Unveiling uncommon connections: Posterior drainage carotid cavernous fistula presenting as isolated oculomotor palsy

Abstract

Isolated third nerve palsy with pupillary involvement is difficult to diagnose, particularly if neuroimaging studies appear normal. A posterior drainage carotid cavernous fistula (CCF) is often missed due to lack of ocular signs and orbital bruit. A 61-year-old female was admitted with a two-week history of insidious-onset, progressive drooping of the right eyelid and binocular double vision. On examination, the patient had complete ptosis of the right eyelid and right oculomotor nerve palsy. A CCF may not always present with ocular congestion; oculomotor palsy with pupillary involvement may be caused by a posterior drainage CCF, also known as a “white-eyed shunt.”

Introduction

Many factors can cause isolated oculomotor nerve palsy with pupillary involvement, the most life-threatening one being an intracranial aneurysm. A carotid cavernous fistula (CCF) is an abnormal vascular connection between the internal carotid artery or external carotid artery and the venous channels of the cavernous sinus.[1] Carotid cavernous fistulas are classified based on the arterial system involved, hemodynamics, and etiology.[2-4] A posterior drainage CCF is often missed as a potential cause due to unapparent congestive signs and orbit bruit.[5-7]

Case Report

A 61-year-old postmenopausal woman was admitted due to a two-week history of insidious-onset, progressive drooping of the right eyelid and binocular double vision. The patient had no periorbital pain or redness in the eyes, exophthalmos, or decreased visual acuity. The patient had no history of trauma, any iatrogenic intervention, or venous thrombosis. On examination, near complete ptosis of the right eyelid with restriction of adduction was observed. The right pupil was dilated with a 6-mm diameter and nonreactive to direct and indirect light reflexes, whereas the left pupil was 3 mm in diameter and normally reactive to light. The fundoscopy was normal. The patient did not have chemosis, proptosis, conjunctival injection, swollen eyelids, or ocular bruits. No other extraocular involvement or other cranial nerve involvement was noted. A compressive/congestive cause was considered due to the oculomotor nerve palsy with pupillary involvement; however, a 3 Tesla (3T) magnetic resonance imaging of the brain, cavernous sinus, and orbit was unrevealing. Additionally, cranial magnetic resonance angiography and venography were performed, which did not reveal any obvious abnormality. However, a strong clinical suspicion of compressive or congestive etiology led to the decision to perform digital subtraction angiography. Written informed consent was obtained from the patient.

The subsequent angiogram revealed an indirect dural fistula with feeders from the right middle meningeal artery (artery to cavernous sinus) and ascending pharyngeal artery communicating with the right cavernous sinus. Due to the rapid evolution of symptoms and significant disability due to ophthalmoplegia, we decided that the patient should undergo definitive treatment. Hence, the patient was treated with a transvenous coil and liquid embolization. A long sheath was taken into the internal jugular vein during the procedure with a diagnostic catheter in the inferior petrosal sinus. A superselective microcatheter was placed into the cavernous sinus, and subsequently, multiple coils were placed, and a liquid embolic agent (EVOM) was administered over 10 min. Combining coils and the liquid embolic agent reduced the cost and improved percolation into small venous channels.

A control angiogram from the external carotid artery showed complete occlusion of the indirect arteriovenous fistula.[8] At the four-week follow-up, there was a complete improvement of ptosis with only partial restriction of extraocular movement (Figure 1).

Figure 1. (a) Axial T2-weighted section shows normal cavernous sinuses. (b) An axial maximum intensity projection image obtained from time-of-flight magnetic resonance angiography shows a normal study. (c, d) Cerebral angiography revealed indirect dural fistula with feeders from the right middle meningeal artery and right ascending pharyngeal artery communicating with the right cavernous sinus (see white arrows). (e) Intraoperative cerebral angiogram showing that microcatheter was taken into the cavernous sinus and blocking of the right cavernous sinus with multiple coils and the liquid embolic agent was administered (see white arrow). (f) Embolization of feeders was performed using the embolic agent (see white arrow). (g) Cerebral angiogram after embolization revealed a significant reduction in the flow across the embolized and coiled site (see white arrow). (h) Initial image of the patient showing near-complete ptosis of the right eye. (i) Patient’s image at the four-week follow-up shows near-complete improvement in ptosis.

Discussion

Direct CCFs, which typically have a high flow, present with prominent ocular features such as chemosis and orbital bruit. Indirect fistulas, which are usually spontaneous, present with more subtle clinical signs. Our case can be classified into Barrow type C CCF, as there was a connection between the cavernous sinus and the dural branches of the external carotid artery. A literature review of similar cases is summarized in Table 1, and the Barrow classification is described in Table 2. A venous drainage-based classification system was developed to describe venous drainage patterns, symptomatology, treatment approach, and outcome more accurately.[3,9] Posterior/inferior drainage was defined primarily through the superior and inferior petrosal sinuses, pterygoid, and parapharyngeal plexus. Anterior drainage denotes drainage via the superior and inferior ophthalmic veins. Cortical drainage was defined as filling the superficial middle cerebral veins, peri mesencephalic, and cerebellar venous system.[3] Congestive symptoms are conspicuously absent if the increased fistular flow is directed posteriorly, leading to delayed diagnosis. The possible mechanisms for isolated oculomotor nerve palsy in indirect CCF can be compression of the ocular motor nerves, vascular steal, thrombosis, focal midbrain ischemia due to hemodynamic alterations, and congestion of the muscles.[10,11] Spontaneous CCFs account for up to 30% of all CCFs reported in the literature and are more common in postmenopausal patients. Thin-section magnetic resonance imaging is emerging as a sensitive tool for identifying CCF; findings include abnormal contour of the cavernous sinus, internal signal void of the cavernous sinus, prominent venous drainage flow, and orbital/ periorbital soft tissue swelling. However, it does not replace magnetic resonance angiography or computed tomography angiography.[12] A CCF may not always be present with ocular congestion; oculomotor palsy with pupillary involvement may be caused by a posterior drainage CCF, also known as a “white-eyed shunt,”[13] which can be easily missed unless specifically looked for with cerebral angiography.

Table 1. Review of literature on indirect CCF cases and their presentation

Table 2. Barrow classification

In conclusion, we presented a patient with right oculomotor nerve palsy with pupillary involvement due to a right external carotid artery indirect dural fistula. The clinical presentation of CCFs primarily depends upon venous drainage pattern and shunt flow rate.

Cite this article as: Agrawal A, Sahu C, Kohat AK, Fatima A, Gupta M. Unveiling uncommon connections: Posterior drainage carotid cavernous fistula presenting as isolated oculomotor palsy. Turk J Neurol 2025;31(2):224-228. doi: 10.55697/tnd.2025.237.

The data that support the findings of this study are available from the corresponding author upon reasonable request.

All authors contributed equally to this article.

The authors declared no conflicts of interest with respect to the authorship and/or publication of this article.

The authors received no financial support for the research and/or authorship of this article.

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