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

Background and purpose: Spontaneous intracranial hypotension (SIH) can be caused by cerebrospinal fluid-venous fistulas (CVFs), which often require a specialized lateral decubitus exam 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 effort to reduce the risk of misdiagnosis.

Materials and methods: 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 diverticular. Results were obtained on both the left and right side for each patient.

Results: Data was obtained for 34 patients. Among these, 74% (25/34) demonstrated at least one 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).

Conclusions: 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.

Abbreviations: CVF = CSF-venous fistula, DSM = Digital subtraction myelography, SIH＝ Spontaneous intracranial hypotension.