Aneurysm, 442.9
Hydrocephalus, 331.4
I. Definition
A. Abnormal dilatation of an arterial wall in which the intima bulges outward
B. Usually caused by abnormal weakening
C. Usually, a sudden increase in systolic blood pressure caused by events such as straining or sexual intercourse, which may precipitate a rupture
II. Types
A. Berry (saccular)—congenital aneurysm of a cerebral vessel
1. Tends to occur at arterial bifurcations
2. More common in adults
3. Frequently multiple
4. Usually asymptomatic
5. May be associated with polycystic kidney disease or coarctation of the aorta
B. Fusiform—aneurysm that is tapered at both ends and spindle-shaped; all walls of the blood vessel dilate more or less equally, creating tubular swelling
C. Mycotic—caused by or infected by microorganisms (bacterial)
D. Traumatic
III. Location
A. Most intracranial aneurysms (80%-85%) are located in the anterior circulation.
1. Most commonly at the junction of the internal carotid artery and the posterior communicating artery
3. At the trifurcation of the middle cerebral artery
B. Aneurysms of the posterior circulation are most frequently located at the bifurcation of the basilar artery or at the junction of a vertebral artery and the ipsilateral posterior inferior cerebellar artery.
C. Multiple intracranial aneurysms, usually two or three in number, are found in 20% to 30% of patients.
IV. Risk factors
A. Evidence supports the association of intracranial aneurysm with heritable connective tissue disorders (e.g., polycystic kidney disease, Ehlers-Danlos syndrome type IV, neurofibromatosis type I, Marfan’s syndrome) and their familial occurrence.
B. 7% to 20% of patients with aneurysmal SAH have a first- or second-degree relative with a confirmed intracranial aneurysm.
C. Cigarette smoking is an environmental factor.
1. Risk of an aneurysmal SAH is about 3 to 10 times higher among smokers.
2. Risk increases with the number of cigarettes smoked.
3. Smoking decreases the effectiveness of alpha1-antitrypsin, the main inhibitor of proteolytic enzymes (proteases) such as elactase; the imbalance between proteases in smokers may result in the degradation of a variety of connective tissues, including the arterial wall.
D. Risk is higher among women than among men after age 50.
1. Suggests a role for hormonal factors
2. Premenopausal women have a low risk of aneurysmal SAH.
3. Postmenopausal women have a relatively high risk.
4. Postmenopausal women receiving hormone replacement therapy have an intermediate risk.
E. A moderate to high level of alcohol consumption is an independent risk factor for aneurysmal SAH. Recent heavy use of alcohol in particular appears to increase the risk of SAH.
V. Clinical manifestations
A. Most aneurysms are asymptomatic until they rupture, at which time SAH results (see Signs and Symptoms of SAH in Chapter 1).
B. Some focal neurologic deficits may be related to compression of adjacent structures.
C. Small amounts of blood from the aneurysm (“warning leaks”) may precede the major hemorrhage by a few hours or days. These may cause the patient to have headaches, nausea, and neck stiffness.
D. Ophthalmologic examination may reveal unilateral or bilateral subhyaloid hemorrhages in approximately one fourth of patients with aneurysmal SAH. These hemorrhages are venous in origin, are located between the retina and the vitreous membrane, and are convex at the bottom and flat on the top.
E. Some aneurysms have a mass effect, causing the patient to become symptomatic. These aneurysms are generally large or giant (25 mm or larger).
1. The most common symptom of mass effect is headache.
2. The most common sign is palsy of cranial nerve III (pupils).
3. Brain stem dysfunction, visual field defects, trigeminal neuralgia, cavernous sinus syndrome, seizures, and hypothalamic-pituitary dysfunction may also occur, depending on the location of the aneurysm.
4. These aneurysms carry a high risk of rupture (approximately 6%/year).
VI. Diagnostics
A. CT scan or magnetic resonance angiography can be performed to obtain a baseline value for ventricular size and to rule out infarct/hemorrhage. These studies are noninvasive and carry a lower complication rate than is associated with conventional catheter angiography.
1. CT scans are sensitive in detecting acute hemorrhage, and they show the presence of SAH in 90% to 95% of patients who undergo scanning within the first 24 hours after hemorrhage.
2. The sensitivity of CT scanning, however, decreases to 80% at 3 days after hemorrhage, 70% at 5 days, 50% at 1 week, and 30% at 2 weeks, because blood is cleared rapidly from the subarachnoid space.
3. CT scans are also useful in detecting any associated ICH or hydrocephalus, and the distribution of blood may offer important clues to the location of the ruptured aneurysm.
B. Cerebral angiography can be ordered to discern the size, shape, location, and number of aneurysms, as well as the occurrence of arterial spasm. The risk of permanent neurologic complications is lower than was previously recognized, and cerebral angiography has a high level of diagnostic accuracy. Angiography provides superior spatial resolution and lacks the flow-related artifacts that may affect magnetic resonance angiography.
C. MRI angiography does not require contrast material and can be used to detect intracranial aneurysms as small as 2 to 3 mm in diameter.
D. Standard MRI is the best method for detecting the presence of a thrombus within the aneurysmal sac.
E. Since the late 1990s, helical CT angiography has been used to detect intracranial aneurysms, and preliminary reports indicate that the detection rate with this technique is similar to that with MRI angiography. Helical CT angiography has the ability to demonstrate the relation of the aneurysm to bony structures of the skull base; it can be performed safely in patients who have been treated with ferromagnetic clips, which are a contraindication to MRI angiography.
G. Elevations in WBC count and sedimentation rate are indicators of a ruptured aneurysm.
VII. Management
A. Surgery
1. Choosing surgery for patients with an unruptured intracranial aneurysm involves weighing the risk of intracranial rupture against the risks associated with brain surgery.
2. Size, location, and previous SAH are the most important features for predicting aneurysmal rupture.
a. As was noted in the Cooperative Study of Intracranial Aneurysms and Subarachnoid Hemorrhage, which involved 6038 ruptured aneurysms, the critical size for rupture is 7 to 10 mm. Many studies support the critical size as larger than 10 mm.
b. Major compressive symptoms (e.g., headache, neurologic signs and symptoms) should lead to consideration of surgery.
c. Coexisting medical problems or factors that favor the need for surgery must be considered (e.g., hypertension, poorly controlled hypertension) to prevent the risk of bleeding.
3. Early (within 72 hours of the bleed) surgery is desirable for eliminating the risk of rebleed and for allowing aggressive treatment for vasospasm, should it occur.
4. Late: after 7 days post bleed
5. Methods
a. Clipping
b. Wrapping
c. Embolization
d. Endovascular treatment is emerging. Soft metallic coils are inserted within the lumen of the aneurysm. Goal is complete obliteration of the aneurysmal sac.
B. Medical management if surgery is not feasible, as outlined for SAH in Chapter 1, is continued for about 6 weeks.
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