We suspected the air bubble revealed in the abdominal CT to be a colonic diverticulum before performing colonoscopy (Fig. 1, arrow). NBI disclosed a normal mucosal pattern and concentric rings surrounding the polypoid lesion with an exposed vessel that made the diagnosis of an inverted colonic diverticulum (ICD) in the sigmoid colon (Fig. 3). The exposed vessel was treated with endoscopic hemostatic clips following which hematochezia has not recurred.

Although colonic diverticular disease is common, ICD has been rarely reported.^1-3 It often appears indistinguishable from the colon polyps.² The concentric rings, which are enhanced by NBI or indigo carmine dye, can help in diagnosing the ICD without maneuvers, such as the use of air insufflation, reverting the ICD with forceps, and the water jet deformation.^2,3 To the best of our knowledge, this is the first documentation of ICD associated with an exposed vessel that causes diverticular bleeding. This case emphasized the importance of recognition of ICD for endoscopists to avoid potentially risky procedures.