DOI:10.2214/AJR.07.2453
AJR 2007; 189:893-897
© American Roentgen Ray Society
Double Origin of the Posterior Inferior Cerebellar Artery: Association with Intracranial Aneurysm on Catheter Angiography
Walter S. Lesley1,2,
M. Hasan Rajab3 and
Robert S. Case1
1 Department of Radiology, Section of Surgical Neuroradiology, Texas A & M
Health Science Center, College of Medicine, Scott and White Clinic, 2401 S
31st St., Temple, TX 76502.
2 Department of Surgery, Texas A & M Health Science Center, College of
Medicine, Scott and White Clinic, Temple, TX.
3 Department of Biostatistics, Texas A & M Health Science Center, College of
Medicine, Scott and White Clinic, Temple, TX.
Received January 31, 2007;
revised May 18, 2007;
Address correspondence to W. S. Lesley
(wlesley{at}swmail.sw.org).
Abstract
OBJECTIVE. Double origin of the posterior inferior cerebellar artery
(PICA) is a congenital anomaly in which the PICA forms from two separate
vessels arising from the vertebral artery. The prevalence of double origin of
the PICA on catheter angiography is unknown because only four case reports
have been published. Because some congenital intracranial vascular oddities
are associated with an elevated incidence of aneurysm formation, we sought to
determine the association between intracranial aneurysm and double origin of
the PICA and to measure the prevalence of double origin of the PICA on
catheter angiography.
MATERIALS AND METHODS. A retrospective review was done over a
27-month period to identify patients with double origin of the PICA. Patients
were excluded if both PICAs were not adequately visualized on catheter
angiography. The cohort was then divided into two groups consisting of
patients with and those without intracranial aneurysm.
RESULTS. A total of 207 patients (101 males, 106 females) met the
inclusion criteria. One or more cerebral aneurysms were found in 35.3% and
double origin of the PICA in 1.45% of the patients. Double origin of the PICA
was present in 4.1% of the patients with an aneurysm, and none of the patients
without an aneurysm had double origin of the PICA (p = 0.043). A
majority of the seven known cases of double origin of the PICA described by
angiography in the peer-reviewed literature have associated intracranial
aneurysm disease.
CONCLUSION. Our data show that double origin of the PICA is seen in
4.1% of patients with intracranial aneurysm and on 1.45% of catheter
angiograms. Double origin of the PICA has an increased association with
intracranial aneurysmal disease and may represent a risk factor for subsequent
development of intracranial aneurysm.
Keywords: aneurysm • angiography • congenital anomaly • posterior inferior cerebellar artery • vascular imaging
Introduction
Aposterior inferior cerebellar artery (PICA) with a double origin manifests
itself as two separate vessels arising from the same vertebral artery (VA)
that then converge and form the PICA proper. Our search of the peer-reviewed
literature yielded only four cases
[1–3]
of double origin of the PICA depicted on angiography. It is unclear whether
the double origin of the PICA is a rare entity or is simply an underrecognized
angiographic finding. The prevalence on angiography has never been calculated,
to our knowledge.
Intracranial aneurysms are, with rare exception, acquired lesions
[4]. Certain inherited
congenital anomalies, however, are predisposing factors for formation of
intracranial aneurysms. For example, the vascular disorders of Ehlers-Danlos
type 4 syndrome, coarctation of the aorta, and fibromuscular dysplasia all
carry increased risk of development of intracranial aneurysm
[5]. Because double origin of
the PICA is also a congenital aberrant vessel, an association with acquired
aneurysm might not be unexpected.
Materials and Methods
This study was approved by our institutional review board and was compliant
with the HIPAA. A retrospective review of the primary author's angiographic
database was conducted for the period August 2003 through October 2005 to
identify all cases of double origin of the PICA in patients who had undergone
catheter angiography. Patients were excluded from analysis if both PICAs were
not fully visualized. The patient's sex and clinical history and the presence
of intracranial saccular aneurysm were recorded. We used the Fisher's exact
test to compare the percentage of patients with double origin of the PICA in
the group with an aneurysm versus the percentage in the group without an
aneurysm. Statistical analysis of the data was performed with SAS software
(SAS version 8.2, SAS Institute). The designated level of significance was
p <0.05.
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Fig. 1A —67-year-old woman with double origin of left posterior
inferior cerebellar artery (PICA), trigeminal aneurysm, and vertebrobasilar
junction fenestration. Anteroposterior angiogram of right (A) and
lateral angiogram of left (B) vertebral arteries show two origins of
left PICA (solid black arrows) converging at proximal aspect of
anterior medullary segment of PICA (white arrow). Fenestrated
vertebrobasilar junction (dashed arrow, A) and
bulbous basilar tip–aneurysmal infundibuli of bilateral origins of
posterior cerebral and superior cerebellar artery are evident (A).
Double origin of PICA arises from nondominant vertebral artery.
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Fig. 1B —67-year-old woman with double origin of left posterior
inferior cerebellar artery (PICA), trigeminal aneurysm, and vertebrobasilar
junction fenestration. Anteroposterior angiogram of right (A) and
lateral angiogram of left (B) vertebral arteries show two origins of
left PICA (solid black arrows) converging at proximal aspect of
anterior medullary segment of PICA (white arrow). Fenestrated
vertebrobasilar junction (dashed arrow, A) and
bulbous basilar tip–aneurysmal infundibuli of bilateral origins of
posterior cerebral and superior cerebellar artery are evident (A).
Double origin of PICA arises from nondominant vertebral artery.
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Fig. 1C —67-year-old woman with double origin of left posterior
inferior cerebellar artery (PICA), trigeminal aneurysm, and vertebrobasilar
junction fenestration. Three-dimensional (C) and lateral conventional
(D) angiograms of left internal carotid artery show trigeminal artery
(black arrows, D) arising from small trigeminal aneurysm
(white arrow, C).
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Fig. 1D —67-year-old woman with double origin of left posterior
inferior cerebellar artery (PICA), trigeminal aneurysm, and vertebrobasilar
junction fenestration. Three-dimensional (C) and lateral conventional
(D) angiograms of left internal carotid artery show trigeminal artery
(black arrows, D) arising from small trigeminal aneurysm
(white arrow, C).
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Results
Indications for catheter angiography included intracranial and extracranial
atherosclerotic stenosis, acute stroke, crescendo transient ischemic attack,
vasculitis, epistaxis, leptomeningeal hemosiderosis, dural sinus thrombosis,
saccular aneurysm, arteriovenous malformation, carotid blowout, Wada testing,
intracranial hemorrhage, intracranial neoplasia, and tumoral involvement of
the face and neck. A total of 207 patients, 101 (48.8%) of whom were male (98
men and three boys) and 106 (51.2%) of whom were female (104 women and two
girls), met the inclusion criteria. None of the three boys and two girls had a
double origin of the PICA or aneurysm. Three (1.45%) of these patients were
found to have double origin of the PICA (Figs.
1A,
1B,
1C,
1D,
2A,
2B,
3A,
3B,
3C). Each of the three patients
also had a solitary intracranial aneurysm. Double origin of the PICA was
irrespective of the dominance of the parent VA. The seven known angiographic
cases of double origin of the PICA are summarized in
Table 1.
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Fig. 2A —42-year-old woman with double origin of left posterior
inferior cerebellar artery (PICA) and basilar tip aneurysm. Lateral (A)
and frontal (B) angiograms obtained during left vertebral artery
injection show left PICA has two origins (black arrows, A),
which converge at mid aspect of anterior medullary segment of PICA (white
arrow). Coils are evident in basilar tip aneurysm (A). Double
origin of PICA arises from slightly dominant vertebral artery.
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Fig. 2B —42-year-old woman with double origin of left posterior
inferior cerebellar artery (PICA) and basilar tip aneurysm. Lateral (A)
and frontal (B) angiograms obtained during left vertebral artery
injection show left PICA has two origins (black arrows, A),
which converge at mid aspect of anterior medullary segment of PICA (white
arrow). Coils are evident in basilar tip aneurysm (A). Double
origin of PICA arises from slightly dominant vertebral artery.
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Fig. 3A —82-year-old man with double origin of right posterior
inferior cerebellar artery (PICA) and superior hypophyseal aneurysm. Frontal
(A) and lateral (B) angiograms obtained during right vertebral
artery injection show right PICA has two origins (arrowheads), which
converge at mid aspect of anterior medullary segment (arrow) of
PICA.
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Fig. 3B —82-year-old man with double origin of right posterior
inferior cerebellar artery (PICA) and superior hypophyseal aneurysm. Frontal
(A) and lateral (B) angiograms obtained during right vertebral
artery injection show right PICA has two origins (arrowheads), which
converge at mid aspect of anterior medullary segment (arrow) of
PICA.
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Fig. 3C —82-year-old man with double origin of right posterior
inferior cerebellar artery (PICA) and superior hypophyseal aneurysm. Lateral
right internal carotid angiogram shows small unruptured superior hypophyseal
aneurysm (arrow).
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TABLE 1: Double Origin of the Posterior Inferior Cerebellar Artery (PICA):
Summary of Clinical and Angiographic Data
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At least one cerebral aneurysm was found in 73 (35.3%) of the 207 patients:
28.7% of the males and 41.5% of the females. Three (4.1%) of the 73 patients
with aneurysm had double origin of the PICA, and none of the 134 patients
without an aneurysm had double origin of the PICA (p = 0.043). More
than one half of all angiographically reported cases of double origin of the
PICA in the peer-reviewed literature (PubMed search) were associated with
intracranial aneurysmal disease.
Discussion
Double origin of the PICA represents an embryologic persistence of the
normal anastomosis between the lateral spinal artery and the PICA
[1]. The origin of the lateral
spinal artery is lateral in relation to the medulla. The artery typically
arises from either the intradural VA or the PICA, forming the caudal component
of the double origin of the PICA. The distal component of double origin of the
PICA is the PICA proper, which developmentally represents a hypertrophied
radiculopial artery. The two components of double origin of the PICA converge
into a single vessel at the anterior medullary segment. Bifid origin of the
PICA is both an acceptable alternative name and an accurate descriptive term
for double origin of the PICA.
Double origin of the PICA can be confused with fenestration or duplication
of the PICA. Fenestration is defined as focal division of a single originating
vessel that results in two distinct endothelium-lined channels that may or may
not share an adventitial layer
[6,
7]. Fenestration of the PICA is
quite rare, as evidenced by a single citation
[8] in the PubMed abstract
database. Duplication requires two distinct vessels with separate origins and
no distal arterial convergence. Double origin of the PICA should not be
confused with the common anteroinferior cerebellar artery–PICA
configuration that Icardo et al.
[9] call duplication of the
origin of the PICA, which occurs when the basilar origin of the anteroinferior
cerebellar artery and the vertebral origin of the PICA both contribute to the
PICA territory. Fenestration of the VA that spans the origin of the PICA can
be difficult to differentiate from double origin of the PICA. For purposes of
classification, we propose that a double-origin PICA exists when the PICA
arises from the smaller of the two fenestrated vessels, whereas in VA
fenestration the PICA originates from the larger fenestrated vessel.
Double origin of the PICA can develop on either the dominant or nondominant
VA, and it can arise from either the right or the left VA. Five (71%) of the
seven angiographically detailed cases of double origin of the PICA, a 5:2
ratio, were left-sided. This ratio is similar to the left-sided preponderance
of both VA duplication (9:5) and left VA dominance (3:1)
[10]. No explanation for these
side preferences has been offered.
Although double origin of the PICA is found more frequently in men, the
male-to-female ratio is 2:1, an interesting finding in light of the male
preponderance of duplication of the VA. Double origin of the PICA spans
boundaries of genetic heritage, having been found in persons identified as
Asian and those identified as white. The prevalence of double origin of the
PICA in the general population, determined at autopsy, was reviewed by Pasco
et al. [2]. In other studies
[11,
12], double origin of the PICA
was identified in only two (0.36%) of 550 brains. We found a fourfold greater
prevalence (1.45%) than that in our angiographic study. Because the patients
with aneurysm in our cohort had a similarly higher prevalence than the general
population, we believe this correlation is supporting evidence that double
origin of the PICA occurs more frequently in persons with an intracranial
aneurysm than in those without an aneurysm.
We do not believe that the relatively high percentage of our cohort with
aneurysms skews our conclusion that double origin of the PICA is associated
with intracranial aneurysm. Despite the overall 35.3% incidence of aneurysm in
our cohort, double origin of the PICA was not seen in any patient without an
aneurysm. If double origin of the PICA has no association with intracranial
aneurysm, our results would be highly unexpected given that the pretest
prevalence likelihood of harboring both an intracranial aneurysm and double
origin of the PICA would be 0.018% (0.05 aneurysm prevalence x 0.0036
autopsy-based prevalence of double origin of the PICA). The prevalence for
these two variables occurring simultaneously in the cohort was 4.5%, which is
250 times greater than predicted (4.5/0.018). In essence, the high incidence
of intracranial aneurysm in the cohort effectually allows elucidation of the
association between an infrequent variable (aneurysm) and a nearly rare
variable (double origin of the PICA). We conducted a statistical analysis of
the two subgroups of our patients and determined that those with intracranial
aneurysm were significantly more likely than those without aneurysm to have
double origin of the PICA (p =0.043).
We believe the aneurysm group in our study was a demographically
representative sample for three reasons. First, it was derived from a pool in
which there were nearly equal numbers of each sex. Second, the cohort
comprised patients undergoing evaluation of a variety of ailments other than
aneurysm and subarachnoid hemorrhage. Third, the sex distribution of the
aneurysm group followed the well-known 3:2 female-to-male demographic profile
of the general population.
One of our patients with double origin of the PICA had a trigeminal artery,
a trigeminal artery aneurysm, and a fenestrated vertebrobasilar arterial
junction. Although previous case reports have described intracranial aneurysm
in association with the trigeminal artery variant, Cloft et al.
[13] disproved this
association in their analysis of 34 patients with a trigeminal artery. Cloft
et al. found that only 3% of the trigeminal artery patients in their cohort
had an associated aneurysm. This percentage is no greater than that in the
general adult population. Regarding the fenestrated vertebrobasilar artery
junction, Campos et al. [14]
found that in 35.5% of cases of these congenital malformations an aneurysm was
intimately involved with the fenestration, a specific constellation of
findings not present in our patients. It may be reasonable to speculate,
however, that the presence of one congenital vascular anomaly presents
increased risk of the presence of additional vascular malformations. We
propose that double origin of the PICA may be a manifestation of an underlying
incomplete or regional vascular developmental disorganization that weakly yet
measurably elevates the tendency toward formation of acquired intracranial
aneurysms.
Among the seven known cases of angiographically proven double origin of the
PICA, at least four (57%) have been associated with intracranial aneurysm. In
two of the four previously reported cases, however, details about the
intracranial vasculature were incomplete. Exclusion of these two cases
suggests that as many 80% of all angiographically depicted PICAs with a double
origin are associated with intracranial aneurysmal disease. Our data show that
double origin of the PICA occurs in 4.1% of patients with intracranial
aneurysm and on 1.45% of catheter angiograms, demonstrating that the anomaly
has an increased association with intracranial aneurysm and may represent a
risk factor for subsequent development of an intracranial aneurysm.
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Abstract
Introduction
