Far lateral approach: quantification of the exposure with the aid of a frameless stereotactic system

Objective: The purpose of the study was to evaluate the far lateral transcondylar transtubercular approach (FLTTA) based on the quantitative measurements of the exposure of the foramen magnum and clivus, obtained through different steps of this approach. Methods: The FLTTA was reproduced in 8 specially prepared injected cadaver heads (15 sides). The approach was divided into 6 steps (Table). After each step the same standard set of measurements was performed, using a frameless stereotactic device. This set of measurements determined two parameters: the size of the exposed clivai area and the size of the spatial cone, directed to the anterior rim of the foramen magnum, which depicted the surgical freedom for manipulation with the instruments. Results: Results of the measurements are presented in the table: Exposed Surgical clivai area freedom (% of final (% of final Steps of the FLTTA approach exposure) result) 1. Cl hemilaminectomy and suboccipital craniotomy 21 ±6% 18 ±9% 2. Partial resection of the occipital condyle 28 ±9% 40 ±12% 3. Resection of the jugular tuberculum 71 ±12% 52 ±18% 4. Limited mastoidectomy 80 ±17% 68 ±19% 5. Resection of the lateral mass of the Cl 94 ±18% 83 ±18% 6. Complete condylectomy (complete FLTTA) 100% 100% Conclusions: The most significant improvement of the exposure of the clivai area takes place after removal of the jugular tuberculum, although the surgical freedom still remains significantly limited. The presented data should be taken to consideration while planning the FLTTA.