Intracranial Granular Cell Tumours in Three Dogs: Atypical Magnetic Resonance Imaging Features and Immunohistochemical Study

SIMPLE SUMMARY: Intracranial granular cell tumours are rare tumours of unknown cellular origin. In this case series. we describe three dogs with neurological signs that had magnetic resonance imaging of the brain, and were diagnosed with granular cell tumours through histopathological and histochemical studies. Magnetic resonance imaging characteristics were atypical, showing hypointense lesions on T2-weighted images in all cases. Immunohistochemical studies helped in characterising the tumours and excluded a Schwann cell origin. The findings of this case series indicate that granular cell tumours can be hypointense on T2-weighted magnetic resonance images, and that the cell of origin remains to be determined. ABSTRACT: Intracranial granular cell tumours (GCT) are uncommon neoplasms of uncertain cellular origin that are rarely reported in dogs. This case series describes three aged dogs that presented with neurological signs in which magnetic resonance (MR) imaging revealed plaquelike extra-axial lesions that were hypointense on T2-weighted (T2w) images. The surgical biopsy of the lesions and necropsies were followed by histochemical characterisation with periodic acid–Schiff (PAS) staining and immunohistochemistry with ubiquitin, S-100, and SOX-10 to elucidate the cellular origin. The immunohistochemical study indicated that these intracranial GCTs were not of Schwann cell origin. In conclusion, GCTs should be considered a differential diagnosis of intracranial, extra-axial hypointense brain lesions on T2w MR images.