Rectal gastrointestinal stromal tumor mimicking a vaginal wall cyst in a young female: a case report of diagnostic challenge and review of the literature

Introduction and importance: Rectal gastrointestinal stromal tumor (GIST) is a rare neoplasm of mesenchymal origin. It usually presents with gastrointestinal bleeding and abdominal pain; however, it may rarely present with atypical features mimicking gynecological or urological problems. Presentation of the case: We report a case of GIST in a 36-year-old female with a rare location in the rectum and an atypical presentation of vaginal pain and burning micturition, without gastrointestinal symptoms. The gynecologist clinically suspected a vaginal wall cyst and referred her to a urologist and a general surgeon. The digital rectal examination revealed a firm rectal mass. Magnetic resonance imaging was recommended, which revealed a well-defined enhancing endo-exophytic lesion arising from the lower rectal wall. Surgical excision was performed, and histopathological examination with immunohistochemistry strongly supported a diagnosis of rectal GIST; the tumor was positive for DOG1, CD117, CD34, and Ki-67 (5%) and negative for S-100. She was started on adjuvant imatinib therapy. Clinical discussion: GIST has a broad differential diagnosis, ranging from benign to malignant tumors. Our case involved a grossly polypoid, firm mass in the rectum, a rare site for GIST, with an unusual presentation, highlighting the spectrum of mimickers. If diagnosed early, complete surgical excision remains the standard treatment for localized GIST, while adjuvant imatinib therapy is recommended if there is an increased risk of recurrence. Conclusion: This report highlights the diagnostic challenge of a tumor with an unusual presentation and a rare location. Histopathological examination, along with IHC, remains the gold standard for diagnosis and outcome prediction.