Enlargement of internal carotid artery aneurysm presenting with severe visual sequela: A case report and anatomy review

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1 Optometry (2009) 80, Enlargement of internal carotid artery aneurysm presenting with severe visual sequela: A case report and anatomy review Amanda Mendez Roberts, O.D., and Amy L. Grimes, O.D. Southern Arizona VA Health Care System, Tucson, Arizona. KEYWORDS Intracranial aneurysm; Carotid artery, internal; Optic atrophy; Vision disorders Abstract BACKGROUND: The majority of intracranial aneurysms arise from the internal carotid artery (ICA) circulation. The proximity of cranial nerves II to VI to the pathway of the internal carotid artery make them susceptible to damage from an ICA aneurysm, which may cause a variety of neurologic effects. Although vision loss is a relatively uncommon sequela of an ICA aneurysm, compression of the optic nerve by an aneurysm can cause visual field loss, decreased visual acuity, or both. CASE REPORT: An 85-year-old man with sudden-onset, painless, and profound monocular vision loss from compression of the optic nerve caused by an enlarged internal carotid artery aneurysm is described. Clinical presentation, detection, and treatment of an ICA aneurysm are discussed. CONCLUSIONS: An intracranial aneurysm or other compromise to the cerebral circulation should be ruled out in cases of vision loss that remain unexplained after a thorough ocular health evaluation, especially in patients with a history of cardiovascular disease or head injury. Optometry 2009;80:76-82 An aneurysm is a dilatation of a blood vessel, typically an artery, caused by injury, disease (such as atherosclerosis or sepsis) or congenital defect. 1 Unruptured aneurysms can be divided into 2 major classifications: saccular and fusiform. Saccular aneurysms are rounded, focal dilatations of the arterial lumen arising from bifurcations. 1 They can be caused by congenital vascular abnormalities, trauma, infection, tumor, or drug abuse, and can be associated with high-flow states (such as those caused by arteriovenous malformations), polycystic kidney disease, fibrovascular muscular dysplasia, connective tissue disease (e.g., Marfans, Ehlers-Danlos), and coarctation of the aorta. 1 Fusiform aneurysms are arterial ectasias thought to be formed Corresponding author: Amy L. Grimes, O.D., 3601 S. 6th Avenue (2-112A), Tucson, Arizona amy.grimes@va.gov from a severe type of atherosclerosis. 1 These aneurysms may involve a considerable length of the artery. 1 Approximately 85% of intracranial aneurysms arise from the carotid circulation, including the internal carotid artery (ICA) and its terminal branches: anterior cerebral, anterior communicating, posterior communicating, and the middle cerebral arteries. 1 The internal carotid artery enters the skull through the carotid canal in the petrous portion of the temporal bone, then runs anteriorly along the medial wall through the cavernous sinus. It then turns to exit through the roof of the sinus, piercing the dura mater to enter the cerebrum proper. As it ascends, it runs laterally to cranial nerve II and medially to cranial nerve III, and sends a branch to supply the eye (the ophthalmic artery) as it passes medial to the anterior clinoid process of the sphenoid bone. 2,3 At its terminus, it branches into the anterior cerebral, middle cerebral, and posterior communicating arteries as they, along with branches from the /09/$ -see front matter - This is a U.S. government work. There are no restrictions on its use. Published by Elsevier, Inc. on behalf of the American Optometric Association. doi: /j.optm

2 Mendez Roberts and Grimes Clinical Care 77 vertebro basilar circulation, form the circle of Willis that encompasses the optic chiasm 2 (see Figure 1). Intracranial aneurysms can cause damage by different mechanisms. They can compress (leading to cranial nerve palsies), thrombose (leading to cerebral, ocular, or brainstem infarction), or rupture (leading to hemorrhagic stroke). 1 Hemorrhagic stroke is the gravest of complications due to its high rate of morbidity and mortality. However, many other sequelae can arise before rupture, depending on the size and location of the aneurysm. Cranial nerves II VI can be compressed by a cavernous ICA aneurysm, with the abducens and oculomotor nerves being most commonly affected. 4 Vision loss can occur from involvement of the optic nerve, chiasm, or optic tracts. The pattern of visual loss should provide a clue as to where the lesion lies because the main cause of visual dysfunction from an unruptured aneurysm is usually direct compression. However, mass effect can cause the blood supply to the optic pathway to be compromised, and indirect compression onto bony structures may also affect the pattern of visual dysfunction. 4,10 Aneurysms can be visualized by magnetic resonance imaging (MRI), computed tomography (CT), and angiography. Angiography is the accepted standard for identification of intracranial aneurysms. Over the last decade, noninvasive approaches to angiography, such as CT angiography (CTA) and magnetic resonance angiography (MRA), have developed a role in detecting aneurysms. 5 Traditional catheter angiography is still the gold standard for definitive diagnosis and preoperative delineation of aneurysms. 1,6 However, the accuracy of CTA has been found to approach that of catheter angiography and can been used in place of catheter angiography in certain cases. 5 MRA may also be used, as recently developed sequences allow for successful detection of the size and orientation of an aneurysm. 1 Despite advances in imaging technology, the sensitivity of both MRA and CTA in detecting cerebral aneurysms decreases significantly when the aneurysm is less than 5 mm in diameter. 5 It is also known that small aneurysms of the paraclinoid ICA can be difficult to visualize because of the complex anatomy of the region. 6 The appearance of an aneurysm varies by type of imaging used. An unruptured aneurysm on MRI can appear hyperor hypointense (depending on flow characteristics and pulse sequences used), and lumen flow can be visualized. 1 An unruptured aneurysm on CT scan will appear as a slightly hyperdense mass. 1 Both MRI and CT can be useful diagnostic tools because they show the aneurysm in relation to other structures. The type of an ICA aneurysm most likely to cause vision loss involves the paraclinoid (also referred to as supraclinoid or carotid-ophthalmic) segment of the ICA, which is the segment that runs between its exit from the cavernous sinus and its terminus at the Circle of Willis. Surgical treatment of these aneurysms can be difficult because of the proximity of cranial nerves and other fragile structures in this location. 7-9 Treatment of intracranial aneurysms can Figure 1 Course of the major intracranial arteries (including the internal carotid and its branches) in relation to cerebral architecture. Reprinted with permission from Beers MH (ed). The Merck Manual of Diagnosis and Therapy, ed 18.; Whitehouse Station, NJ: Merck & Co, Inc., 2006:1790. Available at: be separated into 2 broad categories: surgical repair and endovascular treatment. Surgical repair consists of performing a selective craniotomy to reveal the aneurysm and placing a clip at its neck to occlude flow into the aneurysm. If the aneurysm is deemed unclippable, trapping the aneurysm may be necessary. 9 This includes performing a bypass and occluding the aneurysm on both ends by either clipping or ligation. For paraclinoid aneurysms, a fronto temporal craniotomy is performed in which the roof of the orbit is also removed during the procedure. 9 Often the optic nerve canal and the anterior clinoid process must be resected. Also, the optic nerve dural sheath is opened to prevent injury during the procedure. 9 A review of 21 recent and older reports by Thornton et al. 7 regarding surgical clipping outcomes of paraclinoid aneurysm reports varying outcomes of 0% to 80% mortality rate and up to 20% morbidity rate, although 3 more recent (1990 to 1999) studies show mortality rates ranging from 1% to 4% and morbidity rates of 12% to 28%. 7 Their recent study of endovascular treatment of paraclinoid aneurysms, involving 71 aneurysms, showed 2.2% mortality and 3.3% morbidity, of which 2.2% were visual deficits from emboli to the retinal artery. 7 Endovascular treatment of an intracranial aneurysm

3 78 Optometry, Vol 80, No 2, February 2009 involves catheterization of the artery and may use detachable balloons to occlude the artery harboring the aneurysm or, more favorably, use detachable electrocoils to close off an aneurysm while preserving the parent vessel. 12 Although endovascular coiling is somewhat safer than surgical clipping, clipping can be more durable. 1 Regardless of treatment type, deciding whether to treat an intact paraclinoid aneurysm is a complex decision that takes into account the patient s age, overall health, symptoms, and the size and morphology of the aneurysm. 1 Case report An 85-year-old white man presented to our clinic with a chief concern of the inability to see out of his left eye, which had occurred upon awakening 7 months prior. The sudden vision loss was painless and had not improved. He noted no associated symptoms. His pertinent ocular history included moderate cataracts and mild nonexudative age-related macular degeneration (ARMD-NE) in both eyes (OU). His medical history was remarkable for hypertension, hyperlipidemia, prostate cancer, and cerebrovascular accident (CVA) 2 years before, which affected his left motor function. The MRI of his brain taken after the CVA found a large (1.2-cm anterior-posterior! 2.0-cm transverse) fusiform aneurysm of the paraclinoid left ICA, a smaller (1.3 cm) fusiform aneurysm of the paraclinoid right ICA, an acute cortical infarct involving the Rolandic distribution of the right middle cerebral artery, and extensive bilateral microangiopathic ischemic changes (see Figure 2). Upon examination, his best-corrected visual acuity (BCVA) was 20/50 in the right eye (O.D.) with standard Snellen acuity testing and 2/400 in the left eye (O.S.) with Feinbloom acuity cards tested at 2 feet (BCVA 1 year before was 20/40 O.D. and 20/50 O.S. with decreased acuity attributed mostly to moderate cataracts OU). Pupil testing found a mild afferent pupillary defect (APD) O.S., which was not noted on previous records. Extraocular motility was full and without pain. Confrontation visual fields (CVF) showed a right superior quadranopsia O.D. and O.S., not previously documented at previous eye examinations when he was tested with CVF and Amsler grid. Goldmann applanation tonometry was 15 mmhg O.D. and 16 mmhg O.S. Dilated eye examination found 2-31 nuclear sclerotic cataract with cortical vacuoles OU, mild macular drusen and mottling OU, and a cup-to-disc ratio (C/D) of 0.45 O.D. with no pallor (stable to last year) and 0.65 O.S. with mild generalized pallor (0.55 with no pallor was noted last year). Mild progression of the cataract explained the mild decrease in acuity O.D. The patient s present illness (severe, persistent vision loss noted upon awakening), medical history (hypertension, hyperlipidemia), and demographic (elderly male) seemed most consistent with a nonarteritic anterior ischemic optic neuropathy (NAION) occurring 7 months before. However, considering the patient s history of prostate cancer and Figure 2 T2-weighted axial MRI taken 2.5 years before presenting with severe vision loss O.S. highlighting a large fusiform aneurysm of the left internal carotid at the level of the chiasm (arrow). It is important to note that at this time the patient had no visual complaints. bilateral ICA aneurysms, optic atrophy from metastasis or enlargement of the aneurysm affecting the left optic nerve or chiasm needed to be ruled out. Therefore, an MRI of the brain was ordered. The MRI found that there had been an interval increase in the size of the previously noted left ICA aneurysm. The aneurysm now measured 1.9 cm anterior-posterior, 2 cm transverse, and 2.8 cm cranio caudal, and appeared to be exerting significant mass effect on the prechiasmal portion of the left optic nerve accounting for visual loss in the left eye (see Figure 3). The right ICA aneurysm appearance was relatively stable, and the right optic nerve appeared free of any significant mass effect. The diffuse ischemic findings in the brain remained stable, and there was no evidence of metastasis. The radiologist also noted that the recent enlargement of the left ICA aneurysm increased its likelihood of rupture and recommended an immediate neurosurgery consult for possible endovascular treatment. The patient and his daughter consulted with the neurosurgeon the day after receipt of the MRI report. They decided against surgical clipping of the aneurysm but were open to the potential of an endovascular coiling procedure. Thus, a consult to interventional radiology for cerebral angiography and discussion of possible treatment were scheduled. The bilateral internal carotid angiogram confirmed a fusiform aneurysm on each side. The angiogram showed both aneurysms extending from the level of the cavernous sinus to the terminus at the bifurcation with the anterior

4 Mendez Roberts and Grimes Clinical Care 79 Figure 3 T2-weighted axial MRI image shows enlargement of the left internal carotid aneurysm at the level of the chiasm (yellow arrow), taken after presenting with severe vision loss O.S. Note the significant lateral displacement of the left optic nerve (red arrow) from the mass effect of the aneurysm pushing on the optic nerve. cerebral and middle cerebral arteries (see Figure 4). At the level of the cavernous sinus, the right aneurysm measured 0.8 cm in diameter and at the terminus reached a diameter of 1.2 cm. The left aneurysm was much larger, with an overall diameter of 0.88 cm at the level of the cavernous sinus expanding to 1.77 cm anterior-posterior! 2.64 cm transverse! 4 cm cranio-caudal at the paraclinoid level (involving its terminus at the Circle of Willis). On review of the angiogram, the neurovascular surgeon concluded that the left ICA aneurysm was too large to be amenable to endovascular treatment. Together with his primary care physician, the patient decided against undergoing any attempt to repair the aneurysm because surgical clipping involved too much risk (based on size and location of the aneurysm as well as the patient s age), and the aneurysm was too large for successful endovascular treatment. After consultation with the neurovascular surgeon, the patient was seen again in the eye clinic 4 months after his initial presentation for vision loss O.S. His BCVA, pupils, and anterior and posterior segments were unchanged from the previous examination. Because confrontation fields showed bilateral visual field defects, a frequency doubling threshold (FDT) visual field N-30 was performed O.D. and O.S. for an estimation of the severity of these defects. It showed an absolute right (nasal) hemianopsia O.S. and an incomplete right (temporal and mostly superior) hemianopsia O.D. (see Figure 5). The patient was educated about Figure 4 Digital subtraction angiogram of the left ICA taken 1 month after the MRI shows enlargement of the aneurysm. Note the overall increased diameter of the ICA lumen at the aneurysm site (arrow) near the terminus of the ICA at the Circle of Willis. his visual field loss and its relation to the aneurysm and was scheduled for Humphrey visual field testing with gaze tracking for confirmation and further delineation of the visual field deficits. However, a Humphrey visual field was not obtained because the patient did not keep his future appointments with the eye clinic. Discussion Cerebral aneurysms can cause a variety of effects on the eye and visual system depending on their size and location. Several case reports in the literature document different types of visual loss from intracranial aneurysm. One such report by Peiris and Ross Russell 10 reports on 19 patients who presented with visual field loss from large intracranial aneurysms of the carotid system. They conclude that although one might expect the ability to predict the type of visual loss based on the location of the aneurysm, it is not that simple. 10 This is not only because the aneurysm may grow in a variety of directions, but also because compression may not be the only factor involved in the vision loss. 10 Traction and indirect pressure on the nerves from the optic foramina as well as distortion or occlusion of the blood supply to the nerves can occur. 10 The group of supraclinoid aneurysms in the Peiris and Ross Russell case series all had bilateral but asymmetric visual field loss and associated headaches. 10 Our patient did not report headaches but had a right superior quadranopsia on confrontation initially. It is important to remember that

5 80 Optometry, Vol 80, No 2, February 2009 Figure 5 Frequency doubling threshold N-30 visual fields show generalized depression O.S. and a right incongruous hemianopsia.

6 Mendez Roberts and Grimes Clinical Care 81 his confrontation fields and Amsler grid test results were unremarkable before his significant vision loss O.S. and subsequent discovery of aneurismal growth. The FDT N-30 test showed an overall depression and absolute right hemianopsia O.S., and a right incomplete (mostly superior) hemianopsia O.D., although the boundaries of the field loss are imprecise because of lack of gaze monitoring and significant loss of central vision O.S. One would expect a full field defect ipsilaterally and a partial superior temporal quadrant defect contralaterally from a lesion affecting the left optic nerve at its junction with the chiasm. Our patient s visual field results did show a generalized depression on the affected side but also an absolute nasal hemianopsia on this side and an incomplete hemianopsia contralaterally. This pattern of incomplete homonymous hemianopsia is characteristic of a lesion affecting the optic tract. (Recall that anterior posterior dimension of our patient s left aneurysm at its terminus with the Circle of Willis, as measured with angiography, was found to be 1.77 cm. The average optic chiasm has an anterior posterior dimension of 0.8 cm. 3 Thus, the aneurysm was large enough to compress the left optic nerve, chiasm, and tract.) Compromise of the blood supply to the optic chiasm may have also been a factor in our patient s visual loss. The chiasm s superior capillary network is supplied by the anterior cerebral and anterior communicating arteries, whereas the inferior network is supplied by the posterior cerebral, posterior communicating, and internal carotid arteries. 3 Because our patient s vision loss was sudden, we postulate that it had an ischemic component, probably from extreme compression of the chiasm from the inferior side and notable distension of the left optic nerve at its junction with the chiasm (see Figure 3). In a case described by Kuzniecky et al., 11 a woman with sudden monocular blindness was found to have an ipsilateral carotid ophthalmic aneurysm that, at the time of surgery, was observed to be distending the optic nerve to such a degree that there was a small hemorrhage on the surface of the optic nerve. 11 In general, early treatment of aneurysms compressing the pregeniculate optic pathway is necessary to prevent permanent visual loss, other severe neurologic deficits, or death. 12 However, treatment of these aneurysms, whether surgical or endovascular, also carries risk of morbidity and mortality. Our patient s left ICA aneurysm was large enough to be categorized as giant (.2.5 cm). In a study by Vargas et al. 12 involving 26 patients with giant cerebral aneurysms causing visual loss, 17 patients suffered visual acuity loss in the most affected eye. Three patients presented with no light perception, 10 had VA of 20/200 to light perception, 4 had 20/40 to 20/160, and 9 had 20/30 or better. 12 Visual field loss occurred in the most affected eye in 25 of 26 patients. 12 In 15 of the 26 patients (58%), visual loss was from a supraclinoid aneurysm. About half of these patients had monocular optic neuropathy, and half of those who had monocular optic neuropathy had field loss in the fellow eye, much like our patient. 12 This study also followed the endovascular treatment of these aneurysms and found that 5 of the 17 patients (29%) who underwent treatment had improvement in visual acuity. Five had improvement in visual field instead of, or in addition to, the VA improvement. Nine (53%) had no improvement. 12 Another case series, reported by Date et al., 4 analyzed their experience treating intracranial aneurysms causing visual symptoms. They had 9 cases of ICA-ophthalmic aneurysms that had visual dysfunction before surgery. All of these aneurysms were either large (1.5 to 2.5 cm) or giant. Five were clipped successfully, 2 underwent ligation instead, and 2 died of hemorrhage before treatment. 4 They found that only those who were treated surgically within 2 months of the onset of visual symptoms had improvement. 4 Considering the reports in the literature, along with our patient s age (85 years), length of time our patient had a visual loss (more than 7 months), and lack of additional severe or progressive symptoms, it was decided that his prognosis for visual recovery would be poor and that the risks of surgical intervention outweighed the potential benefits at this time. Instead, he would be monitored at regular intervals for any signs that may warrant reconsideration of treatment options. Our role as his primary eye care provider is to regularly monitor his visual system for signs of progression and report them to his primary care physician or neurosurgeon. Conclusion An intracranial ICA aneurysm can be a visually devastating condition. It can behave like a space-occupying lesion, compressing the optic nerve and causing slowly progressive visual field or acuity loss; or, less commonly, it can mimic an acute optic neuropathy, quickly diminishing vision (as in our case). A variety of neurologic effects, like headache or periorbital pain, and cranial nerve III or VI palsy, can accompany the visual loss. It is also possible that these neurologic effects may present without visual loss or that visual loss may be the only presenting sign. Much of this depends on the location and size of the aneurysm. A patient with a visual loss or other neuro ophthalmic manifestations, having no discernable cause, should undergo brain imaging to rule out cerebral aneurysm and other potentially treatable intracranial anomalies. References 1. Brisman, JL, Soliman E, Kader A, et al. Cerebral aneurysm. E-Medicine. Available at: htm. 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