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Diagnostic Procedures
Balloon Occlusion Test
Several vascular diseases may be best treated by deconstructive endovascular procedures. These include giant cavernous carotid artery aneurysms and end stage head and neck cancer, which involve the carotid artery. Physicians need to know whether there is enough collateral circulation in the brain to supply the brain without the risk of stroke.
The angiogram and test occlusion is a 3-4 hour procedure done with the patient awake with conscious sedation. Following a standard angiogram of the head and cervical vessels, a temporary balloon is placed in the carotid artery to be tested. Patients are given heparin for anticoagulation to prevent strokes from occurring. The balloon is inflated to block flow in the artery, and the patient is evaluated neurologic tests for the next 20-25 minutes. During this time, a closely monitored hypotensive challenge is given to mimic physical activity. A nuclear medicine test is done for evaluation following the angiographic exam. The nuclide is administered at the time of lowered blood pressure. This is fixed during the first pass through the circulation and provides a snapshot of blood flow to the brain analogous to a cardiac stress test. At the end of the test, the balloon is deflated and another angiogram and final neurologic test are performed. Patients are then observed for a few hours before discharge. Some patients may be admitted to undergo a permanent occlusion of the artery on the following day if the angiographic study, neurologic exam and nuclear medicine study are in accord.
Cerebral Angiogram
Diagnostic angiography is a procedure which physicians use to investigate abnormalities of the blood vessels. For the procedure a catheter is placed in the selected blood vessel and contrast is administered while a rapid set of x-rays is obtained analogous to time lapsed photography. It is the most accurate method to identify and define aneurysms, arteriovenous malformations, carotid stenosis and many other disease processes of vessels supplying the central nervous system. It is a relatively safe procedure, but a full explanation of the risks is given to each patient before the test.
Conscious sedation and local anesthesia is given before catheters are placed. For most angiography access to the arterial or venous system is safely via the femoral artery or vein in the hip area. The catheter is navigated into the aorta and then up into the cervical vessels under flouroscopy. Contrast is administered and xrays are taken to examine the arteries and veins in the head or spine. Typically, the two carotid arteries in front and the two vertebral arteries in the back of the head are studied, so the angiogram may last from 1-3 hours.
As part of this, a 3-D Rotational Angiogram may be obtained. Here the x-ray tube rotates around the patient collecting images. The tube then moves in reverse while contrast is given. The images are subtracted and reconstructed into a 3 dimensional model.
Afterwards, the puncture site must be compressed manually and the leg held straight for up to 3-6 hours to allow the artery to heal sufficiently before discharge. Most patients undergoing diagnostic angiography need to stay in the hospital for 3-6 hours depending on the type of catheter used and the type of closure used. This may include hemostatic patch with manual compression. Patients are always seen by a physician prior to discharge. After angiography, patients are instructed to avoid heavy lifting or exercise for 10 days and avoid swimming for 5 days. If bleeding should occur patients are instructed to go to have someone apply direct pressure to the site and go to the nearest emergency room.
CT Angiogrpahy
CTA is used for the diagnosis and treatment planning of neurovascular diseases. This includes aneurysm detection, acute stroke and venous occlusive disease. CT angiography is performed with a series of thin slice axial images during a bolus of IV contrast. Detection of aneurysms 3 mm or greater is excellent. It is possible to distinguish berry or saccular aneurysms, which occur at bifurcations in the Circle of Willis from other types. These include fusiform (spindle shaped) aneurysms and dissecting aneurysms due to a tear in the artery wall. Distal vessel aneurysms may have infectious, traumatic or neoplastic etiologies. CTA is also used to define carotid or vertebral artery diseases such as stenosis or dissection. It is invaluable for evaluating patients in the Emergency Room who present with acute stroke. CTA is usually obtained of the entire cerebrovascular system from the aortic arch to the top of the head to determine the cause of the stroke. A CT perfusion scan identifies blood flow abnormalities in regions of the brain.
MR Angiography
MRI and MR angiography provide another method of examining the brain, spine and vasculature. MR imaging of the brain yields a more detailed examination of the tissues than CT, but it is a more involved procedure. MR angiography is used as a screening method for cerebrovascular diseases such as aneurysms or stenoses. It is the study of choice for patients with suspected carotid or vertebral artery dissection and utilized T1 weighted imaging with fat saturation technique. With gadolinium enhanced MRA, the data provided is similar to CTA for carotid stenosis. Diffusion and perfusion weighted MR imaging is a good method of evaluating ischemia and blood flow to the brain.
Diffusion weighted MR imaging (DWI) examines the passive movement of water molecules, which tend to be restricted in areas of acute infarction. It can identify an acute stroke within an hour of onset in 95% of cases. Perfusion weighted MR imaging is a bolus tracking method using rapid spin echo or gradient echo techniques. This multislice imaging identifies areas of ischemia. In combination with DWI, one can look for areas of tissue at risk for infarct. Many times these areas can be saved by neuro-interventionalists.
Spinal Angiogram
Spinal angiography is the definitive diagnostic procedure for evaluation of spinal dural AV fistulas. Spinal angiography is a laborious invasive test and technically difficult to perform which exposes the patient to the risk of multiple catheterizations of the segmental vessels from the aorta. As these patients are frequentlly elderly with atherosclerotic disease, these risks can involve embolization of the spinal arteries with the risk of subsequent myelopathic infarction. Although these complications are rare, they do need to be considered in advance of any such procedure. Additionally, the procedure usually requires general anesthesia, lasts for approximately three to four hours, and involves administration of an unusually high dose of contrast up to 400 cc or more. Nevertheless, in patients in whom the diagnosis of spinal dural arteriovenous fistula is suspected, this test is warranted as the definitive process for establishing the diagnosis.
During spinal angiography which is done through a transfemoral catheterization, each of the segmental vessels which supply the dura are catheterized in sequence on each side of the body. This can involve over 40 total catheterizations from the upper cervical level to the pelvis. As only one of these vessels will demonstrate the abnormality and all of the other vessel injections will be normal, there is no way of shortening the procedure and usually at the start of a procedure, there is no way of knowing which segmental level will be involved by the disease. The angiographic findings related to the disease will be evident at the level of the fistula where opacification of an abnormal distended venous channel following the course of the nerve root up to the conus will be identified with subsequent opacification of an abnormal rete or plexus veins around the spine. Additionally, on injection of the level at which the artery of Adamkiewitz (anterior spinal artery) is performed, the angiogram will demonstrate slowing of flow. Localization of the positions of the anterior and posterior spinal arteries is an important part of the procedure if surgery is contemplated. However, all other levels of injection will be completely normal and thus the technique needs to be extremely precise so that no single vessel is inadvertently omitted during the procedure.
Ultrasound
Carotid ultrasound is used to evaluate arterial stenosis or dissection in the cervical region. In addition it is employed in the follow up of patients after endarterectomy or stent placement. Transcranial Doppler ultrasound can evaluate similar processes inside the head. Cerebrovascular reserve studies measure the functional capacity of the intracranial vasculature. It can determine whether there is a limitation of blood flow to the brain during physical stress. These techniques can identify patients at risk for stroke and along with clinical evaluation helps direct preventative treatment.
WADA Testing
Patients with epilepsy can sometimes be helped by neurosurgery. In preparation there are several tests a patient may undergo. MRI with high-resolution coronal FLAIR imaging through the temporal lobes at 1.5 or 3 Tesla field strength can delineated anatomic changes. 18-FDG PET study may show metabolic changes. However, angiography may be required to define the laterality of language function. This is essential in choosing the appropriate therapy. A WADA test is an angiographic procedure, which is done in concert with a epileptologist.
A catheter is placed in the femoral artery in the groin and advanced into the aorta. The catheter is navigated into one of the carotid arteries and an angiogram is done to look at the anatomy. Sodium amytal (125 mg) or brevital (7-8 mg) is then administered through the catheter, which temporarily anesthetizes that part of the brain. Over the next few minutes a neurologist tests the patient’s motor and language skills. After 20 minutes the catheter is navigated into the other carotid artery and the process is repeated. At the end of the procedure, the catheter is removed and manual compression is used to achieve hemostasis. The patient will need to keep his or her leg straight for 3-8 hours depending on their anatomy and closure method used.
Hemorrhagic Stroke
Aneurysm Endovascular Treatment
Catheter angiography remains the gold standard for detection of aneurysms. Diagnosis of aneurysms can be accomplished by MRI or CT angiography, although lesions less than 2-3 mm can be missed by these methods. Patients are given the treatment, which addresses their particular aneurysm and clinical situation with consideration given to the potential risks.
Options for treatment of an aneurysm include coil embolization, which is done through a catheter inside the artery. The Neurointerventionalist places a catheter in the femoral artery in the groin, which is brought up to the neck using fluoroscopic x-ray guidance. A microcatheter is then brought through this guide catheter and navigated into the aneurysm. Small platinum coils are then passed through this system to fill the aneurysm and prevent arterial pressure from causing a bleed. In complicated aneurysms a temporary balloon or a stent may be placed to hold the coils in place. The catheters are removed, and the access site in the femoral artery is sealed using a closure device or manual compression. The neurosurgical alternative is to place a clip across the neck of the aneurysm excluding it from the circulation.
The International Subarachnoid Aneurysm Trial (ISAT) data suggests that patients who can be treated by either method have a better outcome than those treated surgically. The relative and absolute risk reductions in dependency or death after allocation to an endovascular versus neurosurgical treatment were 22.6% (95% CI 8.9-34.2) and 6.9% (2.5-11.3), respectively. In some cases occlusion of the artery with reliance on collateral circulation or bypass may be the treatment of choice. These procedures are done under general anesthesia.
Patients with unruptured aneurysms usually stay in the hospital for three days, the first of which is spent in the Neuro-intensive care unit for close monitoring. Patients with ruptured aneurysms need to stay in the hospital for at least 14 days to be watched for several important medical reasons including the grade of the initial bleed, hydrocephalus and vasospasm.
Cerebral Aneurysm
An aneurysm is an abnormal bulge in the wall of an artery due to weakness or injury to one or more of the three layers of tissue. Most are likely the result of a genetic alteration, although infection, trauma, or atherosclerosis can cause aneurysms. Many patients are asymptomatic or present with mild headaches. 40% of patients may have warning signs such as localized headache, cranial nerve paralysis, nausea or vomiting. There are about 30,000 patients in the U.S. each year with ruptured aneurysms. They may have severe headache, photophobia, neck stiffness or even loss of consciousness resulting from the intracranial hemorrhage. 20% are multiple and cigarette smoking may play a role in aneurysm development.
Cerebral Arteriovenous Malformation
An arteriovenous malformation (AVM) is an abnormal collection of blood vessels occurring within the brain itself. Normally, blood is pumped under pressure from the heart into the arteries, which carry it to the brain and body. These branch into smaller vessels and eventually into tiny capillaries, which supply the tissue with oxygen and nutrients. From here the veins return the blood under low pressure back to the heart and lungs. In an AVM, there is a short circuit and blood travels rapidly from the arteries directly into the veins. Pressure can build up causing bleeding from the AVM or the veins, which do not have enough support in their walls.
AVM’s are graded by size, type of venous drainage and whether they involve eloquent tissue such as speech or motor cortex (Spetzler-Martin Classification). On average, there is a 1% per year likelihood of intracranial bleeding. Patients can be asymptomatic or may present with headaches, seizures, or deterioration of neurologic function. If hemorrhage occurs patients may experience severe headache, stroke-like symptoms or even loss of consciousness. If patients get to the hospital in time, they undergo a work up including CT scan and rapid treatment to stabilize their condition followed by admission to the Neurointensive care unit.
Treatment of AVM’s may include surgical excision, radiation treatment or embolization. In many cases, embolization is used to block supply to the AVM and make definitive treatment safe. This may include reduction in size of the AVM, closure of large fistulas, and treatment of aneurysms, which are associated with the AVM nidus or arterial feeders. Before a patient is treated he or she may undergo a series of tests such as MRI, functional MRI, CT, and CT angiography. Diagnostic angiography is also performed with the possibility of sodium amytal testing. The multidisciplinary team of physicians carefully reviews this data.
Embolization is performed under general anesthesia. A sheath and catheter system is placed in the femoral artery, usually in the right groin. The catheter system is brought up to the neck and diagnostic angiogram is obtained. Using this information and live fluoroscopic visualization, a microcatheter is placed through the guide catheter and navigated into the arteries supplying the AVM. Another angiogram is done to determine whether it is a safe artery to block off. If so, then liquid embolic agent is used such as ONYX or N-butyl cyanoacrolate in a mixture with radio-opaque material. This process is repeated up to several times after which the catheters are removed and the arteriotomy site is closed. The patient is awakened from anesthesia and transferred to the Neurointensive care unit. Patients are usually in the hospital for elective procedures for 2-3 days.
Blood flow to the AVM may be treated in stages to prevent thrombosis or hemorrhage from occurring. In some cases, embolization may fully treat a lesion, but most patients will undergo surgical resection or radiation therapy. Angiography is used following these treatments to insure the lesion is fully treated.
Cerebral Dural Arteriovenous Fistula
Dural arteriovenous fistulas (AVF) are abnormal connections of the arteries to veins. Normally, the high-pressure arteries branch into smaller vessels until the capillaries supply the tissues with oxygen and nutrients. Blood then flows into veins, which are of low pressure and high capacitance. When there is a short circuit of this system, the high flow arteries overwhelm the veins inside the head or spine. Patients may present with symptoms such as headache, pulsatile tinnitus, cranial nerve deficit, seizure, intracranial bleeding, hydrocephalus, neurologic decline or stroke-like symptoms.
Detection of DAVF is often accomplished by MRI/MRA. Different subtypes have a graduated risk profile and those with retrograde flow into the cortical veins are at significant risk for intracranial bleeding. Treatment for these patients is recommended and this can often be accomplished by endovascular means.
Embolization of a DAVF is performed under general anesthesia. A sheath is placed in the femoral artery in the groin, and a catheter is passed through this into the aorta and eventually into the carotid and vertebral arteries supplying the head and neck. Angiography is performed with contrast and x-rays to obtain a map of the arteries and veins. The abnormal connection of the arteries and veins are identified. A microcatheter is passed though the larger guide catheter and positioned in the fistula site. Materials may be used to block these connections such as coils, PVA particles, gelfoam, or liquid agents such as N-BCA, ONYX or pure alcohol. A final angiogram is done to identify the changes after treatment. Some of these lesions need to be treated by blocking off the venous side of the AV fistula. This is accomplished using a catheter system through the venous system also accessed in the groin.
Patients treated electively may spend 2-3 days in the hospital while patients who have had intracranial hemorrhage as a presenting symptom may spend 2 weeks or more in the hospital. Some patients with complicated lesions may require multiple stages of treatment.
Some lesions may require additional therapy to disconnect the abnormal A-V fistula such as surgery. Large and complicated DAVFs may need treatment by combined procedures with neurosurgery or radiotherapy targeted to the lesion. These patients are followed by imaging until the lesion is optimally treated.
Spinal Dural AVM and AVF
Vascular lesions affecting the spine and spinal cord are categorized into 4 basic types:
Arteriovenous fistula (AVF) arising within the dura of a nerve root with intradural drainage
Arteriovenous malformation (AVM) in the spinal cord tissue
Juvenile AVM (metameric) which involves all of the tissue at contiguous levels
Perimedullary fistula on the surface of the spinal cord
AVM’s consist of artery to vein connections, which pass through a nidus of rapidly shunting channels. AVF’s are direct end to end connections from artery to vein with fast flow, and they may be single or multiple. Some AVM’s have fistulous components. This group of spinal lesions is treated differently from one another depending on the arterial supply to the lesion, degree of cord involvement, and location arteries supplying the cord itself. They may be treated by a single modality or they may require a combination embolization, surgery or radiation therapy.
As part of the work up for a spinal vascular lesion most patients undergo an MRI study with gadolinium contrast enhancement. MRA with gadolinium may also be of assistance to identify the levels of involvement. The definitive diagnostic study is spinal angiography, which may be done under general anesthesia while focused spinal studies can be done with conscious sedation in some cases. The goal is to identify both normal and pathologic vascular anatomy to allow proper decision-making.
Ischemic Stroke
Acute Stroke Therapy
Stroke is the leading cause of serious, long-term disability with approximately 500,000 cases of stroke each year. It accounts for about 160,000 deaths, and in stroke survivors, there is a 25-29% recurrence rate over 5 years (4-14% annual rate). The goal of treatment of these patients is to diagnose the problem as quickly as possible and triage them to the appropriate therapy.
Patients are evaluated in the emergency room according to physical exam using the NIH stroke scale and clinical history. Non-contrast head CT is performed followed by a CT angiogram (CTA) and CT perfusion (CTP) study. This takes just a few minutes to review and provides information about the nature of the stroke. It assists in excluding hemorrhage or edema from brain swelling. 80% of strokes are ischemic and 20% are hemorrhagic. The CTA defines the location and cause of the blockage in the artery from the aortic arch up through the brain. The CTP shows is how the brain is affected by the change in blood flow, identifying the tissue undergoing and at risk of stroke. In some cases an MRI may be performed instead or in addition to the CTA.
For patients reaching the hospital within three hours of onset of symptoms, IV tissue plasminogen activator (tPA) is the FDA approved treatment.
Carotid Stenting
Stroke is the leading cause of serious, long-term disability with approximately 500,000 cases of stroke each year. It accounts for about 160,000 deaths, and in stroke survivors, there is a 25-29% recurrence rate over 5 years (4-14% annual rate).
Angioplasty and stenting for the treatment of cerebrovascular disease has grown in recent years. Patients are screened for this procedure by a team of physicians including Interventional Neuroradiology, Neurosurgery and Neurology. This ensures a patient is selected by proper criteria and receives long-term follow up. Typically, a patient should be symptomatic and have at least 70% stenosis of the affected carotid artery. Patients may have had previous stroke or TIA’s. Most will have undergone MRI/MRA or CTA and carotid/Transcranial Doppler Ultrasound to determine if an artery is narrow. If a patient has had a stroke, the procedure may be done several weeks afterward to limit the chances of bleeding from the anticoagulation regimen used in stenting. Medication instituted prior to the procedure includes aspirin and plavix with heparin used during the procedure itself. This prevents clot from developing on the catheters or stent and causing a stroke.
The procedure is done under monitored anesthesia care with the patient sedated but awake or with general anesthesia depending on medical condition. Under sterile conditions the femoral artery is accessed in the right or left groin area. A sheath is placed through which a catheter is placed for diagnostic angiography. This shows the Neurointerventionalist the precise location and degree of narrowing in the artery and the collateral circulation around the brain. Under direct fluoroscopic visualization, a guide catheter is placed in the affected artery, and a small guide wire is passed beyond the stenosis. This wire may have a built in protection device to collect any debris from the angioplasty, which follows. The next step is placement of the stent over this guidewire and possibly a second angioplasty to secure the stent in place. Any debris collected by the protection device is retrieved, and the catheters are removed. The arteriotomy may be closed with a Perclose device or by manual compression following removal of the sheath in 24 hours when the heparin is stopped. Patients usually spend 3 days in the hospital the first of which is in the Neuro-intensive care unit. Instructions on care of the arteriotomy site in the groin are standard for angiography. Patients are continued on aspirin and plavix and followed by our staff and Neurology following discharge from the hospital
Precautions are taken to avoid potential complications such as stroke. Anticoagulation is used as described above to limit the possibility of stroke. Angioplasty can cause temporary bradycardia due to pressure on the carotid body, and we may administer atropine or glycopyrolate for heart rate or blood pressure control. Reperfusion syndrome is a rare problem, which may occur in patients who have extremely tight stenosis. The cerebral vasculature loses its normal autoregulation and in some cases patients may develop cerebral edema and blood pressure control must be strictly regulated. Transient ischemic events are uncommon but can happen with the use of angioplasty balloon despite distal protection devices.
Intra-arterial tPA
Patients reaching the hospital within 3-6 hours are treated with only the catheter system using tPA or urokinase, placed in the artery which is blocked. This is administered with a catheter placed directly into the blockage under general anesthesia, and usually takes a few hours.
Mechanical Removal of Brain Clot
Patients reaching the hospital between 6-8 hours following a stroke may be offered endovascular treatment with a clot removal device such as the Concentric or the clot retrieval wire. These procedures are performed under general anesthesia. Patients are then followed in the Neuro-intensive care unit.
References
Sources
Practical Neuroangiography
by Pierce Morris
MGH Interventional Neuroradiology
http://www.mgh-interventional-neurorad.org
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