title: Expanding the Horizon of the Suboccipital Retrosigmoid Approach to the Middle Incisural Space by Cutting the Tentorium Cerebelli: Anatomic Study and Illustration of 2 Cases.
abstract: OBJECTIVE
  Complex skull base approaches are often used to treat lesions within the middle incisural space; yet the well-known retrosigmoid route may provide an effective avenue to this difficult-to-reach region. The purpose of this study was to quantify the exposure advantages on the middle incisural space provided by cutting of the tentorium cerebelli via a standard suboccipital retrosigmoid approach (i.e., via the cerebellopontine cistern route). Also, 2 illustrative cases are presented.
  
  
  METHODS
  A suboccipital retrosigmoid approach to the middle incisural space was performed bilaterally in 3 specimens in the semisitting position. A quantitative analysis of the brainstem surface exposed above the origin of the trigeminal nerve was performed before and after tentorial incision.
  
  
  RESULTS
  Tentorial cutting significantly improved the exposure of the middle incisural space cisternal structures such as the oculomotor and trochlear nerves and the superior cerebellar and posterior cerebral arteries. The mean brainstem surface exposed more than doubled (2.13-fold increase) after tentorial incision with an average increase from 73.18 mm(2) to 155.76 mm(2). When the endoscope was used, it was possible to follow the entire course of the cisternal, infratentorial trochlear nerve segment during the opening of the tentorial free edge, facilitating its preservation. In the illustrative cases, 2 cerebellopontine angle meningiomas with supratentorial and infratentorial extension were removed without any postoperative complication.
  
  
  CONCLUSIONS
  Tentorial incision may be useful to extend the rostral exposure of the middle incisural space via a simple retrosigmoid approach, avoiding the need for more complex skull base routes.
authors.affiliation: Dardinger Microneurosurgical Skull Base Laboratory, Department of Neurological Surgery, Wexner Medical Center, The Ohio State University, Columbus, Ohio, USA; Department of Neurosurgery, Umberto I General Hospital, Università Politecnica delle Marche, Ancona, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Colasanti
authors.affiliation: Dardinger Microneurosurgical Skull Base Laboratory, Department of Neurological Surgery, Wexner Medical Center, The Ohio State University, Columbus, Ohio, USA.
authors.forename: Al-Rahim Abbasali
authors.initials: AA
authors.lastname: Tailor
authors.affiliation: Department of Radiology and Wright Center of Innovation in Biomedical Imaging, Wexner Medical Center, The Ohio State University, Columbus, Ohio, USA.
authors.forename: Jun
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Dardinger Microneurosurgical Skull Base Laboratory, Department of Neurological Surgery, Wexner Medical Center, The Ohio State University, Columbus, Ohio, USA. Electronic address: mario.ammirati@osumc.edu.
authors.forename: Mario
authors.initials: M
authors.lastname: Ammirati
mesh_terms: D002102:Cadaver; D002531:Cerebellum / Q000000981:diagnostic imaging / Q000601:surgery*; D004388:Dura Mater / Q000601:surgery*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008875:Middle Aged; D009464:Neuroma, Acoustic / Q000000981:diagnostic imaging / Q000601:surgery*; D019635:Neurosurgical Procedures / Q000379:methods*; D009777:Occipital Bone / Q000601:surgery*; D013116:Spinal Cord / Q000601:surgery*
keywords: Endoscopic assistance; Microsurgical anatomy; Middle incisural space; Quantitative anatomic study; Retrosigmoid approach; Tentorium cerebelli cutting