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Cerebral Arteriovenous Malformation

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Vol. 9 •Issue 20 • Page 33
Cerebral Arteriovenous Malformation

With proper management, this potentially fatal defect in the cerebral circulatory system can be treated effectively and even cured

While at home getting ready for his work as a police officer, 42-year-old Hector suddenly experiences the worst headache of his life and calls out to his wife. She comes running into the room and finds her husband in a kneeling position on the floor with his head down; she helps him to lay down safely, then quickly calls 911.

Within minutes, emergency medical services arrive. Finding no evidence of acute injury, they quickly stabilize Hector and transport him to the emergency department of a nearby hospital. Fortunately for Hector, he was discovered by his wife immediately and taken to the nearest hospital, which happens to be a large academic medical center.

Hector is again evaluated in the ED; his airway remains stabilized and his vital signs monitored. A full neurological exam is performed and the results are documented. Additionally, clinicians perform a stat non contrast CT scan of Hector's head. Because Hector was taken to a large academic medical center, a neurologist on call is available and consults with the ED physician about further evaluation and management.

Hector is admitted to the neuroscience ICU following the CT scan. Results of the scan reveal a small hemorrhage in the right frontal lobe of Hector's brain. Based on his benign past medical history, his age and initial presentation, the neurologist suspects a cerebral arteriovenous malformation (cAVM) and consults with neurosurgery.

Cause & Frequency

cAVMs are complex anatomical defects of the cerebral circulatory system believed to occur during embryonic or fetal development. They are often asymptomatic until the affected individual reaches adulthood. Typically, symptoms appear between 20 and 40 years of age.1

The circulatory defect that predisposes a person to the development of a cAVM is the lack of an intervening capillary bed between arterial and venous blood vessels within the brain. Normally, the intervening capillary bed reduces flow velocity and pressure as blood circulates from the higher-pressure arterial vessels to the lower-pressure veins. Without an intervening capillary bed, the veins cannot accommodate either the velocity or pressure of arterialized blood; therefore they dilate, forming a complex vascular aggregate, or nidus, of a cAVM. In addition to vessel dilation, oxygenated blood is shunted away from otherwise healthy brain tissue, putting it at risk for ischemia and infarction.2

Another significant risk is rupture of a dilated and weakened vein within the nidus. Rupture can lead to hemorrhage into brain tissue, and is a most feared and devastating complication associated with cAVMs.

Experts estimate there are approximately 300,000 people in the U.S. with cAVMs, of which 30,000-40,000 become symptomatic annually. The malformations often are found incidentally during treatment for an unrelated or associated disorder, such as headache or seizure, or they may be found at autopsy.2

Identifying Symptoms

Although general symptoms such as headache or seizures are common in people with cAVMs, the malformations also can cause a variety of symptoms directly related to their size and location. The variation in symptoms between people can range from migraine-like headaches, weakness and loss of coordination to an inability to concentrate, confusion, visual disturbances, difficulties understanding or using language, seizures or a range of progressive neurological deficits.3

In addition, cAVMs can cause significant neurological symptoms from several mechanisms. These mechanisms of neurological dysfunction include cerebral or subarachnoid hemorrhage, seizures, ischemia from a vascular steal syndrome due to shunting of oxygenated blood away from otherwise healthy brain tissue, compression or physical distortion of surrounding brain tissue due to an enlarging cAVM, and venous engorgement leading to increased intracranial pressure.4

The annual bleeding risk from untreated cAVMs is 2-4 percent but increases to 18 percent in the year following initial hemorrhage, regardless of size. Rates of morbidity and mortality increase with each episode of rebleeding. Estimates suggest a 50 percent incidence of new neurological deficit and 10-20 percent incidence of death with each episode of rebleeding from cAVMs.1,4,5

In approximately two-thirds of adults diagnosed with cAVMs, a history of subtle learning disability is discovered. Findings as subtle as a learning disability suggest effects of cAVM can be subclinical and, as such, can result in the affected person seeking medical attention only following a catastrophic event such as a seizure or rupture with subsequent cerebral hemorrhage.4

Headache and seizure may be the presenting symptom of a cAVM — with or without hemorrhage — in 35-45 percent of cases. A cAVM may be found incidentally during the workup following a seizure or chronic headaches in some patients.3

Diagnosis

Following a high degree of clinical suspicion, the diagnostic workup of cAVMs is undertaken. It is designed and focused to detect, locate and grade the vascular disorder using a variety of interventions.

A noncontrast CT scan is useful to identify cerebral hemorrhage and often is the first imaging technique applied. If the CT is positive for hemorrhage in an otherwise low-risk, young patient, this unexpected positive finding for hemorrhage then focuses the clinicians' attention to the presence of a cAVM. However, if there is no hemorrhage associated with a cAVM, the CT scan is limited in that it can identify only large cAVMs.

MRI is an essential intervention to diagnose cAVM, as the malformation(s) may be small and deep within subcortical white matter and visible or detectable only with MRI. Once a cAVM is detected and diagnosed with the aid of an MRI, a cerebral angiogram will be performed. The benefit of cerebral angiogram is to assess the morphology and hemodynamics of the cAVM accurately. Important anatomical features are identifiable and measurable with cerebral angiogram, including the size of the cAVM, identification of feeder arteries, presence of associated arterial and/or venous aneurysms, and the venous drainage patterns.6

A variation of MRI known as a functional MRI (fMRI) can localize or map brain function to assist in development of the treatment plan. The fMRI can identify eloquent brain regions, including those responsible for language, memory, vision, and motor or sensory function in or near the cAVM. Damage to these areas may be unavoidable and can result in significant and permanent neurological deficits.

The results from diagnostic testing of cAVMs including the CT, MRI, fMRI and cerebral angiogram are applied to the cAVM grading system known as the Spetzler-Martin scale. Using Spetzler-Martin, the cAVM is graded based on the location, size and adequacy of venous drainage. The scale ranges from I-V, with I being the lowest risk and V the highest. Spetzler-Martin determines both the degree of surgical difficulty in resecting the cAVM and predicting the likelihood of a successful outcome following surgical intervention.2,4,6-8

Neurosurgery involving a craniotomy is generally recommended for cAVMs with a Spetzler-Martin grade of I, I I or I I I and occasionally grade IV, but due to the substantial risk, surgery is not recommended for grade V.1

Treatment Options

Carefully calculating the risk of hemorrhage from the cAVM is important in developing an individualized treatment plan. In some cases, for example, an older patient or someone without identifiable hemorrhagic risk factors might be offered a conservative, noninterventional medical management approach as the best option. For those identified as low-risk individuals, many nonsurgical, noninterventional options exist to manage the cAVM, including seizure prophylaxis, blood pressure control, blood sugar control, weight loss (if applicable), smoking cessation, diet management, exercise, stress reduction and appropriate analgesia for headaches.

However, for younger people at risk for hemorrhage from a cAVM, there are several possibly curative treatment options to consider. The options include endovascular embolization, surgical resection and stereotactic radiosurgery.

When treatment options are used in combination, one option can enable another to be more successful than if used alone. For example, endovascular embolization as a pre-surgical adjunct can decrease the size of the cAVM, which can reduce the risk of intraoperative hemorrhage and the technical difficulty of surgical resection. The interventions may be used alone or in combination depending on the individual's age, condition and unique cAVM features.7

Nursing Care & Concerns

A multidisciplinary team approach is necessary when cAVM is diagnosed. Clinicians involved should include a neurosurgeon, interventional neuroradiologists, stereotactic radiation specialists and expert neurosurgery critical care nurses.

As a nurse admitting and caring for a patient following repair of a cAVM, there are many important concerns beyond airway management and maintaining hemodynamic stability. The patient may return from the operating room with a femoral sheath in place that must be flushed and transduced according to hospital policy. The patient also may have an extraventricular drain, which must be managed and transduced as the hospital permits.

Nurses also will have to focus on neurovascular protection, while maintaining cerebral perfusion throughout the brain. Because approximately half of patients with cAVMs present to the hospital following vascular rupture with cerebral hemorrhage, postop nursing care will be directed toward aggressive blood pressure control to prevent hypertension, which could lead to rerupture of the repaired cAVM.

After Surgery

Postop complications associated with cAVMs can rapidly become lethal if not recognized quickly and treated, or they can leave the patient with permanent neurological deficits despite timely and appropriate interventions. It is essential for the nurse to perform a thorough neurological exam to establish the patient's baseline.

Subsequent exams will be compared to baseline and any acute or progressive neurological deficits must be detected. Immediate detection of any neurological deficit in the postoperative patient must be investigated aggressively to prevent permanent damage and possibly death.

Nurses may need to facilitate a stat head CT scan following detection of any neurological deficits. The neurological exam should include the patient's level of consciousness, ability to follow commands, pupillary responses, extraocular eye movements, strength and sensation of all four limbs and, if monitored, the intracranial pressure.

Nurses will provide appropriate seizure prophlyaxis, as seizures occur in a quarter of patients with cAVMs. Seizures that occur postoperatively can quickly lead to a potentially lethal cerebral hemorrhage.

Nurses also should manage pain, especially for migraine-like headaches. Inadequately controlled pain can increase the cerebral metabolism and intracranial pressure, putting the cerebral vasculature at risk for hemorrhage.

Patients with cAVM often experience neuropsychological symptoms from a vascular steal syndrome. Recognition and treatment of such manifestations as agitation and delirium are essential to control intracranial pressure and protect cerebral vasculature from rupture and hemorrhage. 9

Appropriate postoperative analgesia can facilitate recovery and prevent complications such as agitation, confusion and delirium.

Accuracy & Timing

The desired treatment goal is complete eradication of the cAVM lesion. The cAVM treatment approach is made collaboratively by taking into account the patient's physical and psychological symptom profile, current neurological deficits, risk for future neurological deficits, current quality of life and Spetzler-Martin grade.

With accurate and timely diagnosis and an appropriate individualized treatment plan, cAVM can be treated successfully and in many cases cured.

To access references and resources for this article, go to www.advanceweb.com/nurses and click on References tab under Education on the left side of the homepage.

Vincent Vacca is nurse educator in the neuroscience ICU at Brigham and Women's Hospital, Boston.




     

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