Abordaje a la Cisterna Ambiens

OBJECTIVE: To describe a step-by-step approach to the ambient cistern by the suboccipital retrosigmoid supracerebellar infratentorial (RSI) approach. DESCRIPTION: The RSI approach is performed in the same manner as the suboccipital retrosigmoid approach, usually used to access the pathology of the cerebellopontine angle, with the following modifications: (1) we always use the semi-sitting position, (2) the craniotomy-craniectomy must expose the transverse sinus and extend 5 cm medially to the inion, (3) when performing the dural opening it is necessary to mobilize the dura with the transverse sinus upwards, (4) under magnification with surgical microscope the cerebellomedullary cistern should be opened in order to drain cerebrospinal fluid for relaxing the cerebellum, and (5) arachnoidal adherences and bridging veins must be coagulated and cut if necessary. These maneuvers create a wide corridor to the ambient cistern. CONCLUSION: This approach allows a safe access to the ambient cistern, especially to the infratentorial portion.