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Case Report: Caudal Fossa Meningeal Cyst Formation in a five-year-old Cavalier King Charles Spaniel.

A 10.2kg, male, entire Cavalier King Charles Spaniel was referred for investigation of a right-sided head tilt.  He had undergone investigations six months previously for paraparesis of two months duration; MRI scans at that time had revealed mild syringomyelia of the cervical spine and concurrent degenerative changes to the Ce2-3 intervertebral disc.  Brain images were normal, but there was Chiari-like malformation of the caudal fossa, typical of the breed.  At that time, the dog had initially shown a good response to a short course of anti-inflammatory doses of prednisolone, with complete resolution of the weakness within a few weeks.  One month prior to presentation, progressive ataxia with conscious proprioceptive deficits developed in all limbs.  A head tilt also began a week later, but nystagmus was not noted.


General physical examination was unremarkable.  There was a reduced menace response in the left eye, but cranial nerves were otherwise normal.  There was a right-side-down head tilt as well as reduced conscious proprioception in all limbs.

Further Investigations

fig. 1 - T2W sagittal MRI scan showing cystic structure within caudal cerebellum. Note: Ce2-3 disc is not diseased - parasagittal slice.

Routine blood-testing revealed a mild, non-regenerative anaemia (Hb 11.0g/dl{12.0 -18.0}, HCT 36.0% {37.0 -55.0}).  Coagulation studies and biochemistry were unremarkable.  MRI scans of the cervical spine (fig.1) revealed a minimally-enhancing, large, expansile, cystic structure, caudoventral to the cerebellum, to the left of the midline.   The cervical syringomyelia and disc disease was unchanged since the previous scans six months earlier.

Exploratory craniotomy via a caudal approach revealed a transparent, thin-walled structure arising from the axial surface of the dura to extend rostrally, ventral to the left paramedian lobule of the cerebellum.  The cyst was aspirated and fluid submitted for cytology; this revealed very rare, single cells consistent with lining cells.  The cyst was excised along with a section of the surrounding dura, and all tissues were submitted for histopathology; this revealed cyst-like tissue characterised by thin multiloculated fibrous septae lined by a single layer of attenuated cells. Minimal lymphoplasmacytic inflammation was noted.  The surgical wound was closed in layers, and the dog made an uneventful recovery from surgery.  By 24 hours post-op, the patient was bright and ambulatory.  He was discharged on a tapering course of prednisolone and gabapentin, which were both withdrawn completely after six weeks.

There has been no recurrence of signs in the nine months since surgery.  Recent control MRI scans revealed no evidence of re-formation of the cyst, and the cervical syrinx was reduced in size.  Further scans are scheduled for 12 month’s time to monitor for recurrence of cyst formation.


The lesion localisation, together with the absence of discernable pathology within either the central or peripheral vestibular systems suggested the head tilt was  of cerebellar origin (paradoxical).

Histopathology results were consistent with a subarachnoid/ meningeal cyst.  The absence of an identifiable cyst in the MRI scans performed six months previously suggests overcrowding of the caudal fossa (as a result of Chiari-like malformation) not only resulted in mild syringomyelia, but may also have had a role in the development of the meningeal cyst seen here.

Late-onset, developmental, meningeal cysts are relatively uncommon; the majority are congenital and are occasionally seen as incidental findings in survey spinal MRI scans.

The degree of compression of neural structures seen in this case would explain the clinical findings and necessitated decompressive surgery; medical therapy would have had little effect on the signs.

Although surgery appears to have been successful in the medium term, monitoring for a recurrence of signs is on-going, given the possibility that the cyst may reform.  In addition, cicatrisation of the occipital approach may predispose to progression of the cervical syrinx at some stage in the future.