The snake-head sign on MRI in craniocervical junction dural arteriovenous fistulas: a novel imaging feature and a hypothesis of venous remodeling and congestion.

The snake-head sign was present in 31 of 64 reported craniocervical junction-region dAVF cases (48.4%).

• Cases were retrospectively reviewed from the published literature between 1996 and 2026.
• Only cases with retrievable sagittal T2-weighted or FLAIR images were included.
• The sign was defined as intramedullary T2 hyperintensity involving the medulla and upper cervical cord, with a rostral end divided into ventral and dorsal limbs.

The snake-head sign was not significantly associated with age, sex, symptom duration, feeding artery, treatment modality, or outcome.

• Associations were assessed using univariate analyses.
• The authors state that no significant associations were found for these variables.
• The study was retrospective and literature-based with a limited sample size, so the authors considered the findings hypothesis-generating.

A non-significant trend linked the sign to venous drainage configuration: cranial convergence of the draining vein toward the CCJ was more often associated with the sign, while purely caudal drainage was less often.

• The trend did not reach statistical significance.
• The authors interpret it as suggesting the sign reflects venous outflow geometry rather than arterial source or fistula location.

Fistulas at lower cervical nerve-root sleeves, which require a longer cranial venous course, showed a higher frequency of the sign.

• This was a trend, not a confirmed significant association.
• It is consistent with the hypothesis that cranially directed venous drainage concentrates congestion at the CCJ.

The authors propose that the sign may reflect concentrated venous congestion and remodeling at the craniocervical anatomical transition zone.

• This hypothesis rests on the trend toward more frequent sign presence with cranially convergent venous drainage.
• Identifying the sign may raise suspicion for CCJ-related dAVF in unexplained venous congestive myelopathy.

Prospective multicenter studies with standardized imaging review and angiographic correlation are needed to confirm the diagnostic value of the sign and its underlying mechanism.

• Limitations include the retrospective literature-based design, limited sample size, and reliance on published images.
• The authors describe the findings as hypothesis-generating.