Stapedial Artery: From Embryology to Different Possible Adult Configurations

Abstract

The stapedial artery is an embryonic artery that represents the precursor of some orbital, dural, and maxillary branches. Although its embryologic development and transformations are very complex, it is mandatory to understand the numerous anatomic variations of the middle meningeal artery. Thus, in the first part of this review, we describe in detail the hyostapedial system development with its variants, referring also to some critical points of ICA, ophthalmic artery, trigeminal artery, and inferolateral trunk embryology. This basis will allow the understanding of the anatomic variants of the middle meningeal artery, which we address in the second part of the review.

FIG 1.

Embryologic segments of the ICA. Consecutive stages of ICA embryologic development. The first stages of development (A) are characterized by the presence of 3 aortic arches that link the ventral aorta (VA) and the dorsal aorta (DA). The VA regresses together with the ventral part of the aortic arches. The dorsal remnants of the aortic arches persist as embryonic arteries. These embryonic arteries divide the ICA into 7 embryologic segments: 1) the cervical segment: it derives from the remnant of the third aortic arch (III AA); 2) the ascending intrapetrous segment: it is the remnant of the DA between the second (II AA) and third (III AA) aortic arches; the division point between segments 2 and 3 is at the point of origin of the hyoid artery (HA), that is, the dorsal remnant of the second aortic arch (II AA); 3) the horizontal intrapetrous segment: it is the remnant of the DA between the first (I AA) and second (II AA) aortic arches; the division point is at the point of origin of the mandibular artery (MA), which corresponds to the dorsal remnant of the first aortic arch (I AA); 4) the intracavernous ascending segment: it originates from the DA between the first aortic arch (I AA) and the primitive maxillary artery (PMA), which connects the DA of the 2 sides (dorsal aorta left [DAl]; dorsal aorta right [DAr]). The trigeminal artery origins at the junction between the segment 4 and 5 of the ICA; this latter represents a primitive connection between the cavernous ICA and the basilar artery (BA); 5) the horizontal intracavernous segment: it derives from the DA between the PMA and the primitive dorsal OA (PDOA); 6) the clinoid segment: it corresponds to the DA between the PDOA and the primitive ventral OA; and 7) the terminal segment: the terminal ICA between primitive ventral OA and the primitive ICA bifurcation into the future anterior cerebral artery (ACA) and the future posterior communicating artery (PComA). The figure also shows the hypoglossal artery (HypA) and the proatlantal artery (PA), which originate proximal to the third aortic arch and will contribute to the formation of the external carotid artery (ECA) branches.

FIG 2.

Persistent SA and intratympanic flow of the ICA. A, The normal regression process of the hyostapedial system. After the SA proximal regression, its proximal remnant originates from the ICA as the carotico-tympanic artery (CTA). Its distal part is annexed by the ventral pharyngeal artery, the future external carotid artery, to give the internal maxillary artery its first and major branch, the middle meningeal artery (MMA). The MMA side of the SA persists as the petrosal branch (PB), which gives birth to the superior tympanic artery (STA). The anastomotic branch to the hyostapedial system from the ascendant pharyngeal artery (APhA) persists as the inferior tympanic artery (ITA). The CTA, STA, and ITA contribute to the adult vascularization of the middle ear. B, Persistent SA. In the case of complete SA persistency, this artery originates from the petrous ICA and gives, intracranially, the MMA, and the internal maxillary artery exits the middle fossa skull base through the foramen spinosum as the extracranial branch. This variant is due to the lack of annexation of the maxillary-mandibular branch by the ventral pharyngeal artery. C, Pseudopetrous or aberrant intratympanic ICA. This variant is due to the agenesis of the cervical ICA (third aortic arch). The cervical ICA agenesis is bypassed through a hypertrophic inferior tympanic artery, which courses from the APhA through the inferior tympanic canal and reaches the CTA. The intratympanic ICA flow is called “aberrant” because the artery does not course into its usual canal but into an enlarged inferior tympanic canal. D, Pseudopetrous ICA with or without SA persistency. This variant is due to 2 phenomena: the agenesis of the cervical ICA and SA persistency. In this case, the ITA does not reach the CTA but the persistent SA (pSA).

FIG 3.

DSA with a bilateral partial persistent SA in a patient with Moyamoya disease. A and B, show the right and left ICA injection, respectively, with the MMA (red arrow) arising from the petrous ICA. This phenomenon is possible because of bilateral SA persistency. B, The ICA is narrowed and stopped at the level of the OA due to Moyamoya disease. C, A 3D reconstruction of the right ICA from which the MMA originates (red arrow). D, The left external carotid artery injection without the MMA enhancement because of its absence.

FIG 4.

The MMA origin of the OA: a case of a complete OA origin from the MMA. The selective injection of the MMA in the anteroposterior projection (A) shows that the sphenoidal artery (SphA) arises from the MMA after its bifurcation into the anterior (red arrow) and posterior division (blue arrow). It courses along the inner surface of the temporal and sphenoidal bone and enters the orbit through the superior orbital fissure (SOF) to give rise to the OA. B, An oblique ICA injection, highlighting the absence of the OA.