A Colorectal Myxoid Nodule: Is It a BUMP or a Myxoma?

Abstract

Benign polyps from the mesenchyme can arise in the mucosa or submucosa anywhere in the Gastrointestinal tract. They are typically solitary, small, and found incidentally on screening colonoscopies. Most are asymptomatic, however, some may lead to bleeding, abdominal pain, obstruction, or local invasion. Anatomical and molecular pathology are important in categorizing these lesions. A 33 y.o. female presented for the evaluation of rectal bleeding and chronic intermittent, dull and crampy lower abdominal pain that resolves with defecation. She had rectal bleeding at age 9, and, at that time, a polyp was identified on flexible sigmoidoscopy. The pathology report was unavailable. Her brother also had polyps in his 40s requiring surgery. No family history of colon cancer was reported. Her general physical exam was normal and her abdominal exam was benign. Blood work showed a normal complete blood count, basic metabolic panel, and liver function test. A colonoscopy was recommended, which revealed a single sessile polyp measuring 5 mm in size at the recto-sigmoid junction along with another 5 mm flat polyp in the rectum. (Image 1) Saline was injected at the base of the polyp for lifting and complete removal with a hot snare cautery polypectomy. Upon withdrawal of the needle from the polyp after a saline lift, oozing white mucoid material was noted from needle site. Firm texture was appreciated during polypectomy. On pathologic examination, routine light microscopy revealed colonic mucosa overlying a hypo-cellular submucosal hyalinized myxoid nodule. (Image 2) Additional histochemical staining was negative for collagenous or elastic fibers on a trichrome-elastic stain and negative for amyloid on a Congo red stain. (Image 3) The second polyp was also removed and pathology showed a small well-differentiated neuroendocrine tumor. This is the first documented case of a colorectal myxoid nodule. All myxoid nodules of the large intestine should be characterized on a case by case basis to determine whether they are clinically indolent and pathologically benign or locally aggressive and potentially pathologically malignant. The anatomic layer in which they are found, among other histologic features, helps elucidate these lesions. For lesions that do not fit into a currently well-described entity, the Benign Unclassified Mesenchymal Polyps category may be appropriate. Their full clinical significance will be better understood when more are reported in the literature.1559_A Figure 1. A single sessile polyp measuring 5 mm in size at the recto-sigmoid junction on colonoscopy.1559_B Figure 2. The submucosa is expanded by a hypocellular myxoid matrix with scattered smooth muscle cells and hyalinized blood vessels (H&E, X100).1559_C Figure 3. The myxoid matrix is non-collagenous and without elastosis. There are scattered smooth muscle cells from splaying of the muscularis mucosae fibers (Trichrome/elastic, X100).