This article includes discussion of fusiform and dolichoectatic aneurysms, nonsaccular aneurysms, dilatative arteriopathy, basilar artery ectasia, s-aneurysm, and tortuous basilar artery. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.
In this updated article, the author reviews current knowledge about 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 present in a wide variety of ways, ranging from hemorrhage to cranial nerve or brain parenchymal compression to embolic stroke. 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.
• Fusiform and dolichoectatic (nonsaccular) aneurysms can present with hemorrhage, ischemia, or symptoms related to compression of cranial nerves or brain structures, but are also often asymptomatic and detected incidentally.
• Fusiform and dolichoectatic aneurysms can occur from a variety of etiologies, including atherosclerosis, arteritis, connective tissue disorders, and as a primary disorder termed “dilatative arteriopathy.”
• 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.
• 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
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) (Flemming et al 2004). “Fusiform” refers to nonsaccular, spindle-shaped aneurysms with focal circumferential dilatation whereas “dolichoectatic” aneurysms are predominantly elongated and tortuous with a uniform enlarged circumference (dolichos=long; ectasia=distended).Steel et al 1982), but important differences in their clinical features and pathophysiology can be distinguished. A third subtype, “transitional”, has been proposed, which features focal circumferential dilatation, elongation, and displacement. Notably, the recent 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 (Caplan 2005; Lou and Caplan 2010).
Classically, 2 forms of nonsaccular aneurysms are separated by their pathophysiology: (1) acute dissecting and (2) chronic fusiform or dolichoectatic aneurysms (Nakatomi et al 2000). Acute dissecting aneurysms will not be addressed in this article. These aneurysms, as well as those occurring from infection or neoplastic infiltration of the arterial wall, are addressed under separate headings.
Some radiologists describe nondistended tortuous and elongated arteries commonly visualized on CT and MRI as dolichoectatic, but distension is much more closely correlated with hemorrhage than elongation, making the distinction clinically relevant. Aneurysms greater than 2.5 cm in diameter are referred to as "giant" (Wehman et al 2006). When a giant aneurysm partially thromboses, revealing tortuous vascular channels, it is called a “giant serpentine” aneurysm (Segal and McLaurin 1977; Sari et al 2006). Additional names for nonsaccular intracranial aneurysm of the basilar artery include ectasia, S-shaped aneurysm, wandering basilar artery, tortuous basilar artery, cirsoid aneurysm, megadolichovascular malformation, megadolichobasilar artery, dolichomegavertebralis anomaly, and aneurysmal malformation (Flemming et al 2004).
Moniz provided the first angiographic demonstration of a dolichoectatic aneurysm in 1934, but the clinical condition had been previously described by Dandy in 11 instances in the vertebrobasilar circulation and in 6 instances in the internal carotid artery circulation (Moniz 1934; Dandy 1944).
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