Management of a challenging dura-embedded anterior inferior cerebellar artery loop during a retrosigmoid hearing-preserving vestibular schwannoma resection: microsurgical technique and operative video. Illustrative case

Abstract

Background: Anatomical variants of the anterior inferior cerebellar artery (AICA), such as an anomalous "AICA loop" embedded in the dura and bone of the subarcuate fossa, increase the complexity and risk of vestibular schwannoma resections. Classically, osseous penetrating AICA loops are the most challenging to mobilize, as the dura must be dissected and the surrounding petrous bone must be drilled to mobilize the AICA away from the surgical corridor and out of harm.

Observations: The authors present a rare case of a dura-embedded, osseous-penetrating AICA loop encountered during a hearing-preserving retrosigmoid approach in which they demonstrate safe and efficient microdissection and mobilization of the AICA loop without having to drill the surrounding bone.

Lessons: Although preoperative recognition of potentially dangerous AICA loops has been challenging, thin-sliced petrous bone computed tomography scanning and high-quality magnetic resonance imaging can be useful in preoperative diagnosis. Furthermore, this report suggests that a retrosigmoid approach is superior, as it allows early intradural recognition and proximal vascular control and facilitates more versatile mobilization of AICA loops.

Keywords: anatomy; anterior inferior cerebellar artery; subarcuate fossa; vestibular schwannoma.

FIG. 1.

Preoperative constructive interference in steady-state (CISS) magnetic resonance imaging (MRI) showing a small, left-sided, intracanalicular vestibular schwannoma (VS) and an anterior inferior cerebellar artery (AICA) loop embedded in the dura posterolateral to the internal auditory canal (IAC).

FIG. 2.

Preoperative audiogram showed intact hearing in both ears. S = Unmasked sound field; A = Aided sound field; CID = Central Institute for the Deaf; W-22 = Phonetically balanced test for word recognition (i.e. speech discrimination).

FIG. 3.

Intraoperative photographs after a left retrosigmoid craniectomy and dural opening. A: A long subarcuate artery, apart from the AICA loop, was bipolar coagulated and divided early. B: The AICA loop embedded in the dura and temporal bone. C: The dura around the AICA loop was cut with a beaver blade, the dura was dissected down off the bone, and the portion of the AICA loop entering the petrous bone was mobilized out, exposing the end of this deep subarcuate fossa (SF). D: The facial nerve was mapped, and the vestibular nerves can also be visualized. E: The posterior lip of the IAC was removed using a bone-removing claw attachment of an ultrasonic aspirator. F and G: The distal pole of the intracanalicular tumor was dissected off the dura, and the cochlear nerve was identified. H: The tumor was dissected off the facial, cochlear, and part of the superior vestibular nerve; the tumor origin from the inferior vestibular nerve was identified and cut; and the tumor was removed in one piece. Inf. = inferior; Sup. = superior.

FIG. 4.

Postoperative CISS MRI showing complete resection of the left intracanalicular VS and the mobilized AICA loop.

FIG. 5.

Immediate postoperative audiogram showed slightly diminished but preserved hearing on the left side.