St. Elizabeth's Medical Center, Tufts University School of Medicine Brighton, MA
Padmavathi D. Srivoleti, MD1, Erik Holzwanger, MD2, Rohit Dhingra, MD2, Sandeep Krishnan, MBBS, PhD1; 1St. Elizabeth's Medical Center, Tufts University School of Medicine, Brighton, MA; 2Tufts University Medical Center, Boston, MA
Introduction: The differential for rectal subepithelial lesions is broad. One of the differentials is a gastrointestinal stromal tumor (GIST), which is a rare mesenchymal tumor that most commonly occurs in the stomach and small intestine. It has an annual incidence of 0.68 per 100,000 people in the United States. In exceedingly rare cases, GISTs can be seen in the rectum. We present a case of an incidental finding of rectal GIST on screening colonoscopy in an asymptomatic woman.
Methods: A 50 year old, otherwise healthy, woman presented for her initial screening colonoscopy. Prior to her colonoscopy, a rectal exam was done that was significant for a well-circumscribed mass from posterior midline to right lateral anal verge. Subsequent colonoscopy revealed a possible subepithelial mass versus extrinsic compression in the distal rectum. As a result, a CT scan of the abdomen/pelvis was done which demonstrated a 6 cm solid rectal mass and a 2.7 x 2.5 x 2.2 cm right adnexal lesion. Transvaginal ultrasound confirmed a 1.8 cm complex ovarian cyst. A rectal endoscopic ultrasound (EUS) was done which revealed a hypoechoic, non-circumferential 4 cm subepithelial mass with irregular borders located 0.5 cm from the anal verge. While the precise layer of origin of the mass could not be ascertained clearly due to its large size, it appeared to arise from the muscularis propria. Fine needle biopsy (FNB) was performed and pathology was consistent with GIST. Immunohistochemical staining was positive for CD117 (c-kit) and CD34 and was negative for smooth muscle actin and desmin negative. Further imaging classified the tumor stage as TII (a tumor >2 cm, but £5 cm). She is currently initiated on neoadjuvant chemotherapy with Imatinib and is planned for surgical resection of the mass. Discussion: We present an exceedingly rare entity of rectal GIST in a middle aged, otherwise healthy woman. While some of the differentials for subepithelial lesions are benign, there are those that have malignant potential, such as in this case. For GISTs, 5-year relative survival rate dramatically decreases from 94% for localized disease to 52% for distant disease. It is of the utmost importance for early tissue diagnosis with EUS and FNB to differentiate the lesion and allow for early treatment with medical and surgical therapies. This in turn can decrease the risk of progression of disease and improve outcomes.
Figure 1: Rectal subepithelial lesion revealed on colonoscopy
Figure 2: Rectal subepithelial lesion characterized on endoscopic ultrasound
Figure 3: MRI pelvis revealing subepithelial lesion in the rectum (time of diagnosis)
Disclosures: Padmavathi Srivoleti indicated no relevant financial relationships. Erik Holzwanger indicated no relevant financial relationships. Rohit Dhingra indicated no relevant financial relationships. Sandeep Krishnan indicated no relevant financial relationships.