Vacuolar meningioma: a new and rare variant of canine meningioma.

A 10-year-old female neutered boxer was presented with a two-month history of progressive ataxia and left-sided head tilt. General physical examination was unremarkable. Neurological evaluation revealed ataxia and hypermetria in all four limbs, falling to the right, left-sided head tilt, decreased menace response bilaterally, and increased segmental spinal cord reflexes. The neuroanatomical localisation was consistent with an infratentorial lesion. Complete blood count and serum biochemistry prior to referral were unremarkable. Magnetic Resonance (MR; Hitachi Aperto open magnet 0.4T) revealed a cystic extra-axial caudal fossa mass arising from the region of the right tentorium cerebelli. The bulk of the mass was cystic and uniformly FLAIR (Fluid Attenuated Inversion Recovery) suppressing with a smaller solid area in close association with the tentorium. This solid tissue was isointense to grey matter in T1-weighted images (Fig 1c), and hyperintense in T2-weighted and FLAIR images. It was mildly and slightly heterogeneously contrast-enhancing following intravenous administration of paramagnetic contrast agent (gadoteric acid, DOTAREM, Guerbet) (Fig 1d). There was no contrast enhancement of the rim of the cystic component of the mass. A broad-based, central, signal-void area was noted, and suspected to represent tentorial hyperostosis with mineralisation (Fig 1a,c). Mass effect resulting in right rostral subtentorial and mild foramen magnum herniations, and brainstem compression, were also observed (Fig 1b). The lesion was suspected to be a cystic extra-axial neoplasm. Cerebrospinal fluid analysis was not performed. Thoracic radiographs and abdominal ultrasound were unremarkable. FIG1 Magnetic resonance images of the extra-axial cystic mass in the caudal fossa. (a) Transverse T2-weighted image (TR 3198, TE 120) at the level …