Gastrointestinal Tract Schwannoma
Definition
- Gastrointestinal tract mesenchymal neoplasm exhibiting features of Schwann cell differentiation
Diagnostic Criteria
- Circumscribed, non-encapsulated nodule centered in muscularis propria
- Microscopically entraps adjacent muscle fibers
- Occasional lesions are lobular
- Benign gi intramucosal Schwann cell proliferations are a different lesion(s)
- S100 positive
- Predominantly bland spindled cells
- Scattered cells with large hyperchromatic nuclei present in nearly all cases
- Mitotic figures <5/50 HPF
- PAS/d+ crystalloids described in some cases
- Nearly all have surrounding lymphoid cuff
- Predominantly B cells
- Frequently contains germinal centers
- Smaller number of lymphocytes scattered throughout
- GI schwannomas frequently resemble neurofibromas
- Bundles of spindle cells alternating with fibrovascular trabeculae
- Occasional sheets and storiform pattern
- Vague palisading at most
- May be myxoid
- May have cystic degeneration
- No necrosis
- Epithelioid patterns have been reported
- From focal to complete
- Most lack lymphoid cuff
- May form pseudoglandular spaces or microcystic spaces
- One reported with metaplastic bone
- Epithelioid lesions confined to the lamina propria are classified separately
- >90% in stomach, mostly antrum
- Rarely reported in colorectum and esophagus
- GI schwannoma differs significantly from soft tissue schwannoma and may be a separate lesion
- Rare cases of plexiform schwannoma reported(Sarlomo-Rikala 1995)
- Multiple nodules, transmural
- Palisaded with prominent Verocay bodies
- No lymphoid cuff
- Hyalinized vessels
- This may represent a soft tissue type schwannoma
- It is not clear if the 5 reported cases of GI microcystic/reticular schwannoma (Liegl 2008)are part of this spectrum
- All lacked peripheral lymphoid cuffs, atypia or mitotic figures >5/HPF
- One had a component of typical GI schwannoma
- One was intramucosal and could perhaps be classified with benign epithelioid intramucosal nerve sheath tumors
- Regardless of classification, the critical points for microcystic tumors are:
- Pseudoglandular structures may simulate carcinoma
- Keratin and S100 resolve this question
- No association with NF1 or other syndromes
- Pseudoglandular structures may simulate carcinoma
| GI Schwannoma | Soft Tissue Schwannoma |
| Prominent lymphoid cuff | No lymphoid cuff |
| Non-encapsulated | Encapsulated |
| Vague palisading at most | Prominent palisading and Verocay bodies |
| Lacks hyalinized vessels | Frequent hyalinized vessels |
| Lacks xanthoma cells | Frequent xanthoma cells |
| No NF2 mutations | 40-60% have NF2 mutations |
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342
Original posting : November 29, 2009; latest update 5/4/15
