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Digital Case Challenge: Rectal mucosal "schwannona"

Posted Jan 18 2011 4:16pm

I'm finally emerging from a hiatus from blogging after the holidays and discoursing second-year medical students on lung pathology for the last 2 weeks.  So I'd like to kick 2011 off with an interesting little case I recently saw.  The patient is a 62-year-old man undergoing screening colonoscopy and a small sessile polyp was found and removed from the rectum.  Here 'tis--

  Rectal polyp schwannoma

The low power view confirms a polypoid lesion but doesn't declare itself as a obvious adenomatous or hyperplastic polyp.  However, the lamina propria appears modestly cellular and mildly distorts the crypt architecture.

Rectal polyp schwannoma1
Rectal polyp schwannoma2
Higher power views demonstrate an intercryptal spindle cell proliferation of uniform bland cells with fibrillar eosinophilic cytoplasm.  The way these cells focally stack up reminded me of Verocay bodies.  I'm a little embarassed to show our S-100 stain, which is a little weak in this batch, but--

Rectal polyp schwannoma4S100

I diagnosed this as a "mucosal schwannoma" but preferred the less specific but nevertheless accurate term "benign mucosal neural polyp."  Perhaps this was an unconscious effort to avoid any uncomfortable conversations regarding inherited syndromes?  I was also struck by the way that the neoplastic cells are permeate between the crypts rather than producing a more homogeneous polyp/mass.  In doing some further prospecting in PubMed, I came across a report in the World Journal of Gastroenterology published in May 2009 from a group from Roma, Italia describing a similar lesion to this one.  Their pictures are very similar to mine.  They also appreciated the distinctive growth pattern of S-100-positive bland spindle cells in the lamina propria "entrapping" colonic crypts.  They suggest the term "mucosal Schwann cell hamartoma," which is interesting.  I don't like the term "hamartoma" for this, however, as it implies that the crypts and other stromal cells contribute to the abnormal growth.  It looks to me that it is only the "Schwann" cells are growing abnormally.  Perhaps this is just an early schwannoma.  In any case, I'm not sure that it is accurate to conclude that these are "Schwann" cells anyway, at least, just because of their immunoreactivity.  Whatever one decides to name this polyp, this is a curious lesion.  I suggest the term "mucosal neurogenic polyp" but feel free to be creative.

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