Rare Case of Gastric Schwannoma Simulating Gastrointestinal Stromal Tumour-A Case Report

Gastric schwannoma (GS) is a rare, benign, slow-growing neoplasm representing 0.2% of all gastric tumors. We report a rare case of Gastric schwannoma in a 56 year old woman who presented with abdominal discomfort and vomiting since few years. Contrast enhanced Computed Tomography showed a well-dened homogeneously attenuating lesion with homogenous enhancement. Wedge gastrectomy was done with a possible diagnosis of Gastrointestinal stromal tumor, but was conrmed to have Gastric schwannoma on histopathology showing spindle cells with peripheral cuff of lymphoid aggregates and S-100 protein positivity on immunohistochemistry. Gastric schwannoma should be included in the differential diagnosis of a gastric intramural or exophytic mass when Computed Tomography shows a well-dened homogeneously attenuating lesion with progressively increasing homogenous enhancement without hemorrhage, necrosis, and degeneration.

was done with a possible diagnosis of Gastrointestinal stromal tumor, but was con rmed to have Gastric schwannoma on histopathology showing spindle cells with peripheral cuff of lymphoid aggregates and S-100 protein positivity on immunohistochemistry.
Gastric schwannoma should be included in the differential diagnosis of a gastric intramural or exophytic mass when Computed Tomography shows a well-de ned homogeneously attenuating lesion with progressively increasing homogenous enhancement without hemorrhage, necrosis, and degeneration.

Introduction:
Schwannomas are benign, slow growing neoplasms arising in any nerve that has a Schwann cell sheath.
Gastrointestinal tract (GIT) Schwannomas arise from Schwann cells of the Auerbach's plexus of the GIT wall 11 . Computed Tomography (CT) and upper GI endoscopy are not pathognomonic 9 and correct diagnosis is by histology and Immunohistochemistry(IHC).The key in the immunohistochemical study is S100 protein positivity. 3,4,5 Gastrointestinal stromal tumor (GIST) is its major differential diagnosis clinically, endoscopically, radiologically and histopathologically 9 . GS is not widely recognized by clinicians, making it di cult to distinguish GS from GIST preoperatively 10 .

Case Presentation:
A 56 year old woman with abdominal discomfort and vomiting since few years ,presented with gradually progressive worsening of symptoms. She had history of hysterectomy and incisional hernia repair.
Physical examination revealed mild tenderness in epigastric region. On upper GI endoscopy, submucosal nodular lesion was seen on the lesser curvature of stomach (measuring ~5 x 8cm) with mucosa showing small central ulceration.
Non contrast CT scan showed well-de ned, homogeneous, hypodense mass arising from the anterior wall of body of stomach measuring 3.1 x 4.8 x 5.1 cm with a CT attenuation value of 35 HU (Fig. 1a).
Contrast-enhanced CT scan of abdomen and pelvis was performed. On the arterial phase, mild homogenous enhancement of both endophytic and exophytic components of the mural mass was seen with a CT value of 45 HU (Fig. 1b). Gradual homogeneous enhancement of the lesion was seen in the portal venous phase (Fig. 1c) with a CT value of 82 HU. Delayed scan showed increase in the CT attenuation value of the mass further to 114 HU. Focal central ulceration was seen along the luminal surface (Fig. 1d). There was no adjacent organ invasion, lymphadenopathy or metastases, indicating a possible GIST. Wedge gastrectomy was performed to relieve the obstruction symptoms. been reported. GS are frequently seen in the 5th to 8th decades with female predominance. 1,9,10,12 They can occur in children and, can be malignant rarely. 8,10 They are usually asymptomatic or present with non-speci c symptoms. 8,9 Initial evaluation by upper GIT endoscopy may be normal or show non-speci c ndings such as extrinsic mass effect or ulceration. 2 Since GS's are submucosal tumours, endoscopic biopsy may not provide de nite diagnosis.
CT is the mostly used imaging modality for gastric tumors, providing information for surgical planning by identifying the tumor, location, extent and relationship with neighbouring structures. 8,9 GS appears as well circumscribed, spherical, ovoid or multilobulated solid hypodense mural tumors. 8 Its characteristic CT feature is the homogeneous tumor attenuation due to lack of hemorrhage, cystic change, necrosis or degeneration within the tumors 1, 11 .They show mild enhancement in the arterial phase with progressively increasing enhancement in the venous and delayed phases. 1,10 They rarely appear cystic, although large tumors may show cystic degeneration, and calci cation is uncommon. 8 MRI shows low signal intensity on T1 weighted images and high signal intensity on T2-weighted images.
Details about its internal features such as hemorrhage, necrosis or cystic changes and its relationship with the surrounding structures can be assessed . 10 Fluoro-Deoxy Glucose (FDG)-PET is of limited value for the differentiation of GS and GIST, as the FDG uptake in them does not signi cantly differ. However, it can assess the recurrence or metastasis of malignant tumors. 10 GS should be differentiated from GIST, which may be malignant or have malignant potential. 1 CT features of GIST depends on its size and aggressiveness. The most important feature for differentiation is the heterogeneous appearance with hypervascularity of GIST with hemorrhage, necrosis, and cystic change resulting in peripheral enhancement (in 92% of case). 1,6 However GS demonstrates homogeneously enhancement. 1,6 Smaller GISTs appear similar to GS on CT making it impossible to distinguish them by imaging alone 12 . However, GS is frequently exophytic or shows mixed growth pattern, homogeneous enhancement, perilesional lymph nodes and grow slower than GIST. 6,11 Final diagnosis is by histopathological and immunohistochemical examination.
Histologically, the pathognomonic feature of GIT schwannomas is a well circumscribed lesion surrounded by a cuff of lymphoid aggregates. 9 They are spindle cell tumors with a microtrabecular pattern, peripheral lymphoid cu ng 2,6,9 , lymphoplasmacytic in ltrate and occasional germinal centers. 1,3,4 Spindle-shaped cells are noted in 70% of all GISTs and 20% contain epithelioid type or they can be pleomorphic. Immunohistochemistry is con rmatory for distinguishing GS and GIST. 6 Immunohistochemistry shows positive staining for S100 and vimentin and negative staining for smooth muscle actin and CD34 in neurogenic tumour. 9 GISTs are mostly CD117-positive, CD34-positive, actinpositive, and S100-negative. 6 In our case, the tumor cells were positive for S100 and negative for CD117, Actin and Desmin consistent with gastric neurogenic tumor. Lymphoid aggregation and presence of capsule highly suggested schwannoma rather than neuro broma. Calretinin is a good marker to differentiate schwannomas and neuro bromas. 6 Other differential diagnosis are primary /secondary lymphomas and adenocarcinomas. Lymphomas show homogeneous CT attenuation before treatment, similar to GS. However, they are commonly associated with lymphadenopathy. 1 Spiculated margins associated with regional adenopathy is seen in adenocarcinomas. 1,11 The goal of surgery is to achieve R0 resection, including the lesion and any involved adjacent structures.
Follow-up is not offered unless there are signs of malignant transformation. 9 The treatment for lesser curvature, middle and distal third gastric neoplasms is subtotal gastrectomy. 6 Conclusions Gastric schwannomas should be considered when a well-de ned intramural or exophytic gastric mass with homogeneously attenuation lacking hemorrhage, necrosis, and degeneration, is encountered, helping in its differentiation from GIST. Knowledge of these characteristic ndings helps to prevent unnecessary surgery and improve planning for minimally invasive surgery. 11 Declarations Funding: Nil.
Con icting of interests /Competing interests: The authors declare that they have no competing interests Ethics approval: Ethics has approved this study.
Consent to participate: The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal Written Consent for Publication: The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.  Surface ulceration noted at the endoluminal surface of the lesion (↔). After wedge resection, the lesion was con rmed as a gastric schwannoma.