Neurosurgical Consultants: Vascular Malformations: Arteriovenous Malformation

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CAVERNOUS ANGIOMA

Cavernous Angiomas (also known as Cavernous Malformations, Cavernous Hemangiomas or Cavernomas) are being discovered with increased frequency due to the accuracy and availability of MRI and CT scanning. These malformations are well-defined structural lesions which frequently reach a significant size and can be confused with a Brain tumor. Structurally these malformations consist of enlarged capillaries with areas that are dilated and which lack the smooth muscle and elastic fibers of normal vessels. They can occur anywhere in the Central Nervous System (CNS). A small proportion of Cavernous Angiomas are hereditary.

One of the unique characteristics of these lesions is that the Cavernous Angiomas vessels are directly adjacent to one another without having any normal Brain tissue between them. These abnormalities are not associated with enlarged feeding arteries or draining veins. Blood flow within the lesion is quite slow and often stagnated. The lesions are known to become clotted and may calcify as part of a progressive "degenerative" process.

Cavernous Angiomas are known to occur with a higher frequency in Mexican-American families (who also have a higher incidence of multiple lesions) compared to the general population. These lesions are often identified on neuroimaging studies with small hemorrhages that also tend to leave some residual products of that bleeding called "hemosiderin". This hemosiderin is a "breakdown" product from the blood and includes some "iron salts" that are precipitated in the adjacent Brain tissue. These "left over" products of the haemorrhage can result in changes that incite a scar reaction (gliosis) within the Brain. The "gliotic" areas can then become a focus for abnormal electric activity that causes Epilepsy.

The statistical likelihood for any lesion to haemorrhage is less than 1%; however, the re-haemorrhage rate dramatically increases in the event that the lesion enlarges within one year of initial identification.

Cavernous Angiomas are also referred to as Cryptic Arteriovenous Malformations or Occult Malformations because they usually do not show up on routine cerebral angiograms. In some patients who have suffered an intracerebral haemorrhage, neuroimaging investigations (including angiography) may not be able to identify the source of the bleeding. In fact, the "source" (which was a "Cryptic AVM") "obliterated" itself with the haemorrhage.

SYMPTOMS

Approximately 75% of patients with a Cavernous Angioma never develop any symptoms. Of those who do develop problems, the commonest symptoms are epilepsy, hemorrhage and headache consequent to a "mass" lesion (blood clot). Once a patient becomes symptomatic they are likely to remain symptomatic.

NEUROIMAGING

CT scans often show evidence of focal calcification, recent hemorrhage and/or mass effect from a blood clot. There may be faint "enhancement" when intravenous "contrast" material is given as part of the neuroimaging study. Cerebral angiograms are often entirely normal whereas MRI scans reveal well-defined lesions on T1 and T2 sequences. The hemosiderin ring is best seen on T2 sequences. Evidence of previous bleeding is often seen in the center of the lesion as well as local Brain swelling which results from the hemorrhage.

TREATMENT

Surgery

Surgical removal is appropriate for patients with intractable seizures, patients who have experienced an increase in lesion size on MRI scan and/or where there has been a significant gross hemorrhage. The advantages to surgical removal in symptomatic patients include: definitive removal of the lesion as well as the blood clot (mass); elimination of any subsequent risk of hemorrhage; removal of the seizure focus in cases where the lesion is associated with Epilepsy. Approximately 50% of patients experience elimination of seizures with the remainder having a decreased frequency of seizures. Elimination of seizures is more likely if the patient has not had seizures for many years.

Radiosurgery

The role of Radiosurgery is not well defined in the absence of scientific evidence supporting its use for these lesions. There is limited scientific information regarding large numbers of patients treated by Radiosurgery and followed with neuroimaging studies over an extended period of time.