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Vol. 27. Num. 4.July - August 2016Pages 155-206
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Vol. 27. Num. 4.July - August 2016Pages 155-206
Case Report
DOI: 10.1016/j.neucir.2016.01.006
Dural arteriovenous fistula at the foramen magnum: Report of a case and clinical-anatomical review
Fístula dural arteriovenosa en el agujero occipital: caso clínico y revisión clínico-anatómica
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José L. Llácera,
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josellrt@gmail.com

Corresponding author.
, Guillermo Suaya, José Piquera,b, Victor Vazquezb,c
a Department of Neurosurgery, Hospital de la Ribera, Spain
b Neuroscience Department-CEU, Spain
c Department of Radiology, Hospital de La Ribera, Spain
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Abstract

Arterial supply and venous drainage at the foramen magnum is variable. Two main forms of clinical presentation, intracranial and spinal, can be differentiated when a dural arteriovenous fistula (DAVF) is found at this level.

We describe a case of a 68-year-old patient with a progressive paraparesis, diagnosed of dural arteriovenous fistula located at the posterior lip of foramen magnum. We review, in this setting, the vascular radiological anatomy of those fistulas and its important correlation with neurologic clinical symptoms.

Keywords:
Dural arteriovenous fistula
Foramen magnum
Venous drainage
Myelopathy
Resumen

El aporte arterial y el drenaje venoso en el agujero magno son variables. Dos formas principales de presentación clínica, intracraneal y medular pueden ser diferenciadas en las fístulas durales arteriovenosas encontradas a este nivel. Se presenta el caso de un paciente de 68 años que, tras un cuadro de paraparesia progresiva, se diagnostica de una fístula dural arteriovenosa dural localizada en el borde posterior del agujero magno. A propósito de este caso se revisa la anatomía radiológica y vascular de estas fístulas y su importante correlación con los síntomas neurológicos.

Palabras clave:
Fístula dural arteriovenosa
Agujero occipital
Drenaje venoso
Mielopatía
Full Text

Dural arteriovenous fistulas (DAVFs) are one of the most common vascular disorders of the spinal cord. They reach up to 70% of all of them. They do not appear until adulthood. The origin of the fistula can be found from the sacrum to the foramen magnum. At this level, DAVFs are rare, that is, they are only 2% of them.1 Arterial supply of these fistulas comes from meningeal branches of the vertebral and external carotid artery. However, its venous drainage is very important because it is variable and it is related with two main forms of clinical presentation that can be well differentiated: intracranial and spinal. When the presentation is intracranial, venous drainage takes place in ascending route into venous sinus. When the presentation is spinal, there is a descending drainage rout and a slow and insidious clinical picture of myelopathy is seen. This is a less common initial presentation and diagnosis is often missed or delayed because symptoms are nonspecific.

Case reportHistory and examination

We present the case of a 68-year-old man who came with initial diagnosis of left meralgia paresthetica. In addition to pain, the patient referred progressive weakness of his legs during 18 months. That was more evident when walking on inclined planes, and it later associated sphincter disorder. On exploration, hyperreflexia was manifest in both lower extremities with an increased reflexogenic area and atrophy of the right quadriceps. The patient did not refer any relevant related history. The patient provided a magnetic resonance imaging (MRI) of the lumbar spine in which only signs of lumbar spondylosis were found. Given these symptoms, brain and cervical MRI were performed. Aside from degenerative changes, multiple serpiginous hypointense structures were found inside the dural sac and pial surface, mainly between C5 and D1. That was compatible with arteriovenous malformation. Following these findings, a spinal cord and cerebral arteriography was done showing a DAVF at the foramen magnum, which drained into the anterior spinal vein. Afferents arose from the posterior meningeal branches of the right occipital and vertebral arteries. They penetrated into the spinal canal between the occipital bone and C1. A magnetic resonance angiography was also performed, finding a serpiginous vessel that originated in the right vertebral artery and drained into the anterior spinal vein, in the arterial phase (Fig. 1).

Fig. 1.
(0.38MB).

Angiography shows the DAVF. (a) Meningeal branch of the right vertebral artery (arrow). (b) Meningeal branch of the right occipital artery (arrow). (c) Selective catheterization of the occipital artery. (d) Image of anterior spinal vein of the fistula in frontal MRI after gadolinium enhancement (arrow).

Treatment

DAVF was embolized, as a step prior to surgery, with Glubran diluted with lipiodol through the occipital artery branch of the external carotid. The study of the right vertebral artery showed the origin of the perimedullary vein, although no blood flow was observed inside. The control at the end of the procedure showed a total occlusion of the fistula (Fig. 2).

Fig. 2.
(0.23MB).

Post-embolization control shows occlusion of the DAVF. (a) Right vertebral artery (arrow). (b) Right occipital artery (arrow).

Evolution after treatment

The clinical response was favorable, with gradual improvement of motor deficit, regaining the ability to walk soon after hospital discharge. Two months later, the patient got significant improvement. The patient continued with rehabilitation and he had an almost complete recovery. One year after treatment, control arteriography was performed showing persistent occlusion of the DAVF.

Discussion

It is believed that spinal DAVFs (SDAVFs) are an acquired pathology, although its exact etiology is unknown. Arteriovenous communication occurs between a dural branch of the radicular artery, with the nest of vessels located in the dura near the radicular exit, and a vein, which drains intradurally into the venous perimedullary plexus.2,3 Dural arteriovenous fistulas (DAVFs) at the craniocervical junction are uncommon but they produce clinical important abnormalities. These lesions have two main forms of clinical presentation; acute subarachnoid hemorrhage (SAH) and myelopathy.4 However, there are another less common clinical forms; brainstem dysfunction, radiculopathy, cranial nerve palsy and occipital neuralgia.5

At the foramen magnum, the posterior meningeal artery arises from the posterosuperior surface of the vertebral artery, during its course around the lateral mass of the atlas, and penetrates the dura before reaching the posterior border of the foramen magnum. It supplies the dura of the posterolateral and posterior part of the posterior fossa, and anastomoses with the meningeal branches of the ascending pharyngeal and occipital arteries.6 The meningeal branch of the occipital artery is inconstant and if it is present, it enters the skull through the mastoid foramen. In our case, posterior meningeal branches of the right vertebral and right occipital arteries supplied the DAVF, which drained into the anterior spinal vein.

Venous structures in the foramen magnum region are divided into extradural veins, dural venous sinuses and intradural veins. These three groups have their anastomoses through the bridging and emissary veins. The intradural veins in the region of the foramen magnum drain the lower part of the cerebellum and brainstem, the upper part of the spinal cord, and the cerebellomedullary fissure. The veins of the medulla and spinal cord form longitudinal plexiform channels which anastomose at the foramen magnum. The median anterior medullary vein courses on the anterior median sulcus of the medulla and it continuous with the median anterior spinal vein that courses in the anterior median spinal fissure deep to the anterior spinal artery.6 As mention before, the venous drainage is very important because it is variable and it is related with two main forms of clinical presentation that can be well differentiated.4

When the presentation is intracranial, patients suddenly develop subarachnoid hemorrhage (most frequently presentation). When the presentation is spinal, they present slow and insidious clinical picture of myelopathy.

The 6 cases of arteriovenous fistula at the craniocervical junction with subarachnoid hemorrhage described by Kai et al.4 were all characterized by intracranial venous sinus drainage. In their review of 41 previous cases, it is interesting to note that all of those that presented subarachnoid hemorrhage manifested an ascending venous drainage. They provided angiographic evidence of two types of retrograde leptomeningeal venous drainage in intracranial dural fistulas. Type 1, which drained in more than one venous sinus and in which one or more ecstatic venous dilatations were observed. Type 2, which had a single drain and in which no varicose dilations were observed. Patients with type 1 fistula experienced high frequency of bleeding episodes, while those with type 2 did not have them. This would be explained by greater hemodynamic stress in type 1, in contrast to type 2, where stress would be lower due to the low volume of retrograde venous drainage and slower blood flow. In patients with descending drainage flow into the spinal canal, the drainage pattern would resemble type 2. Such patients manifested clinically only as a result of myelopathy. In review cases, Kai et al.4 observed that the fistulas, draining only inferiorly into one draining vein, had relatively slow flow.

Kinouchi et al.7 described a series of 10 patients with DAVF at the craniocervical junction. 7 of them presented subarachnoid hemorrhage, 1 myelopathy and 2 were incidental findings. In all cases, the contribution of the fistula arose from the meningeal branches of the vertebral artery. In the case of myelopathy, there was also an additional branch of the ipsilateral occipital artery and it had a single draining vein with slow flow, the same we found in our case.

In SDAVFs and DAVFs of foramen magnum with progressive myelopathy, increased spinal venous pressure results in a decrease in venous return and venous congestion, which causes intramedullary edema, given that intramedullary veins and radicular veins share a common flow.8 The normal venous anatomy of the spinal cord includes the presence of medullary veins that serve to drain venous blood from the spinal cord to the epidural plexus. Therefore, it has been postulated that is the lack of normal venous drainage that permits the development of venous hypertension.9 Degenerative changes of the spine may contribute to a reduction of the potential reservoir of draining radicular veins.10 Congestion, in turn, leads to chronic hypoxia and progressive myelopathy.11 Direct measurement of the pressure of the fistula shows values that it even reaches 74% of systemic blood pressure.12 This could explain why, in some patients, symptoms worsen with physical exercise and when they have a large increase in blood pressure. The lower thoracic region has relatively few venous flow channels compared with the cervical region13 and therefore, congestive edema usually moves into caudocranial direction through the spinal cord. Hence, the first symptoms of myelopathy sometimes show a dysfunction of the medullary cone, although the shunt could be located on craniocervical junction.14 Symptoms of venous congestion are nonspecific and include weakness in the lower extremities—which is reflected in some difficulty for activities like climbing stairs—paresthesias, diffuse sensory loss, or radicular pain in both lower extremities (sometimes only in one extremity). Sometimes, pain also appears in the lower back area without radicular distribution. These neurological symptoms evolve over time and are usually ascending.15 Others symptoms, such as fecal and urinary incontinence, erectile dysfunction and urinary retention are more common in the later course of the disease. Although deficits are slowly progressive, abrupt changes in clinical course may occur. A spontaneous thrombosis of congested vessels increases the pressure in draining veins and may even cause subarachnoid hemorrhage. This is more common in cases where there is ascending venous drainage.2

Treatment of DAVFs requires the elimination of venous congestion that causes spinal cord injury, acting either at the arterial contribution or at the venous level by surgical shunt interruption. Although treatment of DAVFs at the craniocervical junction can be either surgical or endovascular, surgery is usually chosen in most cases. For transarterial embolization, arteries are usually small and tortuous. They arise directly from the vertebral artery and they have a high risk of embolic complications. For transvenous embolization, access is not usually, possible due to the small size of the draining veins of these fistulas.15 In our case, we chose the initial embolization of the meningeal branch of the occipital artery as a step prior to surgery. When monitoring the vertebral artery, a virtual absence of blood flow was seen in the draining vein, probably due to the anastomosis of the meningeal branch of the occipital artery with the meningeal branch of the vertebral artery. After the procedure, the patient started improving without showing any sign of clinical worsening, so further surgery was not considered. Angiography performed one year after treatment showed occlusion of the fistula.

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Copyright © 2016. Sociedad Española de Neurocirugía
Neurocirugía (English edition)

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