Ocular Signs Caused by Dural Arteriovenous Fistula without Involvement of the Cavernous Sinus: A Case Series with Review of the Literature

Discussion

Cranial dural arteriovenous fistulas are often symptomatic, with a pulsatile tinnitus with or without headache, focal neurologic deficit, or compressive signs.^1,3,6 The occurrence of an intracerebral hematoma is also a well-known entity, in particular in cases of venous reflux, cortical vein involvement, or venous ectasia.¹ In rare cases, a dAVF could be symptomatic by ocular signs such as chemosis, exophthalmia, loss of visual acuity, or oculomotor nerve palsy.⁵ The literature of these dAVFs is exclusively represented by case reports and small case series.^3,16,19 These articles generally described the symptoms and angiographic anatomy of the fistula well but detailed analysis of the pathophysiology was always missed except for the series of Cognard et al.⁴

The first and most frequent type of fistula in our series occurred when the ocular signs could be explained by a direct venous reflux into the orbital veins. This was also the most frequent type in the literature.⁷ These fistulas are generally located on the transverse sinus,⁸ with a reflux through the vein of Labbé or at the foramen magnum. For a venous reflux to produce orbital venous hypertension, thrombosis or noncompetence of a large venous collector (jugular bulb or transverse sinus) is necessary. The middle cranial fossa is also described with reflux into the sphenoparietal sinus.³ The anatomic variant of the paracavernous sinus could be an important factor in venous reflux into the superior orbital vein. Two case reports^9,10 of tentorial dAVFs with venous reflux into a basal vein, an uncal vein, and a superior ophthalmic vein are also described, but they seem to be rare. The importance of the venous reflux and the high frequency of venous ectasia in these fistulas are 2 reasons for aggressive management. These fistulas were treated by an arterial approach in all cases described. In the literature and in our series, ocular symptoms and signs were reversible after endovascular treatment of the fistula. With a similar pathologic mechanism, few cases of cerebral arteriovenous malformations¹¹ with ocular signs were reported.

Intracranial hypertension syndrome could also explain the ocular signs. Patients had a loss of visual acuity secondary to papillary edema or optic disc atrophy.^1,12,13 Generally, these dAVFs were multiple arteriovenous shunts located on large sinuses, important because they could influence the venous drainage of the encephalon.⁴ The venous engorgement or reflux provoked by the high flow of the fistula causes hydrocephalus and possibly parenchymal edema. The first article describing an elevation of intracranial pressure in a posterior fossa dAVF was that of Lamas et al¹⁴ in 1977. In 1998, Cognard et al⁴ published a series including 13 patients with dAVFs with signs of intracranial hypertension. Among these 13 patients, 8 had a papilledema and 4 had optic disc atrophy. Other clinical signs described were seizures, tinnitus, headache, and diplopia.

As for patients in our series, the location of the fistula was always on a large dural sinus with multiple arteriovenous shunts. We found a sinus anomaly (thrombosis, agenesis) in 7 of 13 patients. The treatment of this type of fistula must be aggressive to avoid the progression of intracranial hypertension signs and irreversibility of optic disc atrophy. This treatment is always challenging because of the multiplicity of shunts. Partial embolization could be an alternative to decrease the flow of the pathology without risking occlusion of a large dural sinus. This partial treatment is often temporary. An aggressive arterial embolization of the fistulas could be performed with concomitant inflation of a large balloon into the dural sinus, but this treatment exposes the patient to a higher risk of complications.¹⁵ The placement of a ventriculoperitoneal shunt is also a palliative solution. The choice of treatment depends on the anatomy of the arteriovenous shunts, their location, the severity of the clinical signs, and the patient's comorbidities.

The compression of a cranial nerve by venous dilation in case of arteriovenous shunt is well-known, especially for the trigeminal nerve. The occurrence of an oculomotor paresis secondary to the same diagnosis is rarely reported in the literature, perhaps due to lack of knowledge of anatomic details. Only 1 case report¹⁶ of a trochlear nerve deficit caused by a tentorial dAVF and, in particular, a venous ectasia could be found in the literature. The anatomic details and the relationship between the trochlear nerve and the venous structures in the perimesencephalic cisterns were not well-developed in this article. In our series, a similar case is presented. This is a dAVF located in the posterior incisural space with its venous drainage involving the posterior part of the basal vein. As described by Ono et al¹⁷ and by Joo and Rhoton,¹⁸ the trochlear nerve has an intimal relationship with the third portion of the basal vein and with the superior cerebellar artery into the ambient cistern. A dilation of the basal vein in its ambient course could easily result in trochlear nerve compression and a dilation of the lateromesencephalic vein. The other case in our series with the same pathologic mechanism is a dAVF located in the region of the superior orbital fissure with drainage into the sphenoparietal sinus and the superior ophthalmic vein. This latter vein had an important dilation at its intracanalicular portion that caused a compression of nerves (third, fourth, and sixth nerves associated with an ophthalmic hypoesthesia, typical of superior orbital fissure syndrome).

Another type of fistula with ocular signs is an intraorbital fistula, with direct drainage into the superior ophthalmic vein. We did not have fistulas of this type in our series, but in 2 case reports,^7,19 they are well-documented. These fistulas were fed by ethmoidal branches and were directly drained by the superior ophthalmic vein; this scenario created intraorbital hypertension. One of these 2 cases was successfully treated by arterial embolization⁷; the other, by a venous approach after surgical exposure of the superior ophthalmic vein. Pan et al⁵ also reported 3 other cases of intraorbital shunt treated by radiosurgery, but not enough details were reported to understand the pathophysiology of these fistulas.