Figure 1

Imaging of the colon demonstrated indentation of the caecal wall (A, red arrow) on air contrast barium enema and thickening of the caecal pole (B, red arrow) and a mucocele of the appendix (B, blue arrow) on CT scan with oral contrast. Examination of the gross specimen (C) showed a flat tumour of the caecum and a separate lesion in the appendix. The appendix had ruptured and mucinous deposits had extruded onto the serosa (C red arrow). Haematoxylin and eosin stained sections of the two tumours demonstrated distinct morphologies. The caecal tumour showed complex glandular structures lined by highly atypical cells infiltrating through the bowel wall and inciting an inflammatory and stromal desmoplastic reaction indicative of invasive adenocarcinoma (D). By contrast, the appendiceal lesion showed an architecture resembling adenoma, composed of villous structures lined by columnar cells with mucin vacuoles (E). The basally located nuclei showed only mild cytological atypia and the proliferative activity as measured by immunostaining for Ki-67 was predominantly at the basal layer. The lesion appeared to have an expansile growth pattern without evidence of destructive infiltration of the wall of the appendix. Although mucin was seen on the outer serosal surface, no viable tumour cells were identified outside the lumen of the appendix.