The Elusive Sessile Serrated Adenoma

The detection of sessile serrated adenomas (SSA) has gained increasing importance with the discovery of their premalignant potential. Diagnosis can be challenging given similarities between the hyperplastic polyp (HP) and SSA in endoscopic appearance. This case presents a bizarre appearing ascending colorectal polyp with premalignant potential and emphasizes the importance of being familiar with SSAs both endoscopically and pathologically. Accurate diagnoses will affect recommendations for surveillance colonoscopy and decrease the risk of interval colorectal cancer (CRC) rates. 55 year old male was referred to the gastroenterology clinic for a routine screening colonoscopy. Patient denied any symptoms of abdominal pain, melena, hematochezia, or weight loss. Labs were unremarkable. Initial colonoscopy revealed several sub centimeter polyps in the left colon, and a 2 cm lesion at 50cm which was biopsied and tattooed. This oddly shaped 2cm lesion had the appearance of a giant wide mouthed diverticulum with heaped up borders and an inverted center (Figure 1). There were small vessels on the mucosal surface noted. On initial pathology, all of the polyps were read as HP, including the 2cm lesion at 50cm. However, due to a high level of suspicion that the 2cm polyp was an SSA, a three month interval colono-scopy was ordered, along with a CT scan which was negative to rule out a fistula. On repeat colonoscopy, the 2cm polyp at 50cm was resected (Figure 2). Pathology now revealed a sessile serrated adenoma with cytologic dysplasia (Figure 3) and the patient was recommended to follow-up with repeat colonoscopy in 3 years. Overall, this case highlights the challenges a gastroenterologist faces in the diagnosis of the SSA. Both HP and SSA can be sessile and even flat, have a mucus cap, and have color that appears similar to the surrounding colonic mucosa. On pathology, typical pattern of proliferation with dilation at the crypt base are not always consistently seen under the microscope. Therefore, location in the colon and size become strong considerations for accurate diagnosis. Follow-up was also affected by the change in diagnosis from HP to SSA from 10 years to 3 years. The astute clinician must have a high index of suspicion for lesions that appear peculiar on initial colonoscopy. Specific features such as size, location and dilated vessels can be assessed and can increase suspicion for an SSA and significantly improve the outcomes of CRC screening programs.Figure: Polyp at 50cm.Figure: Polypectomy site.Figure: Pathology showing the dilated crypt bases classic for sessile serrated adenomas often referred to as boot shaped.