Cardiovascular

Spinal CSF-Venous Fistulas as the Potential Cause of Chronic Subarachnoid Hemorrhage: Superficial Siderosis and Adhesive Arachnoiditis.

Schievink W, Maya M, et al. • AJNR. American journal of neuroradiology • 2026

PubMed 42209145 DOI 10.3174/ajnr.A9179

TL;DR

The occurrence of infratentorial superficial siderosis and adhesive arachnoiditis, the halting of iSS progression, and elimination of xanthochromia after treatment of spinal CSF-venous fistulas all suggest the presence of bidirectional flow in at least some CSF-venous fistulas.

Key Findings

Results

CSF xanthochromia resolved in all patients with spinal CSF-venous fistulas who had post-treatment CSF analysis.

9 patients with CSF-venous fistulas had xanthochromia on CSF analysis
8 of these patients underwent treatment for their CSF-venous fistula
5 of the 8 treated patients had post-treatment CSF analysis performed
Xanthochromia resolved in all 5 patients who had post-treatment CSF analysis
Xanthochromia indicates bleeding into the subarachnoid space

Results

All patients with infratentorial superficial siderosis (iSS) and CSF-venous fistulas who underwent treatment showed improvement or stabilization of iSS symptoms with no radiographic worsening.

16 patients with iSS and CSF-venous fistulas were identified
11 of these 16 patients underwent treatment for their CSF-venous fistula
All 11 treated patients had improvement or stabilization of iSS symptoms
No radiographic worsening of iSS was noted on follow-up MRIs in any patient
iSS, like xanthochromia, indicates bleeding into the subarachnoid space

Results

There was considerable overlap between patients with CSF xanthochromia and those with infratentorial superficial siderosis in the context of CSF-venous fistulas.

Of 16 patients with iSS and CSF-venous fistulas, 6 (37.5%) also had xanthochromia on CSF analysis
Total cohort comprised 19 patients (9 men and 10 women) with a mean age of 55.4 years (range 17–82 years)
Single-center cohort study using a prospectively maintained database
Patients were identified as a consecutive group

Results

Severe and symptomatic spinal adhesive arachnoiditis (SAA) developed in 2 patients with spinal CSF-venous fistulas, suggesting CSF-venous fistulas may be a previously unrecognized cause of this condition.

2 patients with spinal CSF-venous fistulas developed severe and symptomatic spinal adhesive arachnoiditis
The authors characterize this as a 'previously unrecognized cause of adhesive arachnoiditis'
SAA is considered consistent with chronic subarachnoid hemorrhage caused by bidirectional flow through the fistulas
Both iSS and SAA development are cited as evidence supporting bidirectional flow through at least some CSF-venous fistulas

Discussion

The findings support the hypothesis of bidirectional (two-way) flow through spinal CSF-venous fistulas, contrasting with a previously held view that flow was one-way.

Spontaneous spinal CSF-venous fistulas were first described in 2014, and the directionality of flow has been a point of contention
Bidirectional flow implies that blood or blood products from venous circulation can enter the subarachnoid space through the fistula
Resolution of xanthochromia, halting of iSS progression, and development of SAA are all cited as evidence for bidirectional flow
The authors conclude that bidirectional flow occurs in 'at least some' CSF-venous fistulas

What This Means

This research suggests that abnormal connections between the spinal fluid space (subarachnoid space) and nearby veins — called CSF-venous fistulas — can allow blood or blood products to leak back into the spinal fluid, not just allow spinal fluid to escape into the blood. The study followed 19 patients who had these fistulas along with signs of chronic bleeding into the spinal fluid, such as yellow discoloration of the spinal fluid (xanthochromia) or iron deposits around the brain (infratentorial superficial siderosis, or iSS). When these fistulas were treated, the yellow discoloration resolved in all five patients who had follow-up spinal fluid testing, and all 11 patients with iron deposits around the brain showed stabilization or improvement with no worsening seen on follow-up MRI scans. The study also found that two patients developed a serious and painful condition called spinal adhesive arachnoiditis — scarring and inflammation of the protective membrane surrounding the spinal cord — which the authors suggest may be caused by chronic blood exposure from these fistulas. This is described as a previously unrecognized potential cause of this condition. Taken together, these findings suggest that at least some of these fistulas allow two-way flow: spinal fluid leaks out, and venous blood or blood products leak in. This research matters because it helps explain why some patients with spinal CSF-venous fistulas develop neurological problems like progressive hearing and balance difficulties (from iSS) or severe spinal pain and neurological deficits (from adhesive arachnoiditis). It also suggests that successfully treating the fistula can stop the progression of these complications, pointing to the importance of identifying and treating these fistulas in affected patients.

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Citation

Schievink W, Maya M, Parikh S, Boyke A, Prasad R, Wadhwa V, et al.. (2026). Spinal CSF-Venous Fistulas as the Potential Cause of Chronic Subarachnoid Hemorrhage: Superficial Siderosis and Adhesive Arachnoiditis.. AJNR. American journal of neuroradiology. https://doi.org/10.3174/ajnr.A9179

Key Findings

What This Means

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