Carotid rete mirabile (means wonderful net in Latin) (CRM) is a physiological network
between the internal carotid artery (ICA) and external carotid artery (ECA) found
in lower mammals such as dogs, cats, goats, oxeas, sheep, and pigs.
1
,
2)
CRM is typically located around the cavernous portion of the ICA. CRM supplied by
the branches of the ECA compensates for deficient intracranial blood supply and regulates
heat and intracranial blood pressure.
1
,
2)
Similar vascular networks between the ICA and ECA can be rarely developed as anastomotic
collateral pathways following segmental dysplasia of the ICA in the human. Those anastomoses
between the ICA and ECA resemble morphologically to a rete (net in Latin), and several
authors call those anastomotic pathways as carotid rete although those pathological
anastomotic collaterals are different from true physiological CRM in the lower mammals.
Those carotid rete-like collaterals in the human result from the dysplasia of the
ICA during the fetal stage. Herein, we present a case of these rare vascular networks
supplying a segmental hypoplastic ICA via the ECA, which was visualized well on 3D
volume-rendering reconstructed images. In this case presentation, we call those rete-like
vascular collaterals CRM for convenience of explanation.
A 36-year-old man with a past intracerebral hemorrhagic episode underwent a follow-up
angiography. The hypoplasia of the left ICA exiting from the foramen lacerum to the
proximal to the bifurcation of the meningohypophyseal trunk (horizontal intracavernous
segment, 5th segment defined by the classification of Lasjaunias) was disclosed. The
left carotid canal was also hypoplastic. The left distal ICA was fed contralaterally
by the right ICA
3)
and ipsilaterally by the left ECA via developed vascular networks. The right twig-like
anterior and middle cerebral arteries were also disclosed (
Fig. 1
). 3D reconstructed rotational digital cerebral angiography showed the anastomoses
between the ECA and distal ICA. The arteries branching from the internal maxillary
artery and ascending pharyngeal artery developed and passed through the superior orbital
fissure, foramen ovale, foramen spinosum, carotid canal, jugular foramen, and hypoglossal
canal, respectively. These arteries forming vascular networks among themselves entered
the inferolateral trunk or meningohypophyseal trunk (
Fig. 2
). The anastomoses between the ICA and ECA formed CRM morphologically.
Fig. 1
Angiographical findings. The left ICA (double arrows) distal to the horizontal intracavenous
segment was fed contralaterally through the anastomosis between the ICAs and ipsilaterally
via the carotid rete. The right twig-like anterior and middle cerebral arteries (black
arrowheads) were also disclosed (right internal carotid angiography: anteroposterior
[A] and lateral projection [B], left common carotid angiography: anteroposterior [C]
and lateral projection [D]). (E–G) The left ICA (double arrows) and right twig-like
anterior and middle cerebral arteries (white arrowheads) were demonstrated (3-D volume-rendering
reconstructed images of right internal carotid angiography [E],and those of left common
carotid angiography [F, G]). (H–K: multiplanar reconstruction images) The left carotid
canal was hypoplastic, but the ICA (double arrows) was observed. The left inferolateral
trunk (black arrowheads) and meningohypophyseal trunk (black arrows) were both developed.
The distal left ICA (double arrows) was anastomosed with the inferolateral trunk and
meningohypophyseal trunk. ICA: internal carotid artery
Fig. 2
Vascular network of the bilateral carotid arteries and left carotid rete. (A) The
schema demonstrates the anastomoses of carotid rete. In this case, carotid rete consists
of the branches through the superior orbital fissure, foramen ovale, foramen spinosum,
carotid canal, jugular foramen, and hypoglossal canal. (B) Postero-oblique view of
3D volume-rendering reconstructed images of the right internal carotid angiography.
(C) Postero-oblique view of 3D volume-rendering reconstructed images of the left common
carotid angiography. A: anterior; A1: A1 portion of the anterior cerebral artery;
Ab: anterior branch of the middle meningeal artery; AMA: accessory meningeal artery;
AphA: ascending pharyngeal artery; ASOF: artery of the superior orbital fissure; Cb:
carotid branch of the AphA; CC: carotid canal; DMA: dorsal meningeal artery; FO: foramen
ovale; FR: foramen rotundum; FS: foramen spinosum; H: head; Hb: hypoglossal branch
of the AphA; HC: hypoglossal canal; ICA: internal carotid artery; ICaA: inferior capsular
artery; ILT: inferolateral trunk; IMA: internal maxillary artery; Jb: jugular branch
of the AphA; JF: jugular foramen; L: left; LCA: lateral clival artery; MCA: middle
cerebral artery; MHT: meningohypophyseal trunk; MMA: middle meningeal artery; OphA:
ophthalmic artery; PCab: posterior cavernous sinus branch of the middle meningeal
artery; R: right; SOF: superior orbital fissure
The exact pathogenesis of CRM in the human remains unclear. However, the residual
carotid canal, which was observed in our case, can be considered as an evidence supporting
that the segmental regression (not agenesis) of the ICA occurs,
4)
and considering that the collateral flow of the distal ICA is supplied by the ECA,
not by the carotid-basilar anastomosis, segmental regression of the ICA can occur
in the late fetal stage (at least after five or six weeks of gestation). Thus, in
the pathogenesis of CRM, the most accepted hypothesis is the late segmental regression
of the ICA and development of rich collateral flow from the ECA.
1
,
4)
In case that segmental agenesis of the cervical portion or cavernous portion of the
ICA occurs, the ascending pharyngeal artery or internal maxillary artery branches
can work intracranial arterial supply.
2)
Development of the internal maxillary artery and ascending pharyngeal artery is considered
an angiographical feature of CRM in the human. These developed arteries usually feed
the cavernous portion of the ICA.
4
,
5)
In our case, the artery of the foramen rotundum did not develop. However, the cavernous
ICA was fed by the branches of the internal maxillary artery and ascending pharyngeal
artery via the inferolateral trunk and meningohypophyseal trunk.
Bilateral CRM is described more frequently than unilateral CRM.
2)
Typically, CRM is not accompanied by any abnormal vessels in the intradural circulation.
4)
In our case, CRM was unilateral and accompanied by a twig-like right anterior and
middle cerebral artery and a rare infundibular anastomosis.
3)
These features seem unique in our case.
In a review article of Paschoal et al., CRM is often reported from Asian countries
and can be found not only incidentally but also following neurological deficits, ischemic
stroke, and subarachnoid hemorrhage.
2)
This anomaly could have resulted in a hemorrhagic event. Coexistence of “carotid and
vertebral rete mirabile” is also described.
2)
Coexistence of multiple vascular anomalies including CRM may result from genetic conditions
in individual cases.
Though CRM is a rare vascular anomaly, this collateral network can contribute to analyze
the potential anastomoses between the ICA and ECA (the so-called dangerous anastomosis
in endovascular surgery) that generally regresses during the normal development. Due
to the recent development of 3D volume-rendering reconstructed images, we can evaluate
the anastomoses between the ICA and ECA in detail.
Disclosure Statement
The authors have no conflicts of interest concerning this study.