Vascular malformations are abnormal collections of blood vessels. They are considered neurological problems when they occur in the brain or spinal cord. There are four major types of vascular malformations:
- Arteriovenous Malformations (AVM)
- Cavernous angiomas
- Venous angiomas
- Capillary telangiectasias
AVMs (also referred to as high flow AVMs) consist of an abnormal network of arteries and veins that are directly connected without the usual intervening capillary network. They are thought to arise during fetal development and occur in less than 1% of the population. AVMs can cause problems by various means, but bleeding is the most common presentation. AVMs can also cause seizures, and pressure from an enlarging AVM may lead to a neurological deficit. Bleeding from AVMs usually takes the form of intraventricular, intraparenchymal, or subarachnoid hemorrhage.
When a patient's history or clinical presentation suggests an AVM, a CT or MRI scan will usually confirm the presence of the lesion and show its exact location. An angiogram may then be performed to give a more detailed picture of the structural characteristics of the AVM. An angiogram is essential to planning any treatment for the AVM.
AVM treatment usually involves one or a combination of the following three therapies:
- Endovascular Surgery
- Stereotactic Radiosurgery
Microsurgery uses traditional surgical techniques under high magnification and sometimes with computerized guidance to remove the AVM. One of the major advantages of microsurgery is that it can result in an immediate cure. However, some lesions may be too large, too deep, or located in too important of an area of the brain for safe microsurgical excision. In such cases other treatments may be necessary.
In endovascular surgery, treatment is performed from within the affected blood vessel. Specially designed microcatheters are navigated by means of an angiogram right up and into the AVM itself. The lesion is then occluded from the inside using a process of embolization with either particles or glue. Some forms of endovascular treatment may be investigational and therefore require a special consent. Although very effective in reducing the size of an AVM, endovascular embolization is rarely able to completely obliterate all but the smallest of AVMs. Endovascular therapy, therefore, is usually combined with either microsurgery or stereotactic radiosurgery to give the best chance of a cure.
Stereotactic radiosurgery involves the delivery of a highly focused beam of radiation to the AVM. The two most common forms of radiosurgery are linear accelerator based radiosurgery (also known as LINAC or photon knife) and gamma ray based radiosurgery (gamma knife). Radiosurgery may be less risky when compared to microsurgery for patients with AVMs that are deep or located in important brain areas. However, the ability of conventional radiosurgery to cure an AVM drops off sharply as the AVM diameter goes above 2.5 cm (1 inch). With radiosurgery, cure is not immediate and may take up to two or three years. During this time, the patient may require follow-up tests and will still be at risk for problems from the AVM. For these reasons, radiosurgery is especially appropriate for small lesions that are located in or near critical brain areas or are very deep.
Many AVMs treated by Penn State's Neurovascular Surgery Service require more than one form of treatment. As such, our staff use a multidisciplinary approach to the evaluation and treatment of patients with these lesions. Complex cases are reviewed at a multidisciplinary conference with professionals from all the major treatment areas. After careful consideration, an individualizes treatment plan is developed, often using a combination of microsurgery, endovascular surgery, and stereotactic radiosurgery to achieve a complete cure.
A cavernous angioma (also know as a cavernous malformation or cavernoma) is a type of arteriovenous malformation. These lesions consist of a collection of slow flow vessels under low pressure. The malformations are not visible on a conventional angiogram, for this reason, cavernous angiomas are often referred to as angiographically occult vascular malformations (AOVM). AOVMs may cause seizures and frequently bleed or leak blood. Severe or frequent bleeding may lead to the development of a neurological deficit. Microsurgery is the treatment of choice for lesions that are symptomatic and accessible. Removal of these cavernous angioma at surgery eliminates the risk of bleeding. In the case of epilepsy, surgery may cure or at least reduce the severity of seizures. Since cavernous angiomas are not visible on an angiogram, endovascular embolization is not possible. Stereotactic radiosurgery may have a role in the treatment of some deep or inaccessible lesions. However, this remains uncertain.
Here at Penn State Milton S. Hershey Medical Center, we have considerable experience and special training in the treatment of AOVMs of the brain and spinal cord. Using specialized skull base microsurgical techniques and a computerized image guidance system, we are able to safely remove many challenging AOVMs that might previously have been left untreated.