The Mid-Clival–Presigmoid Angle: A New Variable for Vestibular Schwannoma Surgery

Background: Vestibular schwannomas (VS) management represents one of the most difficult challenges in neurosurgery due to the controversy and complexity of selecting a proper treatment strategy. When surgery is favored, the choice among the available techniques is also a matter of debate. Many variables have been described to assist in the selection of an adequate surgical approach. Nevertheless, objective factors are needed to compare the most common approaches employed. The presence of a high jugular bulb represents a relative contraindication of the translabyrinthine (TL) approach in VS surgery. Theoretically, an anteriorly running sigmoid sinus, narrowing the presigmoid window, may represent an additional limitation to the TL approach selection.

Objective: To describe and study a new variable, the mid-clival–presigmoid angle, and compare objectively the surgical access provided by the TL and the retrosigmoid (RS) approaches for the treatment of vestibular schwannomas.

Methods: A retrospective review of patients who were operated on for VS at our tertiary-referral center was conducted. Patients were subdivided into an RS and a TL group. Ten patients per group were retrieved and subsequently analyzed. The axial sections of T1-weighted post-gadolinium images were considered and used for measurements. Two angles with their vertex located anteriorly on the midpoint of the clivus, a posteromedial point at the most anterior and prominent point of the sigmoid sinus and posterolateral points at the floor and the roof of the IAC were measured in MRI axial sections ([Figs. 1] [2]). In addition, anatomic (Koos grade and jugular bulb location), and functional (facial and hearing functionality) variables were analyzed.

Results: The angles considered, objectively quantified the width of the presigmoid window. No statistically significant differences (p > 0.05) in the superior (TL: mean = 10.032 ± SD 1.32 - RS: mean = 10.838 ± SD 2.93) ([Fig. 3]) and inferior (TL: mean=8.521 ± SD 1.42 - RS: mean = 8.419 ± SD 3.18) ([Fig. 4]) angles measured in patients who underwent TL and RS approaches were observed, regardless of the anatomical and functional findings.

Conclusions: The angles here studied reflect the width of the presigmoid window, providing an objective variable to guide the selection process between TL and RS approaches. A narrow presigmoid window may not represent a limitation of the TL approach during surgical strategy selection for the VS treatment. Further prospective studies are necessary to prove the reliability of this variable.

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Publication History

Article published online:
01 February 2023