From the questions on page 619

Observation with crystal violet dye disclosed concentric folds around the lesion (fig 1). By magnifying colonoscopy, the same normal round pit pattern (type I) was shown on the lesion as on the surrounding mucosa (fig 2). The lesion was soft and easily compressible to palpation by gentle probing with a closed pair of forceps, indicating an inverted colonic diverticulum. The stigmata of gastrointestinal bleeding were not identified but were attributed to diverticulosis of the sigmoid colon. He has been asymptomatic during the follow-up.

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Figure 1

Concentric folds were present around the polypoid lesion, shown by crystal violet dye.

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Figure 2

Magnifying colonoscopy disclosing the same normal round pit pattern on the polypoid lesion as on the surrounding mucosa.

Inverted colonic diverticula have been reported only rarely. Most lesions were located in the sigmoid colon. Recognition of an inverted colonic diverticulum may prevent unnecessary “polypectomy” (diverticulectomy) which results in perforation of the colon. Gentle air insufflation or probing with a biopsy forceps to reconstitute the normal configuration of the diverticulum have been the key to the diagnosis of inverted colonic diverticulum. The “concentric sign” and a normal pit pattern recognised with crystal violet or indigo carmine dye shown here may have novel value for this diagnosis.