Sir,

A 65-year-old gentleman noticed blurred vision in his left eye after spraying a cleaning liquid. It was 6/5 and 6/12 in right and left eyes, respectively. Since he had iritis, G. Maxidex was advised 2 hourly in the left eye.

During the follow-up, redness, chemosis, and arterialisation of conjunctival vessels were noted. He had also noticed an occasional swishing noise in the head. The eyes were quiet with no proptosis. Intraocular pressure (IOP) was 12 in right and 28 in left eye. Bruit, however, was not heard initially; but became evident in left lateral position with a Valsalva manoeuvre.

Hence, we suspected a left caroticocavernous fistula. A carotid angiography confirmed left type D dural caroticocavernous fistulas (Figures 1 and 2).1 They closed spontaneously the following year.

Figure 1
figure 1

Angiogram of the left internal carotid artery showing filling of the dural cavernous fistula, with early shunting of the blood into the cavernous sinus (arrow), from the cavernous part of the internal carotid artery.

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Figure 2
figure 2

Angiogram of the left external carotid artery showing early filling of the superior ophthalmic vein (arrow 1) from the dural branches of the middle meningeal artery (a branch of the external carotid artery). It also shows filling of the dural caroticocavernous fistula (arrow 2).

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Dural fistulas are difficult to diagnose. They lack a history of trauma. Redness is absent in a third, bruit in a half, proptosis in 80%, and ocular pulsation in almost all cases.2 IOP is raised only in 38% of all fistulas.3 Hence, noninvasive investigations like ultrasound B scan, CT, MRI, intravenous digital subtraction angiography, and colour Doppler are advised. However, they involve a waiting period and are inconclusive. Although hazardous, carotid angiography is decisive.

A simple clinical test that screens the patients for angiography is useful. A difference in IOP between systole and diastole of more than 1.6 between the eyes is 100% sensitive and 93% specific of caroticocavernous fistulas.4 This requires a pneumo, contact lens, or dynamic tonometer, which are not universally available.5 Standard tonometers are useful if there is a wide fluctuation.6

Another clinical sign, bruit, is heard in arteriovenous communications, Paget's disease, vascular meningioma, carotid and aortic stenosis, and normal individuals.

A bruit can be made audible by worsening the turbulence by increasing the flow through the fistula.

Valsalva manoeuvre increases the flow through the internal carotid artery by 56.5% and supine position redistributes blood from the lower limbs.7 This explains why the bruit became evident later. Hence, eliciting bruit in a doubtful case is helpful, but its predictive value needs to be determined.