Microsurgical Anatomy of the Labyrinthine and Subarcuate Arteries and Clinical Implications

Objective: The labyrinthine and subarcuate arteries are two small arteries that are usually exposed during the approaches to cerebellopontine angle. Both arteries arise most frequently from the anteroinferior cerebellar artery (AICA), but they may have different origins, as well as trajectories, and relationships with the surrounding neurovascular structures. Being able to identify and differentiate them is crucial due to the different clinical implication of their surgical compromise as sacrifice of the labyrinthine artery (LA) can result in hearing loss, whereas no clear clinical implications have been related to the subarcuate artery (SA) injury. The objective of the present work is to study the surgical anatomy and anatomical variations of the LA and the extrapetrous portion of the SA and their anatomical relationships.

Methods: 10 formalin-fixed latex-injected specimens were dissected (20 sides). After a retrosigmoid craniotomy was performed, the dura mater was opened and dissection of the neurovascular structures was achieved under microscopic magnification. A 4 mm, 0- and 30-degree endoscopic lenses (Storz) were then used to improve the exposure, visualization, and assessment of the vascular anatomy. The results were statistically analyzed.

Results: The LA was identified as the artery following the vestibulocochlear nerve into the internal auditory canal; its distal portion was posteroinferior to the vestibulocochlear nerve in 85.7% of the cases and in 14.3% was anterosuperior. The SA ended blindly in the dura mater around the subarcuate fossa and its distal portion was anterosuperior to the vestibulocochlear nerve in all cases. The origin of the LA was also posteroinferior to the vestibulocochlear nerve in the majority of the cases (57.1%), inferior in 28.6% and anterosuperior in the remaining 14.3%. The origin of the SA was posterosuperior to the vestibulocochlear nerve in 50% of the specimens, and posterior and between the facial and vestibulocochlear nerves in the remaining 50%. The main distance between the origin of the LA and SA was 7 mm. The LA branched off from the AICA in all cases but one, in where it arose from the basilar artery. The LA arose from the AICA loop in 85.7% of the cases and from the pre-loop AICA in the remaining 14.3% whereas the SA branched off from the preloop AICA in all cases. The average length of the LA was 13.6 mm (7–24 mm). It was found to be a single artery in 83% and two arteries in17%. The SA was present in 33.3% of the specimens; its average length was 8.5 mm (5–12 mm) and it was a single artery in all cases.

Conclusion: The LA is a constant artery that follows the vestibulocochlear nerve into the internal auditory canal whereas the SA ends in the dura mater of the subarcuate fossa and is only present in 33% of the cases. Both arteries arise mainly from the AICA. The LA is usually posteroinferior to the vestibulocochlear nerve at its distal aspect, whereas the SA is anterosuperior to the vestibulocochlear nerve. Understanding the surgical anatomy of the labyrinthine and subarcuate arteries and their anatomical relationships is important in approaches to the cerebellopontine angle.