Definition/General
Introduction:
Gastric schwannoma is a benign nerve sheath tumor arising from Schwann cells
It represents 2-3% of gastric mesenchymal tumors
Also known as neurilemmoma
Most are sporadic but can occur in neurofibromatosis.
Origin:
Arises from Schwann cells of peripheral nerves
Commonly from Auerbach myenteric plexus
May originate from submucosal nerve plexus
Associated with NF-2 more than NF-1.
Classification:
Conventional schwannoma (most common)
Ancient schwannoma (degenerative changes)
Cellular schwannoma (hypercellular variant)
Plexiform schwannoma (multiple fascicles)
Melanotic schwannoma (rare pigmented).
Epidemiology:
Peak incidence in 4th-6th decades
Female predominance (2:1)
Associated with NF-2 (bilateral acoustic neuromas)
Rare in children except in NF patients.
Clinical Features
Presentation:
Asymptomatic mass (40-50%)
Epigastric pain (30-40%)
Gastrointestinal bleeding (20-30%)
Early satiety (15-20%)
Dyspepsia and bloating
Obstruction rare unless large.
Symptoms:
Upper GI bleeding from mucosal ulceration
Postprandial discomfort
Iron deficiency anemia
Nausea and vomiting
Weight loss in large lesions.
Risk Factors:
Neurofibromatosis type 2 (NF-2)
Schwannomatosis syndrome
Previous radiation exposure
Genetic predisposition
Female gender.
Screening:
Upper endoscopy for symptomatic patients
CT/MRI for characterization
Endoscopic ultrasound helpful
Genetic counseling for NF patients
Audiometry to rule out acoustic neuromas.
Master Schwannoma Pathology with RxDx
Access 100+ pathology videos and expert guidance with the RxDx app
Gross Description
Appearance:
Well-encapsulated nodule with smooth surface
Yellow to tan cut surface
Firm consistency
Whorled appearance on cut section
Cystic degeneration in ancient type.
Characteristics:
Homogeneous appearance in conventional type
Hemorrhage and necrosis in ancient schwannoma
Calcification may be present
Well-demarcated from surrounding tissue.
Size Location:
Size ranges from 1-10 cm (average 3-5 cm)
Body and antrum equally affected
Intramural location most common
Subserosal and submucosal also possible.
Multifocality:
Usually solitary (>90%)
Multiple schwannomas in NF-2 and schwannomatosis
May be part of syndrome
No malignant potential in conventional type.
Microscopic Description
Histological Features:
Biphasic pattern: Antoni A and Antoni B areas
Antoni A: Compact spindle cells with Verocay bodies
Antoni B: Loose, myxoid areas with scattered cells
Thick-walled blood vessels
Hyalinized vessel walls.
Cellular Characteristics:
Spindle cells with elongated nuclei
Eosinophilic cytoplasm with indistinct borders
Nuclear palisading in Antoni A areas
Verocay bodies (acellular eosinophilic zones)
Minimal mitotic activity.
Architectural Patterns:
Encapsulated tumor
Fascicular growth pattern
Alternating cellularity (Antoni A and B)
Prominent vasculature
Degenerative changes in ancient type.
Grading Criteria:
Benign tumors by definition
Mitotic count <4/10 HPF
No significant atypia
Ancient changes (degenerative atypia) acceptable
Cellular variant may have higher cellularity but benign behavior.
Immunohistochemistry
Positive Markers:
S-100 protein (100% positive, strong diffuse)
SOX10 (95% positive)
GFAP (variable, 30-50%)
Vimentin (positive)
Calretinin (focal positive).
Negative Markers:
Desmin (negative)
Smooth muscle actin (negative)
KIT (CD117) (negative)
CD34 (negative in tumor cells)
Neurofilament (negative)
Cytokeratins (negative).
Diagnostic Utility:
S-100 positivity is diagnostic hallmark
SOX10 confirms neural crest origin
KIT negativity distinguishes from GIST
Desmin negativity excludes smooth muscle tumors
Ki-67 typically low (<5%).
Molecular Subtypes:
Most schwannomas are NF2-associated (merlin loss)
SMARCB1 loss in schwannomatosis patients
LZTR1 mutations in some cases
22q loss common.
Molecular/Genetic
Genetic Mutations:
NF2 mutations (merlin/schwannomin) in majority
SMARCB1 mutations in schwannomatosis
LZTR1 mutations
22q12 deletions
Somatic NF2 loss in sporadic cases.
Molecular Markers:
Merlin protein loss by IHC
Low Ki-67 proliferation (<5%)
p53 expression variable
VEGF expression in vascular areas.
Prognostic Significance:
Excellent prognosis with complete excision
No malignant potential in conventional type
Local recurrence if incompletely excised
Syndromic cases need surveillance.
Therapeutic Targets:
Complete surgical excision curative
Enucleation possible for well-encapsulated tumors
No adjuvant therapy needed
Genetic counseling for NF patients.
Differential Diagnosis
Similar Entities:
GIST (spindle cell variant)
Leiomyoma
Neurofibroma
Malignant peripheral nerve sheath tumor
Solitary fibrous tumor
Inflammatory myofibroblastic tumor.
Distinguishing Features:
Schwannoma: S-100 positive, encapsulated
GIST: KIT positive, S-100 negative
Leiomyoma: Desmin positive, S-100 negative
Neurofibroma: S-100 positive but not encapsulated
MPNST: High-grade, S-100 variable.
Diagnostic Challenges:
Distinguishing cellular schwannoma from MPNST
Separating from neurofibroma (encapsulation key)
Ancient schwannoma with atypia vs malignancy
Adequate sampling important.
Rare Variants:
Cellular schwannoma
Ancient schwannoma
Plexiform schwannoma
Epithelioid schwannoma
Melanotic schwannoma (psammomatous).
Sample Pathology Report
Template Format
Sample Pathology Report
Complete Report: This is an example of how the final pathology report should be structured for this condition.
Specimen
[type], [size] cm
Diagnosis
Schwannoma
Features
Encapsulated spindle cell tumor with Antoni A/B pattern
IHC
S-100: strongly positive, KIT: negative
Final Diagnosis
Gastric schwannoma, [size] cm, completely excised