Meningeal granular cell tumour in a green tree python (Morelia viridis).
Granular cell tumours (GCTs) are uncommon neoplasms mostly reported in man, dogs and horses. The origin of GCT is thought to be Schwann cells, with the associated characteristics of neural crest morphology. Neoplastic cells often demonstrate positive immunoreactivity for S100, LC3, vimentin and p62. They are also periodic acid-Schiff (PAS) positive and diastase resistant. A female green tree python (Morelia viridis) was presented for severe constipation and hyporexia of 4 month's duration and, despite treatment, died the next day. A 4.8×3.4 mm intracalvarial GCT was identified, compressing the overlying cerebrum without invasion. Neoplastic cells were immunoreactive to S100 and had brightly eosinophilic cytoplasmic granules that were PAS positive and diastase resistant. Electron microscopy revealed numerous cytoplasmic lysosomes in neoplastic cells. GCTs are reported rarely in non-mammalian species with three reports in birds. This represents the first report of a GCT in a reptile.