Intracranial aneurysms are a significant cause of morbidity and
mortality. Aneurysm rupture is the most common cause of atraumatic
subarachnoid hemorrhage. Death or severe disability in seen in 40
to 60% of patients following the initial hemorrhage. When
untreated, an additional 25 to 35% of these patients die due to
subsequent hemorrhagic events.1,2,3
Berry aneurysms comprise the vast majority (97%) of intracranial
aneurysms. They are found in 1% of the general population,2 and
have a female to male occurrence ratio of 3:2. The incidence of
berry aneurysm increases with advancing age and with associated
conditions, including adult polycystic kidney disease,
Ehlers-Danlos syndrome, neurofibromatosis, aortic coarctation, and
Historically, the first anatomic description of intracranial
aneurysm dates back to 1778, when Biumi reported an intracavernous
aneurysm of the internal carotid artery.2 The first radiographic
description of intracranial aneurysms is credited to Moniz who, in
1933, published an angiogram demonstrating a large aneurysm of the
internal carotid artery at the skull base in a young man affected
by syphilis. More recently, the advent of computed tomography4 and
magnetic resonance imaging, along with improved angiographic,
endovascular, and neurosurgical techniques, have allowed for more
rapid and accurate diagnosis and treatment of intracranial
aneurysms. The diagnosis is commonly suggested by the presence of
subarachnoid hemorrhage on unenhanced computed tomography. In some
patients, however, a less common pattern of hemorrhage may be
present. Prompt recognition of the unusual patterns of hemorrhage
resulting from aneurysm rupture is important for a better chance of
a favorable treatment outcome. The following pictorial essay will
discuss and illustrate the spectrum of uncommon patterns of
hemorrhage associated with ruptured intracranial aneurysms.
Unenhanced CT examination is undoubtedly the initial exam of
choice in the diagnosis of a ruptured intracranial aneurysm, due to
its high sensitivity for acute hemorrhage (90 to 95%).1
Extraluminal blood will appear as high attenuation material along
the subarachnoid cisterns. The pattern of distribution of
subarachnoid blood seen on computed tomography can offer clues as
to the likely location of the aneurysm. For instance, hemorrhage
found predominantly in the interhemispheric fissures is suggestive
of an anterior communicating artery aneurysm; hemorrhage collecting
mainly along the sylvian fissure suggests a middle cerebral artery
aneurysm. Posterior cerebral artery aneurysms may display
significant hemorrhage in the basilar cisterns.
While subarachnoid hemorrhage is essentially a universal finding
of aneurysm rupture, other less common patterns of hemorrhage may
be present. These include intraparenchymal, intraventricular, and
subdural hemorrhage. The pathophysiology of these unusual patterns
of hemorrhage has not been established. However, it has been
postulated that aneurysms which have ruptured previously may become
associated with fibrosis along the surrounding tissues, and this
may predispose to later rupture into the parenchyma or the subdural
Anterior cerebral, pericallosal, and anterior communicating
artery aneurysms (figures 1-3) may be associated with
intraparenchymal hemorrhage in the frontal lobe. The hematoma can
have intraventricular extension, often involving the frontal horns
of the lateral ventricles and, at times, extending to the third
ventricle. The hematoma also may dissect along the sulcus of the
corpus callosum to the region of the splenium.
Middle cerebral artery and carotid terminus aneurysms (figures
4-6) also can present as intraparenchymal hemorrhage, often
affecting the region of the basal ganglia. As this area is a common
site for hypertensive hemorrhage, the radiologist must determine
that a hemorrhage that is felt to be hypertensive in nature is not
contiguous with the sylvian fissure, i.e., with the subarachnoid
space. In such cases of hemorrhages with a basal
ganglia and a subarachnoid component, further study with
conventional angiography is necessary to exclude an aneurysm.
Rarely, a ruptured middle cerebral artery aneurysm can present
as a subdural hematoma (figure 6). Such a finding may be seen in up
to 2% of those patients eventually diagnosed with a ruptured
intracranial aneurysm;2 most of these involve the middle cerebral
artery bifurcation, likely owing to its lateral location.
Intraparenchymal hemorrhage secondary to aneurysm rupture can also
affect the temporal lobes; such a pattern has been seen in the
setting of posterior communicating artery aneurysms that project
laterally (figure 7).
Aneurysms affecting the posterior circulation (figures 8-9) can
likewise demonstrate unusual patterns of hemorrhage.5 For instance,
intraparenchymal cerebellar hemorrhage involving the tonsils has
been seen in the setting of aneurysms in the distal posterior
inferior cerebellar artery. When such aneurysms are found, they are
not infrequently associated with arteriovenous malformations that
are being fed from the aneurysmal artery.6 Rupture of a posterior
inferior cerebellar artery aneurysm may be associated with isolated
subarachnoid hemorrhage at the level of the foramen magnum; such a
finding may be fairly subtle on computed tomography (figure 8) due
to the beam-hardening artifact. Intraventricular hemorrhage also
can be seen in cases of a ruptured posterior circulation aneurysm.
Posterior inferior cerebellar artery, superior cerebellar artery,
or basilar tip aneurysms can present with hemorrhage extending into
the fourth ventricle.7 AR
1. Camarata PJ, Latchaw RE, Rufenacht DA, Heros RC: Intracranial
aneurysms. Invest Radiol 28(4):378-382, 1993.
2. Heiserman J, Bird R: Cerebral aneurysms. Neuroimaging Clin
North Am 4(4):799-822, 1994.
3. Atlas S: Intracranial vascular malformations and aneurysms.
Radiol Clin North Am 26(4):830-837, 1988.
4. Schwartz R, Tice H, Hooten S, et al: Evaluation of cerebral
aneurysms with helical CT: Correlation with conventional
angiography and MR angiography. Radiology 192:717-722, 1994.
5. Kamiya K, Nagai H, Koide K, et al: Peripheral anterior and
inferior cerebellar artery aneurysms. Surg Neurol 42(1):46-51,
6. Mabuchi S, Kamiyama H, Abe H: Distal aneurysms of the
superior cerebellar artery and posterior inferior cerebellar artery
feeding and associated arteriovenous malformations: Case Report.
Neurosurgery 30(2):284-287, 1992.
7. Zingale A, Chiaramonte I, Consoli V, Albanese V: Distal
posterior inferior cerebellar artery saccular and giant aneurysms:
Report of two new cases and a comprehensive review of the
surgically treated cases. J Neurosurg Sci 38(2):93-104, 1994.
Dr. Iaia, Dr. Schwartz, and Dr. Klufas are in the Department of
Radiology at Brigham and Women's Hospital and Harvard Medical
School in Boston, MA. Dr. Steig is in the Department of
Neurosurgery, also at Brigham and Women's Hospital and Harvard