The posterior surface of the petrosal portion of the temporal bone is the back side of the Petrous part of the temporal bone, which is a complex and compact bone located in the skull. The petrous portion of the temporal bone is involved in the formation of the base of the skull and is adjacent to the middle and inner ear structures. The posterior surface of the petrosal portion of the temporal bone is relatively flat and forms part of the posterior cranial fossa. It is separated from the occipital bone by the sigmoid sulcus and is in close proximity to the sigmoid sinus and internal auditory canal, which contain important structures such as the facial nerve and cochlea. Knowledge of the anatomy of the posterior surface of the petrosal portion of the temporal bone is important for a range of clinical applications, including skull base surgery and middle ear surgery.

Different microsurgical transcranial approaches (MTAs) have been described to expose the posterior surface of the petrous bone (PPB). A quantitative, anatomical comparison of the most used MTAs, for specific areas of the PPB, is not available. Anatomical dissections were performed on five formalin-fixed, latex-injected cadaver heads (10 sides). Six MTAs were analyzed: Kawase approach (KWA), retrosigmoid approach (RSA), retrosigmoid approach with suprameatal extension (RSAS), retrolabyrinthine approach (RLA), translabyrinthine approach (TLA), and transcochlear approach (TCA). Surgical volumes and exposed areas of each approach were quantified with a dedicated neuronavigation system (ApproachViewer, part of GTx-Eyes II, University Health Network, Toronto, Canada) and adjuvant software (ITK-SNAP and Autodesk Meshmixer 3.5). Areas and volumes were compared using linear mixed models. Transcochlear approach (TCA) provided the best exposure of Trautmann's triangle and the retromeatal, suprameatal, meatal, and premeatal regions. Retrosigmoid approach (RSA) provided the best exposure to the inframeatal region, with retrosigmoid approach with suprameatal extension (RSAS) gaining significant exposure to the suprameatal region. KWA had the highest surgical volume, and RLA the lowest. Transpetrosal approaches offer the widest exposure of PPB proportionally to their invasiveness. Retrosigmoid approaches, which get to the studied region through a postero-lateral path, are paramount for the exposure of the inframeatal and suprameatal region and, given the adequate exposure of the remaining PPB, represent an effective approach for the cerebellopontine angle (CPA). These anatomical findings must be considered with approach-related morbidity and pathological features in order to choose the most appropriate approach in clinical practice ¹⁾.