Origin of the Labyrinthine Artery
The labyrinthine artery originates from the vertebrobasilar system, the vessels of which, along with the circle of Willis, supply the brainstem and adjacent structures.
- Primary origin: Most commonly, the vessel arises directly from the basilar artery (a. basilaris), an unpaired trunk formed by the confluence of the two vertebral arteries.
- Alternative origin: Less frequently, the labyrinthine artery may originate from the anterior inferior cerebellar artery (a. cerebelli inferior anterior), which branches off the basilar artery.
Topography and Course
The labyrinthine artery courses toward the internal ear (auris interna).
- Internal acoustic meatus (meatus acusticus internus): The vessel enters this meatus, which runs from medial to lateral.
- Contents of the meatus: Along with the labyrinthine artery, the meatus transmits the facial nerve (n. facialis, cranial nerve VII), intermediate nerve (n. intermedius), and vestibulocochlear nerve (n. vestibulocochlearis, cranial nerve VIII). The labyrinthine artery passes through the meatus acusticus internus alongside the n. vestibulocochlearis to reach the internal ear.
Branches of the Labyrinthine Artery
Within the internal acoustic meatus, the labyrinthine artery divides into cochlear and vestibular branches.
- Cochlear branch (r. cochlearis) — runs along the axis of the cochlea. It gives off branches to the spiral canal of the cochlea and the osseous spiral lamina. In the subepithelial layer of the scala vestibuli, this branch forms numerous arterial glomeruli of the cochlea (glomeruli arteriosi cochleae). The cochlear branch supplies the basilar membrane, the spiral organ, and the periosteum of the osseous labyrinth.
- Vestibular branches (rr. vestibulares) — supply the membranous vestibule, providing blood to the utricle (utriculus), saccule (sacculus), and the ampullae of the semicircular ducts.
Supplied Structures of the Internal Ear
The internal ear is located within the petrous part of the temporal bone between the tympanic cavity and the internal acoustic meatus. Its blood supply is provided by the labyrinthine artery.
- Osseous labyrinth (labyrinthus osseus): Comprises the centrally located vestibule, the cochlea anterior and medial to the vestibule, and the osseous semicircular canals posterior and lateral to it. The osseous semicircular canals (anterior, posterior, and lateral) communicate with the vestibule via 5 openings.
- Membranous labyrinth (labyrinthus membranaceus): A connective tissue structure enclosed within the osseous labyrinth, mirroring its shape but smaller in volume. It contains endolymph.
- Perilymphatic space: The cleft between the osseous and membranous labyrinths, filled with perilymph.
Additional Blood Supply and Venous Drainage: In addition to the labyrinthine artery, small branches of the stylomastoid artery (a. stylomastoidea) travel through the fenestra cochleae to reach structures of the internal ear. Venous drainage occurs into the superior and inferior petrosal sinuses.