1. What is a spinal arachnoid cyst?
A spinal subarachnoid cyst is not actually a cyst; instead it is a fluid-filled dilation within the subarachnoid space. It’s best referred to as an Arachnoid Diverticulum (plural=Diverticula). The term “pseudocyst” has been used to describe this abnormality as well.
2. What are the clinical signs and history of a Spinal Arachnoid Diverticulum?
It depends on the location. If found in the thoracolumbar spine, spastic long-strided pelvic limb weakness with spinal ataxia that is slowly progressive over several months is one clinical sign. Fecal incontinence is another common sign with thoracolumbar arachnoid diverticulae. Anal tone is normal; however dogs will drop stool in the house or outside while walking (without posturing and without apparent awareness).
3. Who is affected by an Arachnoid Diverticulum?
Any dog can be affected; however middle-aged Pugs and juvenile to young adult Rottweilers are over-represented. Arachnoid diverticula have also been reported in cats, but is relatively rare.
4. How is an Arachnoid Diverticulum diagnosed?
MRI (like the ones shown below) is the safest and most complete way to evaluate for this spinal anomaly; however, CT coupled with myelography can be used, as well.