ABSTRACT. A 3-month-old male Japanese cat with feline parvovirus infection, showing central and cervical nerve abnormalities, was diagnosed as hydrocephalus and syringomyelia by use of magnetic resonance imaging (MRI). The cat was maintained clinically by medical treatment even though he could not stand. The MRI scans obtained about 5 months later showed that the ventricles had increased in size and the cervical syrinx had extended into the thoracic spinal cord. Ventriculoperitoneal (VP) shunt was performed. One week after surgery, neurological conditions had improved. At the postoperative MR images, the ventricles had decreased in size and the syrinx in the cervical and thoracic spinal cord could no longer be seen. The cat was still alive and was able to walk well. KEY WORDS: feline, magnetic resonance imaging, syringomyelia.J. Vet. Med. Sci. 63(12): 1331-1334, 2001 Hydrocephalus is a term commonly used to describe a condition involving abnormal dilatation of the ventricular system within the cranium [11,15]. Viral infections such as feline infectious peritonitis (FIP) are a common cause of hydrocephalus in cats [15,18]. Syringomyelia has been defined as fluid-filled cavities in the substance of the spinal cord, with destruction of the nervous tissue [19]. Its cause is unknown, but it may be associated with or result from hydrocephalus [16,24]. Ventriculoperitoneal (VP) shunts are commonly used to divert the flow of cerebrospinal fluid (CSF) from the ventricles of the brain to the peritoneal cavity in human neurosurgery [11], and have proved to be an effective surgical treatment for hydrocephalus in dogs [15] and cats [23]. Several investigators [12,15,16,24] in the veterinary field have suggested magnetic resonance imaging (MRI) to be a useful technique for the antemortem diagnosis of several cranial and spinal disorders in animals. This article describes the clinical findings in, and management of, a cat with hydrocephalus and syringomyelia, together with temporal changes in MR images obtained before and after the insertion of a VP shunt.A 3-month-old male Japanese cat was referred because of severe ataxia following an inadvertent fall onto the floor from a height of about 2 m. The cat had not been vaccinated against any diseases. The owner stated that the cat had walked well until the event. Laboratory examination revealed neutrophilia (56,400/µl; Segmented neutrophils 99%, Lymphocytes 1%). Physical examination revealed severe muscular atrophy over the whole body and myotonus of all four limbs. Neurological examination revealed several cranial nerve abnormalities such as torticollis to the right, nystagmus and depression, and cervical nerve abnormalities such as clasp-knife rigidity of fore limbs. The menace response was absent, but the papillary light reflex and the palpebral reflex were normal. Asymmetry of the pupils was also observed. Patellar reflexes were exaggerated and flexor reflexes were detected in all four limbs. Elevated rectal temperatures (40.8, 40.6 and 39.6°C) were noted on days 7, 8 and 9, ...