Dynamic transition from spinal arachnoid diverticulum to syringohydromyelia in a cat: Correlation between computed tomography myelography and magnetic resonance imaging.

Background: Diseases characterized by impaired spinal cord function due to fluid accumulation include syringohydromyelia (SHM) and spinal arachnoid diverticulum (SAD). SHM refers to fluid-filled cavities within the spinal cord, whereas SAD involves fluid accumulation in the subarachnoid space. Although the true incidence of SHM and SAD in cats is unknown, both conditions are rare based on the limited number of published case reports. Computed tomography (CT) myelography and magnetic resonance imaging (MRI) are regarded as the diagnostic gold standards. Case Description: An approximately 1-year-old female Japanese domestic shorthair was referred for pelvic limb paresis. 4 months before presentation, CT myelography had revealed a teardrop sign suggestive of SAD. Subsequent MRI and CT myelography identified focal SHM at T13. T12-T13 dorsal laminectomy was performed, during which cerebrospinal fluid (CSF)-like leakage was observed. Durotomy was also performed, but no abnormalities were detected in the spinal arachnoid membrane. 5 months postoperatively, the cat regained ambulatory function, although mild residual ataxia persisted. Follow-up MRI revealed a T2-hyperintense region and a slit-like signal void on fluid-attenuated inversion recovery at T13. Conclusion: This case demonstrates how the combination of MRI and CT myelography can effectively capture temporal changes in fluid accumulation within the spinal cord. Accurate imaging is essential for accurate diagnosis and treatment planning. Restoration of CSF perfusion and fluid drainage may contribute to clinical improvement in cats with focal SHM.