Unlike cerebral arteriovenous malformation (AVM), a common cerebrovascular malformation, dural arteriovenous fistula (DAVF) is an acquired cerebrovascular disease that occurs at a low frequency. The onset symptoms of AVM include cerebral hemorrhage or convulsions; however, DAVF presents with various symptoms depending on the pattern of venous drainage. As the cavernous sinus (CS) and transverse-sigmoid sinus (TS) are the most common sites, the most common symptoms include ocular symptoms (hyperemia or ocular protrusion) or tinnitus. Accompanying cortical venous drainage (CVD) increases the risk of cerebral hemorrhage or convulsions. Although asymptomatic DAVF is occasionally treated, symptomatic improvement can be an important treatment goal. Among the treatment options, embolization is an effective treatment that can provide immediate symptom improvement. However, considering the associated complications and the difficulty in performing embolization, stereotactic radiosurgery (SRS) has been proposed an alternative treatment method [1-4]. In particular, one of the advantages of SRS compared to transvenous embolization, which is frequently performed these days, is that it maintains the patency of the normal venous system. The present review summarizes DAVF and SRS and proposes indications for SRS as a good treatment option for DAVF.

DAVF is characterized by direct shunting between dural feeding arteries and venous sinuses without a nidus [5-7]. A main theory regarding its pathogenesis is related to the development of dural sinus thrombosis and/or venous hypertension [8]. Normal arteriovenous shunts in the dura are hypothesized to enlarge after sinus thrombosis in response to venous hypertension. Thus, increased blood flow via these shunts causes further venous hypertension. Hypercoagulability may also predispose patients to venous sinus thrombosis and development of DAVF [9].

DAVF most commonly occurs in the CS and TS in Eastern and Western populations, respectively. DAVF symptoms are determined by the pattern of venous drainage. Cases of CS generally show symptoms such as chemosis, proptosis, bruit, diplopia, and cranial neuropathy. More than 80% is drained into the superior ophthalmic vein and approximately 40% is drained into the inferior petrosal sinus, and approximately 23% is drained into the contralateral CS [10]. In the case of TS, palpable tinnitus is a characteristic symptom. With the increasing number of magnetic resonance imaging (MRI) examinations performed for health checkups, the number of incidental findings without symptoms has been increasing. Cerebral digital subtraction angiography (DSA) is the definitive diagnostic method in cases of suspected DAVF based on brain MRI findings. CVD can cause bleeding or epilepsy. In particular, 75% and 33% of bleeding DAVFs are related to tentorial DAVF and venous varix, respectively [11]. The bleeding source is known as a thin arterial vein rather than the fistula itself.

Various approach exists for the treatment of DAVF. Conservative treatment is known to induce occlusion by compressing the ipsilateral carotid artery (Fig. 1). However, the results may be questionable. Approximately 1%-3% cases show conversion from benign to aggressive drainage patterns [12]. The indications for DAVF treatment include worsening symptoms or development of exophthalmos and cerebral hemorrhage or CVD.

From 2009 to 2021 (approximately 13 years), Kyungpook National University Hospital treated approximately 110 DAVFs with SRS using Gamma Knife (Elekta Inc.). The number of DAVFs was less than the number of patients with AVM treated during the same period. However, the number of patients receiving treatment for DAVF has been increasing. Compared to AVMs that cause cerebral hemorrhage or convulsive seizures, DAVFs have relatively benign symptoms such as ocular hyperemia or tinnitus depending on the location of the lesion. Therefore, many patients in external hospitals receive conservative treatment without active treatment. Among treatment options, embolization may directly lead to sequelae, and is a complex procedure requiring expertise to perform. In addition, the clinical course of DAVF is dynamic and presence of hereditary hypercoagulable state must be considered during treatment. Therefore, our hospital, widely performs SRS using a Gamma knife for the treatment of DAVF as it seems safer than endovascular embolization.

In abnormal blood vessels irradiated with radiation, endothelial cells proliferate and the blood vessels are gradually occluded. This phenomenon is equivalent to radiosurgery for AVM and DAVF. In the case of radiosurgery for AVM, the treatment goal is occlusion of abnormal blood vessels such as the mass that form the nidus. However, in the case of DAVF, treatment targets a smaller shunting fistula in the dural wall; therefore, a higher level of radiation energy can be applied. Therefore, SRS shows better therapeutic effects in DAVF than AVM. Moreover, since the amount of radiation applied to surrounding normal tissues is small, the incidence of the radiation-induced complications is relatively low.

Recently, SRS was recommended as a non-invasive, low-risk treatment option for DAVFs in patient with risks associated with conventional treatment or a history of treatment failure [10-16]. Treatment success rate of SRS is similar to that of endovascular embolization. SRS has an obliteration rate >90% and a symptom improvement rate >85% [12]. In particular, CS DAVF has a high cure rate. However, compared to embolization, there is a latency period before complete occlusion; thus, it may take time for symptoms to improve and the risk of bleeding remains during this latency period. However, SRS can be considered the primary treatment for DAVF cases with low risks of developing fatal symptoms or bleeding. The following summarized each case as an indication for SRS as the primary treatment method for DAVF.

SRS may be helpful if endovascular surgery for DAVF is expected to be difficult or if there is residual DAVF after endovascular embolization. I think it is important to determine the appropriate treatment method considering the patient's condition or angiographic characteristics.