs arising in the perianorectal region are extremely rare. We report the case of a primary perianorectal EGIST, which was initially diagnosed preoperatively as a rectal GIST.

A 74-year-old woman presented with a palpable mass on her left buttock. Histopathological analysis of the biopsy specimen confirmed the diagnosis of GIST. MRI revealed a 46 × 28 mm mass on the left dorsolateral aspect of the lower rectum, which was preoperatively diagnosed as rectal GIST. Partial resection of the rectum via a posterior approach was planned. Intraoperatively, however, no continuity between the tumor and rectal wall was observed. Based on pathological and operative findings, the tumor was diagnosed as a perianorectal EGIST, and complete resection was achieved without rectal resection.

This case underscores the clinical significance of considering EGIST as a differential diagnosis for anorectal GIST lacking clear continuity with the intestinal wall. Furthermore, our experience suggests that posterior approach is less invasive, facilitates anus preservation, and should be considered for resection of both rectal GISTs and perianorectal EGISTs.