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Endoscopictransnasalapproachtoanteriorandmiddlecranialbaselesions

ARTICLEinNEUROLOGYINDIA·OCTOBER2015

ImpactFactor:1.23·DOI:10.4103/0028-3886.166539

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SienHuiTan

UniversityofMalaya

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YvesBrand

UniversityofBasel

29PUBLICATIONS61CITATIONS

SEEPROFILE

NarayananPrepageran

UniversityofMalaya

136PUBLICATIONS368CITATIONS

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Availablefrom:YvesBrand

Retrievedon:28January2016

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Neurology India Official Publication of the Neurological Society of IndiaSeptember‐October 2015 / Vol 63 / Issue 5

ISSN 0028‐3886www.neurologyindia.com

673© 2015 Neurology India | Published by Wolters Kluwer - Medknow

ABSTRACTWe present our experience in managing pathologies involving the anterior and middle cranial base using an endoscopic transnasal approach, highlighting the surgical technique, indications, and complications. The different types of endoscopic approaches used include the transtuberculum/transplanum, transcribiform, transsellar, and cavernous sinus approaches. The common indications include repair of cerebrospinal fluid leaks (both spontaneous and post traumatic) and excision of pituitary adenomas, meningiomas, craniopharyngiomas, esthesioneuroblastomas, and other malignancies of the anterior cranial base. Careful reconstruction is performed with the multilayer technique utilizing fat, fascia lata, and fibrin sealant. The endoscopic transnasal approach, coupled with the present‑day sophisticated neuronavigation systems, allows access to lesions in the midline extending from the cribriform plate to the craniovertebral junction. However, preoperative planning and careful selection of cases with evaluation of each case on an individual basis with regard to the lateral extension of the lesion are imperative.

Key words: Cerebrospinal fluid leak; craniopharyngioma; endoscopy; meningioma; pituitary neoplasms; skull base

Introduction

The minimally invasive endoscopic transnasal approach, coupled with sophisticated neuronavigation systems, allows direct access to midline skull base pathologies with less manipulation of neurovascular structures while avoiding brain retraction. The endoscope provides excellent visualization under magnification and in hidden angles, which aids in assessing the completeness of tumor dissection. In addition, the concept of team surgery and collaboration between neurosurgeons and otorhinolaryngologists play an important role. We present our experience in managing pathologies involving the anterior and middle cranial base using an endoscopic transnasal approach, highlighting the surgical technique, indications, and complications.

Preoperative Planning and Case Selection

The endoscopic transnasal approach allows access to the midline lesions extending from the cribriform plate to the craniovertebral junction. The lateral access in the anterior and middle cranial fossa extends to the medial orbital walls, the cavernous sinus, and the medial aspect of the temporal lobe for selected lesions.

Prior to surgery, all patients undergo the following:• Acomputedtomography(CT)scanforevaluationofthe

bony structures and bony anatomy. This is also important

Endoscopic transnasal approach to anterior and middle cranial base lesionsSien Hui Tan, Yves Brand1, Narayanan Prepageran, Vicknes Waran2

Department of Otolaryngology, Faculty of Medicine, University Malaya, Lembah Pantai, 50603 Kuala Lumpur, Malaysia, 1Department of Otorhinolaryngology, Head and Neck Surgery, University Hospital Basel, Switzerland, 2Department of Neurosurgery, Faculty of Medicine, University Malaya, Lembah Pantai, 50603 Kuala Lumpur, Malaysia

Address for correspondence: Prof. Narayanan Prepageran, Department of Otolaryngology, Faculty of Medicine, University Malaya, Lembah Pantai, 50603 Kuala Lumpur, Malaysia. E-mail: prepageran@yahoo.com

This is an open access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 License, which allows others to remix, tweak, and build upon the work non-commercially, as long as the author is credited and the new creations are licensed under the identical terms.

For reprints contact: reprints@medknow.com

How to cite this article: Tan SH, Brand Y, Prepageran N, Waran V. Endoscopic transnasal approach to anterior and middle cranial base lesions. Neurol India 2015;63:673-80.

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Review Article

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674 Neurology India / September 2015 / Volume 63 / Issue 5

to assess for any potential skull defects in patients with cerebrospinalfluid(CSF)leak

• Amagneticresonanceimaging(MRI)scanforpreoperativediagnosis of the pathology and a better understanding of the relationship of the lesion with its surrounding structures such as the pituitary gland and stalk, the circle of Willis, the various cranial nerves, and other important structures. In addition, the consistency of a lesion can be determined based on its appearance on T2‑weighted imaging. This is important because softer tumors are easily removed endoscopically compared to firm or calcified lesions

• Pituitaryhormone assessment for lesions around thesella and the necessary hormonal corrections prior to surgery

• Visual field assessment for lesions that may be in direct contact with the optic nerve.

Neuronavigation is used in all our skull base surgeries as it provides better intraoperative anatomic orientation, allowing a more extensive and complete resection. It ensures that one is forewarned regarding the proximity of the important neurovascular structures in the vicinity of the surgical dissection and identifies the possible location of residual tumors. Neuronavigation is especially useful as the error due to brain shift is not a very important consideration for skull base lesions provided the operator references his or her instruments to the normal anatomical structures at the skull base.

We also routinely use devices such as a microdebrider for removal of soft tissues of the nasal passages and an ultrasonic aspirator with a long nozzle for removal of intracranial tumors.

Indications

The common indications for endoscopic transnasal approach are as follows:• Repair of CSF leaks (both spontaneous and post

traumatic)• Pituitaryadenomas• Meningiomas• Craniopharyngiomas• Esthesioneuroblastomas and other malignancies of the

anterior cranial base.

Cerebrospinal Fluid Leaks

EndoscopicrepairofCSFleakshasevolvedsosubstantiallythat its safety and efficacy have exceeded that of traditional open methods.[1‑7] The endoscopic transnasal approach allows adequate exposure of the site of CSF leak tofacilitate not only the intraoperative localization of the defect, but also to create enough working space to seal

the CSF leak. The transcribriform, transtuberculum, andtranssellar approaches are excellent for midline structures. However, as one moves further away from the midline skull base, the degree of difficulty, and required expertise increases. Nonetheless, endoscopic repair of almost all skull base defects is now possible through the four endonasal corridors: Transnasal, transsphenoidal, transethmoidal, and transmaxillary.[6]

Pituitary Adenomas

Endoscopic removal of pituitary adenomas has at least similar results in terms of tumor removal, relief of endocrinologic or visual symptoms, and cure of the underlying disease as the conventional microsurgical technique.[8‑15] The extended endoscopic approach is particularly beneficial for managing tumors with suprasellar or parasellar extension [Figures1and2].Foradenomasthatdonotdescendintothe sella (fibrous, dumbbell‑shaped, previous radiationorpharmacologicaltherapy)orwithcavernoussinusinvasion,the endoscopic approach allows greater access and improved visualization.[16]

Craniopharyngiomas

For craniopharyngiomas, the transsphenoidal approachis classically limited to the intrasellar or intra‑suprasellar subdiaphragmatic tumors with the results being comparable with the microscopic and open transcranial methods.[16‑19] With the expanded endoscopic approach now offering better visualization of anatomical structures, the risk of injury to vital structures is reduced. Nevertheless, the endoscopic technique is generally reserved for small and medium‑sized suprasellar lesions located primarily in the midline without encasement of vascular structures [Figure 3a‑c].[20‑22] With sufficient experience, it is possible to access larger lesions that extend into the floor of the third ventricle provided the

Figure 1: Pituitary adenoma: (a) Preoperative sagittal magnetic resonance imaging (MRI) showing a 1.9 cm × 1.8 cm × 1.7 cm enhancing pituitary mass with suprasellar extension compressing the optic chiasm. (b) Postoperative sagittal MRI demonstrating complete excision of the lesion

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inferior extent reaches either the sella or the planum sphenoidale[Figure3d].

Meningiomas

In well‑chosen cases of meningiomas, the endoscopic approach attains rates of gross total resection equal to that seen in transcranial approaches.[23‑28] The endoscopic technique is suitable for small meningiomas restricted to the midline with limited lateral extension, not going beyond the internal carotid artery bifurcation or the optic nerves[Figure4].Contraindicationsincludeanextensiontothe anterior clinoid processes and clear encasement of the internal carotid artery, anterior cerebral artery complex, or optic nerves.[29] Occasionally, with large tumors and in the presence of significant brain edema, debulking is done first endoscopically, followed by a transcranial approach to achieve total excision.

Esthesioneuroblastomas and other Malignancies of the Anterior Cranial Base

When choosing the optimal surgical approach for neoplasms of the anterior cranial base, the tumor features and its anatomic extensions are important. Apurely endoscopic transnasalapproach is suitable for lesions restricted entirely in nasal passages without dural breach or lateral bony involvement. Intracranial extension of the tumor can be resected as long as it is not extensive, and it is possible to remove a cuff of the normal dura. In these cases, reconstruction is always necessary. However, the prognosis of these malignancies is poor. Huge, irregularly shaped tumors, with significant lateral extension and encasement of major vessels, or those spreading beyond the pia mater usually require a combination of endoscopic and transcranial approaches.

Endoscopic Equipment and Instruments

Visualizationisachievedusingrigid‑rodendoscopes4mmindiameterand18cminlengthwithlensanglesof0°and30°.The electromagnetic navigation system and a recording high definition system for documentation are crucial. High‑speed electric microdrills with long handpieces and microdebriders are utilized. Over the last decade, special instrumentation for skull base surgery has been developed.

Figure 2: Pituitary adenoma  in a patient with acromegaly. Preoperative sagittal  (a)  and  coronal  (b) magnetic  resonance  imaging  showing  a pituitary mass encasing the cavernous carotid on the left side. The tumor was resected using a single nostril approach. First, the sphenoid keel was visualized (c) and the sella was exposed (d). Then, the tumor was dissected from the cavernous carotid (e). The cavernous carotid can be seen after complete tumor resection (f). A small cerebrospinal fluid leak was sealed with fat and tissue glue at the end of surgery

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Figure 3: Craniopharyngioma. Preoperative (a) sagittal and (b) axial magnetic resonance imaging showing a 4 cm × 3.4 cm × 3.4 cm midline suprasellar cystic mass extending inferiorly into the pituitary gland without encasement of vascular structures. (c) Postoperative axial computed tomography scan demonstrating complete excision of the lesion. (d) Endoscopic view of the third ventricle after  removal of  the  tumor  (craniopharyngioma) via  the transplanum approach

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Hemostasis is achieved using clips, bipolar diathermy, or absorbable hemostat packing. Alternatively, hemostaticmatrices can also be used.[30]Attheendoftheprocedure,weusually pack both nasal cavities with nasal tampons.

Surgical Technique

Afterorotracheal intubationundergeneralanesthesia, thepatient is positioned supine, and the head is placed in a Mayfieldheadfixationdevice.ThenasalpassagesarepreparedwithMoffat’s solution (1mlof1:1000adrenaline,2mlof10%cocaine,and4mlof8.4%sodiumbicarbonate).Inourcenter,weadopta“twonostriland4‑handed”technique.Itisimportant to create a wide surgical corridor for exposure and instrument maneuverability. This is achieved by performing a unilateral inferior turbinectomy and posterior septectomy. The remaining contralateral inferior turbinate and bilateral middle turbinates are preserved to retain moisture of the nasal cavity, maintain the normal laminar flow of air and decrease postoperative crusting. The exposure required is modified according to the surgical target areas and pathology.

However, in the management of pituitary adenomas, we prefer to employ a single nostril approach. The otorhinolaryngologist manages the endoscope while the neurosurgeon uses both hands to deal with the tumor. The

exception is when the operation is a redo surgery, where a binostril approach is preferred.[31]

Transtuberculum/Transplanum Approach

First,completeposteriorethmoidectomiesarecarriedoutwhereby the bony septae are resected up to the ethmoid roof and the cribriform plate. This is followed by the drilling of the planum sphenoidale at the rostral portion of the sella. The bone covering the superior intercavernous sinus is then removed to provide access to the suprasellar segments of the tumor up to the prechiasmatic cistern [Figures5aand6].Forintraduralresection,theextracapsularresection of extracranial tumors can be achieved through the parachiasmatic cistern. The paraclinoid carotid artery emerges intradurally at the level of the medial opticocarotid recess(OCR)andwhenfollowed,willenableidentificationofthe optic nerve. There should be adequate thinning of the capsule to aid in sharp dissection of the arachnoidal fibers.[32] The boundaries are denoted by the falciform ligament and the posterior ethmoidal arteries anteriorly, the upper half of thesellaposteriorlyandtheOCRlaterally.[33]

Transcribriform Approach

Completeethmoidectomiesandremovalofthesuperiornasalseptum at the skull base are performed. The lamina papyracea

Figure 4: Planum sphenoidale meningioma. Preoperative  (a)  sagittal and (b) coronal magnetic resonance imaging (MRI) showing a 1.9 cm × 2.1 cm × 2.0 cm mass restricted to the midline and not extending beyond the internal carotid artery bifurcation or optic nerves. Postoperative (c) sagittal and (d) coronal MRI demonstrating excision of the lesion

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Figure 5: Cadaveric dissection of the anterior skull base. (a) Overview from the clivus to the cribriform plate. Red lines indicate the area of the transcribiform approach. Green lines indicate the area of a transtuberculum/transplanum approach. (b) Close view of the cribriform plate. The dura and the anterior ethmoidal artery can be seen on the right side. Laterally, the periorbita is exposed. (c) Close view of the region of the pituitary gland: C ‑ paraclival carotid, P – pituitary, CS ‑ cavernous sinus, O ‑ optic nerve, D ‑ dura

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may be removed, but care should be taken to preserve the periorbital fascia. Upon coagulation of the anterior and posterior ethmoidal arteries, the cribriform plate and crista galli are removed. The dura is opened by incisions on bilateral sides of the falx because opening it anteriorly to the tumor canresultinherniationofbrainparenchyma.Afterresectionof the tumor separately on both sides, the falx is incised to attain a single working area followed by debulking of the tumormedially[Figures5a,band7].Injurytothevesselsat the interhemispheric fissure during the extracapsular dissection should be prevented.[32] The boundaries include the frontal sinuses anteriorly, the medial wall of the orbits laterally and the anterior part of the planum sphenoidale at the level of the posterior ethmoidal arteries posteriorly.[33]

The Transsellar Approach

Septations of the sphenoid sinus should be resectedcarefully and the sinus floor can be drilled down to the level

of the clivus to maximize the trajectory in the direction of the supra‑ and retrosellar region. The mucosa below the sella is stripped off to expose the bony anterior face of the sella.Removalofboneofthesellaabovethemedialpartof the cavernous sinus is continued in a cranial and caudal direction until the superior and inferior intercavernous sinuses are visible. If the tumor spreads to the suprasellar and lateral opticoocarotid cisterns, exposure of the medial OCRthenbecomesnecessary.Afteropeningofthedurawith a cruciate incision, the inferior portion is maintained in a caudal position to prevent obstruction of vision by a suprasellar tumor. The posterolateral portion of the tumor is removed first, followed by the superior opening of the dura and continuation of the tumor resection superiorly andlaterally[Figures2and5c].Attentionisgiventothearea posterior to the carotid genu in the cavernous sinus, themedialOCR, and the anterior aspect of the dura atthe level of the superior intercavernous sinus for tumor remnants.[32]

The Cavernous Sinus Approach

The medial pterygoid process is drilled to reach the lateral recess of the sphenoid sinus. The sella is then opened and drilledlaterallytodisplaythecarotidprominence[Figure2].Depending on the extension of the tumor, the opening of the dura is performed either medial or lateral to the internal carotid artery.[33]

Figure 6: Transplanum approach in the patient seen in Figure 3. (a) On both sides,  a pedicled vascularized  septal flap was  raised, and  the  sphenoid sinus has been opened. Next,  the planum was drilled  (b) and  the dura exposed (c). The tumor was identified between the optic chiasm and the pituitary  (d and e) and successfully removed (f). The cerebrospinal fluid leak was closed using a multilayer seal with fat, fascia lata, tissue glue, and vascularized pedicled septal flaps

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Figure 7: Transcribiform approach  in a patient with an olfactory groove meningioma.  (a) On the right,  the dura and the periorbita are exposed. Olfactory fibers can be seen exiting the cribriform plate. (b) Exposing the dura on  the  left  side after drilling  to allow access  to  the meningioma. (c)  Exposure of  the  tumor  (meningioma).  (d)  Successful  removal of  the meningioma results in a cerebrospinal fluid leak

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Reconstruction

The fundamental objectives for reconstruction are the prevention of postoperative CSF leaks and intracranialinfections, protection of neurovascular structures, and maintenanceoffunction.Materialsavailableincludesyntheticmaterials (dural substitute) or autologousmaterials (fat,mucosa or nasal septum, conchal cartilage, temporalis fascia andfascialata).Fibrinsealantsholdthegraftinplaceandensure a temporary watertight seal.[34]

Atourcenter,wepreferamultilayerclosureconsistingofanunderlaygraft,overlaygraft,andoverlyingsupport[Figure8].

Underlay

Forsmalldefectsfollowingtheexcisionofapituitarytumor,a piece of fat harvested from the periumbilical region is insertedandgluedintoposition.Forlargerdefects,asheetof fascia lata is inserted into the dural layer. This fascia layer should be sufficiently large to cover the entire defect with anareaofoverlap.Careshouldbetakentoensurethatthislayerislaid“flat”sothatatunneldoesnotexist.Followingthis, a layer of tissue glue is used to hold it in place.

Overlay

The underlay graft is then covered with either another layer of fascia lata or fat. This layer should cover the entire defect with sufficient overlap and is glued in place.

Overlying Support

Finally,thedefectissupportedbyfatfollowedby2typesofabsorbable hemostatic agents. The entire repair is then held in position by a vascularized turbinate flap or nasoseptal flap.

Complications

ReportedratesofpostoperativeCSFleaksafterconventionalapproachesrangefrom13%to29%[35‑38] compared to those of endoscopic approaches varying from 1.5% to 6.4%.[39] Meningitisandintracranialabscessesarealsowell‑recognizedcomplications. Nonetheless, the incidence rate is relatively low, ranging from 0.5% to 10%.[38‑42] Other concerns include effectively managing vascular injuries owing to a limited working space, intraoperative neural injury, and delayed neurological deficits.

In our center, the rates of postoperative CSF leaks areminimal after careful reconstruction with the multilayer technique. Creation of awide surgical corridor ensuresadequate exposure and instrumentation to successfully secure hemostasis via the endoscopic technique. We have also developed our own device that enables the delivery of hemostatic agents with a patty accurately over the site of brisk bleeding to maintain simultaneous compression and suction for a more effective hemostasis.[43] We believe these limitations can be overcome with experience and improvement in the surgical technique. In fact, a promising overall permanent morbidity and mortality rates of 1.8% and 0.9%, respectively, has been reported using the endoscopic approach.[38]

Conclusion

The endoscopic transnasal approach allows access to lesions in the anterior and central cranial fossa in most cases. However, each case must be evaluated individually with regard to the lateral extension.

AcknowledgementOne of the authors of this paper, Vicknes Waran, is supported byUniversityofMalaya’sHIR‑MOHEresearchgrantinitiative(H‑50001‑00‑A000026).

Financial support and sponsorshipNil.

Conflicts of interestThere are no conflicts of interest.

Figure 8: Repair of the cerebrospinal fluid leak after transcribiform removal of  a meningioma  in  the patient  seen  in  Figure 5. Multiple  layers were used. (a) First, an overlay of fat stabilized with tissue glue was used. (b) Next, fascia lata with another layer of tissue glue, and finally (c) a vascularized middle turbinate flap was applied

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