The Lateral Suboccipital Retrosigmoid Approach and Its Variations

Abstract

The lateral suboccipital retrosigmoid approach, one of the common procedures used in neurosurgical operations, is indicated for lesions at the cerebellopontine angle CPA. The location of the craniotomy varies according to the main location of the pathology in the superior, middle, or inferior CPA. Here we introduce the basic procedure of the technique and its variations. First, the diagnosis of the pathology, and the relationship between the sutures and sinuses should be confirmed by preoperative magnetic resonance imaging MRI and computed tomography CT. Three dimensional MRI CT fusion images are a great help in performing secure operative planning. Neuromonitoring techniques using cranial nerve stimulators or auditory evoked potentials, are also essential for CPA surgery. The lateral positioning obtained, with suitable head fixation, is especially important. Two different skin incisions, either a lazy S or V shaped, are used in consideration of the hair pattern of the patient. The bulk of the posterior nuchal muscles are caudally reflected, to avoid damaging them, which prevents postoperative shoulder stiffness and muscle contraction headaches. Performing the appropriate craniotomy is also key for a successful outcome. A superior CPA approach is taken for lesions around the trigeminal nerve, a middle CPA approach is used for pathological conditions around the auditory and facial nerves, and an inferior CPA approach is best for lesions around the lower cranial nerves and the pontomedullary junction. A high speed drill and kerrison rongeurs are used for the craniotomy in order to obtain secure exposure of the posterior margin of the sigmoid sinus and to maximally preserve the autologous bone. The opening of the foramen magnum and removal of the posterior arch of the C1 are not necessary however, a transcondylar or extreme lateral approach should be considered when a more ventrocaudal visual axis is required. For intradural procedures, careful attention should be paid to the preservation of the veins, direction of the optic axis of the microscope, and circulation of the cerebrospinal fluid. In conclusion, there are three basic craniotomies of the lateral suboccipital retrosigmoid approach, which broadly correspond to addressing pathological conditions in the superior, middle, and inferior CPA.