Angiitis of the Central Nervous System
This heading includes primary (granulomatous) angiitis of the CNS, systemic angiitis with CNS involvement, secondary angiitis due to infections (viral, bacterial, fungal, rickettsial, mycoplasmal, and protozoal), connective tissue diseases, other systemic diseases (other than vasculitides), and malignancies (Fig. 1). These diseases all have severe consequences, and need urgent diagnosis, sometimes based on brain biopsy (as in primary CNS angiitis) and treatment, usually based on corticosteroids and other immunosuppressive agents.
Noninflammatory Angiopathies of the Central Nervous System
These diseases include poorly understood syndromes such as benign angiopathy of the CNS and postpartum cerebral angiopathy (Fig. 2), both of which are characterized by spontaneously reversible (within a few days to several months) vasoconstriction. They therefore need no aggressive treatment. Sneddon syndrome is characterized by multifocal ischemic strokes accompanied by cutaneous livedo reticularis. Susac syndrome consists of small-vessel occlusion in the retina, cochlea, and brain, predominantly affecting young women. Angiopathies caused by recreational or medicinal agents such as vasoconstrictors, cocaine, or external radiation therapy make up another group of noninflammatory angiopathies of the CNS (Fig. 3). Finally, hypertensive encephalopathy is an acute small vessel disease characterized clinically by headaches, visual disturbances, and seizures, radiologically by widespread white matter edema with diffuse hyperintense signal on MRI-T2 images, and histologically by fibrinoid necrosis. This syndrome is reversible, provided that blood pressure is promptly lowered.
CHRONIC SMALL VESSEL DISEASES OF THE BRAIN
More common than acute small vessel diseases, clinical presentation of these diseases includes ischemic strokes (usually small deep infarcts), intracerebral hemorrhages, and dementia (6,7). Stepwise or gradual progression of neurologic deficits occurs over years, often leading to pseudobulbar palsy and subcortical dementia. Neuroimaging shows small deep infarcts sometimes accompanied by hemorrhages, and widespread white matter abnormalities (leukoencephalopathy) attributed to chronic ischemia. Cerebrospinal fluid, duplex scanning, cerebral angiography, and cardiac investigations are usually normal.
Four main varieties of chronic small vessel diseases have been identified:
1. Arteriolar sclerosis: this occurs invariably with aging but increases in severity with vascular risk factors, particularly hypertension and diabetes. It is characterized by a vessel wall thickening with various degrees of sclerosis, hyalinosis, lipid deposition (hence the term lipohyalinosis coined by Fisher), microaneurysms and sluminal narrowing (4,5). There may be a severe leukoencephalopathy called Binswanger disease when it occurs in patients with severe chronic systemic hypertension.
2. Cerebral amyloid angiopathy, also known as congophilic angiopathy, characterized by amyloid infiltration of the media and adventitia of small cortical and leptomeningeal vessels, usually in the absence of systemic amyloidosis (8). It can occur in numerous conditions such as Down syndrome, dementia pugilistica, and Alzheimer disease. The clinical presentation is mostly that of recurrent cortical hemorrhages, but small infarcts and leukoencephalopathy with dementia are frequent. Different varieties have been identified based on the accumulated protein (beta-amyloïd, Cystatin C, transthyretin, and gelsolin). The disease is mostly sporadic but familial forms are increasingly recognized and a number of mutations have been identified on chromosomes 1, 13, 20, and 21.
3. Mitochondrial encephalopathy with lactic acidosis and stroke-like episodes (MELAS) (9): characterized by migraine headaches, seizures, and ischemic strokes, usually in the occipital lobes. It usually affects children or young adults. Pial arterioles and small cortical arteries contain markedly increased quantities of giant cortical mitochondria in the smooth muscle cells and endothelial cells.
4. Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL): a small vessel disease of the brain characterized by lesions of smooth muscle cells (Fig. 4). Its clinical manifestations begin during mid-adulthood and include recurrent ischemic subcortical events, attacks of migraine with aura, severe mood disorders, subcortical dementia, and on the MRI, widespread leukoencephalopathy. A specific treatment has yet to be found. Disabling dementia and focal neurologic symptoms usually develop 20 years after the onset of disease. CADASIL is most frequently a familial disorder with an autosomal dominant mode of transmission. Its gene, Notch 3, is located on chromosome 19. This gene, previously unknown in humans, is expressed in the smooth muscle cells of small vessels and encodes for a large transmembrane receptor (12).
Twenty years ago, most patients with clinical and neuroimaging features of small vessel disease were thought to have arteriosclerosis (or lipohyalinosis) of penetrating arteries, particularly in the presence of vascular risk factors. Recent identification of conditions such as amyloid angiopathy, MELAS, and CADASIL suggests that there are probably many other varieties of chronic small vessel diseases of yet undetermined nature. From a pathophysiologic point of view, all these disorders are characterized by major abnormalities of smooth muscle cells that probably play a crucial role in the pathogenesis.
The identification of responsible genes for small vessel diseases of the CNS (as in CADASIL) allows the creation of animal models that will help to understand the pathophysiology of the vessel wall disorder and perhaps lead to development of specific treatments. (10,11)
1. Adams HP Jr, Bendixen BH, Kappelle LJ, et al. Classification of subtype of acute ischemic stroke: definitions f or use in a multi-center clinical trial. Stroke
2. Fisher CM. Lacunes: small, deep cerebral infarcts. Neurology
3. Millikan C, Futrell N. The fallacy of the lacune hypothesis. Stroke
4. Khang-Loon H, Garcia JH. Pathology of hypertensive cerebral angiopathy. In Batjer H, Louis R, Friberg L, et al, eds. Cerebrovascular Disease
. Philadelphia: Lippincott-Raven; 1997:85–95.
5. Lammie GA, Brannan F, Slattery J, et al. Nonhypertensive cerebral small-vessel disease. An Autopsy study. Stroke
6. Hommel M. Small artery occlusive disease. In Welch KMA, Caplan LR, Reis DJ, Siesjö BK, Weir B, eds. Primer on Cerebrovascular Diseases
. San Diego: Academic Press; 1997:303–7.
7. Caplan LR. Chronic vascular disease of the brain. In Welch KMA, Caplan LR, Reis DJ, Siesjö BK, Weir B, eds. San Diego: Academic Press 1997:307–12.
8. Vinters HV. Cerebral amyloïd angiopathy: a critical review. Stroke
9. Pavlakis SG, Phillips PC, DiMauro S, et al. Mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke like episodes: a distinctive clinical syndrome. Ann Neurol
10. Tournier-Lasserve E, Joutel A, Melki J, et al. Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy maps to chromosome 19q12. Nature genetics
11. Joutel A, Vahedi K, Courpechot C, et al. Strong clustering and stereotyped nature of Notch 3 mutations in CADASIL patients. Lancet
© 2004 Lippincott Williams & Wilkins, Inc.
12. Joutel A, Andreux F, Gaulis S, et al. The ectodomain of Notch 3 receptor accumulates within the cerebrovasculature of CADASIL patients. J Clin Invest