Dural Fistula (AV Fistula Brain, Pulse Synchronous Tinnitus)

What Is a Dural fistula?

A dural arteriovenous fistula, or dural AVF, refers to a pathological short-circuit connection between the arteries and the veins at the level of the meninges. As a result, blood flows with arterial pressure into the venous blood conduits. It can lead to various symptoms, depending on the location and extent of the fistula.

The most common location is a blood conductor that runs at the base of the skull near bony structures that house the middle and inner ear. Affected patients, therefore, usually report a pulse-synchronous ringing in the ear, which the physician can also perceive from the outside with a stethoscope.

In other localizations, the increase in pressure in the venous limb may be more at the forefront of the symptoms. Thus, blood may back up in veins of the orbit with subsequent visual deterioration, redness, and swelling of the conjunctiva, or a stroke or bleeding may occur if blood backs up into the cerebral veins.

Very rarely, the vessels of the spinal canal are affected by a dural AV fistula. Depending on the location of the fistula and the venous backflow into the spinal cord, the symptoms are usually dominated by a slowly increasing weakness of the legs and vegetative disturbances (e.g., impaired defecation and bladder emptying).

Causes of an AV Fistula

The cause is thought to be a change in the arteriovenous pressure gradient of the dura mater. Accordingly, venous hypertension, sinus thrombosis, traumatic brain injury, viral infections, and transcranial neurosurgical procedures are predisposing factors.

Since women during pregnancy and menopause and patients with positive thrombophilia, factor V-suffering, or factor II-mutations are at increased risk for cranial dural fistula, increased systemic thrombotic activity may also influence.

At the base of the skull, so-called direct fistulas can be caused by trauma, e.g., from a fall or traffic accident. Here, the symptoms are usually acute and clearly pronounced. Indirect fistulas can sometimes be traced back to thrombosis of the venous blood vessels based on the history of angiographic findings. However, it is often not possible to determine the cause with certainty. In the more common indirect fistulas, the symptomatology is usually less spectacular than in the traumatic ones.

Diagnostics: How Is a Dural fistula Diagnosed?

For classification and differentiation of "dangerous fistulas," Gizewski refers to the systematics according to Cognard et al. Type I fistulas, according to Cognard, have a comparatively favorable prognosis with a very low risk of bleeding due to their physiologically orthograde venous flow. However, the risk of intracranial hemorrhage increases significantly from type IIb to IV; type V fistulas have an additional risk of spinal complications.

If a change in venous drainage occurs, transition to a higher stage is possible in principle at any time. If there is a clinical suspicion of a cranial dural fistula, Gizewski recommends a CT to exclude or prove cerebral hemorrhage. Imaging the intracranial vessels should preferably be performed with MR angiography and examined concerning dilated vessels, thickened dura, or brain parenchymal changes due to venous hypertension. "Ultimately, however, catheter angiography is necessary if symptoms are typical," Gizewski says. According to the expert, digital subtraction angiography is the only method to date that can reliably assess the danger of a fistula.

Classification and Therapy

Once the diagnosis of AV fistula has been established and confirmed by magnetic resonance imaging (MRI) or catheter angiography, various treatment options can be applied.

One option is treatment via the vascular system, in which, depending on the location and type of fistula, its closure strives via the veins and/or arteries. For this purpose, the fine arteries supplying the fistula can be probed with a microcatheter and closed by placing particles or tissue glue. In addition, it is possible to close the affected portion of the blood vessels with platinum coils or remodel the affected segment with a stent through the veins. Sometimes a combination of procedures is necessary. The treatment may then be performed in several individual steps.

Neurosurgical treatment of the fistula with complete resection of the pathologic area of the dura mater, clipping, or endoluminal sinus sealing, with or without preceding endovascular embolization, promises the most excellent possible therapeutic success but also involves the potential complications associated with surgery under general anesthesia. "In Innsbruck, especially since the introduction of the onyx embolization, endovascular therapy is performed first whenever possible," Gizewski reports.

The goal of endovascular therapy is either complete elimination of the fistula or conversion to a benign fistula grade. "Embolization is indicated for dangerous fistulas that are at high risk for bleeding or for a fistula that has bled acutely," Gizewski explains. Interventional treatment can be applied transarterial, transvenous, or in combination. Embolization materials used include polyvinyl alcohol, liquid adhesive agents such as ethylene-vinyl alcohol copolymer, adhesives such as enbucrilate, methacryloxysulfonal, platinum coils, or, more rarely, balloons. There is a relative contraindication to transvenous embolization for patients with venous stasis or previous thrombosis of the draining sinus.

Frequently, endovascular or microsurgical therapy is supplemented with stereotactic treatment. Although very well tolerated, Radiosurgery is not suitable as a long-term treatment alone for patients with cerebral hemorrhage or dangerous fistulas. However, as monotherapy, radiotherapy may be considered for benign type I and IIa arteriovenous dural fistulas. "For less dangerous fistulas, it depends on how much the patient is affected by the ear bleed. If the quality of life is massively impaired, this fistula can also be treated. However, there is no compelling indication," Gizewski said.

Sources:

• Jaeger, Meixensberger: Die traumatische Subarachnoidalblutung und ihre klinische Relevanz. In: Intensivmedizin und Notfallmedizin . Band 41, Nummer 3, 2004, doi: 10.1007/s00390-004-0407-6.
• Schwab et al. (Hrsg.): Neurointensiv. 3. Auflage. Springer 2015, ISBN 978-3-662-46499-1.
• Hacke (Hrsg.): Neurologie. 14. Auflage. Springer 2016, ISBN 978-3-662-46891-3.
• Linn et al. (Hrsg.): Atlas Klinische Neuroradiologie des Gehirns. Springer 2011, ISBN 978-3-540-89568-8.
• Hufschmidt et al.: Neurologie compact. 6. Auflage. Thieme 2013, ISBN 978-3-131-17196-2.