OBJECTIVE: The most used neurosurgical approach to reach cerebellar-pontine angle is the retrosigmoid route. This article describes the presigmoid approach which requires excellent knowledge of the labyrinthine block together with quantitative analysis of temporal bone CT.
METHODS: CT-based quantitative measurements were obtained in patients undergoing vestibular neurectomy with a presigmoid approach. Eighteen patients were enrolled, and five measures were taken: Trautmann\'s area, the petro-clival angle, presigmoid dura length and its angle. The relationship between these measurements and hospitalization days, operating times, and complications was explored.
RESULTS: The posterior semicircilar canal (PSC)-sigmoid sinus (SS) distance, presigmoid dura- internal auditory canal (IAC)-PSC angle, and duration of surgery are predictors of complications. Specifically, a PSC-sigmoid sinus distance <11 mm, a dura presig-IAC-PSC angle <14 are associated with the highest risk of complications.
CONCLUSIONS: Preoperative temporal bone CT scan can guide the surgeon through the narrowest areas of the surgical approach. Trautmann\'s triangle area and petro-clival angle reduction are challenging and can be faced with combined microscopic-endoscopic technique, and with optics angulation-rotation. The retrolabyrinthine approach can enable hearing preservation and minimal cerebellar retraction.

Transpetrosal approaches are known to be associated with a significant risk of complications, including CSF leak, facial palsy, hearing impairment, venous injury, and/or temporal lobe injury. We aimed to evaluate the morbidity of the standard combined petrosal approach (CPA), defined as a combination of the posterior (retrolabyrinthine) and the anterior petrosal approach. We performed a systematic review and meta-analysis of articles reporting on clinical series of patients operated on for petroclival meningiomas through CPA. Studies that used the terminology \"combined petrosal approach\" without matching the aforementioned definition were excluded as well as clinical series that included less than 5 patients. A total of 8 studies were included involving 160 patients. The pooled complication rates were 3% (95% CI, 0.5-5.6) for CSF leak, 8.6% (95% CI, 4.1-13.2%) for facial palsy, 8.2% (95% CI, 3.9-12.6%) for hearing impairment, 2.8% (95% CI, 0.9-6.5%) for venous complications, and finally 4.8% (95%, 1.2-8.4%) for temporal lobe injury. Contrary to the general belief, CPA is associated with an acceptable rate of complications, especially when compared to alternative approaches to the petroclival area. In view of the major advantages like shorter trajectory, multiple angles of surgical attack, and early tumor devascularization, CPA remains an important tool in the armamentarium of the skull base surgeon.

The removal of petroclival meningiomas (PMs) is considered a neurosurgical challenge due to the critical mobilization of key neurovascular structures. Limited knowledge about the benefits of operating on patients with PMs using the combined presigmoid-subtemporal approach (CPSA) in a semi-sitting position has precluded its generalizability. We report on ten patients with PMs operated in a semi-sitting position using CPSA. We remark that before the surgical approach was accomplished in our group of patients, the CPSA via semi-sitting position was conducted and standardized in six adult cadaveric heads. The neuroanatomic dissections made in cadavers allowed us to confidently use CPSA in our set of patients. There were no comorbidities, perioperative complications, or deaths associated with the surgical procedure. CPSA via a semi-sitting position can be considered a safe approach to remove PMs.

BACKGROUND: The retrolabyrinthine approach is classified among the posterior petrosectomies. Its goal is to achieve an enlarged mastoidectomy while sparing the intrapetrous neurotologic structures in order to offer maximal exposure of the posterior cerebellopontine angle compound.
METHODS: The stages of the procedure are subsequently the skeletonization of the sigmoid sinus, wide opening of the mastoid antrum and exposure of the semicircular canals. We present herein the technique, indications and limitations of the retrolabyrinthine approach.
CONCLUSIONS: The retrolabyrinthine approach is a demanding technique. Nowadays the retrolabyrinthine approach is routinely combined to additional resections of the petrous bone, so-called \"combined petrosectomies\", to target the jugular foramen or the petroclival area.

This video is the second part of a 2-part video presentation demonstrating the microsurgical technique of a combined petrosal approach for resection of a large trigeminal schwannoma in a 54-yr-old woman involving multiple cranial fossae extending anteriorly into Meckel\'s cave. The patient presented with long-standing worsening headache and facial tingling and numbness. After discussing the benefits and risks of the surgery as well as the alternative management strategies, the patient decided to proceed with surgery and informed consent was obtained. The surgery was performed in a single stage. The technical nuances of anterior and posterior (retrolabyrinthine) petrosectomy are demonstrated and discussed. Microsurgical resection of the tumor is also demonstrated emphasizing the important steps of dural opening, arachnoid dissection, identification and preservation of cranial nerves, and exploration of Meckel\'s cave. Use of endoscopic-assistance for visualization of the cerebellopontine angle and neurovascular structures is also demonstrated.  Table in video reprinted by permission from Copyright Clearance Center: Springer Nature, Acta Neurochirurgica, Frontotemporal epidural approach to trigeminal neurinomas, Dolenc VV, Copyright 1994.

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.

BACKGROUND: In this video abstract, we present a one burr-hole craniotomy for a modified presigmoid approach developed in Helsinki Neurosurgery to access the space extended to both middle and posterior fossa. Thus, indications for this approach are lesions that extend to both middle and posterior fossa, petroclival tumors, basilar tip aneurysms located extremely low below the posterior clinoid process, trunk basilar aneurysms, and bypass procedures from the P2 segment of the posterior cerebral artery. The procedure is composed by three stages: a temporal and presigmoid craniotomy, a partial petromastoidectomy, and the dura opening with section of the superior petrosal sinus (SPS) and the tentorium. Even though some risks related to the opening of the mastoid cells or cut of the SPS may exist, benefits of this optimized craniotomy are higher compared with the complications.
METHODS: The patient with a giant petroclival meningioma is placed in park bench position and spinal drainage is inserted. Skin incision starts in front of the ear curve going to 1 inch behind the mastoid line. Strong retraction with hooks keeps a clean space for the craniotomy. Hemostatic Raney clips are placed at the superior border of the skin flap. A burr-hole is made at the most cranial part of the temporal bone. After the detachment of the dura with long flexible blunt dissectors, the craniotomy is performed to expose the sigmoid sinus, the SPS and the dura of the inferior temporal lobe, and the floor of the middle fossa. Aiming to access the posterior fossa by a presigmoid route, a partial petromastoidectomy is performed preserving the semicircular canals. Few drill holes are made for tack-up sutures. Once we properly reach the dura of the middle and posterior fossa, dura of the temporal lobe and later, the presigmoid dura are opened joining at the level of the SPS. The SPS, which is running over the petrous bone between the posterior and the middle fossa, is coagulated, ligated, and cut. After SPS is sectioned, the tentorium is cut anterior to the drainage of vein of Labbé and posterior to the deep tentorial insertion of the fourth nerve. Finally, special care should be taken to seal the opened mastoid cells with muscle and glue, and for the hermetic dura closure using pericranium or temporal muscle aponeurosis.
CONCLUSIONS: The described one burr-hole craniotomy may represent the more efficient approach for the management of the deep and hardly accessible lesions extended to both middle and posterior fossa.
UNASSIGNED: http://surgicalneurologyint.com/videogallery/presigmoid-approach-craniotomy-lt.

BACKGROUND: Petroclival and ventral brain stem tumors require a complex approach.
METHODS: The combined petrosectomy is an epidural transtentorial-transpetrosal otoneurosurgical approach to achieve a retrolabyrinthine presigmoidal approach and an anterior petrosectomy in one single procedure. The different steps of this approach are described and illustrated by figures and a video. The indications and limitations of the technique are presented.
CONCLUSIONS: The combined petrosectomy offers multiple corridors to the petroclival region and ventral brainstem while preserving the intrapetrous neurotological structures. Meticulous stepwise bony resection optimizing the dural opening and preservation of veins contributes to reducing the risk inherent to this technique.

BACKGROUND: The presigmoid retrolabyrinthine space is characterized by a widely variable size. The main structure involved in this large variability is the sigmoid sinus. Few studies have attempted to establish a reliable classification of sigmoid sinus to predict the presigmoid retrolabyrinthine space. We used tomographic mapping of human cadaver temporal bones to classify the position of sigmoid sinus and performed a cadaveric study to assess the validity of a novel classification in predicting the presigmoid retrolabyrinthine space.
METHODS: Ten human cadaver temporal bones were randomly selected and subjected to fine-cut computed tomography scanning to classify the position of sigmoid sinus using a reference line. The specimens were classified into medial and lateral groups and each specimen was then subjected to mastoidectomy. The groups were compared using quantitative and qualitative analysis.
RESULTS: The medial group showed a larger distance between the sigmoid sinus and the external auditory canal and a shallower lateral semicircular canal. In the lateral group, the mastoidectomy was more demanding, and the Trautmann\'s triangle was typically narrower and often \"hidden\" medially to the sigmoid sinus.
CONCLUSIONS: The tomographic classification proposed in this study predicts, in a cadaveric model, the presigmoid retrolabyrinthine space. It may help the surgeon select the best approach to reach the petroclival region and lead to safer neurological and otological surgeries.