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Screening To Diagnose Brain Aneurysms
Through routine checkups and recognizing symptoms and causes that are potentially related, one can get the proper screening and scanning needed to diagnose an aneurysm. Special imaging tests are used to detect the presence of a brain aneurysm, some non-invasive to the body, some invasive, and all with differing degrees of risk, accuracy and cost. As of yet, there is no health care insurance coverage for routine aneurysm screening.
One limiting factor for broad-based population screening is the logistical and financial burden. One study in Ireland examines the costs associated with screening first degree relatives (parents, siblings and children) 18-65 years with a history of family intracranial aneurysms (IA) (Roberts et al., Screening for familial intracranial aneurysm: resource implications. Br J Neurosurg. 1999 Aug;13(4):395-8). A study screening first-degree relatives in Northern Ireland found a 15% yield. This translates to finding 700 asymptomatic patients with intracranial aneurysms in a national screening of the population of Northern Ireland. The time it would take to screen the population once would be 2.3 years by catheter angiogram, and 1.1 years by magnetic resonance angiography (MRA). Unfortunately, the study does not take into account the treatment cost should those undiscovered aneurysms rupture.
Another study (Raaymakers et al), Aneurysms in relatives of patients with subarachnoid hemorrhage: frequency and risk factors. MARS Study Group. Magnetic Resonance Angiography in Relatives of patients with Subarachnoid hemorrhage, Neurology. 1999 Sep 22;53(5):982-8) cites the incidence of IA (MRA diagnosis) in first-degree relatives of SAH patients as 4.0%, with female gender, increasing age, polycystic kidney disease, hypertension and elevated levels of glucose and cholesterol in the blood as risk factors. Atheroscelerosis, smoking, alcohol use or a previous history of SAH, were not significant factors.
One study, from 1996, shows that 80% of familial aneurysms occurred in women versus the 59% of sporadic aneurysms among women (LeBlanc, Familial Cerebral Aneursyms, Stroke. 1996 Jun;27(6):1050-4). Clearly more research is needed to determine the utility of more widespread screening.
Scans To Locate Brain Aneurysms
There are several different diagnostic scans used to locate aneurysms. Your doctor may choose any combination of them based on your particular case and condition:
Angiogram (arteriogram): This is the "gold standard" for diagnostic evaluation, according to an American Heart Association statement, as it is the most comprehensive, specific, and sensitive. It is, however, a more expensive and invasive procedure.
Angiogram done under fluoroscopy. These images
are used in angiosuite during a diagnostic or interventional procedure.
The following non-invasive tests have been developed as alternatives to the angiogram:
MRI - Magnetic Resonance Imaging: This non-invasive test allows your doctor to see many internal organs including the brain without surgery, x-rays or pain. The magnetic resonance machine creates a magnetic field, sends radio waves through your body, and then measures the response with a computer creating an image or picture.
Patient Procedure: You will lie on a special table, which will slide you under the MRI machine. While undergoing the exam, you will hear clicking noises as the machine scans you. You will be asked to remain as still as possible during the exam which generally lasts no longer than an hour.
MRA - Magnetic Resonance Angiography: This combines the MRI procedure with a contrast agent (similar to a dye). A solution called a contrast agent, which typically has few or no side-effects, is injected into a vein. The dye clarifies the picture, allowing the radiologist to construct a 3-D image and better distinguish the structure of the aneurysm.
CT - Computer Tomography: Also a painless, safe test, the CT examines cross-sections of the brain through x-ray and an interpretive computer. As it is only captures a flat 2-D slice of the brain (like a piece of paper), usually several scans are done to provide the doctor with layers of anatomical information at different depths.
Cylinder - One of the components inside the
CT scanner that captures the diagnostic images.
To view a video clip of the image, select one of the formats below. in action
MPEG (MP4 format -
246 KB)
QuickTime (1.77 MB)
- AVI (3.51 MB)
Color mapped and enhanced head CT scans:
showing perfusion (Green, white globs) - Click image for a larger view.
CTA - Computer Tomography Angiography: This augments the CT scan with a contrast dye injected into a vein which allows for 3-D imaging, highlighting the blood vessels in the brain.
Toshiba Aquilion 32 Multislice CT System.
Can make 3-D imaging using CTA angiography function, with 32 slices of
.5mm per rotation.
3-D reconstruction of CTA scan showing main
arteries - Click image for a larger view.
To view a video clip of the image, select one of the formats below.
MPEG (MP4 format -
75 KB)
QuickTime (620 KB)
-
AVI (1.24 MB)
Patient Procedure: Prior to the day of the procedure, you will go to a hospital pre-admission clinic for a discussion of your medical history, a physical exam and blood testing. You will be instructed not to eat or drink after midnight of the night before the procedure.
On the day of the angiogram you will wear a hospital gown and be asked to remove all items you are wearing, including metallic and memory devices, such as, hearing aid, watch, dentures, contact lenses, etc. Since the catheter will be inserted into the femoral artery, a small area of your groin will be shaved in preparation. An intravenous line will be inserted into your arm to administer medications and fluids during and after the procedure. A local anesthetic will be injected in the shaved area of your groin, and when the area is numb, the neuroradiologist will insert a catheter in the artery and then inject the dye, and you may feel a sensation of warmth in your face and head. The dye will go into the femoral artery through blood vessels to the heart and then the brain. Once the dye has reached the brain, fluoroscopy pictures will be taken and analyzed by the neuroradiologist. After satisfactory pictures have been obtained, the catheter will be removed and pressure will be applied to the opening for about fifteen minutes. You will be required to lie flat for six to eight hours. You will then be released from the hospital and may resume your activities without restriction unless otherwise instructed.
Discussion of Screening Techniques - which ones are right for you?
According to the American Heart Association statement, CT (standard computed tomography) with or without contrast agents is considered too imprecise for adequate diagnosis of brain aneurysms. However, CTA (computer tomographic angiography) may pinpoint aneurysms as small as 2 to 3 mm. Magnetic resonance Angiography (MRA) is useful for screening, especially for aneurysms 3 to 5 mm or more in diameter, and is the most heavily used test.
Keep in mind that 5mm is thought by many to be the critical threshold size for aneurysm rupture risk. However, MRA’s are expensive ($500-$1,000 or more) so there is currently only support for screening people with a significant demonstrated risk. Moreover, the MRI machines distributed throughout the U.S. vary in quality based on their prices, translating to varied degrees of detection accuracy making nation-wide effective screening difficult. If you choose to be screened, ensure that a minimum threshold machine of xxx accuracy, xxx specificity is used.
Although these new technologies have made screening techniques more accurate and less invasive, much research is still needed to make screening more cost-effective so that more people can be screened routinely. However, accuracy is still a concern. CTA and MRA reportedly have the following efficiency limitations: sensitivity 76-98%, specificity 85-100%, with TCD being poorer (Wardlaw and White, 2000). Even then, many of the study subjects had an aneurysm or recent subarachnoid aneurismal hemorrhage, which would artificially increase the accuracy. The detection rate of the scans declines proportionally to the size of the aneurysm, typically. They are poor detectors for aneurysms smaller than 5 mm in diameter, which account for approximately one third of unruptured aneurysms.
Traditionally, the "gold standard" for diagnostic evaluation of IA’s is intra-arterial catheter angiography, an angiogram. Thus, a diagnostic cerebral angiogram is generally performed prior to any treatment of an aneurysm, such as clipping or coiling, being considered in order to equip the doctor with a complete picture of the region.
Prior to the day of the procedure, you will go to a hospital pre-admission clinic for a discussion of your medical history, a physical exam and blood testing. You will be instructed not to eat or drink after midnight of the night before the procedure. On the day of the angiogram you will wear a hospital gown and be asked to remove all items you are wearing, including metallic and memory devices, such as, hearing aid, watch, dentures, contact lenses, etc. Since the catheter will be inserted into the femoral artery, a small area of your groin will be shaved in preparation.
An intravenous line will be inserted into your arm to administer medications and fluids during and after the procedure. A local anesthetic will be injected in the shaved area of your groin, and when the area is numb, the neuroradiologist will insert a catheter in the artery and then inject the dye, and you may feel a sensation of warmth in your face and head. The dye will go into the femoral artery through blood vessels to the heart and then the brain.
Once the dye has reached the brain, fluoroscopy pictures will be taken and analyzed by the neuroradiologist. After satisfactory pictures have been obtained, the catheter will be removed and pressure will be applied to the opening for about fifteen minutes. You will be required to lie flat for six to eight hours. You will then be released from the hospital and may resume your activities without restriction unless otherwise instructed.
