GASTROINTESTINAL SCHWANNOMA: CASE REPORT.

INTRODUCTION

Schwannoma is a benign, neurogenic, slow-growing neoplasia, originated from Schwann cells, which are responsible by the myeline sheath on the peripheral nerves. This type of tumor is found more frequently on the central and peripheral nervous system and rarely occurs on the gastrointestinal tract , , , , , , . Along with leiomyoma, leiomyossarcoma, gastrointestinal stromal tumor (GIST) and others, it makes part of the mesenchymal gastrointestinal tumors group , , , .

CASE REPORT

Female, 74 years old, presented on the emergency room with a chief complaint of abdominal pain, nauseas, vomiting, prostration and dizziness with one week of evolution. She reported past history of diverticulitis and denied weight loss, hematoquezia or previous abdominal surgeries. During the physical examination, she complained of pain on deep upper abdominal palpation, although no abnormal mass could be detected. Proctologic examination and laboratory exams showed no abnormalities.

Abdominal ultrassonography showed a nodular solid heterogenic type image on the left flank, with 6.1x5.6x4.3 cm. Investigation with contrasted computed tomography detected an delimited intramural lesion on the transverse colon, without invasion of surrounding organs (Figure 1).

FIGURE 1

Splenic angle mass: A) CT coronal slice; B) TC axial slice (distal transverse colon)

Colonoscopy, with exploration until the cecum, showed not only sigmoidal diverticulus, but also an intraluminal bulging on the topography of distal transverse colon, with adjacent normal aspect mucosa, suggesting extrinsic mass growth and lumen compression. Since the research for metastatic lesions was negative, extended left colectomy was performed, with ressection of 18 cm intestinal segment, containing a 5.6x5.0x4.8 cm mass, located on the transverse colon, beside the splenic angle. The pacient had a satisfatory evolution, leaving hospital on the 6th postoperative day.

The anatomopathologic analysis have highlighted a fusiform cell mesenchymal lesion, extending from colon submucosa until its subserous layer, with moderate cell nucleus atypia and two mitosis per 50 high-power fields, without evidence of hemorrhage or necrosis.

Immunohistochemical research showed positive results for kit gene products (C-kit/CD117) and for glial fibrillary acidic protein (GFAP) and S-100 protein. The results for hematopoietic cells antigene (CD34), desmine and smooth muscle actin (CD117) were negative. This profile was compatible with a gastrointestinal tract schwannoma diagnosis.

DISCUSSION

Schwannoma represents 0,2-1% of all gastrointestinal tract tumors, occuring more frequently on the stomach and rarely on colon and esophagus , , , , , , . The mean age of incidence is around 50-60 years old, with equal gender prevalence , , , . It usually manifests itself by abdominal pain, constipation, gastrointestinal bleeding, weight loss, but sometimes it shows no significant syntoms , , , . It is classified as a mesenchymal gastrointestinal tumor .

The initial evaluation is made by computed tomography or nuclear magnetic resonance (NMR) to determine location, size, density of the lesion and attempt to identify metastasis . Colonoscopy usually shows unharmed mucosa and an insert image sugesting extrinsic compression of intestinal lumen. However, all mesenchymal tumors have similar colonoscopic image aspect, making it difficult to set an specific diagnosis. In addition, a colonoscopy guided biopsy is not always able to collect sufficient amount of tissue to ensure a correct diagnosis . Thus, anatomopathological and immunohistochemical research of the surgically resected lesion is mandatory , .

Therefore, in case of dealing with a resectable neoplasia, with high probability of mesenchymal tumor, surgical approach is indicated, with wide margin lesion resection, without necessity of lymphadenectomy, since the risk of metastasis in those cases is very low , , , , , , . Considering the higher prevalence of GIST, the majority of schwannomas is misdiagnosed, until histological and immunohistochemical research and differentiation is concluded , . Schwannoma presents significant cell pleomorphism, lymphoid follicles, rare mitotic cells and rare necrotic spots. GIST shows high mitotic index, necrotic and hemorragic spots, without lymphoid follicles. Leiomyoma, on the other hand, does not show any of those characteristics , , . The most important immunohistochemical markers are CD117, CD34, S-100 protein, GFAP, SMA and desmine. Schwannoma is S-100- and GFAP-positive, but CD117- and SMA-negative. GIST is CD117- and CD34-positive, S-100- and GFAP-negative. Leiomyoma is CD117-, CD34-, S-100- e GFAP-negative. However, the latest is desmine- and SMA-positive, which are negative markers on schwannoma and GIST , , , (Figure 2).

FIGURE 2

Mesenchymal tumor immunohistochemical profile

The most important mesenchymal tumors prognosis factors, specially for GIST, are tumor size and mitosis index . The less replicative and smaller is the neoplasia, the better is the prognosis. Radio and chemotherapy role in schwannoma remains uncertain; meanwhile, the recommended treatment is wide margin resection, without need of lymphadenectomy, mostly with excellent results 5,9.