This small polyp was removed from the transverse colon. H&E histology is attached
WHAT IS THE DIAGNOSIS?
■ Serrated polyp
Crypt pattern looks more adenomatous!
■ Adenomatous polyp
Slit-like crypts but that thick capillary doesn't fit!
You're good at histology!
■ Neuroendocrine tumour
That was my guess too but I was wrong!
■ Small CRC
This lesion is submucosal!
I was quite sure that this was a small NET. It's that vessel crawling up it's side which convinced me. The reason that I enclose the histology is because it's not a neuroendocrine tumour! Histology shows interlacing bundles of spindle-shaped, smooth muscle cells. with bland-looking nuclei probably arising from the muscularis mucosa just below the epithelium.
It's a leiomyoma, which are very uncommon in the colon but of course very common in the oesophagus. Endoscopically, it's usually not difficult to tell the two apart. NET's often have a dip in the centre and/or sizeable vessels crawling up their sides. Colonic leiomyomas are usually covered with entirely normal looking epithelium. With immunohistochemistry it's easy to tell the two apart. A GIST (thought to arise from the 'interstitial cells of Cajar') usually stain with c-kit (CD117) while a leiomyoma is (thought to originate from smooth muscle cells) stain positive for smooth muscle actin or desmin, but not for c-kit.
Of course leiomyomas are subepithelial lesions, covered with a normal mucosa. The differential diagnosis of submucosal swellings in the colon include: