AJR 2005; 184:571-573
© American Roentgen Ray Society
Unilateral Agenesis of Internal Carotid Artery with Ophthalmic Artery Arising from Posterior Communicating Artery
Ramin M. Naeini1,
Jitakshi De2,
Tetsu Satow1 and
Goetz Benndorf1
1 Department of Radiology, The Methodist Hospital, Baylor College of Medicine,
One Baylor Plaza, Houston, TX 77030.
2 Department of Pathology and Laboratory Medicine, The University of Texas
Health Science Center at Houston, Medical School, Houston, Texas 77225.
Received April 5, 2004;
accepted after revision July 19, 2004.
Address correspondence to G. Benndorf.
Introduction
Agenesis and hypoplasia of the internal carotid artery are rare congenital
anomalies, occurring in less than 0.01% of the population
[1]. "Agenesis" can
be defined as total failure of an organ to develop embryologically;
"aplasia," as lack of development despite the presence of a
precursor; and "hypoplasia," as incomplete development of the
organ [2]. These terms are used
interchangeably despite their different definitions, and the term
"absent internal carotid artery" is preferred for
simplification.
The ophthalmic artery as the first major branch of the internal carotid
artery typically originates under the lateral aspect of the optic nerve and
passes through the optic canal. Abnormal origins of the ophthalmic artery are
rare and vary depending on the fetal anastomoses established by the artery
with the adjacent vessels. We report an unusual case of unilateral internal
carotid artery absence associated with anomalous origin of the ophthalmic
artery from the ipsilateral posterior communicating artery.
Case History
A 38-year-old woman with acute right-sided headaches but no neurologic
deficit underwent duplex sonography, which raised the suspicion of an acute
ipsilateral internal carotid artery occlusion. To exclude an acute dissection,
we performed cerebral angiography, which surprisingly revealed an absent right
internal carotid artery with an anomalous origin of the ipsilateral ophthalmic
artery from the posterior communicating artery (Fig.
1A,
1B,
1C,
1D,
1E). The right middle cerebral
artery was directly supplied by the posterior circulation through a
hypertrophied posterior communicating artery, whereas the right anterior
cerebral artery was supplied through a patent anterior communicating artery.
Except for a direct origin of the left vertebral artery from the aortic arch,
the remaining extra- and intracranial vasculature was otherwise normal.
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Fig. 1A. —38-year-old woman with acute headaches. Arteriogram shows
aortic arch, left anterior oblique projection, with origin of common carotid
artery (single long arrow) from right subclavian artery
(brachiocephalic trunk) giving rise to external carotid artery only. Double
arrow indicates left vertebral artery; short arrow indicates left vertebral
artery directly arising from arch.
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Fig. 1B. —38-year-old woman with acute headaches. Right external
arteriogram, lateral view, shows no anastomosis to internal carotid artery
territory. Particularly, middle meningeal artery does not supply ophthalmic
artery.
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Fig. 1C. —38-year-old woman with acute headaches. Arteriograms, right
vertebral artery injection, lateral (C) and anteroposterior (D)
views, show origin of right ophthalmic artery (arrows) from posterior
communicating artery. Arrowheads (C) indicate choroidal blush.
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Fig. 1D. —38-year-old woman with acute headaches. Arteriograms, right
vertebral artery injection, lateral (C) and anteroposterior (D)
views, show origin of right ophthalmic artery (arrows) from posterior
communicating artery. Arrowheads (C) indicate choroidal blush.
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Fig. 1E. —38-year-old woman with acute headaches. Schematic drawing
shows anatomic disposition in presented case. MCA = middle cerebral artery,
ICA = internal carotid artery, PcomA = posterior communicating artery, MMA =
middle meningeal artery, OA = ophthalmic artery, ECA = external carotid
artery, and IMA = internal maxillary artery.
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Discussion
Absence of internal carotid artery can be observed as a single anatomic
variant or in association with complex vascular malformations such as in
patients with PHACE syndrome
[3]. It may be asymptomatic if
sufficient collateral circulation exists but may also be associated with
transient ischemic attacks, hemiplegia, and intracranial hemorrhage
[1]. On the basis of his
observations, Lie [2] described
two basic patterns of collateral circulation in association with absence of
the internal carotid artery. The fetal type, seen in nearly all cases,
develops during an early embryogenic stage. The anterior cerebral artery is
supplied by the contralateral internal carotid artery via the anterior
communicating artery, whereas the middle cerebral artery is supplied by an
enlarged posterior communicating artery as in our patient. The second, the
adult type, is believed to occur later in embryogenesis and after completion
of the circle of Willis. Given et al.
[4] recently described six
possible patterns of collateral circulation, surprisingly without including
the ophthalmic artery; little is known about its anomalous origin and
collateral flow to the optic organ in case of internal carotid artery
absence.
According to Padget [5], the
internal carotid artery originates from the dorsal aorta and the third aortic
arch at approximately the 3-mm embryonic stage, but complete development does
not occur earlier than the 16–18 mm stage (40 days). So far, there is no
exact explanation for developmental anomalies of the internal carotid artery,
but all variations are thought to occur because of insults to the developing
embryo. Keen [6] suggested that
mechanical insults to the developing embryo such as excessive folding of the
embryo to one side, pressure effects, or restriction by amniotic bands may
cause unilateral absence of internal carotid artery.
The ophthalmic artery has a complex embryogenesis, which is closely related
to the development of the internal carotid artery. As described by Padget
[5], the primitive internal
carotid artery in a 4-mm embryo gives rise to its cranial and caudal branches
and supplies the orbit with two main primitive arteries. The dorsal ophthalmic
artery arising from the future internal carotid artery siphon reaches the
orbit through the superior orbital fissure. The ventral ophthalmic artery,
arising at that time from the anterior cerebral artery, reaches the orbit
through the optic canal and supplies the optic tract
[7]. By the time the embryo
reaches 18 mm, the dorsal ophthalmic artery and the ventral ophthalmic artery
develop an anastomosis with each other and eventually terminate in a plexus
that supplies the optic cup. At the same time, the ventral ophthalmic artery
forms an anastomosis with the internal carotid artery and its proximal segment
regresses. The stem of the permanent ophthalmic artery, also called primitive
ophthalmic artery [7], is first
identified arising from the supracavernous internal carotid artery and reaches
its definite origin from the future C2 or C3 segment (according to Fischer's
[8] classification) by
considerable caudal migration. The dorsal ophthalmic artery starts to regress
and will be finally reduced to the anteromedial branch of the inferolateral
trunk. (In this stage, the stapedial artery originating from the primitive
hyoid branch of internal carotid artery gives off two branches: the
maxillomandibular and the supraorbital arteries. When the embryo reaches 20
mm, the supraorbital branch of the stapedial artery forms an anastomosis with
the permanent ophthalmic artery. Later, at the 40-mm stage, the anastomosis is
complete and the adult configuration of the ophthalmic artery is
identifiable.
Anomalous origins of the ophthalmic artery from the posterior communicating
artery are very rare with four such variants reported so far
[6,
9–11],
of which the only one proven by cerebral angiography is published in the
non-English literature [11].
The most commonly reported variants are the origins from the middle meningeal
[12] and the anterior cerebral
[7] arteries. Other possible
origins are the accessory meningeal artery, the basilar artery
[7], and possibly the middle
cerebral, the anterior deep temporal, and the external carotid arteries
[12].
The first observation of a posterior communicating artery origin was made
by Fisher [9] in 1914. He
described a bilateral absence of both internal carotid arteries in a cadaver
and showed the origin of the ophthalmic artery from the posterior
communicating artery. Keen [6]
described agenesis of both internal carotid arteries in a 55-year-old man with
a marked enlargement of both the vertebral and the basilar arteries. Each
posterior cerebral artery gave rise to an enlarged posterior communicating
artery, which itself gave off small ophthalmic arteries on either side. Hills
and Sament [10] reviewed the
findings in a 10-week-old infant who died because of severe cardiac anomalies.
Both internal carotid arteries were absent at the base of the brain. The
posterior communicating artery gave off ophthalmic arteries and continued
forward to bifurcate into the anterior and middle cerebral arteries.
So far, the only radiographically visualized case of unilateral internal
carotid artery absence and posterior communicating artery origin of ophthalmic
artery has been reported by Nakata and Iwata
[11] in a 41-year-old woman
with sudden onset of headache and fever. Cerebral angiography revealed
complete absence of the left internal carotid artery and an enlarged left
posterior communicating artery, which gave off the left ophthalmic artery. The
embryologic explanation for an origin from the posterior communicating artery
remains speculative but probably needs involution of internal carotid artery
as a coexisting factor. The type of collateral flow pattern suggests an
interruption before the circle of Willis is completed (24-mm stage). Probably,
the ventral ophthalmic artery had stopped migrating caudally at the segment
where the posterior communicating artery joins the M1 segment of the middle
cerebral artery (usually the terminal internal carotid artery segment).
Otherwise, as discussed in the case of Nakata and Iwata
[11], a part of the posterior
communicating artery in our patient may actually belong to the internal
carotid artery, and the dominant collateral flow through the posterior
communicating artery plays a major role in determining it as an origin for the
ophthalmic artery.
Knowledge of anatomic variants in the cerebral circulation such as internal
carotid artery absence and their association with anomalous origins of the
ophthalmic artery may be helpful in avoiding misinterpretation of clinical and
imaging patterns in ischemic stroke. In patients undergoing carotid
endarterectomy, unilateral supply of brain territories can become crucial.
Furthermore, it may also help to differentiate a questionable internal carotid
artery dissection or occlusion from a simple anatomic variation without
clinical consequence.
Conclusion
Association of an absent internal carotid artery with a posterior
communicating artery origin of the ophthalmic artery is extremely rare. We
provide the first angiographic documentation in the English literature and
discuss related embryologic theories.
References
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Introduction
Case History
