Ascending Colon Schwannoma Surgically Treated after Accurate Preoperative Diagnosis

Abstract

Colorectal schwannomas are rare and usually benign gastrointestinal mesenchymal tumors. However, these tumors are often overtreated, possibly owing to misleading malignant potential. To our knowledge, there have been no previous reports of ascending colon schwannoma preoperatively diagnosed as benign schwannoma. Herein, we report a case of ascending colon schwannoma accurately diagnosed by endoscopic biopsy and successfully treated by wedge resection. The patient was a 76-year-old woman with complaints of bloody stool. She had no relevant past medical history. Radiological findings revealed a protruded mass in the ascending colon, and colonoscopy revealed a submucosal tumor measuring approximately 3 cm in diameter with a reddish and uneven surface. Histological and immunohistochemical analysis for vimentin and S100 protein of the specimen obtained by endoscopic biopsy confirmed the diagnosis of schwannoma. Thus, we performed laparoscopy-assisted endoscopic full-thickness resection of the ascending colon wall, as appropriate for a benign soft tissue tumor. The postoperative course has been uneventful for 2 years. This case demonstrates that colonic schwannoma can be successfully treated with adequate resection if an accurate preoperative diagnosis is made, thereby avoiding overtreatment, such as surgery for colorectal tumor including lymph node dissection. Preoperatively diagnosed schwannomas should be treated by wedge resection, with postoperative pathological findings confirming the presence or absence of malignancy. Additional resection should be considered for very rare cases of coexisting malignant tissue.

Keywords: Colonic submucosal tumor; Schwannoma; Surgical treatment.

Fig. 1

Preoperative diagnostics. Abdominal computed tomography axial (a) and coronal (b) slices revealed a tumor in the ascending colon with a high-density area and a size of 3 cm. c Contrast enema images revealed a steep-edged mass shadow in the ascending colon with clearly defined boundaries. d Colonoscopy revealed a rough mass at the ascending colon that was covered by a white coat, with erosions spreading all over the tumor.

Fig. 2

Biopsy specimen analysis. a Bar: 1,000 μm. Inflamed erosive colon mucosa with spindle cell proliferation in the deeper lamina propria region containing woven nests of compact bundles of slender, wavy spindle cells admixed with a lymphocyte-rich stroma. b−d The spindle cells also formed compact fascicles, occasionally aligning in rows. Individual cells had a distinct eosinophilic cytoplasm and dark fusiform nuclei that varied in shape and size (hematoxylin and eosin stain). b Original magnification: 1:100. c, d Original magnification: 1:400. e All spindle-shaped tumor cells were strongly and globally positive for S100 protein, with both nuclear and cytoplasmic staining. Original magnification: 1:200. f Vimentin was also strongly expressed. Original magnification: 1:200. g, h Tumor cells were negative for CD117 (KIT) and smooth muscle-related antigens (smooth muscle actin, desmin, calponin, and h-caldesmon). g, h Original magnification: 1:200.

Fig. 3

Resected specimen analysis. a Gross inspection revealed a circumscribed but unencapsulated ovoid nodular mass with a polypoid intraluminal component, measuring 3 × 3 × 1.7 cm in size. Wide-spread mucosal erosion was grossly visible. b The cut surface was yellowish without myxoid degeneration or tumor necrosis. The surface revealed that the muscle layer was infiltrated by the tumor. c S100 protein was detected in the immunohistochemical analysis. Original magnification: 1:400. d Hematoxylin and eosin staining revealed that the spindle cells formed compact fascicles, occasionally aligning in rows. The findings were same as those for the biopsy specimens. Original magnification: 1:200.