Microsurgical Anatomy Of The Far Lateral Keyhole Approach

Part I: Design and Microsurgical Anatomy of Retrosigmoid-Retrocondylar Keyhole Approach without Occipital CondyleRemovalObjective: To design a new retrosigmoid-retrocondylar keyhole approach based on minimally invasive keyhole idea and explore its feasibility and indications, which can be regarded as the base of this keyhole approach in clinical use.Methods: Eight adult cadaveric heads fixed in formalin and with intracranial vessels perfused by colored latex were used in this study. To search for the most suitable length and shape of the skin incision, we examined two kinds of incision (longitudinal 'S' shape and a straight one) and two lengths (5cm and 7cm, respectively). Due to the complexity and thickness of suboccipital muscles, two ways of muscle dissection were compared: 1). muscles incised perpendicularly in layers; 2). muscles detached and reflected in layers. A retrosigmoid-retrocondylar bone flap was made about 3cm in diameter with a craniotome. Many anatomic structures can be observed under microscope when cerebellar hemisphere was retracted. After comparing and balancing the above steps in all specimens, a novel,feasible, duplicable retrosigmoid-retrocondylar keyhole approach was devised.Results: The proper incision of retrosigmoid-retrocondylar keyhole approach was a longitudinal'S' shaped skin incision about 7cm length with its super border 2cm behind the middle point of mastoid and inferior margin at the level of C₂. The method of detachment and reflection of occipital muscles is superior to the method of cutting them perpendicularly. By means of adjusting head position and the angle of microscope, the ispilateral vertebral artery, posterior inferior cerebellar artery, anterior inferior cerebellar artery, VIE, IX, X, XI, XII cranial nerves and the ventrally lateral aspect of medulla oblongata were exposed via this keyhole approach.