Suboccipital Midline Approaches to the 4th Ventricle: Step-by-Step Cadaveric Dissection for Trainees and Anatomic Review of the Adjacent Cerebellopontine Angle

Introduction: Safe, effective access to the fourth ventricle for resection of intraventricular and skull base tumors remains challenging given the depth of location, restricted posterior fossa boundaries, and surrounding eloquent neuroanatomy. Resources depicting traditional transventricular routes predominantly emphasize complex three-dimensional relationships rather than a practical operative guide targeted toward all levels of training. The objective of this study was to create a reproducible step-by-step guide for obtaining transventricular access to the fourth ventricle and adjacent cranial base structures.

Methods: Two formalin-fixed, latex-injected specimens were dissected under microscopic magnification with endoscopic-assisted visualization. A midline suboccipital craniotomy and C1 laminectomy with telovelar, transvermian, and supracerebellar-infratentorial superior telovelar approaches was performed by a neurosurgery resident (D.D.D.), under the guidance of senior authors. The anatomical dissections were documented in stepwise 3D photographic images and supplemented with representative case applications to highlight pertinent surgical principles.

Results: The telovelar and transvermian corridors afford excellent access to the caudal two-thirds of the fourth ventricle with the former approach offering expanded access to the lateral recess, foramen of Luschka, adjacent skull base, and cerebellopontine angle. The supracerebellar-infratentorial superior transvelar approach provides access to the rostral third of the fourth ventricle and the cerebral aqueduct in addition to the dorsal midbrain and pineal region. Key common steps for both inferior and superior routes include prone positioning and midline skin incision; myofascial dissection; burr hole and suboccipital craniotomy flap elevation; optional C1 laminectomy; and durotomy ([Fig. 1]). For the telovelar and transvermian approaches, additional steps include identification of PICA, uvulotonsillar arachnoid dissection, retraction of either halves of the vermis (transvermian) or bilateral tonsils (telovelar), incision of the telovelar junction, elevation of the uvula, recognition of dorsal midbrain landmarks, and optional dissection of the lateral recesses, cerebellopontine angle, and adjacent lower cranial nerves ([Figs. 2], [3]). To obtain superior access to the fourth ventricle, modifications to the suboccipital exposure include cephalad extension of the incision and burr holes, elevation of the edge of the dural venous sinuses, and no C1 laminectomy. Key steps for the superior transvelar approach include supracerebellar infratentorial arachnoid dissection to the level of the cerebello-mesencephalic fissure, identification of deep venous anatomy, and midline infratrochlear incision in the superior medullary velum using a 45-degree endoscope ([Fig. 4]).

Conclusion: The midline suboccipital craniotomy represents a foundational cranial approach, particularly for lesions involving the fourth ventricle. Operatively oriented resources that combine stepwise neuroanatomic dissections with representative cases provide a crucial foundation for neurosurgical training. We present a comprehensive guide for neurosurgery residents to optimize familiarity with fourth ventricle approaches and cerebellopontine angle, mastery of relevant microsurgical anatomy, and simultaneous preparation for learning in the operating room.

Die Autoren geben an, dass kein Interessenkonflikt besteht.

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Artikel online veröffentlicht:
01. Februar 2023