Analog Clock as a Road Map to the Cranial Nerves of the Cerebellopontine Angle

Introduction: Tumors of the cerebellopontine angle (CPA) can significantly distort the cisternal anatomy of the posterior fossa, further complicating resection of these lesions. Despite the significant displacement of neurovascular structures in the setting of large CPA pathology, the position of cranial nerves (CNs) at the point where they exit the posterior fossa often does not change. As such, in this study we aimed to relate position of the poruses of the cranial nerves in the exiting the posterior fossa to the porus of the internal auditory canal (IAC), as this structure is often the first landmark identified surgery of the CPA.

Methods: Fifty sides of 25 formalin-fixed, latex-injected anatomical specimens were dissected. A standard retrosigmoid approach was performed bilaterally, followed by a cerebellar hemispherectomy. A photogrammetry model was generated from each dissection. Using the photogrammetry model, the distance from the IAC to the following structures was measured: the superior aspect of the jugular foramen, the porus of Dorello’s canal, the porus of the trigeminal nerve, and the entrance of the trochlear nerve into the tentorium. To better guide surgeons as to where to expect these structures along the petrous bone, we report their position as in with respect to the IAC using the metaphor of an analog clock.

Results: Although at different depths the jugular foramen was positioned at the 2 o’clock direction and 13.2 mm away from the IAC, the trigeminal porus was at the 11 o’clock position and 12.4 millimeters away from the IAC. The entrance of Dorello’s canal was at the 1 o’clock position, approximately 19.8 mm from the IAC. The tentorial entrance of CN VI was at the 9 o’clock position, approximately 19.3 millimeters away from the IAC. The cisternal segment of the oculomotor nerve was at the 10 o’clock position, approximately 28.5 millimeters away from the IAC ([Figs. 1] [2] [3]).

Conclusion: The IAC serves as an excellent reference to aid in locating the porus of the CNs IV to XI as they exit the posterior fossa, which may be especially as lesions rarely displace the CNs entry into the skull base.

Publikationsverlauf

Artikel online veröffentlicht:
07. Februar 2025