Retrosigmoid Craniotomy and Intradural Variations: Role of Patient-Specific Preoperative Imaging to Identify Landmarks and Relevant Structures.

Objective: There are several landmarks to safely identify the limits of the retrosigmoid approach and its intradural variations; however, there has been little discussion about how those landmarks may vary among patients.

Methods: Patient positions; surface landmarks for the retrosigmoid craniotomy; and structures to recognize for transmeatal, suprameatal, suprajugular, and transtentorial extensions were reviewed.

Results: The position of the dural sinuses in relation to the zygomatic-inion line and digastric notch line is readily identified on magnetic resonance imaging. For transmeatal drilling, the position of the semicircular canals, vestibular aqueduct, and jugular bulb is best evaluated on computed tomography. For suprameatal drilling, the labyrinth and the position and integrity of the carotid canal are relevant for planning the anterior extension of the approach. For transtentorial extension, it is desirable to identify incisural structures. For suprajugular drilling, the position of the jugular bulb, invasion of venous structures, and integrity of the roof of the jugular foramen must be checked preoperatively.

Conclusions: The retrosigmoid approach is the workhorse of posterior skull base surgery. By recognizing patient-specific variations in known landmarks, the approach may be tailored prevent complications.