Intracranial Aneurysms:
An Overview
Surgical Classification of Intracranial
Arterial Aneurysms
• Morphology
A.
Saccular
B.
Fusiform
C.
Dissecting
• Size
A.
<3 mm
B.
3-6 mm
C.
7-10 mm
D.
11-25 mm
E. >25 mm (giant)
• Location
A.
Anterior circulation arteries
• Internal carotid
• Anterior cerebral
• Middle cerebral
B.
Posterior circulation arteries
• Vertebral
• Basilar
• Posterior cerebral
Etiology of Saccular Intracranial
Arterial Aneurysms
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Hemodynamic
Structural
Genetic
Traumatic
Infectious
Neoplastic
Other disorders affecting blood vessels
Radiation-induced
Etiology of Fusiform Intracranial
Arterial Aneurysms
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Atherosclerosis
Structural
Genetic
Infectious (syphilis)
Other disorders of blood vessels
Hemodynamic
Radiation-induced
Anatomic Sites of Aneurysms
• 95% of aneurysms occur close to the circle of
Willis.
• Aneurysms usually arise from the distal carina of
a bifurcation.
• They are usually on the convexity of a curve and
point in the direction that the proximal axial
bloodstream would have taken if the curve were
not there.
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Size of Aneurysms
• The size at which aneurysms usually begin to
rupture is about 3 to 4 mm, and the size at which
they begin to produce symptoms by means other
than rupture is around 7mm.
• The mean size of ruptured aneurysms is 8.6 mm.
• Aneurysms of ≤10 mm
16% ruptured.
• Aneurysms of ≥11 mm
91% ruptured.
Multiple Aneurysms
• They constitute about 15% of all intracranial
aneurysms.
• “Mirror” aneurysms!
• Which aneurysm has ruptured?
• The largest one
• The proximal one (if they are on the same
vessel)
• Angiographic signs:
• Local mass
• Local vasospasm
• Irregular aneurysm shape
• Intra-aneurysmal clot
• Localized subarachnoid blood on CT
• Use clinical signs
• Consider an EEG
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Aneurysms and Sex
• There is a clear female predominance overall.
• Female: male = 1.6: 1
• Above age 40, there is an increasingly strong
predominance of females.
Incidence of Aneurysm Rupture
• 2% is the incidence of aneurysms in entire
population. It will rupture in less than 1% of the
population, and will be the cause of death in
0.5%.
• Aneurysmal SAH accounts for 5 to10 percent of
strokes.
• The incidence of aneurysms as a cause of
unexpected sudden death is around 4%.
• Aneurysms constituted 77% of cases of SAH.
• The annual incidence of aneurysmal SAH is 9 to
28 per 100,000.
Familial Occurrence of Aneurysms
• There may be autosomal dominant inheritance in
some families.
• Familial aneurysms tend to rupture at a smaller
size and in younger age.
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• Screening is recommended for family members
aged 35 to 65 years. MRA is a useful screening
tool.
• Associated genetic syndromes are: EhlersDanlos, Marfan’s, and Weber syndromes.
Angiography and surgery are extremely
hazardous in such patients.
• There is increased risk of aneurysms in patients
with polycystic kidney disease.
Aneurysms of Infancy and Childhood
• 2% of all intracranial aneurysms are discovered
under 20 years of age.
• 60% of pediatric aneurysms occur in boys.
• 45% occur in the vertebrobasilar circulation.
• 30% are giant.
• Traumatic and bacterial aneurysms are more
common.
Hemodynamics of Aneurysms
• The impingement of an axial blood stream on a
distal carina can generate forces that cause local
destruction of the internal elastic membrane and
initiate aneurysm formation.
• Aneurysms are less elastic, stiffer and of thinner
wall.
• The distal apex is the actual site of rupture.
Pathology and Pathogenesis of Aneurysms
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• Damage to the internal elastic lamina by
hemodynamic factors is the critical pathologic
change.
• All aneurysms show absence of media, it ends
abruptly at neck of aneurysm.
• Ruptured site is usually the thinnest area of the
dome of the sac.
• Lumen may contain thrombus.
• Parent arteries usually shows atherosclerotic
changes.
• Factors that alter the blood flow (such as vessel
occlusions, AVMs and hypertension) may
accelerate the degenerative process.
Association of Aneurysms with Other
Vascular Lesions
1. Anatomic Variants
– Primitive trigeminal artery
– Hyperplasia of one anterior cerebral artery
2. Arteriovenous Malformations (AVMs)
– 1% of patients with intracranial aneurysms
had intracranial AVMs.
– 10% of patients with AVMs have associated
aneurysms.
– Aneurysms occur on arteries feeding the
AVM in 37 to77% of cases.
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– There is equal rates of hemorrhage from
each lesion. In general, the symptomatic
lesion should be treated first.
. Infundibular Widening of The Posterior
Communicating Artery
4. Hypertension
– It is not a major factor in the etiology of
saccular aneurysms, although it may cause
more aneurysms in susceptible individuals
and may promote aneurysmal rupture.
5. Arterial Occlusions and Stenoses
– Relation of aneurysms to carotid ligation
and carotid endarterectomy.
Predisposing Factors to Aneurysm
Rupture
. Activities at Time of Rupture
– Lifting or bending (12%)
– Emotional strain (4%)
– Defecation (4%)
– Coitus (4%)
– Trauma (3%)
– Coughing (2%)
– Urination (2%)
– Parturition (0.35%)
– During sleep (1/3)
2. Smoking
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3. Alcohol Consumption
4. During Angiography
Diagnosis of Aneurysmal Rupture
– Usually attributed to aneurysm expansion or
minor SAHs.
– Features are:
• Headache (48%)
• Dizziness (10%)
• Orbital pain (7%)
• Diplopia (4%)
• Loss of vision (4%)
• Motor and sensory disturbances (6%)
• Seizures (4%)
• Ptosis (3%)
• Bruits (3%)
• Dysphasia (2%).
– The average interval between the warning
signs and major hemorrhage is about 3
weeks.
– Clinical Presentation of Aneurysmal
Rupture
– 89% of patients with aneurysms present
with SAH; 7% with tumor symptoms; and
4% found incidentally.
– Features occur as follows:
• Meningism (64%)
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• Coma (52%)
• Nausia and vomiting (45%)
• Generalized headache (32%)
• Classic occipital headache (21%)
• Reflex changes (19%)
• Motor deficits (17%)
• Dysphasia (13%)
• Confusion (12%)
• Intraocular hemorrhage (12%)
• Anisocoria (11%)
• Papilledema (9%)
– The cardinal diagnostic feature remains a
headache that is unusually severe for the
patient and has a very sudden onset.
Symptoms and Signs Not due to Rupture
• Distal Embolization from Partially Thrombosed
Aneurysms
• Neurological Signs from Giant Aneurysms (>25
mm)
– Features are related to location, and may
include: seizures, focal neurological deficits,
and pain.
– Giant aneurysms form about 9% of all
intracranial aneurysms.
• Cranial Nerve Signs from Nongiant Aneurysms
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– Posterior communicating-internal carotid
artery aneurysms
third cranial nerve
involvement (87%)
– Ophthalmic- internal carotid artery
aneurysms
loss of vision (29%); third
cranial verve symptoms (19%); fifth (13%);
fourth (10%); and sixth (6%).
Causes of Sudden Severe Headache
• Intracranial
– SAH
• Aneurysm
• AVM (cerebral,
dural, spinal)
– Pituitary apoplexy
– Arterial dissection
– Cerebral venous
thrombosis
– Other intracranial
hemorrhages
– Acute hydrocephalus
– Other intracranial
mass (neoplasm,
abscess)
– Meningitis,
encephalitis
• Extracranial
– Dental disease
– Sinusitis
– Ocular disease
(glaucoma)
• Systemic
– Hypertensive
encephalopathy
– Temporal
arteritis
• Benign
– Migraine
(common,
classic)
– Cluster
– Tension
– Benign
exertional
headache
– Benign coital
headache
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Clinical Grading of SAH
• Grading is important in treatment decisions and
outcome prediction.
• The most important factors predicting outcome
are level of consciousness and presence of
hemiparesis and/or aphasia.
• World Federation of Neurological
Surgeons Scale
Grade
1
2
Description
GCS 15, no motor deficit
GCS 13 to 14, no motor deficit
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3
4
5
GCS 13 to 14, with motor deficit
GCS 7 to 12, with or without motor deficit
GCS 3 to 6, with or without motor deficit
Natural History of Aneurysms
• Asymptomatic aneurysms bleed at a rate of 1 to
2% per year.
• The highest mortality rate occurs immediately
following the hemorrhage and diminishes rapidly
thereafter.
• Rebleeding is estimated to occur in 50% of cases
of ruptured aneurysms within 6 months of the
first hemorrhage, and thereafter at a rate of 3%
per year.
• 60% of patients die after rebleeding, and 25% are
left disabled.
• It is recommended that asymptomatic aneurysms
be clipped in most patients
Medical Complications of Aneurysmal
Rupture as Percentage
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Cardiovascular
Hypertension
Arrhythmia
Hypotension
Cardiac failure
Thrombophlebitis
Respiratory
Pneumonia
Atelectasis
Adult RDS
Pulmonary
edema
16.4
3
2.3
1.6
1.4
5.7
2.3
1.8
1.2
Endocrine
SIADH
2.7
Metabolic
Diabetes
1.8
mellitus
Gastrointestinal
Hemorrhage 3.2
Hepatic failure 1.6
Renal
Failure
1.2
Hematologic
Anemia
4.9
Neurological Complications of
Aneurysmal Rupture
• Intracranial Pressure (ICP) Elevation
– Patients in clinical grades I and II have a
mean ICP of 10 mmHg; and in grades III
and IV, 29 mmHg.
– Patients with no vasospasm have a mean
ICP of 16 mmHg; where as those with
severe vasospasm have a mean level of 27
mmHg.
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– Increased ICP is usually due to an increase
in CSF outflow resistance and block of the
arachnoid villi.
– Higher ICP is associated with higher
mortality.
• Hydrocephalus
– Acute or chronic
• Epilepsy
– It seams reasonable in most young patients
with middle cerebral hematomas should be
treated with anticonvulsants for at least 2
years.
Causes of SAH Excluding Aneurysms
and AVMs
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Angiopathy
Venous thrombosis
Blood diseases
Allergic diseases
Infections
Intoxications
Tumors
Trauma
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