INTRODUCTION
Dural arteriovenous fistulas (dAVFs) are an arteriovenous shunt disease that develops within or adjacent to the dura mater and is primarily supplied by dural arteries. Although most cases are idiopathic, venous sinus thrombosis, infection, trauma, and previous craniotomy have been reported as rare etiological factors [7,8]. dAVFs are commonly classified according to the presence of cortical venous reflux or venous sinus drainage using the Borden and Cognard classifications [3]. Among them, Cognard type V—defined by spinal venous drainage—is rare. Despite its intracranial origin, this type may present with spinal symptoms due to venous congestion [4].
Here, we report a case of Borden type III, Cognard type V non-sinus-type falx cerebelli dAVF that developed following an occipital bone fracture.
CASE DESCRIPTION
A 77-year-old patient had sustained a fall with an occipital head contusion 1 year prior. Approximately 1 month before admission, he developed bilateral lower-limb weakness, predominantly on the right, which rapidly progressed and eventually led to emergency transfer to our hospital.
At presentation, he was alert and oriented. Neurological examination revealed incomplete paraplegia in both legs (manual muscle testing: right 2/5, left 2/5), incomplete right upper-limb paresis (manual muscle testing 4/5), urinary retention, decreased rectal sensation, and hiccups. Magnetic resonance imaging demonstrated a fluid-attenuated inversion recovery hyperintense lesion extending from the left medulla to the cervical spinal cord at the C4 level, whereas T2-weighted imaging showed flow voids along the anterior spinal surface (Fig. 1A-C). However, magnetic resonance angiography demonstrated no shunt suggestive of dAVF. Computed tomography revealed an occipital bone fracture and a traumatic contusion scar in the left frontal lobe (Fig. 1D-F).
Cerebral angiography demonstrated shunt formation at the falx cerebelli supplied by the posterior meningeal artery (PMA) arising from the jugular branch of the right occipital artery. Additional shunt inflow was observed from the mastoid branches of both occipital arteries traversing the fracture site. The shunt point was located at the falx cerebelli, and the draining vein passed through the inner dura mater. Venous drainage exhibited retrograde reflux into the intracranial and spinal veins. In particular, the venous outflow extended beyond the shunt point, coursing from the falx cerebelli bridging vein to the posterior spinal vein, and subsequently to the anterior spinal vein via the coronal venous plexus (Fig. 2A-F). Based on these findings, a diagnosis of non-sinus-type falx cerebelli dAVF, Borden type III, Cognard type V, was made.
Endovascular treatment was performed on hospital day 9. Under general anesthesia, a distal transradial approach was used, and a 6-Fr RIST catheter (Medtronic, Minneapolis, MN, USA) was positioned in the right external carotid artery. A Guidepost catheter (Tokai Medical Products, Aichi, Japan) was advanced into the right occipital artery, and a Defrictor nano microcatheter (Medico’s Hirata, Osaka, Japan) was navigated to the shunt point through the PMA using a CHIKAI X10 guidewire (Asahi Intecc, Aichi, Japan). Transarterial embolization was performed by advancing the microcatheter to the shunt point and injecting 50% n-butyl-2-cyanoacrylate (NBCA) under hypotension, resulting in complete obliteration of the shunt (Fig. 2G-I).
Postoperative serial magnetic resonance imaging demonstrated a gradual reduction of the T2-weighted imaging hyperintensity, with complete resolution confirmed at 9 months. The flow void on T2-weighted imaging had disappeared by postoperative day 1 (Fig. 3). Upper-limb paresis and hiccups improved on postoperative day 1; however, bilateral lower-limb weakness (manual muscle testing 2/5) and bladder/rectal dysfunction persisted.
Ethics statement: This study was approved by the Institutional Review Board (IRB No. 24-01).
DISCUSSION
This report describes a case of post-traumatic Borden type III, Cognard type V dAVF in the falx cerebelli following head trauma.
Most dAVFs are idiopathic [7,8], whereas trauma-related dAVFs are rare and are most commonly associated with the middle meningeal artery. Temporal bone fractures may cause direct injury to the middle meningeal artery, or transient mechanical deformation of the dura may indirectly damage it [6]. Trauma reportedly accounts for up to 75% of middle meningeal artery-related dAVFs [14].
Trauma-induced dAVFs in the posterior fossa, however, are particularly rare, with only five reported cases including the present one (Table 1). Four of these cases involved shunt formation in the occipital sinus or falx cerebelli. As with middle meningeal artery-related dAVFs, localized traumatic force may cause deformation of the occipital sinus or falx cerebelli, leading to vascular injury and shunt formation [2,9]. The lower incidence of posterior fossa dAVFs may be attributable to anatomical differences: the thicker occipital bone is less prone to deformation than the temporal bone, reducing the likelihood of dural vessel injury. In addition, the PMA, which supplies the cerebellar dura, is smaller and typically enters through the foramen magnum rather than a bony canal such as the foramen spinosum, making traumatic vascular damage less frequent [12].
Another possible mechanism is thrombosis of intraosseous veins or venous sinuses, as reported in a case of anterior condylar confluence dAVF associated with a fracture extending to the jugular tubercle [15]. Trauma-induced inflammation at foramina containing emissary veins may also contribute [11]. In our case, although no distinct foramen was identified radiographically, an emissary vein or the meningeal artery near the fracture site may have contributed to shunt formation.
Falx cerebelli dAVFs specifically are exceedingly rare, with only three cases including ours (Table 2). All cases were Cognard type V, likely due to preferential caudal venous drainage in the posterior fossa. All cases presented with myelopathy, suggesting predominant spinal venous congestion [1,2,9]. Brainstem T2 hyperintensity was present in all three reports, and although complete angiographic cure was achieved with transarterial embolization, only our case demonstrated complete postoperative resolution on follow-up magnetic resonance imaging. Functional recovery remained incomplete in all cases [1,2,9].
Among Cognard type V dAVFs, brainstem magnetic resonance imaging abnormalities have been identified as a negative prognostic marker [5]. In one report, 39% of patients with such abnormalities had poor outcomes, whereas only 28% achieved complete recovery. Considering all available cases, falx cerebelli dAVFs appear to carry particularly unfavorable outcomes.
Because treatment delay may worsen symptoms, early diagnosis is important. The median time to diagnosis for Cognard type V dAVFs has been reported as approximately 5 months, with misdiagnoses resulting in diagnostic delays of up to 4 years [4,10]. Although our case was diagnosed after only 1 month of symptoms, neurological recovery remained limited. Therefore, when delayed-onset myelopathy develops after head trauma and imaging demonstrates changes in the brainstem and spinal cord, dAVFs should be considered in the differential diagnosis, and further evaluation should be pursued.
Endovascular treatment is frequently the treatment of choice for dAVFs. Other treatment options include surgical disconnection and radiotherapy. Depending on the location of the dAVFs, surgical disconnection may be the preferred option; in this case as well, it should be considered if endovascular treatment proves difficult, as a previous reports [9]. Although radiotherapy is effective, it takes time to achieve occlusion and is not suitable for cases with venous congestion or symptomatic presentation. In addition, to our knowledge, there have been no reports describing its use in similar cases.
When performing embolization via the PMA, particular attention should be paid to the possibility of anastomoses with other vessels. In addition to arising from the vertebral artery, the PMA may also originate from the ascending pharyngeal artery, occipital artery, or posterior inferior cerebellar artery, and, although rare, anastomoses with the odontoid artery and the lateral spinal artery have also been reported [13].
In this case, transvenous embolization was not considered a viable option because the draining veins were independent of the venous sinuses, making catheter access difficult. In addition, the feeding arteries from the PMA to the shunt site were markedly tortuous, raising concern that Onyx (ethylene-vinyl alcohol copolymer; Medtronic, Minneapolis, MN, USA) embolization could make microcatheter retrieval difficult. Particularly in cases where the distance from the PMA to the shunt point is relatively long, a more meticulous technique is required to prevent migration through anastomoses into nontarget vessels. Because the microcatheter could be advanced into the single draining vein at the shunt point, we considered that high-concentration NBCA could be safely injected under induced hypotension with minimal risk of migration through anastomoses into nontarget vessels. Additionally, because the feeding artery was narrow and tortuous, it was difficult to guide a coil-insertable microcatheter, and a small-diameter microcatheter was therefore used, necessitating the use of NBCA.
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