CSF-venous fistulas are rare and only recently recognized causes of spontaneous intracranial hypotension. They are a direct communication between the spinal subarachnoid space and epidural veins allowing for the loss of CSF directly into the circulation and can be either iatrogenic or spontaneous in etiology.
The number of reported cases is relatively low, however, there does appear to be female predilection in spontaneous cases 1-3. Individuals are typically diagnosed in middle-age (33-72 years of age) 3.
The clinical presentation is that of intracranial hypotension and is therefore discussed in that article.
Importantly, low opening pressures (<6 cm H2O) are only seen in approximately a third of cases 3.
Although CSF-venous fistulas have been a recognized complication of lumbar puncture and myelography, they have also recently been identified in individuals without antecedent intervention 1. It is believed that in at least some individuals these represent rupture of a perineural cyst/arachnoid granulation into an adjacent vein. This is supported by the identification of a nerve-root sleeve arachnoid diverticulum (perineural cyst) in the majority of cases (82%) 3.
Unlike other cases of intracranial hypotension due to CSF leaks, no accumulation of CSF outside of the dura can be identified (i.e. no epidural fluid, no paranasal sinus fluid, no accumulation of radiotracer of contrast in an extra-dural location). The key to the diagnosis is identifying myelographic contrast opacifying an epidural vein 1. This can be achieved either with CT myelography 2, or digital subtraction myelography 1.
The site of fistula is usually in the thoracolumbar spine, most commonly the lower half of the thoracic spine (T7-T12, 68%) 3.
Contrast is introduced into the intrathecal space and a routine CT myelogram performed. The diagnosis hinges on identifying a hyperdense paraspinal vein that represents intrathecal contrast entering the circulation 2. A threshold of 70 HU has been suggested as a cut-off 3, although clearly what is more important is the identification of a single paraspinal vein that is substantially more dense than veins at other levels.
Digital subtraction myelography
Contrast is introduced into the intrathecal space. Using gradual patient tilting the contrast column is allowed to run along the region of suspected fistula. The diagnosis is established by visualizing contrast passing directly from the subarachnoid space into a paraspinal vein 2.
Treatment and prognosis
Although the number of cases reported is low, at least anecdotally, an epidural blood patch may not be effective, presumably not adequately compressing or disrupting the fistula 2. Surgical exploration and disconnection of the fistula is curative 2.
- 1. Wouter I. Schievink, Franklin G. Moser, M. Marcel Maya. CSF–venous fistula in spontaneous intracranial hypotension. (2014) Neurology. 83 (5): 472. doi:10.1212/WNL.0000000000000639 - Pubmed
- 2. P.G. Kranz, T.J. Amrhein, W.I. Schievink, I.O. Karikari, L. Gray. The “Hyperdense Paraspinal Vein” Sign: A Marker of CSF-Venous Fistula. (2016) American Journal of Neuroradiology. 37 (7): 1379. doi:10.3174/ajnr.A4682 - Pubmed
- 3. Kranz PG, Amrhein TJ, Gray L. CSF Venous Fistulas in Spontaneous Intracranial Hypotension: Imaging Characteristics on Dynamic and CT Myelography. (2017) AJR. American journal of roentgenology. 209 (6): 1360-1366. doi:10.2214/AJR.17.18351 - Pubmed