A rare red eye: cavernous sinus dural arteriovenous fistula masquerading as conjunctivitis and sinusitis

Clinical record

A 77‐year‐old woman with a background of hypertension, diet‐controlled type 2 diabetes and bilateral cataract surgery was referred by her general practitioner to the emergency department of the Royal Darwin Hospital with a progressive history of red eyes, lacrimation, rhinorrhoea and, more recently, diplopia. The patient first sought medical attention 6 weeks prior at symptom onset. Her GP had initially diagnosed and managed the presentation as sinusitis and, after failed resolution, as viral conjunctivitis. There was no history of trauma. Following onset of new diplopia, the patient was referred to hospital.

Her regular medications were atorvastatin 40 mg daily, felodipine 10 mg daily and atenolol 100 mg daily. Examination revealed blood pressure 183/84 mmHg and bilateral injected conjunctivae with a corkscrew appearance of the scleral vessels, left‐sided proptosis, diplopia and abducens nerve palsy (Box, A). There was no palpable thrill or audible bruit over either eye, and the remainder of the examination, including peripheral neurological assessment, was unremarkable.

The initial investigation focused on excluding cavernous sinus thrombosis, orbital collection, glaucoma and Graves disease. Routine blood tests were normal, as were inflammatory markers, antithyroid and autoimmune antibodies. Brain magnetic resonance imaging scan excluded stroke, and the globe pressures were normal. Initial computed tomography (CT) angiography found an enlarged cavernous sinus but no other pathology. Subsequent time‐resolved CT angiography demonstrated early arterial phase contrast flow into the cavernous sinus, raising suspicion for a cavernous sinus dural arteriovenous fistula (CS‐DAVF).

The patient was transferred interstate to neurointerventional radiology for further assessment and treatment. Digital subtraction angiography demonstrated both internal and external carotid contributions into the cavernous sinus (Box, B, D and E). The connection was eliminated via transorbital cavernous sinus embolisation.1 Six months later, the patient's red eye had resolved, although the abducens nerve palsy and diplopia persisted and required surgical intervention with transposition of superior and inferior rectus muscles to the lateral rectus (Jensen procedure).

Discussion

A communication between the carotid arterial system and the cavernous sinus is a rare and sight threatening cause of red eye. This pathology, termed CS‐DAVF, historically categorised as an indirect carotid‐cavernous fistula (CCF), is a challenging diagnosis.

CS‐DAVF are formed by the communication of the dural branches of the internal and external carotid arteries with the cavernous sinus. This communication is hypothesised to be due to the thrombolytic response to a cavernous sinus thrombosis.2,3 In contrast, direct CCF are formed by trauma or aneurysmal rupture to the intercavernous portion of the internal carotid artery itself, resulting in a high flow, direct CCF. These entities have classically been combined in classification schema, but there is debate advocating for their separation due to the substantially differing pathophysiology behind each disorder.4

CS‐DAVF is a rare clinical entity predominately seen in older women or patients with hypertension, while trauma or connective tissue disease are risk factors for direct CCF.5 The natural history of the disease is variable and relates to the interplay between fistula location and patient anatomy.2 Typical signs include progressive chemosis, exophthalmos and corkscrewing of the scleral vessels. Diplopia may result from either oculomotor cranial nerve involvement or venous congestion. As the flow through the fistula progresses, these signs become more evident and there is potential for facial pain and glaucoma. Ophthalmic signs include central retinal vein occlusion, retinal detachment and optic disc swelling.2 Signs may be ipsilateral, contralateral or bilateral due to intercavernous communication and individual drainage patterns.3

Common symptoms include red eyes and possibly congestion; a headache may be also present. Uncommon presentations include epistaxis or otorrhagia.3 Posteriorly draining fistulae predispose the patient to intracranial haemorrhage and may lack red eyes or other external findings. Post‐traumatic direct CCF (eg, due to motor vehicle accident) may be overlooked due to distracting injuries.

The gold standard diagnostic test is digital subtraction angiography of the external and internal carotids bilaterally and subsequent demonstration of contrast flow into the cavernous sinus, but access to this procedure is limited to quaternary centres. Plain or contrast CT may reveal superior optic vein enlargement, and additional time‐gated modality may better demonstrate early filling of this superior optic vein, supporting clinical suspicion of CS‐DAVF.

The wide variety of signs and presentations mean that this condition may be misdiagnosed and treatment delayed. This is particularly true of CS‐DAVF, which may progress insidiously until potentially irreversible complications such as diplopia and visual loss are present. Therefore, patients with CS‐DAVF manifesting as a red eye require a high index of suspicion to ensure timely diagnosis, which may be complicated by the lack of specialised diagnostic and treatment resources in rural and remote Australia.

Box – Digital subtraction angiograms showing cavernous sinus dural arteriovenous fistula

---

The patient's eyebrows are held up and she is asked look to the left (A) — note the injected conjunctivae with tortuous vessels consistent with arterialisation of the veins (arrow). Also shown is a near complete abducens nerve palsy of the left eye with a failure to abduct. There is the impression of left‐sided proptosis. Lateral digital subtraction angiograms of the left common carotid pre‐embolisation (B) and post‐embolisation (C). The arrow in B points out contrast flowing through the cavernous sinus, while in C, post‐embolisation, the cavernous sinus is not opacified, indicating successful obliteration of the fistulous communication. D and E — selective angiograms of the external carotid artery and internal carotid artery, respectively — illustrate contrast progression into the cavernous sinus via dural branches (arrows). ◆