An IHC stain for S-100 protein is shown below. IHCs for actin, desmin, CD34, and AE1/AE3 cytokeratins were negative.
Rare ganglion-like cells were identified. My diagnosis is: Mucosal ganglioneuroma.
The histology is typical of this entity and shows a hypercellular lamina propria spindle cell proliferation which displaces colonic crypts. The margins are poorly circumscribed. In some cases, ganglion cells can be identified in clusters, but in others, like this case, they were rare and isolated. Intestinal ganglioneuromas can be separated into three clinicopathological groups: 1) incidental or solitary polypoid ganglioneuromas (most common), 2) ganglioneuromatous polyposis, and 3) diffuse ganglioneuromatosis. These catagories have obviously different clinical implications and I refer you to a specialized GI pathology textbook for a more complete discussion. But the solitary polypoid ganglioneuromas are endoscopically indistinguishable from adenomatous or hyperplastic polyps and require no additional follow-up.
Interestingly, I recently read a paper, "Mucosal Schwann Cell "Hamartoma"," by JA Gibson and JL Hornick in the May 2009 Am J Surg Pathol that was pertinent to this case. They report on 26 morphologically similar polyps that were intramucosal neural proliferations lacking ganglion cells that had variously been diagnosed as "neuromas" or "neurofibromas." The polyps included in the study showed 1) spindle cell morphology and 2) involvement of the mucosa.
Similar to my case, most were asymptomatic and found during screening colonoscopy, were located in the rectosigmoid colon, were the only polyp found at colonoscopy, and were small (mean size 2.5 mm). The discussion of the differential diagnosis in this paper is well-worth the read. Moreover, the authors make a good point that these lesions should not be called "neurofibromas" because of the strong association with GI or visceral neurofibromas and neurofibromatosis type I, nor should they be called "neuromas" because of the strong association between "mucosal neuromas" of the lips and tongue and MEN type 2B syndrome. Actually, had I not identified a few rare ganglion cells, I would have called this a polypoid intramucosal neuroma. I think the weak part of this argument is that, basically, the series they describe are identical clinically and histologically to ganglioneuromas except they do not have ganglion cells. Logically (at least to me), these should be called "solitary polypoid colonic intramucosal neuromas." The propose the less specific term "mucosal Schwann cell hamartoma" for these lesions. Perhaps the syndromic mucosal neuromas of the lips and tongue associated with MEN2B should be called something else since these clearly are different clinically from incidental solitary rectosigmoid polypoid "neuromas."