A Classification for the Anterior Inferior Cerebellar Artery-Subarcuate Artery Complex Based on the Embryological Development

Emergent Revascularization After Transposition of an Unexpected Intraosseous Anomalous Subarcuate Loop During Vestibular Schwannoma Surgery: A Case Report

BACKGROUND AND IMPORTANCE

The presence of an anomalous anteroinferior cerebellar artery (AICA) embedded within the subarcuate fossa increases the difficulty of cerebellopontine angle (CPA) tumor surgery. Iatrogenic injury of posterior fossa arteries can result in serious morbidity.

CLINICAL PRESENTATION

A 70-year-old man presented with right-sided hearing loss and facial dysesthesia. Magnetic resonance imaging showed a tumor with solid and cystic components and 35-mm maximum diameter in the right CPA. The AICA traveled just dorsal to the tumor and was well-developed because the ipsilateral vertebral artery and posteroinferior cerebellar artery (PICA) were aplastic. During surgery, we unexpectedly encountered an anomalous loop of the AICA-PICA which was embedded in the subarcuate fossa. This loop was mobilized using an ultrasonic bone curette to enable further tumor resection. However, it occluded immediately after mobilization and required open thrombectomy and end-to-end anastomosis. After revascularization, near-complete tumor resection was achieved without causing facial nerve dysfunction or brainstem/cerebellar infarction. Pathological examination of the resected anomalous loop showed abnormal focal hypertrophy of the adventitia and the presence of external elastic lamina.

CONCLUSION

Mobilization of an anomalous AICA-PICA loop embedded within the subarcuate fossa during VS resection can result in arterial occlusion which requires thrombectomy and revascularization. Surgeons should be aware of this vascular anomaly and be prepared to deal with its ramifications.

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

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.

The "Deep Subarcuate Fossa" sign and three types of anomalous subarcuate loops encountered during vestibular schwannoma removal

BACKGROUND

An anomalous subarcuate loop (SL) of the anteroinferior cerebellar artery (AICA) is a rare anatomic variation, which increases the complexity and risk of vestibular schwannoma (VS) removal. However, preoperative diagnosis of this anomaly remains difficult. The aim of this study was to report three types of anomalous SLs encountered during VS removal and to describe the "Deep Subarcuate Fossa (SF)" sign and its significance in the diagnosis and treatment of an osseous-penetrating SL.

METHODS

We prospectively observed 963 patients with newly/recently diagnosed VS who underwent surgical treatment performed by the senior author (P.Z.) from 2012 to 2021 and identified 16 patients with an anomalous SL. The SF was retrospectively measured on preoperative thin-slice temporal bone computed tomography in 963 patients.

RESULTS

Three types of anomalous SLs were encountered during VS removal: the apex of the SL was embedded in the dorsal tumor capsule (type I, 1 case), the dura (type II, 8 cases), or the dura and bone (type III, 7 cases) surrounding the SF. The depth of the SF in 7 patients with a type III anomalous SL ranged from 2.3 to 7.0 mm (3.56 ± 1.56 mm), which was significantly larger than that in 845 patients without an osseous-penetrating SL (1.23 ± 0.43 mm) (p = 0.008). When the depth of the SF exceeded 2 mm, the sensitivity and precision of the diagnosis of a type III anomalous SL were 100% (7/7) and 31.8% (7/22), respectively.

CONCLUSION

Three types of anomalous SLs may be encountered during VS removal, and AICA displacement is recommended before tumor removal. The "Deep SF" sign may indicate the existence of a type III anomalous SL and it can predict the depth of the AICA in the bone and guide the drilling of the bone around the vessel loop.