Porus Acusticus Obstruction from a Densely Adherent Loop of Aica during Retrosigmoid Resection of a Vestibular Schwannoma

The retrosigmoid approach to the cerebellopontine angle (CPA) for the microdissection of vestibular schwannomas allows for excellent access to the CPA and medial internal auditory canal (IAC). It also allows for attempted preservation of residual hearing. Challenges of this approach include occasional need for excessive retraction, limited access to the fundus of the IAC, and the management of vascular loops within the CPA. We present a case in which a loop of anterior inferior cerebellar artery (AICA) was found to be densely adherent to the dura of the superior porus acusticus, requiring microsurgical release, and translocation.

A 53-year-old female presented with a left 2-cm, cystic CPA mass on magnetic resonance imaging (MRI). Audiometric testing revealed a speech recognition threshold of 10 dB and a discrimination of 96%. The decision was made to perform a retrosigmoid approach for microsurgical resection of the CPA mass. After creation of the craniotomy and dural flaps, the cerebellum was retracted. The tumor was seen to extend from the tentorium cerebelli to the region of the lower cranial nerves. The cystic regions were then decompressed to allow for access to the porus acusticus and exposure of the entire tumor. Upon decompression, there was immediately noted a pulsatile band of soft tissue plastered against the rostral portion of the posterior wall of the petrous bone. This obstruction was adherent to the dura at the superior porus as well. Further dissection revealed a loop of the rostral trunk of AICA to be adherent to the dura of the porus and the posterior wall of the petrous bone. The dura was incised just superior to the artery which was then carefully dissected free from the underlying bone and reflected inferiorly. This revealed the posterior boney wall of the IAC, which was then drilled out to reveal the entire tumor. Gross total resection was achieved. The AICA loop was then examined and found to be pulsatile and healthy appearing without obvious sign of injury or thrombosis. It was replaced to its naturally lying position prior to closure.

The arteries of the CPA, particularly the AICA, can have a variable relationship with the seventh and eighth cranial nerves. It most often passes below the nerves but can pass between or above them. However, the artery always will divide into a dominant rostral trunk to supply the superior petrosal cerebellar surface and caudal trunk to supply the inferior petrosal cerebellar surface. In situations where the artery passes above the nerve bundle, tumor growth can push the artery forward and superiorly. Previous research has documented the existence of challenging AICAs; however, there is a paucity of literature detailing the management of these situations. We present a case where microsurgical release of an adherent AICA from the dura of the superior portion of the posterior petrous bone allowed for access to the porus acusticus and gross total resection of a CPA vestibular schwannoma.

No conflict of interest has been declared by the author(s).

Publication History

Article published online:
12 February 2021