This article reviews nonsaccular intracranial aneurysms, including fusiform and dolichoectatic intracranial aneurysms. Fusiform and dolichoectatic aneurysms occur in any of the intracranial arteries but particularly in the vertebrobasilar and internal carotid arteries. They can be detected incidentally or present with neurologic complications including ischemic stroke, intracranial hemorrhage, or compression of surrounding neural structures. Treatment of these life-threatening aneurysms must be individualized and can be challenging. Surgical approaches are sometimes feasible. Increasingly, novel endovascular techniques, including placement of flow-diverting stents and stent-assisted coiling, can successfully treat these aneurysms.
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• Fusiform (nonsaccular) aneurysms are elongated dilations of intracranial arteries lacking a distinct neck. Dolichoectasia can be used as interchangeable term but can also describe a less severe spectrum of arterial dilation and/or tortuosity. Fusiform and dolichoectatic aneurysms can occur sporadically, or in association with atherosclerosis, arteritis, connective tissue disorders, and underlying hereditary conditions.
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• The abnormal dilation of the blood vessel results from the fragmentation of the internal elastic lamina, atrophy of the smooth muscle layer, and connective tissue hyalinization.
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• Fusiform and dolichoectatic aneurysms can present with ischemic strokes, intracranial hemorrhage, or symptoms related to compression of cranial nerves or brain structures, but they are also often asymptomatic and detected incidentally.
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• Management of these aneurysms is challenging, but individualized surgical and endovascular approaches, selectively applied to symptomatic or larger aneurysms, can be effective in preventing growth or rupture.
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• Application of advanced endovascular techniques, including flow-directing stents and stent-assisted coiling, has increasingly allowed successful treatment of complex nonsaccular aneurysms.
Historical note and terminology
The first description of abnormal elongated and dilated intracranial vessels is attributed to the Italian anatomist Giovanni Battista Morgagni in his text “De sedibus, et causis morborum per anatomen indagatis libri quinque” in 1761 (39). Before the introduction of cerebral angiography and modern imaging techniques, autopsy studies provided the main source of information about intracranial aneurysms (23). Moniz provided the first angiographic demonstration of a dolichoectatic aneurysm in 1934, but Dandy had previously described the clinical condition in 11 instances in the vertebrobasilar circulation and in 6 instances in the internal carotid artery circulation (38; 08).
An aneurysm is a pathologic, localized blood vessel dilatation, which is called “saccular” when the inflow and outflow points are in common and “nonsaccular” when arterial dilatation is greater than 1.5 times normal without a clearly defined neck (ie, the inflow and outflow points are longitudinally separate) (14). Fusiform aneurysm is a morphological term utilized for the “nonsaccular” type that denotes a circumferential ballooning of the vessel for a short segment, often with a spindle shape. Dolichoectasia comes from the Greek dolikhos meaning long and ektasis meaning distention of a tubular structure. Intracranial arterial dolichoectasia describes the presence of at least 1 ectatic and/or tortuous artery in the cerebral vasculature, usually with a uniform enlarged circumference (46). Conceptually, the terms fusiform aneurysm and dolichoectasia overlap, and some authors use them interchangeably, but important differences in their clinical features and morphology can be distinguished. A third subtype, “transitional,” has been proposed, which features focal circumferential dilatation, elongation, and displacement.
Classically, 2 forms of nonsaccular aneurysms are separated by their pathophysiology: (1) acute dissecting and (2) chronic fusiform or dolichoectatic aneurysms (41). Acute dissecting aneurysms will not be addressed in this article.
Additional names for nonsaccular intracranial aneurysm include basilar ectasia, S-shaped aneurysm, wandering basilar artery, tortuous basilar artery, cirsoid aneurysm, megadolichovascular malformation, megadolichobasilar artery, dolichomegavertebralis anomaly, and aneurysmal malformation (14). Aneurysms greater than 2.5 cm in diameter are referred to as "giant" (19). When a giant aneurysm partially thromboses, leaving tortuous vascular channels, it is called a “giant serpentine” aneurysm (54). In the past, the term “atherosclerotic aneurysm” was often applied to these vascular malformations; however, the cause-effect relationship between underlying atherosclerosis and dolichoectatic aneurysms remains to be elucidated, and the term should be avoided. Notably, the trend in study of dolichoectatic and fusiform aneurysms focuses on dilatation as the main pathologic feature, and consequently, the term “dilatative arteriopathy” has gained currency (31).