الاثنين، يناير 07، 2013

Cavernoma

Cavernoma (also called cavernous angioma), vascular malformation intracranial with unique histological and imaging characteristics. They are quite common and frequently asymptomatic occasional findings on imaging studies; it is estimated that 4% of the population harbours this lesion. They appear as discrete, compact nodules of endothelial-lined sinusoidal vascular spaces, which contain essentially subacute to chronic clotted blood and are not infrequently multiple. They may range from 1 mm to several cm in diameter. They are congenital and may be familial; however, they may appear or manifest late in life, and may evolve and change in size as well as in appearance during life. If symptoms do occur, the clinical presentation may include seizures, haemorrhage, or progressive neurological deficit. The epileptic activity is thought to be due to the irritating effects of haemosiderin, gliosis, and compression on adjacent cortex. Haemorrhage is usually relatively limited to the proximity of the lesion itself, and only rarely life-threatening. Small haemorrhagic events may occur within the capsule of the nodule itself, producing signal changes but no neurological signs; small haemorrhages in critical locations (e.g. brain stem) are more likely to produce symptoms. Cavernous angiomas may be found anywhere in the nervous system; they may be intraparenchymal, intraventricular, subpial, extra-axial. When intraparenchymal they are usually surrounded by a rim of gliotic brain containing haemosiderin most likely due to diffusion of red cell pigment from intracavernous sequestration. Venous angioma intracranial may coexist with cavernomas. Imaging CT shows slightly or densely hyperdense nodules with some enhancement, but may completely miss small nodules (Fig.1). Since these lesions are by definition "occult" to angiography, except in rare cases where some pool of contrast is seen within the sinusoid of the nodule in late venous phase, or when an associated venous anomaly is present, it is through MRI that the diagnosis of the full spectrum of the disease has become clearly evident. The typical features include a well-delineated nodule with mixed signal on T1-weighted images, including hyperintense foci due to methaemoglobin and a mixed signal on T2-weighted images including hypointensity due to haemosiderin. The most characteristic, almost pathognomonic feature, however, is represented by a rim of T2 hypointensity, usually in the surrounding white matter, due to haemosiderin. Gradient echo studies enhance the susceptibility effect of haemosiderin both of the surrounding rim and of the haemosiderin within the nodule. Small nodules, not seen on conventional spin-ehco images, may become evident with gradient echo. Differential diagnosis should be made from melanotic melanoma metastasis, haemorrhagic metastases, granulomas with paramagnetic effect (aspergilloma), metastases of atrial myxoma and previous haemorrhage.

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