Accepted Manuscript

The expansive realm of skull base neuroendoscopy

Anil Nanda, MD, MPH, FACS Ashish Sonig, MD, MS, MCh

PII: S1878-8750(13)00630-X

DOI: 10.1016/j.wneu.2013.04.002

Reference: WNEU 1929

To appear in: World Neurosurgery

Received Date: 22 March 2013

Accepted Date: 19 April 2013

Please cite this article as: Nanda A, Sonig A, The expansive realm of skull base neuroendoscopy, WorldNeurosurgery (2013), doi: 10.1016/j.wneu.2013.04.002.

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Title:

The expansive realm of skull base neuroendoscopy

Authors

Anil Nanda1 MD, MPH, FACS

Ashish Sonig1, MD, MS, MCh

1Department of neurosurgery, Louisiana state university health science center, Shreveport

Corresponding Author

Anil Nanda MD, FACS

Professor and chairman

Department of neurosurgery, LSUHSC, Shreveport

ananda@lsuhsc.edu

318-675-6404-office

318-675-6867-fax

Disclosures: None

Conflict of interest: None

Keywords: surgical freedom, angle of exposure, endoscopic skull base, neuroendoscopy

Running Title: The expansive microcosm of skull base neuroendoscopy

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Collaboration between otolaryngologists and neurosurgeons has been a cradle for innovations in

the field of skull base neurosurgery. The introduction of endoscopy, first as an adjunct to

microneurosurgery and later as a gold standard procedure for certain pathologies, resulted from

such an alliance. German physician Philipp Bozzini(4) is credited for the invention of the

“Lichtleiterin,” a light conduit used in the 18th century to inspect the ear, nasopharynx and

wounds. But it was Victor Darwin Lespinasse(7) who first used it intraventricularly–in an

operation to treat hydrocephalus, he used the a modified cystoscope to coagulate the choroid

plexus. Guiot(8) was the first neurosurgeon to use the endoscope in the endonasal transphenoidal

approach to pituitary tumor. Since then, the endoscope has become a regular feature of

neurosurgery. Noted pioneers Fukushima(5), Apuzzo(1) and Bushe(3) used the endoscope to aid

in microsurgical resection of tumors. The endoscopes they used were still in the developmental

phases and mainly served as an adjunct to microscopes. In The following years,

otolaryngologists increasingly used endoscopes for parasellar approaches. Based on these efforts,

the concept of pure endoscopic transsphenoidal approach to sella emerged, most commonly for

pituitary adenoma. Neurosurgeon Jho HD and otolaryngologist Carrau RL published their

experience of 45 cases of pituitary adenoma(10). Concurrently in Europe , Paolo Cappabianca

and Enrico de Divitiis from Naples and Giorgio Frank and Emesto Pasquini from Bologna

spearheaded the expansion of transnasal endoscopic approach. The developments in

neuronavigation, the angled lens system and neuroimaging led to the expansion of skull base

endoscopy. The concept of expanded endoscopic skull base surgery became a reality, and such

previously unreachable areas as the region from the crista galli to the craniovertebral junction

became accessible(11,12). In the last decade, virtually the complete ventral skull base; middle

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cranial fossa, clivus, petrous bone, infratemporal fossa and pterygopalatine fossa has become

approachable using the endoscope.

In this issue of World Neurosurgery, Wilson et al have performed a meticulous and objective

analysis to compare the trajectory and surgical freedom of endonasal ipsilateral uninostril medial

maxillotomy approach with the Sublabial Anterior Maxillotomy Transpterygoid Caldwell-Luc

Dissection approach for the anterolateral skull base. The authors used a Neuronavigation model

to make the comparison. Neuronavigation has now emerged (2,13) as an ecumenical answer to a

wide variety of situations, all requiring objective and accurate measurements in anatomical

studies. Often, the various surgical approaches, including micro neurosurgical approaches, in

cadaveric studies are compared using parameters like area of exposure or working area, surgical

freedom, trajectory or angle of attack(6). In open approaches the working area is generally

defined as the target region under the microscope. The angle of attack, however, depends on the

type of exposure e.g between the Dura and brain surface or brain surface and bone, etc.

Generally it pertains to the surgeon’s chosen trajectory.

The third aspect is the degree of freedom, known as surgical freedom. It gives an estimate of

how much a surgeon can move his or her instruments/endoscope during the surgery. It is this

third aspect that is more meaningful to the comparison between endoscopic approaches and open

approaches–an angled endoscope can improve a surgeon’s degree of vision, but a concurrently

restricted degree of surgical freedom can impair access at the desired target level. In their

endoscopic anatomic study, De Notaris et al(16) gave their interpretation of these terms as they

relate to the microscope and the endoscope. They defined area of exposure and surgical freedom,

respectively, as

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Area of exposure: considered as the maximal region defined on specific deep

anatomic landmarks that can be exposed using a definite surgical approach

Surgical freedom: considered as an estimate of the movement available to the

surgeon’s hands and instruments, represented by a partial spherical area through

which surgical instruments can be inserted to manipulate a deep target

This concept of surgical freedom is still not widely evaluated in the neuroendoscopic microcosm

of transmaxillary approaches(15,16). In this study Wilson et al concluded that the Caldwell-Luc

approach provides significantly more exposure and surgical freedom than the endonasal

uninostril approach to the target points—foramen rotundum, foramen ovale, and anterior genu of

the petrous ICA.

One limitation of the authors’ analysis is that the endonasal approach they describe utilizes a

zero-degree endoscope with a uninostril approach. This can restrict the surgical freedom and can

alter the trajectory. Additionally there are several other factors that augment approach selection,

such as the side of the lesion, its location and age of the patient.

This model can easily be extrapolated to various endoscopic modifications like four hand

approach / bi nostril approach, posterior septectomy, middle turbinate medialization, wide

maxillary antrostomy and angled (30 - 45 degree) scope. Surgical freedom, trajectory and

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working area for each approach can then be individually evaluated and compared to those of

other techniques.

The future of neuroendoscopy

Neuroendoscopy is increasingly being used to traverse the complex pathologies involving multi

compartmental lesions. Cadaver-based research should focus on target-specific approaches. This

is an important aspect, as we know that restricted spaces can be expanded to accommodate a

“four hand” technique, the multiportal endoscopic approaches. Further facilitation of surgical

freedom can be achieved by adequate bony exposure that can range from a posterior septectomy,

removal of posterior ethmoids to middle turbinectomy.

These developments must parallel advancements in neuronavigation and 3D binocular

neuroendoscopy which increases a surgeon’s depth perception during a procedure. Rapid

progress in the field of robotics(9) and nanotechnology is pushing neuroendoscopy further.

Nanotechnology has produced smaller equipment, mini light sources and sensors. Additionally,

surgeons have used the da Vinci Surgical Robot (Intuitive Surgical Inc, Sunnyvale, California) in

cadaveric models to try to access the anterior and central skull base. The proposed use of

robotics in neuroendoscopy has given rise to the concept of “endowrist,”(9) or increased

maneuverability, providing 7° of freedom and 90° of articulation. However, one limitation of

robotics is that it is essentially a visual guided system, but developments in haptics(14) , though

currently at the research level, robotics still shows promise.

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This brings us to an important discussion on how to decrease the learning curve of

neuroendoscopic training during residency. The answer lies in the advancement of technology,

3D monitors, haptics and the development of virtual reality.

Acknowledgment We thank Katie Matza, Editorial Consultant, department of neurosurgery, LSU Health Sciences Center – Shreveport for editorial assistance.

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