Alexander I. Evins

Dual-Port 2D and 3D Endoscopy: Expanding the Limits of the Endonasal Approaches to Midline Skull Base Lesions with Lateral Extension

Objectiveu2003To investigate a novel dual-port endonasal and subtemporal endoscopic approach targeting midline lesions with lateral extension beyond the intracavernous carotid artery anteriorly and the Dorello canal posteriorly. Methodsu2003Ten dual-port approaches were performed on five cadaveric heads. All specimens underwent an endoscopic endonasal approach from the sella to middle clivus. The endonasal port was combined with an anterior or posterior endoscopic extradural subtemporal approach. The anterior subtemporal port was placed directly above the middle third of the zygomatic arch, and the posterior port was placed at its posterior root. The extradural space was explored using two-dimensional and three-dimensional endoscopes. Resultsu2003The anterior subtemporal port complemented the endonasal port with direct access to the Meckel cave, lateral sphenoid sinus, superior orbital fissure, and lateral and posterosuperior compartments of the cavernous sinus; the posterior subtemporal port enhanced access to the petrous apex. Endoscopic dissection and instrument maneuverability were feasible and performed without difficulty in both the anterior and posterior subtemporal ports. Conclusionu2003The anterior and posterior subtemporal ports enhanced exposure and control of the region lateral to the carotid artery and Dorello canal. Dual-port neuroendoscopy is still minimally invasive yet dramatically increases surgical maneuverability while enhancing visualization and control of anatomical structures.

A 3D endoscopic transtubular transcallosal approach to the third ventricle

OBJECTnSurgical approaches to deep-seated brain pathologies, specifically lesions of the third ventricle, have always been a challenge for neurosurgeons. In certain cases, the transcallosal approach remains the most suitable option for targeting lesions of the third ventricle, although retraction of the fornices and wall of the third ventricle have been associated with neuropsychological and hypothalamic deficits. The authors investigated the feasibility of an interhemispheric 3D endoscopic transcallosal approach through a minimally invasive tubular retractor system for the management of third ventricular lesions.nnnMETHODSnThree-dimensional endoscopic transtubular transcallosal approaches were performed on 5 preserved cadaveric heads (10 sides). A parasagittal bur hole was placed using neuronavigation, and a tubular retractor was inserted under direct endoscopic visualization. Following observation of the vascular structures, fenestration of the corpus callosum was performed and the retractor was advanced through the opening. Transforaminal, interforniceal, and transchoroidal modifications were all performed and evaluated by 3 surgeons.nnnRESULTSnThis approach provided enhanced visualization of the third ventricle and more stable retraction of corpus callosum and fornices. Bayonetted instruments were used through the retractor without difficulty, and the retractor applied rigid, constant, and equally distributed pressure on the corpus callosum.nnnCONCLUSIONSnA transtubular approach to the third ventricle is feasible and facilitates blunt dissection of the corpus callosum that may minimize retraction injury. This technique also provides an added degree of safety by limiting the free range of instrumental movement. The combination of 3D endoscopic visualization with a clear plastic retractor facilitates safe and direct monitoring of the surgical corridor.

Endoscopic extradural anterior clinoidectomy and optic nerve decompression through a pterional port

Since the first description of the intradural removal of the anterior clinoid process, numerous refinements and modifications have been proposed to simplify and enhance the safety of the technique. The growing use of endoscopes in endonasal and transcranial approaches has changed the traditional management of many skull base lesions. We describe an endoscopic extradural anterior clinoidectomy and optic nerve decompression through a minimally invasive pterional port. Minimally invasive optic nerve decompression, with endoscopic extradural anterior clinoidectomy, through a pterional keyhole craniotomy was performed on five preserved cadaveric heads. The endoscopic pterional port provided a shorter and more direct route to the anterior clinoid region, and helped avoid unnecessary and extensive bone removal. An extradural approach helped minimize complications associated with infraction of the subdural space and allowed for the maintenance of visibility while drilling with continuous irrigation. Adequate 270° bone decompression of the optic canal was achieved in all specimens. Endoscopic extradural anterior clinoidectomy and optic nerve decompression is feasible through a single minimally invasive pterional port.

The Meningo-Orbital Band: Microsurgical Anatomy and Surgical Detachment of the Membranous Structures through a Frontotemporal Craniotomy with Removal of the Anterior Clinoid Process

Objectiveu2003To describe the microanatomy of the meningo-orbital band (MOB) and its associated membranes, and propose a stepwise method for their detachment while minimizing potential complications. Designu2003Cadaveric and prospective clinical. Settingu2003Microneurosurgery Skull Base Laboratory, Weill Cornell Medical College (New York, NY) and Shiroyama Hospital (Osaka, Japan). Participantsu2003Five preserved cadaveric heads (10 sides) and five patients requiring surgical detachment of the MOB in 2012. Resultsu2003MOB detachment and subsequent extradural anterior clinoidectomies were successfully performed on five clinical cases. Detachment of the MOB was accomplished using a four-step dissection based on the structures detailed microanatomy and included (1) partial removal of the lateral wall of the superior orbital fissure, (2) incising of the lateral periosteal dura of the superior orbital fissure, (3) peeling off the dura propria of the temporal lobe from the inner cavernous membrane, and (4) fully detaching the exposed MOB from the periorbita. Conclusionu2003Understanding the complex microanatomy of these structures enabled a safe and effective stepwise detachment of the MOB. We recommend that surgeons possess sufficient anatomical knowledge before surgically manipulating this structure.

A Safe and Effective Technique for Harvesting the Occipital Artery for Posterior Fossa Bypass Surgery: A Cadaveric Study

OBJECTIVEnThe occipital artery (OA) is an important donor artery for posterior fossa revascularization. Harvesting the OA is believed to be difficult and time consuming due to its 3-dimensional course through different suboccipital tissue layers. We propose a safe and effective means of dissecting the OA.nnnMETHODSnThe course of the OA was explored in 5 cadaveric heads (10 sides). The OA was divided into 3 segments based on the vertical muscle layer it ran through; subcutaneous, transitional, and intramuscular. Three different approaches were attempted, and their respective advantages and disadvantages were assessed.nnnRESULTSnThe subcutaneous segment of the OA was found to run above the galea without traversing any vertical layers, and was thus easily dissected down to the superior nuchal line (SNL). The segment between the SNL and the digastric groove, traditionally the suboccipital segment, was divided into transitional and intramuscular segments. After detaching and retracting the suboccipital muscles, the OA was found to run in a single vertical layer of connective tissue. Dissection of the transitional segment was more involved as it ran between the SNL and the superior edge of the splenius capitis muscle, and vertically through the galea aponeurotica and the tendon of the sternocleidomastoid muscle.nnnCONCLUSIONSnThis segmentation provided a safe and effective procedure for harvesting the OA, in which dissection of the transitional segment is a critical step. Although the course of the OA is complex, precise anatomical knowledge of the suboccipital muscles and a stepwise dissection make harvesting the OA relatively simple.

Postoperative intracranial hypotension-associated venous congestion: Case report and literature review

Postoperative intracranial hypotension-associated venous conestion (PIHV), formally proposed in 2003 by Van Roost et al. as seudohypoxic brain swelling, is a rapid, severe, and potentially atal postoperative complication following uneventful intracranial r spinal surgery [1,2]. PIHV is characterized by unexpected postoprative deterioration of consciousness; neuroradiological changes n the basal ganglia, thalamus, brainstem, and cerebellum resemling the radiological presentation of hypoxic brain damage; and erebral arteries and veins that remain angiographically intact ith possible neuroimaging signs suggesting intracranial hypotenion [2,4]. PIHV is thought to be caused, pathomechanistically, y intracranial hypotension as a result of subfascial or subgaleal rainage in patients whose dural sutures allow for cerebrospinal uid (CSF) permeation [1–3]. The mortality of PIHV has yet to be fully described in literaure, and as a whole this complication remains subjective among urgeons despite the large number of well documented cases 1–3,5–7].

A combined dual-port endoscope-assisted pre- and retrosigmoid approach to the cerebellopontine angle: an extensive anatomo-surgical study

The use of the endoscope in the cerebellopontine angle (CPA) has been suggested to minimize cerebellar retraction and reduce the size of the craniotomy. 3D endoscopy combines the benefits of conventional 2D endoscopy with the added benefit of stereoscopic perception, though improved visualization alone does not guarantee improved surgical maneuverability and a better surgical outcome. We propose a new combined dual-port endoscope-assisted pre- and retrosigmoid approach to improve visualization and accessibility of the CPA with shortened distances and increased surgical maneuverability of neurovascular structures. We analyze surgical exposure and maneuverability of this approach and compare it with the surgical microscopic and a conventional single-port endoscope-assisted retrosigmoid approach. This combined pre- and retrosigmoid approach was performed on eight cadaveric heads (16 sides). The endoscopic probe was inserted through the presigmoid surgical port while surgical manipulation was performed through the retrosigmoid corridor. The CPA was divided into three compartments, from medial to lateral, the anteromedial, and the middle and the posterolateral. The microscope provided good visualization of the posterolateral and middle compartments, whereas poor visualization was offered of the anteromedial compartment. The dual-port endoscopic approach dramatically improved visualization and surgical maneuverability of the anteromedial compartments, clivus, and related neurovascular structures. Additionally, the 3D endoscope allowed for a better understanding of the surgical anatomy of the CPA and improved visualization of structures located in the anteromedial compartments towards the midline. This approach allowed for full realization of the benefits of endoscopic-assisted technique by improving surgical access and maneuverability.

Optic Nerve Decompression through a Supraorbital Approach

Objectiveu2003We propose a stepwise decompression of the optic nerve (ON) through a supraorbital minicraniotomy and describe the surgical anatomy of the ON as seen through this approach. We also discuss the clinical applications of this approach. Methodsu2003Supraorbital approaches were performed on 10 preserved cadaveric heads (20 sides). First, 3.5-cm skin incisions were made along the supraciliary arch from the medial third of the orbit and extended laterally. A 2u2009×u20093-cm bone flap was fashioned and extradural dissections were completed. A 180-degree unroofing of the ON was achieved, and the length and width of the proximal and distal portions of the optic canal (OC) were measured. Resultsu2003The supraorbital minicraniotomy allowed for identification of the anterior clinoid process and other surgical landmarks and adequate drilling of the roof of the OC with a comfortable working angle. A 25-degree contralateral head rotation facilitated visualization of the ON. Conclusionu2003The supraorbital approach is a minimally invasive and cosmetically favorable alternative to more extended approaches with longer operative times used for the management of ON decompression in posttraumatic or compressive optic neuropathy from skull base pathologies extending into the OC. The relative ease of this approach provides a relatively short learning curve for developing neurosurgeons.

Three-Dimensional Endoscope-Assisted Surgical Approach to the Foramen Magnum and Craniovertebral Junction: Minimizing Bone Resection with the Aid of the Endoscope

OBJECTIVEnTo evaluate objectively the anatomic areas of the cranial base exposed by a three-dimensional (3D) endoscope-assisted far lateral approach.nnnMETHODSnA series of far lateral approaches with only condyle resection, with only jugular tubercle resection, with both partial condyle and total jugular tubercle resection, and without occipital condyle and jugular tubercle resection were performed on 10 cadaveric heads (20 sides). To assess properly the exposure of major anatomic and neurovascular structures, the intradural anatomy of the exposed craniocervical junction was divided into 8 compartments, including 3 superior cranial compartments, 3 inferior cranial compartments, and 2 spinal compartments.nnnRESULTSnThe anteromedial compartments toward the midline were difficult to explore using the microscope and required the aid of the endoscope. The 3D endoscope provided general circumferential visualization of the anatomic structures, even without resection of the jugular tubercle, and afforded good visualization of the more lateral compartments. Safe and optimal surgical corridors for insertion of the endoscope were also identified.nnnCONCLUSIONSnUse of a 3D endoscope allows for minimal resection of the condyle and jugular tubercle, better visualization of the surgical compartments toward the midline, and better in-depth surgical exploration of each intradural compartment. However, the 3D probe is still too large and restricts surgical maneuverability.

The intracranial facial nerve as seen through different surgical windows: an extensive anatomosurgical study.

BACKGROUND: The facial nerve has a short intracranial course but crosses critical and frequently accessed surgical structures during cranial base surgery. When performing approaches to complex intracranial regions, it is essential to understand the nerves conventional and topographic anatomy from different surgical perspectives as well as its relationship with surrounding structures. OBJECTIVE: To describe the entire intracranial course of the facial nerve as observed via different neurosurgical approaches and to provide an analytical evaluation of the degree of nerve exposure achieved with each approach. METHODS: Anterior petrosectomies (middle fossa, extended middle fossa), posterior petrosectomies (translabyrinthine, retrolabyrinthine, transcochlear), a retrosigmoid, a far lateral, and anterior transfacial (extended maxillectomy, mandibular swing) approaches were performed on 10 adult cadaveric heads (20 sides). The degree of facial nerve exposure achieved per segment for each approach was assessed and graded independently by 3 surgeons. RESULTS: The anterior petrosal approaches offered good visualization of the nerve in the cerebellopontine angle and intracanalicular portion superiorly, whereas the posterior petrosectomies provided more direct visualization without the need for cerebellar retraction. The far lateral approach exposed part of the posterior and the entire inferior quadrants, whereas the retrosigmoid approach exposed parts of the superior and inferior quadrants and the entire posterior quadrant. Anterior and anteroinferior exposure of the facial nerve was achieved via the transfacial approaches. CONCLUSION: The surgical route used must rely on the size, nature, and general location of the lesion, as well as on the capability of the particular approach to better expose the appropriate segment of the facial nerve. ABBREVIATIONS: AICA, anterior inferior communicating artery CPA, cerebellopontine angle GG, geniculate ganglion IAC, internal auditory canal PICA, posterior inferior communicating artery