Aneurysms of the internal carotid arteries involving the portion of the vessel contained within the cavernous sinus pose different risks and often are managed differently from other intracranial aneurysms. Unlike other cerebral aneurysms, these lesions usually are contained by the dura of the cavernous sinus outside the subarachnoid space. Therefore the risk of subarachnoid hemorrhage from these lesions is exceptionally low.
Cavernous sinus aneurysms are most common in the elderly population and often present with an indolent ophthalmoplegia. The morbidity of these aneurysms is limited, and many patients do not require treatment. However, in selected patients, endovascular occlusion is an option. It is important to note that cavernous sinus aneurysms are not malignant lesions, and the majority are asymptomatic. Hence good clinical judgment is required in the management of these lesions.
The exact cause of cavernous sinus aneurysms is not known, but experts believe that it may be a combination of degenerative changes in the tissues. These aneurysms are not associated with atherosclerosis, smoking, or hypertension.
Cerebral aneurysms are more common in women than men, and this holds true for aneurysms in the cavernous sinus, a common site for aneurysm formation. Aneurysms, as demonstrated by van Rooij et al. 2006, represent a small percentage of treated cerebral aneurysms (2.7% in their study) given the differences in indication for treatment and subarachnoid hemorrhage risk from aneurysms in other locations.
If ruptured, cavernous aneurysms most commonly cause direct carotid-cavernous fistulas, though they may also cause massive epistaxis if there is erosion into the sphenoid sinus or subarachnoid hemorrhage if there is an extension through the dural ring into the subarachnoid space. However, the most common symptoms from these aneurysms are as a result of a mass effect on the adjacent cranial nerves. Many cavernous carotid aneurysms present without symptoms as incidental findings or with only mild symptoms and require no treatment.
Stiebel-Kalish et al. 2005 reported the most common symptoms at presentation as diplopia (65%), pain (59%), asymptomatic incidental finding (12%), and optic neuropathy with decreased vision (8%). Abnormal neurologic and ophthalmologic examination findings included cranial neuropathies of cranial nerves (CN) III, IV, VI, Horner syndrome, compressive optic neuropathy, CN V dysesthesia, and abnormal corneal reflex. Also, van Rooij et al. 2006 found that, out of 41 symptomatic cavernous aneurysms, 68% presented with visual symptoms or ophthalmoplegia, 24% with a cavernous carotid fistula, 5% with subarachnoid hemorrhage, and 2% with epistaxis.
Evaluation of cavernous aneurysms, as well as other intracranial aneurysms, usually can be evaluated with noninvasive CT or MR angiography. Conventional digital subtraction angiography, however, remains the gold standard for aneurysm detection and anatomic characterization.
Small asymptomatic cavernous sinus aneurysms less than 12 mm do not need emergent treatment. Most small aneurysms have a benign history and a very low risk of rupture. Lesions that are observed should be followed with serial CT scan or MRI imaging. A few small series do indicate that thromboembolic events and acute thrombosis may occur in about 2% of asymptomatic patients with cavernous sinus aneurysms. However, if the lesion is unstable, appears to be growing, or the patient is symptomatic, these patients need to be treated.
Proposed indications for treatment of cavernous aneurysms include disabling pain, diplopia/decline in vision, a cavernous carotid fistula as a result of aneurysm rupture, erosion of an aneurysm through the bone into the sphenoid sinus that can result in life-threatening epistaxis, and extension into the subarachnoid space. Strategies for treatment have evolved in recent decades and employ deconstructive or reconstructive strategies. Deconstructive techniques include open surgical or endovascular parent vessel occlusion. This is most safely accomplished following an angiogram with balloon test occlusion study of the affected internal carotid artery demonstrating adequate collateral circulation to compensate for the occluded vessel. If a cavernous carotid fistula is present this study should be performed with the occlusion balloon distal to the aneurysm/fistula to prevent dumping of the collateral circulation through the fistula during the test occlusion which can result in a falsely positive test. Even if the test occlusion demonstrates inadequate collaterals to support permanent occlusion of the vessel parent vessel, sacrifice is still possible if combined with a surgical bypass.
When a cavernous sinus aneurysm ruptures, this constitutes a surgical emergency and requires a experienced neurosurgeon. The type of surgery depends on the location of rupture, the patient comorbidity and age, and availability of endovascular therapy. The majority of ruptured lesions are managed with endovascular techniques.
In the past, reconstructive methods for the treatment of cavernous aneurysms were limited to surgical clip ligation. This often resulted in significant morbidity secondary to the often large size and atherosclerotic nature of these aneurysms as well as the necessary cavernous sinus dissection which put the adjacent cranial nerves and parent vessel at risk. With advances in endovascular technology, aneurysm embolization with vessel preservation is often possible using a combination of detachable aneurysm coils and stents. Flow-diverting stents represent the newest technological advance in the endovascular management of these lesions. The decreased porosity of these devices results in the disruption of blood flow within an aneurysm and, in most cases, gradual aneurysm thrombosis. The long-term follow-up of the PUFS trial (Pipeline Embolization Device for Uncoilable or Failed Aneurysms) showed a 95% 5-year aneurysm occlusion rate with a 5.6% risk of major stroke neurologic death morbidity, all of which occurred within the first six months of treatment for large internal carotid artery aneurysms treated with flow-diverting devices.
Generally, the prognosis is positive.