A screening colonoscopy was performed on an asymptomatic 68-year-old woman. A diminutive 1 mm diameter Paris-type 0-IIc neoplastic lesion was diagnosed in the ascending colon (fig 1A). Further characterisation using high-magnification chromoscopic colonoscopy and 0.05% crystal violet intravital staining revealed a Kudo-type IIIs crypt architecture in the depressed component, which suggested that this lesion was limited to the mucosal layer. Endoscopic mucosal resection (EMR) was considered to be the most appropriate firstline endoluminal treatment in this case to confirm histologically the absence of neoplastic disease beyond 1000 μm in the vertical margin, where data from both Japan and Europe have shown that despite diminutive endoluminal appearances, such type 0-IIc lesions have an increased potential for local nodal disease (8–10%) in the right colon.^1,2 Further management—that is, continued endoscopic surveillance or progression to surgical resection—is therefore dependent on the “gold standard” histopathological assessment. Hot biopsy, which is a primarily ablative technique, is unable to provide this mandatory information.

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Figure 1

 (A) Colonoscopy after application of 0.2% indigo carmine dye showed a diminutive Paris type 0-IIc neoplastic lesion, 1 mm diameter, in the ascending colon. (B) Colonoscopy showed the yellowish substance, which looked like a sponge and was thinner, and less yellowish than adipose tissue in the serosa, floating in the ulcer created by endoscopic mucosal resection.

The lesion was raised using a submucosal injection of normal saline solution with no evidence of non-lifting or asymmetry, and resected en bloc endoscopically. The patient reported no abdominal pain during the resection. However, a xanthachromic substance mimicking adipose tissue was observed at the vertical resection margin (figs 1B and 2A). This tissue appeared endoscopically distinct from serosal adipose tissue, diagnostic of post-EMR transmural perforation. Furthermore, the muscularis propria was not represented in the resected lesion that histologically revealed a tubular adenoma with moderate atypia only (fig 2B). No free air was present on a chest and abdominal CT. The patient was subsequenty managed conservatively without any late adverse outcome.

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Figure 2

 (A) Colonoscopy showed the yellowish substance, which looked like a sponge and was thinner, and less yellowish than adipose tissue in the serosa, floating in the ulcer created by endoscopic mucosal resection. (B) Macroscopically, the endoscopic picture showed that the muscle layer was not included in the vertical margin of the resected specimen.

During EMR, transmural perforation can occur when the muscularis propria becomes entrapped below the vertical cut margin of the snare. Clinically, patients often report transient abdominal pain during resection, and subsequently a definite perforation can be identified endoscopically.³ Furthermore, serosal adipose tissue may be directly visualised after EMR, diagnostic of transmural perforation. However, xanthachromic submucosal adiposity can also be observed after EMR, and although difficult to distinguish endoscopically from serosal fat represents a “normal” submucosal variant, particularly prominent in the proximal ascending colon and ileocaecal valve (colonic lipohyperplasia).⁴ Given the increased use of EMR for the treatment of Paris type 0-II neoplastic lesions, this case serves to emphasise the importance of normal anatomical variance after resection. Submucosal xanthachromia after EMR should not be confused with the direct visualisation endoscopic appearance of serosal adipose tissue. Differentiation of these two distinct post-EMR appearances is essential to avoid misdiagnosis of perforation leading to unnecessary laparotomy.⁵