Recurrent spinal arachnoid cyst in a cat

Abstract

Spinal arachnoid cysts (SACs) are uncommon expanding lesions in the spinal canal. They are rarely diagnosed in dogs, and there are only four published cases in cats. We report a case of a 12-year-old cat with recurrent signs of intermittent urinary incontinence and hind limb ataxia 2 years after surgical marsupialisation of a spinal arachnoid cyst at T11/12. Recurrence of a cyst was diagnosed by myelography. Repeated marsupialisation after laminectomy was successful and the cat recovered satisfactorily although intensive physical therapy was necessary. SACs are very rare in cats and seem to occur mainly as a secondary lesion to spinal and meningeal trauma or irritation due to bony changes of the vertebrae.

Fig 1.

Laterolateral plain radiograph of the thoraco-lumbar transition of the spine of a 12-year-old Persian crossbreed cat. Note the spondylarthrosis of the articular facets from T11/12 to T13–L1.

Fig 2.

Occipital myelography performed in 2003 (A) and the second one performed 2 years after primary surgery (B). The recurrent subarachnoid cyst is located at a similar site to cyst seen before primary marsupialisation. The outlines of the cyst are more irregular on the second myelogram. The dorsal contrast column extends dorsally due to the former hemilaminectomy on this site.

Fig 3.

Histological slice of a specimen of the cyst wall excised on the transition to the normal dura. The trichrome stain helps to highlight collagenous stroma (A). As the name implies, the tissue is stained in three colours, each colour being selective for the tissue element demonstrated. Collagen fibres stain intense green, nuclei of cells black or brown, cytoplasm stains red. The arachnoidea itself (a) is thickened and is appositioned to glioneural tissue. The silver impregnation method (reticulin stain, B) identifies the reticulin fibres in the wall of blood vessels. The abundant capillaries found in the glial trabecular tissue show fibrous thickening of their wall (B, arrows). There are no reticulin fibres apart from blood vessels (as found in peripheral nerve tissue). Fibrillary gliosis in central nervous tissue was confirmed by immunohistochemistry with antibodies to gliofibrillary acid protein (GFAP); nerve cells and their processes were identified with autoantibodies to neurofilament protein (both reactions not shown here). These changes are consistent with a meningomedullary scar as a residual lesion of a surgical procedure at the meninges.