A fatal, chronically growing basilar artery: a new type of dissecting aneurysm

Clinicopathological features of non-atherosclerotic cerebral arterial trunk aneurysms

Internal elastic lamina (IEL) is the most vital structure of the cerebral arterial wall. Longstanding weakness of the IEL due to hemodynamic stress is compensated by adaptive intimal thickening. Formation of cerebral arterial trunk aneurysm is assumed to be the result of a break in the equilibrium between hemodynamic stress and the condition of the IEL and intima. Cerebral arterial trunk aneurysms unrelated to the branching zones have several lesional patterns of IEL and the state of intima. There is a strong relationship between the pathological features of aneurysms and their clinical courses. We attempt to delineate the concept of cerebral arterial trunk aneurysms including 'dissecting aneurysms' and 'fusiform aneurysms'.

Pathology of a dissecting intracranial aneurysm

The pathological findings of six autopsy cases of dissecting intracranial aneurysm are studied. Clinically, all cases exhibited systemic hypertension or left ventricular hypertrophy. Macroscopically, all cases exhibited rupture of the vertebral artery and subarachnoid hemorrhage. Two types of lesion were present. First, all cases showed the formation of a dilatated pseudoaneurysm with widespread disruption of the entire arterial wall, which was composed of thin adventitia. Second, a medial disruption of the arterial wall and subadventitial dissecting hemorrhage, which formed a false lumen and stenosis of the 'true' lumen of the artery, was also found. However, these lesions were found to be connected to the site of rupture. The autopsy cases within 1 day of onset of intracranial dissecting aneurysm showed the formation of fibrin thrombus, a marked degree of leukocyte infiltration and necrosis of the arterial wall at the site of the lesion. The cases that survived more than 1 week showed smooth muscle cell proliferation, macrophage accumulation and lymphocytic infiltration. No arteriosclerosis was found in any lesion studied. These data suggest that the disruption of the entire arterial wall might initially occur and cause medial disruption and subadventitial hemorrhage. Hypertension and arteriosclerosis might function as causal and protective factors in the pathogenesis of dissecting intracranial aneurysms, respectively.

Proposed classification of nonatherosclerotic cerebral fusiform and dissecting aneurysms

OBJECTIVE

The aim of this study is to classify nonatherosclerotic aneurysms unrelated to the branching zones (including fusiform aneurysms and dissecting aneurysms).

METHODS

Damage to the internal elastic lamina (IEL) is often an associated factor in the pathogenesis of aneurysm formation. In this study, 85 nonatherosclerotic aneurysms arising from an arterial trunk unrelated to the branching zones were classified into four different types, based on the lesional patterns of the IEL and the state of the intima. Type 1 corresponded to classic dissecting aneurysms, the pathogenesis of which was characterized by acute widespread disruption of the IEL without intimal thickening. Patients with Type 1 aneurysms had an ominous clinical course, and many presented with sudden subarachnoid hemorrhage with frequent rebleeding. Type 2 aneurysms were segmental ectasias, which had an extended and/or fragmented IEL with intimal thickening. Weakness of the arterial wall caused by the damaged IEL was assumed to be compensated by the intimal thickening. The luminal surface of the thickened intima was smooth without thrombus formation. The patients with Type 2 aneurysms had a placid clinical course. Type 3 aneurysms were dolichoectatic dissecting aneurysms, pathologically characterized by fragmentation of the IEL, multiple dissections of thickened intima, and organized thrombus in the lumen. Most of them were symptomatic and progressively enlarged over time. Type 4 aneurysms were saccular aneurysms unrelated to the branching zones. They arose in areas with minimally disrupted IEL without intimal thickening, and there was a risk of rupture.

CONCLUSION

There was a strong relationship between the pathological features of the aneurysms and their clinical courses. This classification may provide a rationale for modes of treatment.

Ectasia of the basilar artery in children with sickle cell disease: Relationship to hematocrit and psychometric measures

GOAL

To determine whether children with sickle cell disease (SCD), but without clinical evidence of cerebrovascular disease, have vasculopathy shown by quantitative magnetic resonance angiography (MRA).

METHODS

In a retrospective review of MRA films, we compared 47 SCD patients with 49 control patients. Time-of-flight three-dimensional T1-weighted gradient-echo images were reconstructed, by maximum-intensity projection, to show the basilar artery in coronal view, and basilar volume was calculated from measurements made on films. Basilar volume was correlated with hematocrit and with results of cognitive testing.

FINDINGS

Mean basilar artery volume was 74% larger in SCD patients than in controls (P<.001). If the upper limit of normal is defined as mean adult volume +2 SD (< or =427 mm(3)), 2% (1 of 43) of controls but 37% (17 of 46) of SCD patients exceed this value (chi(2)=19.0; P<.001). Basilar volume correlated inversely with hematocrit (r=-.60; P<.0001), with full-scale IQ (r=-.62; P<.005), and with freedom from distractability (r=-.61; P<.006) in SCD patients. Analysis of basilar artery tissue from a 5-year-old SCD patient showed that basilar dilatation can be associated with pathological changes typical of hypertension.

CONCLUSIONS

Approximately 37% of a heterogenous group of pediatric SCD patients had ectasia of the basilar artery. Quantitative MRA is sensitive to subtle vasculopathy that can go undetected in the qualitative analysis more commonly done. Data suggest that there is a substantial elevation of arteriolar blood volume in pediatric SCD patients, and that such patients may share disease features in common with adult hypertension.