24 Anterior Choroidal Artery Aneurysms
Abstract
Anterior choroidal artery (AChA) aneurysms account for only 2 to 5% of all intracranial aneurysms. Although the frequency of these aneurysms is relatively low, their importance in relation to the critical territory supplied by the AChA is especially high. AChA aneurysms could be classified according to their origin in relation to the AChA origin to anterior (obscuring the AchA origin), superior (above the AChA origin), posterior (behind the AChA origin), or more complex (between duplicated AchA or with other AChA variations). Distal AChA aneurysms are extremely rare, usually small, and often associated with Moyamoya disease, infection, trauma, or arteriovenous malformation (AVM). When an AChA aneurysm presents with subarachnoid hemorrhage (SAH), the most important factor is to distinguish an AChA aneurysm from a posterior communicating artery (PCoA) aneurysm. This distinction can sometimes be done based on computed tomography angiography (CTA). However, cerebral angiogram (digital subtraction angiography [DSA]) with precise three-dimensional (3D) reconstructions is strongly recommended to properly assess anatomical variations and aneurysm morphology, especially the relationship of aneurysm dome and AChA origin. Overall outcome after treatment of AChA aneurysm, regardless of the treatment modality, is slightly worse than in other aneurysm locations. The reason for this outcome is that parent vessel injury/occlusion almost invariably leads to disastrous neurological deficits. As in cases of other intracranial aneurysms, radiological and clinical follow-ups are necessary. An optimal approach is to perform catheter angiography during the same hospitalization after surgical treatment. After endovascular treatment, a final angiogram posttreatment is routine.
Motto: PCoA—the most forgiving artery, AChA—the most unforgiving artery; only 2 mm between the two.
Introduction
Anterior choroidal artery (AChA) aneurysms account for only 2 to 5% of all intracranial aneurysms. Although the frequency of these aneurysms is relatively low, their importance in relation to the critical territory supplied by the AChA is especially high. Injury to the AChA during surgical or endovascular securing of the AChA aneurysm usually causes debilitating neurological deficits (AChA syndrome), including dense hemiparesis, visual field defect, hemianesthesia, or aphasia. In this section, we attempt to deal with an optimal way to treat these aneurysms together with a discussion of complications and their avoidance.
Major controversies in decision making addressed in this chapter include:
Whether or not treatment is indicated.
Identifying AChA aneurysms.
Open surgical or endovascular procedure.
Whether to Treat
According to the International Study of Unruptured Intracranial Aneurysms (ISUIA), small aneurysms (<7 mm in diameter) of the internal carotid artery (ICA) have a 0% 5-year cumulative probability of bleeding in patients without previous subarachnoid hemorrhage (SAH) and a 1.5% 5-year cumulative probability in patients with previous SAH. However, the ISUIA study was not designed specifically to study AChA aneurysms. In one retrospective study based on a review of 747 patients with 1,013 aneurysms, 30 AChA aneurysms were investigated. Of these 30 aneurysms, only 8 (27%) presented with rupture. In comparison with all other locations of intracranial aneurysms, the odds ratio (OR) for rupture presentation was 0.74 (confidence interval [CI], 0.33–1.69; 1 , 2 in algorithm ). It is of interest that these aneurysms lie within their rupture proportion somewhere in between posterior communicating artery (PCoA) aneurysms (OR, 1.77; CI, 1.24–2.53) and other internal carotid (ICA) aneurysms (superior hypophyseal artery aneurysms: OR, 0.12; ophthalmic artery aneurysms: OR, 0.33; ICA bifurcation aneurysms: OR, 0.33). A similar observation was made in the Japanese unruptured cerebral aneurysm (UCAS) study in which non-PCoA ICA aneurysms were grouped together and their OR of rupture against middle cerebral artery (MCA) aneurysms was 0.43 (CI, 0.18–1.01). The annual rupture rate for these aneurysms was 0.14% (CI, 0.04–0.57%) for aneurysms 3 to 4 mm in diameter, 0% for 5 to 6 mm, 1.19% (CI, 0.30–4.77%) for 7 to 9 mm, 1.07% (CI, 0.27–4.28%) for 10 to 24 mm, and 10.61% (CI, 1.49–75.3%) for larger aneurysms. Thus, AChA aneurysms are regarded as low to medium risk. In addition to the case of unruptured AChA aneurysms, other variables that should be considered are age, overall clinical status, family history, aneurysm size (which is usually small in these aneurysms), geometry, presence of associated aneurysms, and patient preference ( 1 , 2 in algorithm ).
Anatomical Considerations
The AChA arises from the communicating segment of the supraclinoid ICA on its posteromedial wall. Its origin is only a few millimeters above and slightly lateral to the origin of the PCoA, usually closer to the PCoA than to the carotid bifurcation. In approximately one-third of the cases, there could be one or two small perforator arteries from nearby structures arising between the origins of the PCoA and AChA. From its origin, the AChA extends posteromedially through cisterns toward the cerebral peduncle, where it turns laterally to the choroid fissure and temporal horn of the lateral ventricle. Thus, the AChA divides into cisternal and plexal segments by the inferior choroidal point. During its cisternal course, the AChA supplies important structures, such as the optic tract, medial temporal lobe structures, posterior limb of the internal capsule, globus pallidus, geniculate body, and cerebral peduncle. Anastomoses with posterior cerebral artery (PCA) branches often appear after the plexal point, where the cisternal segment curves in an acute angle laterally into the choroid fissure. The AChA often anastomoses with posteromedial and posterolateral choroidal arteries. After entering the temporal horn, the AChA follows the choroid plexus, supplying it, sometimes up to the level of the foramina of Monro. The region supplied by the cisternal segment of the AChA is highly variable and, because of the presence of anastomoses, occlusion of the AChA origin is not necessarily disastrous. However, the effect is unpredictable and the occlusion most likely leads to severe AChA syndrome. The above-mentioned anastomoses are able to feed the distal (plexal) territory but are unable to supply the cisternal portion that behaves as a perforating artery. The AChA varies in diameter and could be formed by a rich plexus of small vessels instead of one artery. From other variations, duplicated AChA or only a short single vessel immediately dividing into two branches can be seen. The hyperplastic AChA usually supplies parts of the PCA territory. An ectopic origin (1–4%) of the AChA could be from the PCoA or the MCA. The most important (although very rare) anomaly is probably the AChA origin proximal to the PCoA, which needs to be evaluated on a preoperative cerebral angiogram to avoid the risk of complications during surgery.
Classification
AChA aneurysms could be classified according to their origin in relation to the AChA origin to anterior (obscuring the AchA origin), superior (above the AChA origin), posterior (behind the AChA origin), or more complex (between duplicated AChA or with other AChA variations). Distal AChA aneurysms are extremely rare, usually small, and often associated with Moyamoya disease, infection, trauma, or arteriovenous malformation (AVM).
Workup
Clinical Evaluation
As in other intracranial aneurysms, the frequency of incidental findings of AChA aneurysms is increasing. This fact, together with a relatively lower frequency of hemorrhagic presentation of AChA aneurysms compared with PCoA or anterior communicating artery (ACoA) aneurysms, leads to the frequent treatment of unruptured AChA aneurysms. Hemorrhagic presentation is encountered in approximately one-third of the cases with an AChA aneurysm. As AChA aneurysms are only rarely large or giant, a mass effect presentation is improbable. Third nerve palsy, rather often seen in PCoA aneurysms, is rarely a presentation of AChA, mainly because of its smaller aneurysm size and frequent downward direction. Infarction in AChA territory could occur on the top of SAH.
Imaging
When an AChA aneurysm presents with SAH, the most important factor is to distinguish an AChA aneurysm from a PCoA aneurysm. This distinction can sometimes be done based on computed tomography angiography (CTA). However, cerebral angiogram (digital subtraction angiography [DSA]; ▶ Figs. 24.1 – 24.4 ) with precise three-dimensional (3D) reconstructions is strongly recommended to properly assess anatomical variations and aneurysm morphology (▶ Fig. 24.2 ), especially the relationship between aneurysm dome and AChA origin. Another reason for complete four-vessel DSA is that approximately half of the patients with an AChA aneurysm have another associated aneurysm, most frequently the PCoA or MCA.
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