Persistent Visibility of the Dorsal Subarachnoid Space in Dogs With Compressive Cervical Myelopathy Can Be Explained...

Like with conventional myelography, circumferential attenuation of the subarachnoid space on magnetic resonance (MR) myelography may aid in the diagnosis of an acute compressive disc extrusion. Hydrated nucleus pulposus extrusion (HNPE) is characterized by the presence of extradural material above the intervertebral disc space that is isointense to CSF and may mask the attenuation of the ventral subarachnoid space. Concurrent failure of the dorsal subarachnoid space to attenuate may result in failure to recognize HNPE or underestimate its severity. Magnetic resonance imaging (MRI) studies of dogs diagnosed with cervical HNPE were reviewed for the presence or absence of CSF signal from the dorsal subarachnoid space. Available computed tomography (CT) studies from the same dogs were reviewed with the goal of identifying an anatomic cause of a maintained dorsal subarachnoid space. The dorsal subarachnoid space remained visible in 25/35 (71.4%) and was attenuated in 10/35 (28.6%) of MRI studies reviewed. On the basis of the CT study review, the location of the maintained signal corresponds to the location of the normal gap between adjacent vertebral arches (interarcuate space). This retrospective study describes a potential pitfall in the MR myelographic diagnosis of cervical HNPEs due to a maintained CSF signal in the dorsal subarachnoid space attributed to the displacement of the subarachnoid space into the interarcuate space between adjacent vertebrae.