An odd looking polyp

This is an odd looking sigmoid polyp which is seen arising from a broad stalk. 
WHAT IS YOUR ENDOSCOPIC DIAGNOSIS?

■ Tubular adenoma (TA)

But the crypts don't look slit-like do they?

■ Tubulovillous adenoma (TVA)

Was my first thought but it doesn't look quite right...

■ Villous adenoma (VA)

If your bx forceps disappears into the polyp it's a VA

■ Traditional Serrated adenoma (TSA)

You'd be excused if you got this wrong - these are rare beasts!

explanation

My initial endoscopic diagnosis was that of a TVA. However, it looked a little "exaggerated". Actually it turned out to be a "traditional serrated adenoma" (TSA).

TSA's are rare and mysterious polyps. They only accounting for about 1% of colorectal polyps and are most common in the sigmoid and rectum. Endoscopically they can appear as “exaggerated” tubulo-villous adenomas or as villous adenomas.  In the image below, I've put four examples of TSA's together to illustrate how differently these can appear ! 

It has been proposed that because one-third of "serrated cancers" are found in the distal colon and perhaps these cancers arise from TSA’s!    However, genetically, TSA's are more like adenomatous polyps harbouring low-level microsatellite instability (MSI-L). They usually contain KRAS mutations rather than the BRAF mutations which you find in the 'Sessile Serrated Lesions'.  For this reason, it's perhaps unlikely that they contribute to the 'Serrated Pathway' to cancer. 

By the way, a recent paper has highlighted that patients with TSA's are also at greater risk of 'high risk polyps', elsewhere in the colon.