ARTICLE IN PRESS

Letter to the Editor

Internal Carotid Artery Agenesis with an Intercavernous
Anastomosis: A Rare Case

Background: Agenesis of the internal carotid artery (ICA) is a rare vascular anomaly
that was first observed postmortem. Various anastomoses supply the distal vessels
at the site of agenesis. Of these anastomoses, an intercavernous anastomosis is
very rare. This paper presents a patient with ischemic stroke in whom we discovered
left ICA agenesis and an ipsilateral intercavernous anastomosis. Case: A 58-year-old
man with a history of myocardial infarction and diabetes mellitus presented with
sudden-onset difficulty in speaking, numbness on the left side of the face, and
weakness of the left arm and leg. Neurological examination revealed dysarthria,
left facial paralysis, left hemiparesis, and bilateral absence of the plantar reflexes.
Diffusion-weighted magnetic resonance imaging showed a right middle cerebral
artery (MCA) infarction. On cranial and cervical magnetic resonance angiography, the left ICA could not be seen distal to the bifurcation; the left MCA was
supplied through an intercavernous anastomosis between the right ICA and the
left ICA. Cranial computed tomography (CT) revealed the absence of the left carotid
canal. Digital subtraction angiography led to a diagnosis of left ICA agenesis
with an intercavernous anastomosis. The patient was discharged on acetylsalicylic acid and warfarin. Conclusion: ICA agenesis with an intercavernous anastomosis
is a rare vascular anomaly that should be differentiated from secondary causes
of ICA stenosis and occlusions by showing agenesis of the carotid canal on cranial
CT. Key Words: Agenesis of the internal carotid artery—intercavernous
anastomosis—vascular anomaly embryogenesis.
© 2017 National Stroke Association. Published by Elsevier Inc. All rights reserved.

Dear Editor,
Agenesis, segmental aplasia, or hypoplasia of the internal carotid artery (ICA) is a rare vascular anomaly. It
may be unilateral or bilateral, and it is seen in less than
.01% of the population.1 The distal ICA and intracranial
arteries are supplied through various anastomoses when
there is cervical ICA agenesis. Lie classified the collateral circulation into 6 different pathways. The most
common collateral circulations (types A to C) develop via
the circle of Willis. A type D anastomosis, a trans-sellar,
or an intercavernous anastomosis is seen very rarely.2 In
this report, we present a patient who had an ischemic
stroke and was found to have left ICA agenesis and an
intercavernous anastomosis.

1052-3057/$ - see front matter
© 2017 National Stroke Association. Published by Elsevier Inc. All
rights reserved.

Case
A 58-year-old man presented with sudden-onset
facial numbness, difficulty in speaking, and weakness
of the left arm and leg. He had a history of myocardial
infarction and diabetes mellitus and was taking acetylsalicylic acid irregularly. On neurological examination,
he was alert, attentive, and followed commands. He had
dysarthria and a flattened left nasolabial sulcus. Motor
examination revealed mild paresis of the left arm and
leg. The plantar reflex was absent bilaterally. He had
hypoesthesia on the left side of his face. His vital signs
were normal. The physical examination was normal. His
complete blood count, kidney and liver function tests,
and infection markers were normal. There was no acute
lesion on cranial computed tomography (CT). Diffusionweighted magnetic resonance imaging showed acute
infarction of the right middle cerebral artery (MCA). On
further workup, we discovered left ICA occlusion on magnetic resonance angiography, which revealed an
intercavernous anastomosis between the left ICA and the
right ICA (Fig 1). A review of the cranial CT showed left
carotid canal agenesis (Fig 2). To confirm the diagnosis,

Journal of Stroke and Cerebrovascular Diseases, Vol. ■■, No. ■■ (■■), 2017: pp ■■–■■

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Figure 3. Intercavernous anastomosis is seen on the posteroanterior right
CCA imaging in DSA. Abbreviations: CCA, common carotid artery; DSA,
digital subtraction angiography; PA, posteroanterior; R, right.
Figure 1. On magnetic resonance angiography, the left ICA is occluded
proximally and is supplied through an intercavernous anastomosis arising
from the right ICA. Abbreviation: ICA, internal carotid artery.

Discussion

Figure 2.
agenesis.

Axial cranial computed tomography showed left carotid canal

digital subtraction angiography was performed and showed
left-sided ICA agenesis and an intercavernous anastomosis (Figs 3 and 4). Electrocardiography showed normal
sinus rhythm. The patient was discharged on acetylsalicylic acid and warfarin based on an ejection fraction of
45% on echocardiography.

The formation of the ICA is first seen in the 3- to 5-mm
embryonic stage, and it is completed in 6 weeks of gestation.3
Dorsal aorta, ventral aorta, and third aortic arch are the
structures that give rise to the ICA.3 The formation of the
circle of Willis takes place during the 7- to 24-mm embryonic stage.4 Mechanisms for failure of development of
the ICA and the formation of various anastomoses are speculated. Keen suggested that excessive bending of the embryo
to the one side or compression from amniotic bands may
cause agenesis of the ICA on the affected side.5 Cali et al.
postulated that the type of anastomoses is dependent upon
the time at which the disruption to the embryo occurs.
Disruptions before the 24-mm embryonic stage result in
primitive anastomoses, whereas disruptions after this stage
result in anastomoses via the circle of Willis.4
The origin of the anastomotic vessel is speculated. Lie
stated that a failed connection between the basilar artery
and primitive trigeminal arteries, and the fusion of the primitive trigeminal arteries on both sides were the origin of
the anastomotic vessel.2 Padget described plexiform channels around Rathke’s pouch, which connects the ICAs, and
thought that the origin of the anastomosis can be explained by these vessels.3 Sinha et al put forward that the
contralateral ICA is filled via the primitive maxillary artery.6
Duan et al suggested that the anastomotic vessel is the
same as the capsular artery because it originates from the
horizontal segment of the ICA and courses medially in front
of the cavernous sinus.7 In our case, the anastomotic vessel
originated from the posterior of the cavernous segment
of the right ICA and coursed anteriorly, and then medially

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INTERNAL CAROTID ARTERY AGENESIS AND INTERCAVERNOUS ANASTOMOSIS

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Figure 4. Posterior origin of the intercavernous anastomotic vessel is seen on the left side. After leaving the ICA, the anastomotic vessel courses medially and anteriorly (middle image) in front of the sella (on the right side). The anastomotic vessel than opens into the left ICA on its medial side (middle
image). Abbreviations: CCA, common carotid artery; ICA, internal carotid artery; LAT, lateral; R, right.

in front of the pituitary gland, through the floor of the
sella. The anastomotic vessel opened into the cavernous
segment of the left ICA on the medial side. We believe
that the anastomotic vessel does not originate from the
primitive trigeminal artery or the primitive maxillary artery
because it is related to the medial aspect of the ICA on
the left side. The primitive trigeminal artery courses
posteromedially, and the primitive maxillary artery courses
anterolaterally, whereas our vessel courses anteriorly and
medially. This finding also does not support the primitive trigeminal artery and primitive maxillary artery
hypotheses. We think that plexiform vessels around the
sella give rise to the intercavernous vessels.
Lie classified collaterals associated with ICA agenesis
into 6 different groups.2 The most common pattern is
type A, in which the ipsilateral MCA is supplied via
the posterior communicating artery (PComA) arising
from posterior cerebral artery, and agenesis of the ipsilateral A1 segment of the ACA is seen. In the type B
pattern, the collateral circulation is achieved via the
anterior communicating artery. Bilateral agenesis of the
ICA is seen in the type C pattern, and the anterior
circulation is supplied via the bilateral PComAs arising
from the basilar artery. The type D pattern, which our
patient had, is associated with an intercavernous anastomosis. The MCA is supplied via an intercavernous
anastomosis between the intracavernous segments of
the bilateral ICAs. In these patients, the anastomosis
may be transsphenoidal, intrasellar, or supraclinoid.8,9
In type E anastomosis, both ICAs are hypoplastic, and
they supply only ipsilateral ACAs. MCAs are supplied
from the enlarged PComAs on both sides. Type F anastomosis is a condition in which distal flow is achieved
via collaterals between ICAs and ECAs, and these
collaterals are named as rete mirabile.2
In a literature review, Oz et al. summarized 36 intercavernous anastomosis cases involving 21 men and

15 women.10 The agenesis was right sided in 21 of these
patients and left sided in 15. Zink et al. reported a 2:1
left predominance in ICA aplasia/hypoplasia regardless
of the type of anastomosis, although they did not find
any significant sex difference.11 Another study reported
male predominance in left-sided agenesis.12 Oz et al. did
not report a sex or side predominance in intercavernous anastomosis and stated that the small number of cases
was insufficient to generalize the findings.10
Patients with ICA agenesis may be asymptomatic or
present with different clinical situations, such as subarachnoid hemorrhage due to the rupture of an intracranial
aneurysm or ischemic stroke.10 Intracranial aneurysms are
seen 25%-43% of patients with ICA agenesis, which is
much higher than that in the general population.11 In type
D anastomosis, an incidental diagnosis or nonspecific symptoms are frequent. Of the 36 cases summarized in Oz et al.,
20 presented with nonspecific symptoms (headache, dizziness, tinnitus, and incidental symptoms), and 16 presented
with cerebrovascular accidents (acute ischemia, subarachnoid hemorrhage, or vision loss).10
It is important to differentiate ICA agenesis with intercavernous anastomosis, a rare congenital anomaly,
from ICA stenosis and occlusion related to secondary
causes. Patients may be diagnosed after developing
nonspecific symptoms or having cerebrovascular accidents. The absence of the carotid canal on cranial CT
is important for diagnosing ICA agenesis. After diagnosis, patients need to be followed up regularly to check
for aneurysms. Additionally, this anomaly may lead to
serious complications in endarterectomy or transsphenoidal
surgery.
Mucahid Erdogan, MD
Department of Neurology, Bakirkoy Research and Training
Hospital for Psychiatry, Neurology, Neurosurgery, Istanbul,
Turkey

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Songul Senadim, MD
Department of Neurology, Bakirkoy Research and Training
Hospital for Psychiatry, Neurology, Neurosurgery, Istanbul,
Turkey.
E-mail: songulsenadim@hotmail.com
K. Nur Ince Yasinoglu, MD
Department of Neurology, Bakirkoy Research and Training
Hospital for Psychiatry, Neurology, Neurosurgery, Istanbul,
Turkey
H. Hakan Selcuk, MD
Department of Radiology, Bakirkoy Dr. Sadi Konuk Training
and Research Hospital, İstanbul, Turkey
H. Dilek Atakli, MD
Department of Neurology, Bakirkoy Research and Training
Hospital for Psychiatry, Neurology, Neurosurgery, Istanbul,
Turkey
http://dx.doi.org/10.1016/j.jstrokecerebrovasdis.2017.06.055

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