Case of colonic mucosal Schwann cell hamartoma and review of literature on unusual colonic polyps

Abstract

Mucosal Schwann cell hamartomas (MSCH) are benign mesenchymal tumours rarely seen in the gastrointestinal tract. They occasionally present as incidental sessile polyps during colonoscopy. A 55-year-old asymptomatic female patient with a medical history of multiple sclerosis presented for a screening colonoscopy. A 5 mm low-risk tubular adenoma was noted in the caecum, and a second 5 mm polyp was found in the ascending colon. Histopathology of the ascending colon polyp showed proliferation of spindle cells without ganglion cells in the lamina propria. Immunohistochemical findings are compatible with an MSCH. Surveillance colonoscopy was scheduled in 5 years based on the presence of a single low-risk tubular adenoma.

Background

Although mucosal Schwann cell hamartomas (MSCH) are considered benign and found incidentally during colonoscopies, there are paucity of data on the outcomes and surveillance guidelines on these types of unusual polyps due to their rarity.

Case presentation

A 55-year-old asymptomatic female patient with a medical history of multiple sclerosis presented for a screening colonoscopy. Home medications included glatiramer acetate (Copaxone) 40 mg given subcutaneously three times every week. There was no reported family history of colon cancer or personal history of familial hereditary polyposis syndromes, neurofibromatosis, von Recklinghausen syndrome or Cowden syndrome. Her father had colon polyps of unknown histology diagnosed at the age of 72 years.

Investigations

A 5 mm low-risk tubular adenoma was noted in the caecum, and a second 5 mm polyp was found in the ascending colon (figure 1). Given the small size, these polyps were removed using biopsy forceps in a piecemeal fashion. Histopathology of the ascending colon polyp showed proliferation of spindle cells without ganglion cells in the lamina propria. There was strong and diffuse immunoreactivity to staining with antibody to S100 protein but not with antibodies to neurofilament protein (NFP), CD117 or smooth muscle actin (SMA). These features are compatible with an MSCH (figures 2 and 3).

Figure 1.

A 5 mm polyp in the ascending colon.

Figure 2.

Colon, ×100, H&E. The lamina propria between the two blue arrows contains a spindle cell proliferation, which alters the density of the lamina propria. The green arrow indicates a normal area of lamina propria for comparison.

Figure 3.

Colon, ×200, S100 immunohistochemical. The spindle cells are immunoreactive with antibody to S100 protein (brown stained cells indicated by the blue arrow). The lamina propria away from the proliferation (green arrow) contains only rare cells. The proliferated spindled cells are not immunoreactive with antibodies to CD117, neurofilament protein and smooth muscle actin.

Treatment

Surveillance colonoscopy was scheduled in 5 years based on the presence of a single low-risk tubular adenoma.

Outcome and follow-up

MSCH are usually considered benign and its presence did not alter interval for subsequent surveillance colonoscopy.

Discussion

MSCH of the gastrointestinal (GI) tract are most often reported in middle-aged women. They are rare, benign, range in size from 1 to 6 mm; and mostly seen in the colorectal region. Due to its rare occurrence, the exact incidence and prevalence is unknown. About 10 cases of MSCH have been reported in medical literature so far.¹ They are typically sessile and may resemble other GI tumours—gastrointestinal stromal tumour (GIST), carcinoid, leiomyoma, schwannoma, mucosal neuroma, neurofibroma or ganglioneuroma.¹ These differential diagnoses should be ruled out as further evaluation, recommended treatment and surveillance intervals vary with each tumour (table 1).

Table 1.

Types of unusual polyps and their characteristic features

Polyp type	Cell origin/association	Common site	Immunoreactivity	Other clinical and histological features
MSCH	Mesenchymal	Colorectal	S100 (strong)	Sessile; benign
GIST	Spindle cells	Stomach and small intestine	S100; C-KIT; CD-117; DOG	Malignant
Carcinoid	Enterochromaffin cells	Stomach, jejunum, colon, appendix	Chromaffin Ki-67 index Mitotic rate	Grade based on Ki-67 and mitotic rate; benign (or) malignant
Leiomyoma	Smooth muscle cell	Oesophagus	SMA; desmin	Benign; diagnosed by EUS-FNA
Mucosal neuroma	Mucosal nerves	Lips and tongue	–	Associated with MEN-2b
Schwannoma	Schwann cells	Stomach	S100; GFAP	Peripheral lymphoid cuffs and Antoni-A and Antoni-B regions on histology
Neurofibroma	Superficial nerves	Stomach and small intestine	S100 (variable)	Pathognomic of NF-1
Ganglioneuroma	Ganglion cells, nerve fibres	Colon and rectum	S100; neuron-specific enolase	Associated with Cowden syndrome; NF-1

EUS-FNA, endoscopic ultrasound–fine needle aspiration; GFAP, glial fibrillary acidic protein; GIST, gastrointestinal stromal tumour; MEN, multiple endocrine neoplasia; MSCH, mucosal Schwann cell hamartoma; NF, neurofibromatosis; SMA, smooth muscle actin.

GISTs, the most common spindle cell tumours in the GI tract, are usually found in the stomach and small intestine and rarely in the colorectal region. They may display neural features with S100 protein positivity. They are distinguished from MSCH based on the characteristic immunoreactivity to C-KIT/CD117.^{1 2}

Carcinoid tumours are usually well-differentiated neuroendocrine tumours of the GI tract usually found in the stomach, small intestine, colon, appendix and rectum. Carcinoids are graded based on the Ki-67 index and mitotic rate. These tumours can be differentiated from MSCH by the clinical symptoms (carcinoid syndrome) and pathology.³

Leiomyomas present as polypoid lesions and may resemble either GIST or MSCH endoscopically. They arise within the muscularis mucosae and display smooth muscle cell immunophenotype. There is a strong immunoreactivity to SMA and desmin but not to S100, CD34, CD117 or C-KIT.^{4 5} These characteristics are helpful in differentiating them from GIST, MSCH or neuromas.

Mucosal neuromas are typically seen in patients with multiple endocrine neoplasia type 2b and commonly located on lips and tongue. They often occur as small sessile nodules. Histologically, axons are frequently seen and have hyperplastic bundles of nerve cells, often with thickened perineurium.⁶

GI schwannomas are uncommon tumours mostly found in the stomach (90%) and rarely in the colon.⁷ About 2%–6% of mesenchymal tumours are schwannomas. Histologically, although non-capsulated, they are well-circumscribed lesions with peripheral lymphoid cuffs and Antoni-A and Antoni-B regions, which are absent in MSCH.⁵ Other distinguishing characteristics include absence of nuclear palisading, vascular hyalinisation, Verocay bodies and xanthoma cells.⁸

Colorectal neurofibroma is almost pathognomic of neurofibromatosis-1. They originate from small superficial nerves composed of elongated cells intermixed with collagen bundles or mucin. There is variable positive staining for S100 and consist of Schwann cells, fibroblasts, perineural cells and NFP-positive axons.⁹

Ganglioneuromas are frequently associated with Cowden syndrome. The presence of ganglion cells differentiates them from MSCH.⁵

None of the previously reported cases were associated with inherited syndromes. MSCH has been reported in a patient with ulcerative colitis and primary sclerosing cholangitis.¹⁰ It is unclear if underlying ulcerative colitis is a risk factor for development of MSCH.

Patient’s perspective.

Thank you so very much for sending me the article. So very interesting to me. I would love to be continually updated of the progress of research for this type of unusual polyp. Good Luck with you submission to BMJ!

Learning points.

• Mucosal Schwann cell hamartomas (MSCH) are considered benign tumours.

• It is important to differentiate MSCH from other mesenchymal tumours such as gastrointestinal stromal tumour that can be malignant.

• Based on the observational data, there are no guidelines or recommendation for surveillance colonoscopy for MSCH.