Case Report
A previous healthy 50 years-old female arrived at the emergency department due to severe diffuse abdominal pain, and bloody diarrhea. The patient had been suffering from similar, mild symptoms for about three months and did not seek previous medical assistance before, for fear of being infected with COVID-19. Physical examination was unremarkable except for a slight, diffuse pain during abdominal palpation, without tenderness. She had a surgical history of cesarean section and surgical sterilization, and there was not prior family medical history of congenital diseases. An abdominal CT scan revealed a circumferential thickening on the descending colon with trans-mural involvement, and an increased density of the peripheral fat, with a probable neoplastic origin (Figure 1.), associated with mesenteric adenopathy. The characteristics of the remaining abdominal organs were unremarkable. Upper endoscopy showed a follicular gastritis, positive for Helicobacter pylori in the histopathological analysis, associated with a chronic inflammatory infiltrate with lymphoid follicles formation - most of them with germinal centers - and moderate acute infiltrate. Colonoscopy demonstrated a 4 cm sessile mass located in the descending colon, 40 cm from the anal verge, covered with fibrin and necrotic tissue (Figure 2a.). The lesion occupied around 80% of the lumen, and multiple biopsies were obtained. The histopathological analysis of the biopsies reported necrotic tissue, fibrin and cellular debris without neoplastic features. The patient underwent laparoscopic left hemicolectomy. A 15 cm long colon segment arrived at the pathology laboratory, upon the mucosal surface of which a 4cm sessile polypoid mass, cover in fibrin was identified (Figure 2b.). The lesion was mucosal-submucosal based, the center of the lesion was yellow with hemorrhagic foci, without thickening of the colonic wall. Multiple lymph nodes were extracted from the mesenteric fat.
In the histopathological analysis, the polypoid mass was ulcerated at the surface with a cap of granulation tissue, fibrin, cellular debris and acute inflammatory infiltrate. The center of the lesion was composed of well-circumscribed spindle cell proliferation. The spindle tumor cells had tapered nucleus, uniform chromatin with a single nucleolus, and a fascicular and sheet-like growth pattern. There were moderate pleomorphisms, less than 5 mitotic figures in 50 high power fields, and no variable cellular Antoni A and Antoni B areas or Verocay bodies. The stroma of the tumor was collagenous, hypocellular, with lymphocytic inflammatory infiltrate and small arterial vessels with hyalinized walls. The immunohistochemical profile (Figure 3.) shows diffuse nuclear and cytoplasmatic S100 expression, and positivity for SOX10 and GFAP (Glial Fibrillary Acid Protein). The tumor cells were negative for KIT, DOG1, SMA, Desmin, Caldesmon, HMB45, Melan-A, ALK-1, CD34, CD31, EMA, Chromogranin, Synaptophysin, CD56, TLE-1, EMA and Cytokeratins. With the morphological and the immunohistochemical profile, the colonic polypoid mass was diagnosed as a Schwannoma.