Irregular Cervicothoracic Nerve Sheaths on Digital Subtraction Myelography: A CSF-Venous Fistula Mimic

Spontaneous intracranial hypotension (SIH) can be caused by CSF-venous fistulas (CVFs), which often require a specialized lateral decubitus examination such as digital subtraction myelography (DSM) for diagnosis. DSM interpretations can be confounded by irregular nerve sheath diverticula at the cervicothoracic junction, potentially mimicking a true CVF. This study aimed to characterize anatomic variations of nerve sheaths at the cervicothoracic junction, in an effort to reduce the risk of misdiagnosis.

We retrospectively identified 35 patients with low-risk Bern scores who were negative for CVF on DSM. Nerve sheaths at C6-C7, C7-T1, and T1-T2 were classified as normal (<5 mm), elongated linear (≥5 mm), linear-bulbous, linear-branching, or diverticulum. Results were obtained on both the left and right side for each patient.

Data were obtained for 34 patients. Among these, 74% (25/34) demonstrated at least 1 variant nerve sheath configuration. The most common site of variation was C7-T1 on the right (seen in 55%, 18/33), and the most frequent morphologic variant overall was an elongated linear sheath (28/198 levels; 40% of all variants).

Nerve sheath morphology at the cervicothoracic junction is frequently irregular, and these variants can resemble a CVF on DSM. Recognizing such normal anatomic variations is essential to avoid unwarranted interventions for suspected CVF in patients evaluated for SIH.