ARRI Medical GmbH 1 article published in JoVE Medicine Intrathecal Application of a Fluorescent Dye for the Identification of Cerebrospinal Fluid Leaks in Cochlear Malformation Nora M. Weiss1, Ingo Andus2, Armin Schneider3, Sönke Langner4, Stefanie Schröder1, Sebastian P. Schraven1, Robert Mlynski1 1Department of Otorhinolaryngology, Head and Neck Surgery, University Medical Center Rostock, 2Rostock University, 3ARRI Medical GmbH, 4Department of Radiology and Institute of Diagnostic and Interventional Radiology, University Medical Center Rostock Intrathecally applied fluorescein is used to achieve intraoperative visualization of CSF leaks. This protocol describes a lumbar puncture, the application of 5% fluorescein, and intraoperative visualization using a fully digital microscope.