The Glossopharyngo-Cochlear Triangle—Part II: Case Series Highlighting the Clinical Application to High-Riding Posterior Inferior Cerebellar Artery Aneurysms Exposed Through the Extended Retrosigmoid Approach

Abstract

BACKGROUND Use of the far lateral transcondylar (FL) approach and vagoaccessory triangle is the standard exposure for clipping most posterior inferior cerebellar artery (PICA) aneurysms. However, a distal PICA origin or high-lying vertebrobasilar junction can position the aneurysm beyond the vagoaccessory triangle, making the conventional FL approach inappropriate. OBJECTIVE To demonstrate the utility of the extended retrosigmoid (eRS) approach and a lateral trajectory through the glossopharyngo-cochlear triangle as the surgical corridor for these cases. METHODS High-riding PICA aneurysms treated by microsurgery were retrospectively reviewed, comparing exposure through the eRS and FL approaches. Clinical, surgical, and outcome measures were evaluated. Distances from the aneurysm neck to the internal auditory canal (IAC), jugular foramen, and foramen magnum were measured. RESULTS Six patients with PICA aneurysms underwent clipping using the eRS approach; 5 had high-riding PICA aneurysms based on measurements from preoperative computed tomography angiography (CTA). Mean distances of the aneurysm neck above the foramen magnum, below the IAC, and above the jugular foramen were 27.0 mm, 3.7 mm, and 8.2 mm, respectively. Distances were all significantly lower versus the comparison group of 9 patients with normal or low-riding PICA aneurysms treated using an FL approach (P < .01). All 6 aneurysms treated using eRS were completely occluded without operative complications. CONCLUSION The eRS approach is an important alternative to the FL approach for high-riding PICA aneurysms, identified as having necks more than 23 mm above the foramen magnum on CTA. The glossopharyngo-cochlear triangle is another important anatomic triangle that facilitates microsurgical dissection.

A taxonomy for brainstem cavernous malformations: subtypes of pontine lesions. Part 1: basilar, peritrigeminal, and middle peduncular

“…1,20 These nerve complexes define 3 triangular dissection routes: 1) the supratrigeminal triangle, superior to the trigeminal nerve and inferior to the tentorium and trochlear nerve; 2) the infratrigeminal triangle, inferior to the trigeminal nerve and superior to the vestibular nerve; and 3) the glossopharyngo-cochlear triangle, inferior to the cochlear nerve and superior to the glossopharyngeal nerve. 9,21,22 The supratrigeminal triangle provides a good trajectory to superiorly located lesions despite its small size and limited room between CN V and the tentorium. 23 The infratrigeminal triangle provides the largest corridor and best exposure of the anterolateral pontine surface, with the low origin of the vestibulocochlear nerves and the high position of the trigeminal nerve.…”

“…The ascending courses of CNs VII and VIII relative to the lower CNs form this small access triangle. 21,22 The approach through the cerebellopontine cistern provides an oblique or tangential exposure of the lesion that is not aligned with the lesion's axis. However, opening safe entry zones helps compensate.…”

In Reply: The Glossopharyngo-Cochlear Triangle—Part II: Case Series Highlighting the Clinical Application to High-Riding Posterior Inferior Cerebellar Artery Aneurysms Exposed Through the Extended Retrosigmoid Approach

“…We hope this 2-part study successfully described the elucidation and execution of a patient-specific, microsurgical approach using the glossopharyngo-cochlear triangle (GCT) to treat a select subset of posterior inferior cerebellar artery (PICA) aneurysms. 2,3 We wholeheartedly agree that 2-part studies-in which part I 3 provides an in-depth discussion of the microsurgical anatomy and results of cadaveric dissections and part II 2 highlights the clinical utility and the nuances of "realworld" surgical application of the anatomic principles-are "indispensable prerequisite(s)." 1 We thank the editorial board of Operative Neurosurgery for continuing to publish and support these important endeavors.…”

“…In our clinical manuscript, in addition to reporting increased distance of the aneurysm from the foramen magnum, we reported how the distances from the internal auditory canal (IAC) and jugular foramen (JF) to the aneurysm differed significantly between typical and high-riding PICA aneurysms. 2 High-riding PICA aneurysms had a mean distance below the IAC of 3.7 mm (range 0-6.8 mm) and a mean distance above the JF of 8.2 mm (range 6.9-9.4 mm). In contrast, the control group of typical PICA aneurysms had a mean distance below the IAC of 11.6 mm (range 7.0-18.0 mm) and a mean distance above the JF of 1.9 mm (range −7.3 to 7.3 mm).…”

“…With regard to the definition of a "high-riding PICA aneurysm," we found a measurement greater than 23 mm above the foramen magnum to be the most straightforward clinically applicable measurement. 2,3 However, this is just one of many anatomic clues that can guide approach selection and patientspecific surgical intervention. In our clinical manuscript, in addition to reporting increased distance of the aneurysm from the foramen magnum, we reported how the distances from the internal auditory canal (IAC) and jugular foramen (JF) to the aneurysm differed significantly between typical and high-riding PICA aneurysms.…”