Angiographic Characteristics and Treatment of Cervical Spinal Dural Arteriovenous Shunts

Discussion

The results of our study revealed some unique distinguishing features of cervical spinal DAVSs compared with the typical lesions located in the thoracolumbar area. Five of the 12 patients (42%) presented with hemorrhage as the initial feature. In 3 cases, the spinal DAVS was the main lesion responsible for the hemorrhage. All the SAHs in the upper cervical spine (C1-C2) were associated with a rostral intracranial venous drainage. Hemorrhagic presentation of a thoracolumbar DAVS is considered extremely rare.⁷ However, previous reports have shown that cervical spinal DAVSs may be more frequently associated with hemorrhage.^3,4,6,8–10 According to a review of the literature by Aviv et al,⁴ approximately 45% of patients with cervical DAVSs presented with SAH as their initial symptom. However, many of these patients had DAVSs at the foramen magnum level (37%; 15 of 41 reviewed cases), which were not true cervical spinal DAVSs. The higher flow rate in the lesions of the cervical area compared with the thoracolumbar area has been proposed as a mechanism for increased bleeding tendency.¹¹ Also, due to the anastomosis of medullary and pontomesencephalic veins, rostral venous flow of the shunt may drain the shunted flow into the cranium.^3,4,7 Thus, the relatively high flow of shunted blood into the pial veins of the posterior fossa may be a cause of SAH.

Another distinguishing feature in our series of cervical spinal DAVSs, which has not been elaborated previously, was the high incidence of association with a coincidental vascular lesion in the vicinity of the cervical spinal DAVS. Multiplicity is known to occur in approximately 6%–8% of brain and 2%–3% of spinal DAVSs.^12–14 However, in our series, 5 patients (41.7%) showed an additional complex vascular abnormality associated with a cervical spinal DAVS. Hemorrhagic presentation was noted in 3 of these patients. The types of coincidental lesions consisted of a spinal/brain AVM (n = 2) and a dural/epidural AVF (n = 3). In case 1, the coincidental spinal pial AVF, which was fed from the anterior spinal artery axis from the left VA, harbored an aneurysm, which was most likely the bleeding focus. A brain AVM located in the cerebellum with an associated arterial aneurysm was likely the cause of hemorrhage in case 2.

An incidental intracranial DAVS (transverse sinus and superior petrosal sinus) was identified in 2 cases, 1 of which presented with hemorrhage from the spinal DAVS (case 9). In case 7, 2 discrete coincidental DAVS nidi with feeders from the right C1 VA and left C2 VA were seen with hemorrhagic presentation in addition to a separate epidural shunt at the right C3 level. The hemorrhagic site could not be localized in this case, and both spinal DAVS lesions were surgically treated. The pathogenetic mechanism for these coincidental presentations is uncertain, but the association of both the pial AVM and the dural/epidural AVF type of lesion with the spinal DAVS seems to suggest a hemodynamic relationship. Venous sump effect from the sinus, induced by a dural shunt, may have recruited the development of an additional pial shunt.¹⁵ Alternatively, hemodynamic alterations including venous hypertension associated with venous thrombosis caused by an arteriovenous shunt may have provided an environment conducive for the formation of a separate DAVS lesion.

The prevalence of the main fistula feeder originating from the right-sided vessel of the patient is a prominent finding, which was also noted in other series.^3,4 Ten of 12 patients (83.3%) in our series showed the main feeding artery arising from the right-sided artery (vertebral/costocervical/thyrocervical artery), including 8 cases of the right vertebral artery. The reason for this persistent right-sided dominance of the cervical spinal DAVS remains speculative. The different anatomic courses of the bilateral innominate veins draining the vertebral veins and the frequent compression of the left innominate vein by the aorta causing differences in the upstream venous pressure may have implications in the right-sided dominance of cervical spinal DAVS.¹⁶ The most important implication of this finding is the necessity to include the right vertebral artery—which may be omitted when the contralateral vertebral artery is dominant—especially in cases of hemorrhagic presentation.⁶ Our protocol included bilateral vertebral arteries, especially in cases of hemorrhagic presentation; thus, none of the cases were missed on the initial DSA except for a patient who hemorrhaged from a radicular feeder from the right thyrocervical artery (case 10). Spinal angiography or high-resolution MR angiography should be performed in a patient with SAH and negative findings on cerebral angiography if the patient shows symptoms referable to the spinal cord.^17,18

Previous reports on the treatment of the cervical spinal DAVSs have predominantly focused on surgical ligation of the draining vein due to concerns of recanalization and the difficulty of selecting fine dural feeders.^3,4,6,8,9,19 In our experience, a combined multidisciplinary approach of treatment resulted in symptomatic improvement in 10 patients (83%) in this series. In 2 patients, angiographic cure was achieved with liquid embolic agents only. An initial endovascular attempt for patients with favorable vascular anatomy may be a safe and effective strategy. In cases of failure or residual lesion, the patient may be subsequently treated by surgical resection.^20,21 For patients who present with hemorrhagic coincidental vascular lesions, the main goal of treatment should always include, first of all, eradication of the symptomatic lesion.

The angiographic differentiation of spinal DAVSs from radicular AVMs is a pertinent issue. Even though radicular AVMs are very rare, composing only 0.6% of the spinal cord vascular malformations, these lesions should be differentiated from spinal DAVSs.²² Radicular AVMs are arteriovenous shunts located on the nerve root and show a conglomerate of abnormal nidal vessels around the nerve root with relatively fast flow. Spinal DAVSs will have a shunting zone along the dura with radicular feeding vessels converging onto the draining radicular or leptomeningeal vein with relatively slow flow. Patients with radicular AVMs often present with radicular pain and only rarely show congestive venous myelopathy.²³ In terms of the relationship between spinal and intracranial DAVSs, the spinal DAVS lesions probably are the embryologic homolog of the intracranial DAVSs draining into the petrosal vein or bridging veins of the medulla.¹¹ They represent the lateral epidural group of DAVSs proposed by Geibprasert et al.¹⁴ These lateral epidural shunts are characterized by male predominance, later age of onset, and the presence of cortical venous reflux, which has also been shown in our series.¹⁴ However, the frequent association of the multiple coincidental vascular lesions in the cervical spinal DAVSs seems to be a feature distinguishing them from the intracranial lateral epidural type of lesion.