22 Ophthalmic Artery Aneurysms
Abstract
Ophthalmic artery aneurysms represent 4% of all intracranial aneurysms and are most commonly discovered incidentally, unless compression of the optic nerve causes visual deficits. These aneurysms have a lower risk of rupture, making it imperative that their treatment is carried out with low morbidity. The anatomical constraints surrounding these aneurysms (e.g., anterior clinoid process, carotid artery, optic nerve) require particular attention when considering microsurgical strategies. The requirement of clinoidectomy and concern surrounding injury to the optic nerve have led to the appeal of endovascular options for the treatment of these aneurysms. Primary coiling, stent- or balloon-assisted coiling, and flow-diverting stents have all been successfully used for occlusion of these aneurysms. In this chapter, we review our decision-making process and discuss the microsurgical and endovascular nuances of the treatment of ophthalmic artery aneurysms.
Introduction
Aneurysms of the ophthalmic artery (also known as carotid-ophthalmic artery aneurysms) are relatively rare, representing approximately 4% of all intracranial aneurysms. They commonly project superiorly and may compress the ipsilateral optic nerve. The challenge in any treatment (e.g., microsurgical or endovascular) is preservation of the ophthalmic and central retinal arteries to maintain vision. While aneurysms of the ophthalmic segment may also include dorsal or ventral wall aneurysms and blister aneurysms (so-called paraclinoid internal carotid artery [ICA] aneurysms), this chapter focuses on management and decision making surrounding aneurysms arising from the junction of the ICA and ophthalmic arteries.
Major controversies in decision making addressed in this chapter include:
Whether or not to pursue treatment or observation.
If treatment is pursued, whether to use open microsurgical versus endovascular techniques.
The fate and clinical consequences of the ophthalmic artery following endovascular treatment with flow diversion.
Visual outcomes after endovascular and microsurgical treatment for aneurysms presenting with visual symptoms.
Whether to Treat
Acutely ruptured intracranial aneurysms, including those of the ophthalmic artery, require urgent treatment in the vast majority of cases ( 1 in algorithm ). Exceptions to this include very elderly and moribund patients who may not tolerate intervention. With the advent of endovascular therapies, however, elderly patients who may not have been candidates for surgical aneurysm treatment still may be able to tolerate endovascular occlusion.
The risk and prevention of rupture is central to the decision-making process of any unruptured, asymptomatic intracranial aneurysm. In addition to being rare aneurysms, ophthalmic artery aneurysms are very infrequent causes of subarachnoid hemorrhage (SAH). Aneurysms of the “proximal or ophthalmic region” of the ICA constituted only 1.4% of aneurysms in the International Subarachnoid Hemorrhage Trial (ISAT). Similarly, the risk of rupture of ophthalmic artery aneurysms from several series in the literature ranges from 0 to 3%. While these are exceedingly low rates of rupture and must be taken into account when evaluating ophthalmic artery aneurysms, one must not neglect the devastating (often lethal) consequences of aneurysm rupture ( 2, 3, 4 in algorithm ).
Ophthalmic artery aneurysms are most often discovered incidentally. One of the most common symptoms prompting investigations that reveal ophthalmic artery aneurysms is retro-orbital headache. However, one study reported ophthalmologic findings in 27.8% of patients with these aneurysms. Given their infrequent rate of rupture, they may reach significant size before coming to clinical attention through compression of adjacent neural structures and subsequent visual disturbance. In one series reported by Drake, visual disturbance occurred in 32% of patients—visual field abnormalities were present in all of these patients, while visual acuity was affected in all, but one. Satisfactory visual results were observed in 83% of patients. Given the importance of vision to quality of life, the presence of visual symptoms (or development of visual symptoms in a previously asymptomatic patient) warrants a more aggressive management strategy ( 2, 3, 4, 5 in algorithm ).
Ophthalmic artery aneurysms are rare and infrequent causes of SAH. While ruptured ophthalmic artery aneurysms always warrant treatment, management of unruptured aneurysms requires judicious review of risks and benefits of treatment. Although aneurysm size, patient life expectancy, and preference are considerations in the management of asymptomatic, unruptured ophthalmic aneurysms, we aggressively pursue treatment in patients presenting with visual symptoms ( 2, 3 in algorithm ).
Conservative Management
Patients found to have unruptured, incidentally discovered (i.e., asymptomatic) ophthalmic artery aneurysms are counseled regarding the treatment options with consideration of the low risk of rupture. Multiple factors are considered, including the patient′s life expectancy, visual symptoms, medical comorbidities, family history, aneurysm size, and patient preference ( 2, 3, 4, 5 in algorithm ). Given the proximity of surrounding neural and osseous structures, these aneurysms may be incompletely visualized on noninvasive imaging studies (e.g., computed tomography angiography [CTA] or magnetic resonance angiography [MRA]). Therefore, we advise patients to undergo digital subtraction angiography (DSA) for evaluation of any ophthalmic artery aneurysm discovered on noninvasive imaging. While we follow these aneurysms noninvasively, any development of symptoms or change in appearance on noninvasive imaging is evaluated with DSA.
Anatomical Considerations
Aneurysms of the ophthalmic artery, or carotid-ophthalmic junction, are superiorly projecting aneurysms that develop at the site of maximal hemodynamic thrust as the superior directed intracavernous ICA turns posteriorly. The ophthalmic artery arises from the ICA below the optic nerve. Its short intradural length makes its origin difficult to expose. Rarely, the ophthalmic artery may arise from the clinoidal or cavernous segments of the ICA. Therefore, the surgical anatomy of ophthalmic artery aneurysms and their relationship with surrounding dural and osseous structures vary depending on the origin and course of the ophthalmic artery. We suggest the reader review the extremely descriptive anatomical work of Albert Rhoton et al.
The ophthalmic artery usually arises below the optic nerve from the medial third of the superior surface of the ICA. Mobilization of the optic nerve is often required to expose the ophthalmic artery origin and associated aneurysms. Removal of the anterior clinoid process and orbital roof permits this mobilization. The falciform ligament is a fold of dura that extends medially from the anterior clinoid process to the tuberculum sellae, covering the optic nerve. Therefore, its incision is also required for optic nerve mobilization. If the aneurysm neck is still not well visualized following these techniques, mobilization of the carotid artery can be pursued. Division of the upper and lower dural rings can help mobilize the carotid artery.
Whether endovascular or microsurgical treatment is pursued, critical review of preoperative imaging studies is essential to the successful treatment of ophthalmic artery aneurysms.
Workup
Clinical Evaluation
SAH is a rare presentation of ophthalmic artery aneurysms, representing only 1.4% of aneurysms in the ISAT. Patients presenting with visual symptoms often have already undergone formal ophthalmologic workup. However, those who have not are referred for formal visual field and visual acuity testing. Asymptomatic patients are counseled to inform us of the development of any visual symptoms. The development of visual symptoms in a patient with a known ophthalmic artery aneurysm should raise concern for aneurysm enlargement and appropriate workup and treatment should be pursued (discussed later; 2, 3 in algorithm ).
Imaging
Patients routinely undergo DSA for evaluation of the aneurysm. Follow-up imaging is often performed noninvasively. However, any change (or concern for change) in the noninvasive imaging is evaluated with DSA.
Differential Diagnosis
Unique to ophthalmic aneurysms is their inclusion in the differential diagnosis for disturbances in visual fields and visual acuity. While ophthalmologic symptoms are idiosyncratic to aneurysms in this location, like cerebral aneurysms in other locations, many series in the literature report the discovery of ophthalmic artery aneurysms during the workup for chronic headaches.
Treatment
Cerebrovascular Treatment—Operative Nuances
As with any cerebrovascular operation, superb knowledge of the anatomy is critical to the successful microsurgical management of ophthalmic artery aneurysms (▶ Fig. 22.1 ). Review of preoperative imaging studies is critical to operative success. Balloon test occlusion is also useful in the planning of microsurgical treatment of unruptured aneurysms. Given the often crowded surrounding environment of the aneurysm neck, the presence of neck calcification/plaque is critical to recognize since the ability to manipulate clip placement may be compromised.
Hybrid procedures utilizing both endovascular and microsurgical techniques may be particularly well suited for the treatment of ophthalmic artery aneurysms. The intimate relationship of the aneurysm and proximal parent vessel (i.e., ICA) with dural and osseous structures can make obtaining proximal control challenging (▶ Fig. 22.2 ). Traditionally a separate cervical ICA exposure was necessary to obtain proximal vascular control in complex cases. More recently, endovascular proximal control via balloon occlusion of the petrous ICA is becoming a more popular preference. Additionally, intraoperative angiogram provides immediate angiographic feedback regarding clip placement and parent vessel/branch vessel patency. Though yet commonplace, the addition of endovascular strategies may complement conventional microsurgical techniques.
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