{Reference Type}: Case Reports {Title}: Combined Petrosal Approach for Resection of a Large Trigeminal Schwannoma With Meckel's Cave Involvement-Part I: Anatomic Rationale and Analysis: 2-Dimensional Operative Video. {Author}: Tayebi Meybodi A;Liu JK; {Journal}: Oper Neurosurg (Hagerstown) {Volume}: 20 {Issue}: 3 {Year}: 02 2021 16 {Factor}: 2.817 {DOI}: 10.1093/ons/opaa363 {Abstract}: Resection of large trigeminal schwannomas involving both posterior and middle cranial fossae is challenging. The depth of the surgical target in the superomedial corner of the cerebellopontine angle and the petrous apex makes for a difficult lesion to favorably access, expose, and safely resect. Judicious planning of a skull base approach is therefore the most crucial step in successful management of these formidable tumors. When properly chosen, planned, and executed, the combined petrosal approach sets the stage for an optimal exposure of such tumors that involve both posterior and middle cranial fossae. The present video is the first of a 2-part video presentation that explains the anatomic rationale of selecting a combined petrosal approach (anterior petrosectomy and retrolabyrinthine petrosectomy) for the resection of a large trigeminal schwannoma involving the posterior and middle cranial fossae with an extension into Meckel's cave in a 54-yr-old female presenting with 5-yr history of increasing headaches, left-sided face numbness, and disequilibrium. The benefits, risks, and alternatives of the surgical procedure were discussed in detail with the patient and she consented to proceed with surgery. Part I also discusses the important nuances of positioning the patient, as well as planning and execution of the skin incision, including pericranial flap harvesting.  Of note, the patient consented to the publication of images obtained from her.