Caudal lumbar subarachnoid diverticulum in a Cockapoo

We describe a Cockapoo with a subarachnoid diverticulum (Type III), at the level of L6-7. Magnetic resonance imaging identified a circumferential dilatation of the dural sac, extending from the cranial endplate of L6 to the midbody of L7, containing T2-weighted hyperintense and T1-weighted hypointense material that suppressed on fluid-attenuated inversion recovery sequences, consistent with cerebrospinal fluid. An exploratory dorsal laminectomy confirmed a subarachnoid diverticulum (Type III), and a durotomy was performed. After surgical decompression, full clinical resolution was observed. This case had a clinical presentation that mimicked an intervertebral disc extrusion.