Accessory Dural Sleeve: Imaging Appearance on Lateral Decubitus CT Myelography and Relationship to CSF-Venous...

Cerebrospinal fluid-venous fistulas (CVFs) are a major cause of spontaneous intracranial hypotension (SIH) and are best detected with lateral decubitus-CT myelography (LD-CTM) and lateral decubitus-digital subtraction myelography (LD-DSM). On LD-CTMs, we have often noticed an accessory dural sleeve (ADS) separate from the nerve root sleeve, a previously underrecognized imaging finding. The purpose of this study is to describe the imaging appearance of the ADS and its relationship to CVFs.

Retrospective single-center review of LD-CTM examinations performed between August/2019 and December/2025 for suspected CVF, evaluated for: 1) Presence, location, size and morphology of an ADS; 2) Visibility of a radicular vein in relationship to the ADS; 3) relationship of ADSs to CVFs (when present). ADSs were defined as independent dural projections separate from nerve root sleeves. Morphologic classification (infundibular, linear, diverticular) was based on objective length and diameter criteria. Associations between ADS presence, clinical status, and CVF location were assessed using descriptive statistics, chi-square testing, and permutation-based simulation.

91 LD-CTMs from 59 patients were analyzed. 53 ADSs were identified in 33 patients (55.9%; 95% CI, 43.3%-67.9%), most commonly in the thoracic spine. A radicular vein was seen traversing the ADS in 49.1% of cases. Regarding morphology, 22 were infundibular (41.51%), 18 linear (33.96%) and 13 diverticular (24.53%). Only in 2 cases, the CVF originated from the ADS (6% of CVFs). Co-occurrence of ADS and CVF at the same level and side occurred more often than expected by chance with approaching statistical significance (p = 0.059), but ADS location demonstrated limited predictive value for CVF localization.

ADSs are a common anatomic variant encountered on LD-CTMs that may mimic CSF leaks, particularly CVFs, and only rarely represent true CVFs. Recognition of ADS morphology and reliance on dynamic contrast behavior are essential to avoid false-positive diagnoses. Linear and diverticular morphologies were more likely to resemble fistulas. ADS: accessory dural sleeve; CSF: cerebrospinal fluid; CVF: cerebrospinal fluid-venous fistula; ICHD-3: International Classification of Headache Disorders, Third Edition; LD-CTM: lateral decubitus CT myelography; LD-DSM: lateral decubitus-digital subtraction myelography; SIH: spontaneous intracranial hypotension.