These changes are rare. The most important and most frequently encountered disorder in this group is pulsating exophthalmos.
Acute exophthalmos with palpable and audible pulsations synchronous with the pulse in the presence of a cavernous sinus fistula or arteriovenous aneurysm.
An abnormal communication between thecavernous sinusand theinternal carotid artery (a direct shunt) or its branches (indirect shunt) resultsin distention of the orbital venous network. Eighty per cent of all cases are attributable to trauma; less frequently the disorder is due to syphilis or arte-riosclerosis.
Patients report an unpleasant sound in the head that is reminis-cent of a machine and synchronous with their pulse.
The increased venous pressure leads todilationof the episcleral and conjunctival vessels (Fig. 15.7), retinal signs of venousstasis with bleeding, exudation, and papilledema. Intraocular pressure is also increased. The increased pressure in the cavernous sinus can also result in oculomotor and abducent nerve palsy.
Sounds near the direct fistula are clearly audible with a stethoscope.
Doppler ultrasound studies can confirm a clinical suspicion. However, only angiography can determine the exact location of the shunt.
Selective embolization may be performed in cooperation with aneuroradiologist once the shunt has been located.
Small shunts may close spontaneously in response to pressure fluctua-tions such as can occur in air travel.