Isolated subdural hematoma secondary to Dural arteriovenous fistula: a case report and literature review

Background Dural arteriovenous fistula (DAVF) is an uncommon subtype among the intracranial arteriovenous malformations, which is characterized by pathological anastomoses between meningeal arteries and dural venous sinuses, meningeal veins, or cortical veins. While intracerebral hemorrhage accounts for most of the hemorrhagic cases in patients with DAVF, isolated subdural hematoma (SDH) is rarely reported. Case presentation A 45-year-old man was admitted for a progressively worsening headache over 2 weeks. Head computed tomography on admission revealed an isodense chronic SDH (CSDH) on the left hemisphere with mild midline shift. Further angiography of the external carotid artery revealed a DAVF at the transverse sinus. The DAVF was embolized via the middle meningeal artery. His CSDH gradually resolved without surgical intervention. In order to further elucidate this rare entity, a review of relevant literature was also conducted. Conclusions Isolated SDH is a rare complication of DAVF. In this report, we presented a rare case of CSDH secondary to an intracranial DAVF. According to this case report and our literature review, the so-called benign type of DAVF without cortical venous drainage does not always warrant a benign process and might be complicated with SDH. Careful preoperative investigation is needed for relative young patients presenting with idiopathic or atypical SDH.


Background
Dural arteriovenous fistula (DAVF) is an uncommon subtype among the intracranial arteriovenous malformations (AVMs), which is characterized by pathological anastomoses between meningeal arteries and dural venous sinuses, meningeal veins, or cortical veins [1]. From a recent epidemiologic survey of DAVF in Japan, the initial clinical presentation was intracranial hemorrhage in 16% of the inflicted patients [2]. While intracerebral hemorrhage (ICH) accounts for most of the hemorrhagic cases, isolated subdural hematoma (SDH) is rarely reported [3,4]. In the current study, we report a rare case of DAVF presenting with isolated chronic subdural hematoma (CSDH). Furthermore, a review of the literature was also conducted to further illustrate the clinical profiles of this rare entity.

Case presentation
A 45-year-old man was admitted for a progressively worsening headache over 2 weeks. He denied history of recent head trauma or anticoagulation and antiplatelet medication. General and neurologic examinations were not remarkable on admission. Routine laboratory investigations including coagulation profiles and platelet function were within normal limits. Head computed tomography (CT) on admission revealed an isodense CSDH on the right hemisphere with mild midline shift (Fig. 1a). A CT angiography (CTA) was performed to rule out any intracranial vascular malformation. A DAVF was noticed at the transverse sinus with dilated cortical venous drainage (Fig. 1b). So, a digital subtraction angiography (DSA) of the external carotid artery and DAVF embolization was planned.
No anomaly was noticed during selective angiography of the internal carotid and vertebral arteries and the left external carotid artery. Selective angiography of the right external carotid artery showed that the DAVF was located at the transverse sinus and fed by posterior branch of the middle meningeal artery (MMA), the occipital artery, and the posterior meningeal artery and drained to the occipital cortical veins with venous ectasia (Fig. 2a-b). The DAVF was classified as type IV according to the Cognard classification. The embolization was performed via the MMA. The Headway duo catheter was used and accessed to the DAVF, and Onyx was injected until the shunt disappeared ( Fig. 2c-d). The patient experienced an uneventful recovery. His CSDH gradually resolved in 1 month (Fig. 3). No neurologic deficit was noticed.

Literature review
A PubMed search of published studies written in English and Chinese was conducted on June 30th, 2017. The following key words were used in relevant combinations: dural arteriovenous fistula, dural arteriovenous malformation, subdural hematoma, subdural haematoma, subdural hemorrhage, and subdural haemorrhage. The reference lists of the identified articles were also manually searched for additional studies. Studies of which full text could not be obtained or those without sufficient individualized description of the isolated SDH cases mixed in larger case series were excluded.

Discussion
DAVF is an uncommon subtype of intracranial AVMs [1]. In a Scottish population-based study in adults, the detection rate of DAVF was 0.16 per 100,000 adults per year, whereas the rate of all intracranial vascular malformations was 2.27 per 100,000 adults per year in the same population [16]. The manifestations of DAVF are diverse. In the recent Japanese survey by Kuwayama N et al., the initial clinical presentation was ocular symptoms, tinnitus, intracranial hemorrhage, and non-hemorrhagic neurological deficits in 45, 20, 16, and 20% of the patients respectively [2]. In the hemorrhagic patients, isolated SDH was only reported sporadically [3][4][5][6][7][8][9][10][11][12][13][14][15]. According to the literature, the majority of DAVFs are acquired in an idiopathic fashion, only a small proportion results from causes as trauma, infection, and iatrogenic injury [1,17]. In this study, including our case, the causes of DAVF and associated SDH were only defined in 3 patients (2 iatrogenic and 1 traumatic), with the rest undefined or not mentioned.
The initial clinical presentation is not specific in patients with DAVF associated SDH. Just as presented in our case, headache (chronic, acute, or progressive) was the most common complaint. As a result of its rarity in occurrence, hardly could we ever associate DAVF with an SDH. In case of a patient presenting with SDH, there is no specific indication in imaging and clinical presentation that could imply the possibility of an underlying DAVF. However, there are some points that might indicate the existence of some underlying disorders: a) relatively young age, b) no evident history of head trauma, c) no coagulopathy or anticoagulation and antiplatelet medication, d) spontaneous occurrence of SDH, e) recurrent or refractory SDH that recurs in a short period after previous satisfactory hematoma evacuation.   The natural history of DAVF is primarily determined by the pattern of venous drainage [1,17,18]. Patients with cortical venous drainage (CVD) (especially with venous ectasia) have an aggressive natural history including ICH and nonhemorrhagic neurologic deficits (NHNDs). While DAVF without CVD manifests a benign process and rarely causes ICH or NHNDs. In this literature review, Cognard classification (Table 2) of the DAVF were reported or deduced from the reports in 12 patients, with type I, type III, and type IV in 7, 2, and 3 patients, respectively. Seven (58.3%) of the 12 patients harbored the supposed benign type I DAVF, which is somewhat inconsistent with the classical viewpoint [1,17]. Hence, DAVF with CVD demonstrates an aggressive natural history and might be complicated with any kind of intracranial hemorrhage including SDH. The so-called benign type of DAVF without CVD does not always warrant a benign process and could also be complicated with SDH.
There was no consensus on the treatment of DAVF and its associated SDH. The treatment strategies depend on specific circumstances. In the case of massive ASDH, hematoma evacuation combined with simultaneous DAVF resection was the preferred strategy [7,8,13]. While burr-hole drainage combined with DAVF embolization was more suitable for CSDH patients [4,6,7,12]. When the SDH did not cause evident intracranial hypertension or neurological deficit, mere DAVF embolization could also be selected [4,14,15]. Because the mass effect of CSDH in our patient was mild, we just embolized the DAVF at primary treatment. And the CSDH resolved spontaneously.

Limitations
This is an isolated case report and a review of the literature. The data we interpreted were extracted from sporadic cases. As a result of the nature of this study, statistical analysis could not be conducted. Hence, the conclusion we achieved in the text is just a narrative interpretation of the past studies and future studies with larger case series are anticipated.

Conclusion
DAVF is an uncommon subtype of intracranial AVMs. Isolated SDH including ASDH and CSDH is a rare complication of DAVF. The so-called benign type of DAVF without CVD does not always warrant a benign process and could also be complicated with SDH. Careful preoperative investigation is needed for relative young patients presenting with idiopathic or atypical SDH.