A unusual rare beast

A very odd looking polyp at the anal verge. I removed it but still couldn't really make out what it was!? 
WHAT IS YOUR BEST GUESS AT THE MOST LIKELY DIAGNOSIS? 

■ Inflammatory polyp

Good guess as there is no crypt pattern!

■ Adenomatous polyp

It has the colour of an adenomatous polyp but no crypt pattern...

■ Small adenocarcinoma

Certainly ugly enough but small carcinomas are usually more button-shaped

■ Small SCC

Arising from close to the anal margin but nearby squamous mucosa is unremarkable...

explanation

This is rare stuff!  I was clueless although reassured that the thing was soft and didn't feel malignant when squeezed between my fingers. 

It proved to be a (rare) 'cloacogenic polyp'!  You'd be excused if you have never heard of this (I hadn't).  Apparently these were first described as recently as 1981!  The same year that I was born ☺!  Essentially they are inflammatory polyps arising from the transitional zone of the anorectal junction.  

They can be much larger than this and even be multiple and can occur at any age. Patients are usually asymptomatic but could (naturally) present with some blood on the toilet paper (this patients complaint).  

Histology is similar to that of solitary rectal ulcers with inflammation and fibromuscular hypertrophy. For this reason it is perhaps not surprising that they are linked with constipation and straining.  Rare associations include small nearby cancers and human papillomavirus infection.