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Dural tentorial arteriovenous fistula causing isolated trochlear nerve palsy: remission after endovascular embolization
  1. Giuseppe Mariniello1,
  2. Francesco Briganti2,
  3. Pierluigi Vergara1,
  4. Francesco Maiuri1
  1. 1Dipartimento di Scienze Neurologiche - Cattedra di Neurochirurgia, Università degli Studi di Napoli Federico II, Napoli, Italy
  2. 2Dipartimento di Scienze Neurologiche - Servizio di Neuroradiologia Interventistica, Università degli Studi di Napoli Federico II, Napoli, Italy
  1. Correspondence to Dr Giuseppe Mariniello, Dipartimento di Scienze Neurologiche - Cattedra di Neurochirurgia, Università degli Studi di Napoli Federico II, Via S. Pansini, 5, Napoli 80131, Italy; giumarin{at}unina.it

Abstract

Objectives To report an exceptional case of dural arteriovenous fistula of the tentorial incisura presenting as transient and recurrent isolated paresis of the fourth cranial nerve, and treated by endovascular embolization.

Case report A 63-year-old man presented several episodes of intermittent diplopia which appeared during sudden head movements and in the left lower gaze. Magnetic resonance and cerebral angiography showed a dural arteriovenous fistula of the right tentorial incisura fed mainly by branches of the right occipital artery as well as intracavernous branches of the right internal carotid artery. Embolization of the occipital artery branches resulted in significantly decreased flow within the fistula and in rapid and complete remission of diplopia. Stereotactic radiosurgery of the residual malformation was then performed. The treatment resulted in a good clinical and radiological outcome at the 5-year follow-up.

Conclusion An arteriovenous fistula of the tentorial incisura may exceptionally cause intermittent diplopia owing to compression of the trochlear nerve due to transient increase of blood flow within the malformation. Remission of diplopia may be achieved by endovascular embolization. Dural arteriovenous fistulas with low risk of hemorrhage and brain neurological symptoms may successfully be treated by partial endovascular embolization and radiosurgery.

  • Trochlear nerve
  • trochlear nerve palsy
  • dural arteriovenous fistula
  • embolization
  • radiosurgery
  • artery
  • ventricle
  • orbit
  • MRI
  • cervical
  • CT
  • trauma
  • posterior fossa
  • tumor
  • cranial nerve
  • spinal cord
  • malformation
  • intervention
  • brain
  • aneurysm
  • arteriovenous malformation

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Introduction

Malformative vascular diseases may rarely cause paresis of the fourth cranial nerve as an isolated neurological sign. Even large series of patients with trochlear nerve palsy may not include cases of aneurysms or arteriovenous malformations.1–4 Reports of single cases mainly concern carotid-cavernous fistulas5–8 and aneurysms of the intracavernous carotid artery.9 10 On the other hand, an isolated paresis of the trochlear nerve caused by a cavernous angioma11–13 or an arteriovenous malformation,14 15 is exceptional.

We report a very rare case of dural arteriovenous fistula of the tentorial incisura presenting as transient and recurrent isolated paresis of the fourth cranial nerve.

Case report

In April 2006, a 63-year-old man presented several episodes of intermittent diplopia which appeared during sudden head movements and in the left lower gaze; diplopia was partially alleviated by anteflexion of the neck. No other neurological abnormalities were present.

Computed tomography and MRI showed a round vascular lesion (1.5 cm diameter) in the deep right temporal region, at the level of the tentorial incisura (figure 1A). Cerebral angiography (figure 1B) revealed a dural arteriovenous fistula fed mainly by branches of the right occipital artery and also by dural branches of the intracavernous internal carotid artery; the venous drainage was in the basilar vein and straight sinus.

Figure 1

(A) Computed tomography: round hyperdense enhancing lesion at the level of the right medial temporal region and tentorial incisura. (B) Digital angiography of the right common carotid artery: arteriovenous malformation fed by the occipital artery and by dural branches of the intracavernous internal carotid artery: the venous drainage is in the basilar vein and straight sinus. (C) Digital angiography of the right common carotid artery after endovascular occlusion of the occipital artery branch: significant decrease of size and flow of the malformation.

On April 29, an endovascular procedure for occlusion of the fistula was performed. Through a right transfemoral approach, selective catheterization of the right external carotid and occipital arteries was carried out; thus, embolization of the arterial branch feeding the fistula was performed (figure 1C). Endovascular occlusion of the arterial feeders from the internal carotid artery was not possible, because of their small size and risk of embolization of the internal carotid circulation. The postembolization angiographic control showed a significantly decreased flow within the fistula. An endovascular transvenous approach was not considered because of the risk of retrograde catheterization of the straight sinus and particularly of the basilar vein.

Postoperatively, rapid and complete remission of the episodes of diplopia occurred. Medical therapy with oxcarbazepine (600 mg/day) was also given.

One month later, magnetic resonance with angiographic sequences (figure 2) showed a significant decrease in the size of the fistula. For this reason, together with the lack of clinical symptomatology, open surgery by craniotomy and ligation of the fistula was not performed. Stereotactic radiosurgery of the residual fistula was then performed.

Figure 2

Magnetic resonance 1 month after the endovascular procedure. (A) axial T2-weighted image: decrease in the size of the malformation. (B) angiographic sequence: hypertrophic arterial feeders from the intracavernous internal carotid artery feeding the residual malformation.

At the follow-up, at 30 months, MRI (figure 3) showed the presence of a very small residual venous pouch, with no arterial flow. Thus, control angiography was not performed. Now, almost 5 years after the endovascular procedure, the patient is symptom-free, with no medical therapy. The neuroradiological control by MRI has confirmed the very small residual venous pouch with no arterial flow.

Figure 3

Magnetic resonance, axial T1-weighted postcontrast sequence, performed 30 months after the endovascular procedure and 10 months after stereotactic radiosurgery: very small residual venous pouch in the right incisura with no significant arterial flow.

Discussion

Palsy of the trochlear nerve as the unique clinical manifestation of an arteriovenous fistula is exceptional. It has been described in isolated reports as result of nerve compression at the level of the superior orbital fissure15 or secondary to a mesencephalic vascular malformation.14 Series of arteriovenous fistulas of the tentorial region fail to report similar cases.16–19

Our report is the first case of arteriovenous fistula of tentorial incisura presenting as an isolated palsy of the trochlear nerve. The episodes of diplopia mainly occurred during sudden head movements and in the left lower gaze. This may suggest that sudden movements of the head caused slight flow changes within the fistula, resulting in transient increase of the trochlear nerve compression.

Vascular compression of the entry zone of the trochlear nerve at its exit from the brainstem by arterial branches of the posterior cerebral or superior cerebellar arteries or by a dural arteriovenous fistula has been described as a cause of superior oblique myokymia, a rare disorder causing involuntary movements of the eye presenting as unilateral rotatory microtremor due to intermittent contractions of the superior oblique muscle causing diplopia.20 21 In our case compression of the trochlear nerve by the fistula occurred more distally, at the level of the peripheral segment, thus resulting in diplopia.

The onset with deficit of an oculomotor nerve is a common symptom of aneurysms of the posterior communicating artery as result of the chronic pulsating effect on the nerve. On the other hand, this is quite rare in cases of arteriovenous fistulas, because of the lower blood pressure and the normal lack of a vascular sac compressing the nerve. However, in our case a round vascular nidus was evident at the tentorial incisura, in the area of the trochlear nerve. The endovascular embolization resulted in a decrease in size and significantly reduced flow within the fistula; thus, it is likely that the loss of a chronic pulsating effect on the nerve was the cause of the remission of diplopia.

The management options of this case deserve to be discussed.

In planning the management of patients with a dural arteriovenous fistula, the risks of treatment must be weighted against the lesion's natural history.22–24 Borden et al25 classified these fistulas into three types: type 1 without cortical venous drainage, and types 2 and 3 with cortical venous drainage. Type 1 fistulas are usually benign and should be treated only if associated with intolerable tinnitus or orbital phenomena; for types 2 and 3 urgent treatment is usually recommended. Our case may be classified as a Borden type 2 fistula.

The presence of cortical venous drainage is significantly associated with intracerebral hemorrhage and non-hemorrhagic neurological deficits.26 Patients with fistulas presenting with these symptoms have a poor clinical course, with an overall frequency of hemorrhage of 45.5% and an annual risk of 19%.24 On the contrary, dural fistulas with cortical venous drainage, when incidental or presenting with pulsatile tinnitus or orbital phenomena, have a significantly good outcome, with an overall frequency of hemorrhage or neurological deficits of 5.9% and an annual risk of 1.4%.24

In the previously reported series of dural arteriovenous fistulas the non-hemorrhagic neurological deficits, including cerebral symptoms, seizures, or dementia, were due to cortical venous hypertension.27–29 On the other hand, in our case there were no symptoms of brain vascular impairment, whereas diplopia was the result of trochlear nerve compression.

The above data suggest that dural arteriovenous fistulas with cortical drainage presenting with hemorrhage or brain symptoms require treatment by endovascular or surgical therapy, whereas in cases without hemorrhage and brain symptoms, as in our case, the risk of treatment needs careful consideration. For patients such as ours stereotactic radiosurgery alone or associated with partial embolization may be advisable.30 31

In our case we performed a less invasive treatment including embolization of the main feeders at lower risk followed by radiosurgery. Further embolization of the internal carotid feeders, endovascular transvenous approach and surgical ligation were considered to dangerous, given the absence of clinical symptoms and a low hemorrhagic risk. This management option resulted in good clinical outcome at the 5-year follow-up.

Stereotactic radiosurgery is an effective treatment for dural arteriovenous fistulas, with a low risk of complications.30–32 In a previously reported series the rate of complete obliteration ranged from 68% to 87%,31–36 with a further percentage of significant flow regression. However, the latency interval until obliteration after radiosurgery alone is about 2 years. Thus, radiosurgery alone or associated with partial embolization is a safe treatment for patients with no or few symptoms and a low risk of hemorrhage, as in our patient. On the other hand, patients with increased hemorrhagic risk, rapid neurological deterioration and/or more complex dural arteriovenous fistulas with retrograde venous filling must be treated by endovascular and/or surgical procedures; in these cases radiosurgery may provide an effective adjunct to the management of a small residual fistula.

Conclusion

A dural tentorial arteriovenous fistula may exceptionally cause isolated paresis of the trochlear nerve as result of the chronic pulsating effect over the nerve itself. Even partial endovascular embolization of the fistula results in the remission of diplopia. For dural arteriovenous fistulas without hemorrhage and brain symptoms at presentation, a less invasive management by embolization of the main feeders followed by radiosurgery may be advisable owing to the low risk of bleeding.

References

Footnotes

  • Competing interests None.

  • Patient consent Obtained.

  • Ethics approval Ethics approval was provided by Università degli Studi di Napoli Federico II.

  • Provenance and peer review Not commissioned; externally peer reviewed.