2026 Proffered Presentations
S289: SURGICAL ACCESS TO THE INFEROMEDIAL PONS: ANATOMICAL STUDY OF THE GLOSSOPHARYNGEAL-COCHLEAR TRIANGLE THROUGH STANDARD AND EXTENDED RETROSIGMOID APPROACHES
Kivanc Yangi, MD1; Egemen Gok1; Sahin Hanalioglu, MD, PhD2; Hilal A Aktas, MD, PhD3; Jack T Olson, BS1; Jarett E Prince, BS1; Kashif Qureshi, MS1; Michael T Lawton, MD1; Mark C Preul, MD1; 1Barrow Neurological Institute; 2Department of Neurosurgery, Hacettepe University Medical Faculty; 3Department of Anatomy, Hacettepe University Medical Faculty
Introduction: Anatomical triangles, defined by neurovascular structures, serve as convenient navigational landmarks that can reinforce anatomical knowledge. They may also function as useful neurosurgical guides during dissection toward deep-seated targets. In this context, the glossopharyngeal–cochlear triangle (GCT), bounded by the acousticofacial complex (CNVII–VIII), the petrous bone, and the glossopharyngeal nerve (CNIX), has not been thoroughly investigated. Its potential as a reliable and expandable microsurgical pathway to the cerebellopontine and cerebellomedullary cisterns, as well as the inferomedial pons, merits detailed anatomical evaluation. This study provides descriptive and quantitative analyses of the GCT through a retrosigmoid trajectory focusing on its boundaries, expandability, and surgical exposure, to support its application in microsurgical approaches, particularly in cases such as posterior fossa tumors and high-riding posterior inferior cerebellar artery (PICA) aneurysms.
Methods: Eight formalin-fixed, latex-injected cadaveric heads (16 sides) were dissected using both standard (RS) and extended retrosigmoid (xRS) craniotomies. Neuronavigation-based measurements were obtained to assess the surgical freedom of the RS and xRS approaches and to evaluate triangle dimensions under standard and expanded exposures. Statistical analyses were performed with R software (v4.4.3) to compare RS and xRS approaches, as well as standard and expanded brainstem exposures through GCT. Two additional cadaveric heads were dissected and photographed to illustrate relevant brainstem anatomy. Additionally, ultra–high-resolution 7-Tesla MRI with 3D modeling was employed to visualize the associated fiber tracts.
Results: The GCT is bounded superiorly by the CN VII–VIII complex, inferiorly by CN IX, and anteriorly by the petrous bone, with mean edge lengths of 14.6(2.5) mm, 12.6(2.5) mm, and 7.8(2.1) mm, respectively. Triangle vertex angle analysis showed the widest angle at the inferolateral vertex, 88.5(16.1)°, followed by the superior vertex at 59.5(15.9)° and the inferomedial vertex at 32.0(10.3)°. The standard brainstem exposure through the GCT measured 65.0(17.0) mm², increasing to 109.6(39.0) mm² after mobilization of the retractable edges (p=0.001). The craniocaudal angle of attack was 12.1(4.2)° for the RS approach and 16.0(8.0)° for the xRS approach (p>0.05). The mediolateral angle of attack measured 20.4(5.4)° for RS and 28.8(14.2)° for xRS (p>0.05). The GCT provides access to the distal V4 segment of the vertebral artery, a1–a3 segments of the anterior inferior cerebellar artery, basilar artery, p2 segment of the PICA, abducens nerve, pontomedullary sulcus safe entry zone, and the inferomedial peritrigeminal region.
Conclusions: The GCT represents a reliable and expandable surgical corridor that provides access to the inferomedial pontine region as well as the cerebellopontine and cerebellomedullary cisterns. Quantitative anatomical analysis of this region can provide crucial understanding for neurosurgical planning, particularly for peritrigeminal cavernous malformations and high-riding PICA aneurysms. While the RS approach allows a narrow angle of attack to the GCT, skeletonization of the sigmoid sinus with the xRS approach enhances surgical exposure and provides a more favorable operative angle. Integrating microsurgical dissection with advanced imaging modalities deepens anatomical understanding, thereby refining surgical strategies and ultimately improving precision and patient outcomes.