• Ken Matsushima, Noritaka Komune, Satoshi Matsuo, and Michihiro Kohno.
• Department of Neurological Surgery, University of Florida, Gainesville, Florida, USA; Department of Neurosurgery, Tokyo Medical University, Shinjuku-ku, Tokyo, Japan. Electronic address: ken.matsushima.g@gmail.com.
• World Neurosurg. 2017 Jul 1; 103: 620-630.

ObjectiveThe use of the retrosigmoid approach has recently been expanded by several modifications, including the suprameatal, transmeatal, suprajugular, and inframeatal extensions. Intradural temporal bone drilling without damaging vital structures inside or beside the bone, such as the internal carotid artery and jugular bulb, is a key step for these extensions. This study aimed to examine the microsurgical and endoscopic anatomy of the extensions of the retrosigmoid approach and to evaluate the clinical feasibility of an electromagnetic navigation system during intradural temporal bone drilling.MethodsFive temporal bones and 8 cadaveric cerebellopontine angles were examined to clarify the anatomy of retrosigmoid intradural temporal bone drilling. Twenty additional cerebellopontine angles were dissected in a clinical setting with an electromagnetic navigation system while measuring the target registration errors at 8 surgical landmarks on and inside the temporal bone.ResultsRetrosigmoid intradural temporal bone drilling expanded the surgical exposure to allow access to the petroclival and parasellar regions (suprameatal), internal acoustic meatus (transmeatal), upper jugular foramen (suprajugular), and petrous apex (inframeatal). The electromagnetic navigation continuously guided the drilling without line of sight limitation, and its small devices were easily manipulated in the deep and narrow surgical field in the posterior fossa. Mean target registration error was less than 0.50 mm during these procedures.ConclusionsThe combination of endoscopic and microsurgical techniques aids in achieving optimal exposure for retrosigmoid intradural temporal bone drilling. The electromagnetic navigation system had clear advantages with acceptable accuracy including the usability of small devices without line of sight limitation.Copyright © 2017 Elsevier Inc. All rights reserved.

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