Diagnosis and surgical resection of a choroid plexus cyst in a dog.

A three-year-old neutered male toy fox terrier presented for a Chiari-like malformation. No neurological deficits were found on examination, although diffuse cervical, thoracolumbar and head pain were present. A mass within the fourth ventricle was apparent on magnetic resonance imaging (MRI) of the brain. The lesion was hyperintense to brain parenchyma on T2-weighted images, hypointense on T1-weighted images and there was strong, homogeneous contrast enhancement. The cystic mass was removed through a suboccipital craniectomy. Histopathology was consistent with a choroid plexus cyst. The dog recovered well from the procedure and was clinically normal three months after surgery. To the authors' knowledge this is the first description of the appearance of a choroid plexus cyst on MRI in a dog and of its surgical removal. Although they are an uncommon finding, choroid plexus cysts should be considered as a differential diagnosis for mass lesions within the fourth ventricle.