The gastrointestinal autonomic nerve tumors (GANTs) were first described and defined by Herrera et al. in 1984 [3]. Schwannomas belong to GANT which is a subcategory of gastrointestinal stromal tumor (GIST) [4, 5]. Schwannomas located in the colon and rectum are unrelated to Von Recklinghausen's disease [1]. They can appear in any age group but are most frequently seen in the sixth decade of life [6]. This neurogenic tumour is usually benign and has indolent growth. Although they are generally asymptomatic, they may present with bleeding, obstruction, tenesmus, and rectal pain [1]. In the present report, the patient presented with features of lower urinary tract obstruction and constipation because of a large tumour compressing the bladder neck, and rectum.
MR imaging features that suggest the diagnosis of a neurogenic tumour include the presence of a fusiform-shaped mass with an entering and exiting tail representing the host nerve [7]. Typically, the Schwannomas of the gastrointestinal tract are homogenous. However, in our case, the imaging revealed a heterogeneous cystic lesion and hence a preoperative diagnosis of a tailgut cyst was made [8]. Furthermore, the schwannomas are often diagnosed on histopathological examination of operative specimens and immunohistochemistry, as a preoperative diagnosis is difficult [9]. Macroscopically, schwannomas are well-delimited, solid tumors that range in size from less than 1 cm to a very large tumour up to 28 cm that presents with an increase in abdominal girth [10, 11]. Longstanding tumors may develop degenerative changes such as hemorrhage, calcification and fibrosis, but cystic degeneration is rare [12–14]. Microscopically, schwannomas are encapsulated neoplasms and two histological growth patterns have been described: Antoni A and Antoni B. In Antoni A type, there is a dense growth of fusiform cells, compactly arranged in palisades to form Verocay bodies. In Antoni B, the fusiform cells are more loosely distributed with rounded or elongated nuclei, with a greater quantity of myxoid stroma and xanthomatous histiocytes [6, 9]. Immunohistochemistry plays an essential role in diagnosis with diffuse positive immunostaining for S-100 and Leu7 antigen is suggestive of Schwann cell origin [15]. Myxoid degeneration observed in the present patient is a rare finding in Schwannoma.
Complete surgical resection is the best therapeutic option for Schwannoma. Lymph node dissection is not recommended because of less risk of malignant transformation [4]. The surgical approach varies with the size and location of the tumour. When the tumour is diagnosed preoperatively, the endoscopic approach is feasible for small tumors [16, 17]. Minimally invasive surgery like laparoscopic wedge resection and laparoscopic right hemicolectomy were reported for colonic schwannomas [18, 19]. However, an open approach is frequently used for large rectal schwannomas. Recently, Feifei et al. reported the feasibility of robot-assisted retro rectal schwannoma excision in 12 patients. However, the largest size of the tumour in that series was 4.6x 3.6x 4.1 cm. [20]. In the present report, an 18x 12 cm tumour was resected using the hand-assisted laparoscopic method.