A 51 year-old woman with left iliac fossa discomfort underwent a colonoscopy. Her past medical history only included a breast fibroadenoma diagnosed 4 years earlier. Physical examination and laboratory testing were unremarkable. Colonoscopy revealed a 50 mm polypoid lesion, with normal overlying mucosa, occluding the lumen at 20 cm from the anal verge, compatible with a subepithelial lesion (Fig. 1).
An endoscopic ultrasound (EUS) was performed, showing a 49×32 mm hypoechoic, round, well-demarcated lesion arising from the muscularis mucosa (Fig. 2).
EUS-elastography revealed a predominantly hard lesion with dispersed heterogenic soft areas (Fig. 3).
A EUS-guided fine-needle aspiration was performed using a 22-gauge needle.
Hystological examination showed spindle cells arranged in bundles, with dense distribution of nucleus, forming palisades in dense fibrillar stroma. Immunohistochemical stains revealed that the tumor cells were positive for S-100 and negative for CD117, CD34 and a smooth muscle actin. Cytomorphology and the immunostaining pattern were consistent with schwannoma (Fig. 4). The patient was referred to surgical resection.
Schwannomas are autonomic nerve tumors arising from Schwann cells of the neural sheath (1). They comprise 2-8% of all gastrointestinal mesenchymal tumors and are typically located at the stomach. Colonic schwannomas are exceedingly rare. They are mostly diagnosed in the sixth decade, have no gender preponderance and are usually asymptomatic. Symptomatic patients usually complain of constipation, hematochezia or abdominal pain (2). Endoscopically, schwannomas appear as wide-based sessile subepithelial lesions with a rubbery or firm consistency (3). Computed tomography and magnetic resonance imaging do not provide additional information for the distinction from other mesenchymal tumors (1, 3). On EUS, schwannomas typically arise from the second or fourth layer and usually appear as hypoechoic, round or oval, well-demarcated lesions (4), with a similar appearance to leiomyomas and gastrointestinal stromal tumors (GIST). EUS-elastography is a promising tool showing a predominantly hard pattern (5). Taking into account unspecific endoscopic and ultrasonographic features, tissue sampling is required to obtain the definitive diagnosis. However, preoperatively diagnosis is achieved in a minority of cases given the difficulty of obtaining an adequate specimen. When available, EUS-fine needle aspiration or biopsy is the most accurate method for obtaining tissue. Histologically, schwannomas are composed of bundles of spindle cells aligning in a trabecular pattern, surrounded by fibrovascular septa containing lymphoplasmacytic infiltration. On immunohistochemistry, tumor cells are universally positive for S-100 and vimentin but negative for CD117, CD34 and a smooth muscle actin (3). Currently, complete surgical resection is the best therapeutic choice. (1, 6).
Mafalda João1, Daniel Brito1, Luís Elvas1, José Paulo Magalhães2, Ana Teresa Cadime1.