A rare case of gastric schwannoma

Gastric schwannomas (GSs) are exceedingly rare and account for approximately 0.2% of all gastric tumours. They originate from Schwann cells and are almost always benign. Many cases are discovered incidentally. If causing symptoms, patients typically present with abdominal discomfort, early satiety, melaena or a palpable mass.^1,2

To our knowledge, this is the first reported case in New Zealand literature and one of only a handful of cases under the age of 18. The peak incidence is 60 years old with a female predominance (2:1) apparent in current available research.^2,3

Although rare, GSs are important to distinguish from other gastric tumours, particularly gastrointestinal stromal tumours (GIST), which vastly differ in management and prognosis.^3,4

Case presentation

Our case involves a 17-year-old female without significant medical history who presented with a 5-day history of periumbilical pain, nausea, diarrhoea, fever and reduced oral intake.

An abdominal computed tomography scan performed to rule out appendicitis revealed pancolitis with an incidental nodular lesion posterior to the left lobe of the liver. Further characterisation of this lesion with a magnetic resonance imaging (MRI) scan showed it to be well defined and originating from the gastric lesser curvature with no evidence of local invasion.

At endoscopic ultrasound (EUS), a subepithelial, hypoechoic, well-defined lesion was identified in the lesser curve measuring 11mm×18mm. Biopsies were obtained. The differential diagnoses included gastric leiomyoma or GIST.

Initial cell block preparations showed stromal fragments containing bland spindle cells, which were again suspicious for a GIST. However, immunohistochemical staining showed that the lesional cells were negative for CD34, DOG1, CD117, smooth muscle actin and desmin, yet strongly positive for S100 protein and SOX10. The immunoprofile therefore favoured a diagnosis of a GS.^1–3

General surgical follow-up ensued. Given the patient’s age and the slow-growing nature of this tumour type, follow-up was planned in 1 year with repeat MRI imaging and, if stable, laparoscopic wedge excision at an appropriate time in the future.

View Figure 1, Table 1.

Discussion

This case highlights the discovery of a GS in a 17-year-old female, which is exceedingly rare in this demographic.

Most reported GSs are diagnosed in the fifth to sixth decade of life, often incidentally, during imaging or endoscopy. Case series suggest that the majority are slow-growing, asymptomatic and discovered at sizes ranging from 2 to 10cm.^2,3 This patient presented with gastrointestinal symptoms; however, these were ultimately attributed to infectious colitis rather than the tumour itself.

The key differential diagnoses for gastric subepithelial lesions include GISTs, leiomyomas, GSs and, less commonly, neuroendocrine tumours or ectopic pancreas.^3,4 GISTs represent the most clinically significant differential, given their malignant potential and their relatively higher incidence compared to schwannomas.^3,4 Radiologically and endoscopically, GISTs and schwannomas share overlapping features. Thus, imaging and EUS alone are insufficient to provide a definitive diagnosis.

Even histological examination of spindle cell morphology may be inconclusive. Immunohistochemistry (IHC) therefore plays a crucial role in establishing the diagnosis. This immunoprofile provides the definitive distinction between these entities, guiding management and avoiding unnecessary treatment. Without IHC, the lesion in this case might have been misclassified as a GIST, potentially leading to earlier surgical excision or consideration of adjuvant therapy.^3,4

GSs are benign, with an excellent prognosis following surgical excision. Recurrence after complete resection is rare and there is no malignant potential, in contrast to GISTs, which carry variable malignant risk.^3,4 In our case, a joint decision was made between the general surgical team, the patient and her parents to delay surgery. Our patient was due to begin university studies. Her and her family preferred to minimise the stress during this milestone. Given the small size of the tumour (18mm), absence of invasive features and indolent natural history of this tumour, the decision to delay resection and monitor with interval imaging is reasonable. While it is possible that the tumor may grow over time and complicate surgical management, the surgical team determined that ongoing surveillance would provide sufficient opportunity to act should the tumor progress.