300 S.G. Deiner et al.Fig. 18.1 Skull base anatomyOccipital boneChoanaAdenoidsOpening of auditory(eustachian) tubeSphenoid boneSphenoid sinusSella turcicaCribriform plateof ethmoid boneFrontal boneFrontal sinusSuperior turbinateMiddle turbinateInferior turbinateVestibuleAnterior narisHardpalateSoftpalate UvulaFig. 18.2 Sella turcica and paranasal anatomy
30118 Neurosurgical Otolarynology II: Endoscopic Skull Base and Pituitary SurgeryPreoperative ConsiderationsOtolaryngologist’s PerspectiveAs mentioned above the main endoscopic skull base surger-ies performed are tumor biopsy, excision of both benign andselect malignant neoplasms, orbital and optic nerve decom-pressions, CSF leak repairs, and pituitary surgery. In the caseof skull base biopsies, lesions may be inﬂammatory such asgranulomatous disease, pseudotumor, or Tolosa HuntSyndrome [3, 4]; infectious such as invasive fungal sinusitis[5, 6]; or neoplastic. Certain neoplastic lesions such as lym-phoma do not require surgery for treatment. Depending onthe extent of the disease process and its location, thesepatients may present with preoperative cranial nerve palsies,orbital entrapment, diplopia or impaired vision due to inva-sion of the cavernous sinus and orbital apex. At times, thereis extensive involvement of surrounding vital structures andimaging is not able to conﬁrm a diagnosis.Because this region contains many critical structuresespecially in and around the cavernous sinus (Fig. 18.3), theclinical presentation in these patients depends on the area ofinvolvement. Lesions may extend from an intracranial loca-tion into the paranasal sinuses such as meningiomas or pitu-itarylesions.Tumorsthatinvolvethesellamaycausepituitaryhypofunction or hyperfunction with variable presentationssuch as hypothyroidism, loss of libido, acromegaly, men-strual irregularity, or lactation, to name a few. The proximityof the optic chiasm to the pituitary gland may cause visualﬁelddefectsorclassicallybitemporalhemianopsia(Fig.18.4).Cranial nerve dysfunction is also seen in tumors that involvethe skull base. Some examples are diplopia secondary to cra-nial nerves III, IV, and VI traveling through the cavernoussinus; jaw numbness due to involvement of the mandibulardivision of the trigeminal nerve as it exits the foramen ovale;or aspiration or dysphagia secondary to cranial nerve IX andX compression at the jugular foramen.Lesions that involve the orbital apex, infratemporal fossa,petrous apex, clivus, and sellar/parasellar regions are idealfor an endoscopic biopsy. In these cases if there is an accesspoint via the paranasal sinuses, usually the sphenoid sinus,an endoscopic procedure is an ideal surgical option to obtaintissue for diagnosis. If the diagnosis requires only medicaltreatment, these surgeries may entail only removing a sampleof tissue for pathologic examination or in some cases involveextensive surgical resection if negative margins are possiblewhile preserving vital structures.Cerebrospinal ﬂuid (CSF) leaks and encephaloceles arenow managed almost exclusively through an endoscopicapproach except for select cases [7–12]. Patients commonlypresent with clear rhinorrhea that increases with coughing orValsalva maneuver. CSF leaks may be posttraumatic, post-surgical, or spontaneous. Although 80% of posttraumaticleaks will heal with conservative management such as bedrest and lumbar drainage, there is a 30% long-term risk ofascending meningitis [13, 14]. The patient with a spontaneousCSF leak is considered a separate entity and believed to be avariant of benign intracranial hypertension [10, 15, 16]. It isimperative that the underlying pressure elevation be man-aged either medically with acetazolamide or surgically witha ventriculoperitoneal (VP) shunt; otherwise, the risk ofrepair failure or a new CSF leak is ongoing. There is no clearintracranial pressure level where a VP shunt is recommendedin the literature with respect to the management of CSFleaks. At our institution, if the CSF pressure is above30 cm H2O, a shunt procedure is recommended.Pituitary tumors and sellar lesions such as Rathke cleftcysts or craniopharyngiomas may present with headaches orvisual ﬁeld defects due to silent growth and pressure on theoptic apparatus. Pituitary dysfunction may be seen as well,as mentioned earlier. Preoperative imaging is imperative inPituitary stalk(infundibulum)Oculomotor nerve (III)Trochlear nerve (IV)Abducens nerve (VI)Maxillary nerve (V2)Ophthalmic nerve (V1)Internal carotid arteryOptic chiasmSphenoid sinusFig. 18.3 Cavernous sinusanatomy
302 S.G. Deiner et al.all of these lesions so as to determine the extent of surround-ing tissue involvement and to plan a surgical approach.Medical management and evaluation of these patientsprior to surgery focuses on obtaining appropriate laboratoryinvestigations and imaging before the surgery so the anesthe-siologists can review these data. A full panel including acomplete blood count and comprehensive metabolic panelare necessary at a minimum. Also, depending on the age ofthe patient or comorbid status, further workup may beinvolved as these surgeries are not without risk. If there isany concern that the patient poses a signiﬁcant risk for sur-gery or may be challenging to manage intraoperatively, it isrecommended that the otolaryngologists obtain an ofﬁcialpreoperative anesthesiology consult.Anesthesiologist’s PerspectivePerhaps the single most important consideration guiding appro-priate preoperative evaluation of the patient for endoscopicskull base surgery is an understanding of the surgical proce-dure and tumor type. The surgical procedures vary in terms ofneurovascular structures at risk, operative time, and potentialfor conversion to open surgery. Once the anesthesiologistunderstands the nature of the tumor and the planned procedure,preoperative evaluation can be focused on patient risk factors.We will examine these in a systems-focused manner.GeneralSkull base tumors are generally benign tumors that causecompression of surrounding structures or invasion of adja-cent tissue. Due to the proximity of these tumors to cranialnerves, optic chiasm, and pituitary gland, a variety of symp-toms may be reported. In addition secondary brain edemaand hydrocephalus may be present.All patients presenting with skull base tumor resectionsneed a thorough history and physical to determine the pres-ence of raised intracranial pressure. The presence of raisedintracranial pressure will have major implications on themanagement of pre-sedation, induction, and intraoperativemanagement. Worrisome symptoms include: headache (oftenworse in the morning), vomiting, drowsiness, seizures, focaldeﬁcit in an extremity, difﬁculty with balance, changes invision, auditory loss, speech difﬁculties, bulbar symptoms,facial pain, facial paralysis, or personality changes. Pituitarytumors may cause symptoms both by mass effect on sur-rounding tissue and by secretion of hormones. A pituitarytumor may increase ICP either directly from the tumor itselfor indirectly from its obstruction of the third ventricle result-ing in hydrocephalus (Table 18.1) .Endocrine/Laboratory EvaluationAll patients should undergo preoperative laboratory evalua-tion before surgery. The benign skull base tumors may causelaboratory abnormalities when they are associated with com-pression of other structures. Pituitary adenomas may also be“functioning” tumors of a single cell type, producinghormones (Table 18.2). Generally these tumors present withthe symptoms of anterior pituitary hormone excess .A complete blood count should be obtained. This is par-ticularly relevant for men with pituitary tumors and low tes-tosterone, which is associated with an increased risk ofanemia . Coagulation studies are indicated in patients withother medical or pharmacologic reasons for coagulopathy.Metabolic panels are an inexpensive, efﬁcient way to evalu-ate possible posterior pituitary dysfunction and the presenceof diabetes insipidus secondary to ADH deﬁciency.Hypercalcemia would alert the clinician to the possibleFig. 18.4 Pituitary macroadenoma compressing the optic chiasm andextending into the left cavernous sinusTable 18.1 Possible symptoms of skull base tumors• Headache, usually worse in the morning• Vomiting• Drowsiness• First-time seizures• Loss of sensation in an arm or leg• Difﬁculty with balance and coordination• Dizziness• Vision loss or double vision• Hearing loss• Tinnitus (ringing in the ears)• Speech difﬁculties• Hoarseness• Difﬁculty swallowing• Facial pain, twitching, or paralysis and• Change in personality
30318 Neurosurgical Otolarynology II: Endoscopic Skull Base and Pituitary Surgerydiagnosis of multiple endocrine neoplasia, type I (MEN I).The endocrine evaluation of each patient should include anevaluation for anterior and posterior pituitary dysfunction:thyroid panel [thyroxine, thyroid-stimulating hormone(TSH)], and serum levels of cortisol, adrenocorticotropichormone, insulin-like growth factor-1, testosterone, luteiniz-ing hormone, follicle-stimulating hormone, [alpha] subunit,and prolactin.However, of note the most common cause of secondaryamenorrhea should always be investigated with a pregnancytest. Compression of the pituitary may result in panhypopitu-itarism. These patients should receive hormone replacementtherapy with hydrocortisone and/or thyroxine, and evaluatedfor efﬁcacy by laboratory studies. Additional stress doses ofsteroids (i.e., 100 mg hydrocortisone IV) may be necessaryin the perioperative period; however, not all patients withskull base tumors should receive steroids since a subgroup ofpatients with functional adenomas will have excessive corti-sol production.Cardiac EvaluationCardiovascular evaluation should be based on the patient’ssymptoms, exercise tolerance, medical history, and tumortype. In general, the 2007 ACC/AHA algorithm for periop-erative evaluation of the patient for noncardiac surgery is anappropriate guide . A complete discussion of the approachto cardiovascular disorders can be found in the preoperativecare chapter (Chap. 7). According to the algorithm mostpatients will be low to moderate risk, and most endoscopicskull base procedures are intermediate risk except in certaincases where there is risk to the carotid artery or cerebral vas-culature. Further consideration may be warranted in patientswith functional adenomas resulting in acromegaly (Fig. 18.5)or Cushing’s disease (Fig. 18.6). Both of these diseasespredispose toward structural and/or electrical cardiacpathophysiology.Cardiac disease is the most frequent cause of death inpatients with acromegaly, with 50% of patients dying beforeage 50 . Acromegaly is associated with systemic hyperten-sion, left ventricular hypertrophy, and diastolic dysfunction .Table 18.2 Pituitary tumor types and incidencesHormone secreted Percentage of all tumorsProlactin 40–45ACTH 10–12GH 20Gonadotropins 15Null cell 5–10TSH 1–2Fig. 18.5 Patient with acromegalic facial featuresFig. 18.6 Patient with Cushing’s syndrome facial features
304 S.G. Deiner et al.The latter can be one of the earlier signs of acromegalic car-diomyopathy . While the ventricular hypertrophy mayimprove with treatment of the acromegaly, the diastolicdysfunction is related to myocardial ﬁbrosis and does notresolve [23, 24]. Small vessel coronary artery disease may bepresent, and any signs of angina even in younger patientsshould be thoroughly evaluated . Conduction defects areseen in approximately 50% of patients and may lead to car-diac rhythm disturbances, bundle branch blocks, and ECGchanges including T wave abnormalities .The majority of patients with Cushing’s disease have sys-tolic and/or diastolic hypertension . The etiology of thishypertension is increased endogenous corticosteroids whichcan increase cardiac output as well as the hepatic productionof angiotensinogen resulting in an increase in plasma volume.Additionally, corticosteroids increase the inﬂux of sodium invascular smooth muscle. Glucocorticoid inhibition of phos-pholipase A2 causes a reduction in the synthesis of vasodila-tor prostaglandins increasing the tone of vascular smoothmuscle . Inositol triphosphate production in vascularsmooth muscle leads to increased sensitivity to vasoconstric-tors (e.g., angiotensin I). The increased vasoconstriction anddecreased modulation of vasodilation may result in septaland/or left ventricular hypertrophy. ECG abnormalities arecommon in patients with Cushing’s disease including thoseindicative of left ventricular hypertrophy and left ventricularstrain. Both electrical and functional changes tend to regressafter tumor resection .Certainly all patients with acromegaly and Cushing’sdisease should have preoperative electrocardiograms.Acromegalic patients should have an echocardiogram, and ifthey have symptoms of dysrhythmias or chest pain, furtherevaluation with Holter monitoring and a stress test may bewarranted.Respiratory EvaluationSimilar to cardiac considerations above, the evaluation of therespiratory system of the patient for skull base tumor surgeryis identical to the evaluation of a patient for general surgery,except in the case of patients with functional adenomasresulting in acromegaly or Cushing’s disease.The second most common cause of death in acromegalicpatients is respiratory disease . Respiratory tract changesinclude: hypertrophy of the soft tissue of the nose, mouth,tongue, lips, pharynx, and larynx causing reduction in thesize of the glottic opening, hypertrophy of the periepiglot-tic folds, calcinosis of the larynx, and recurrent laryngealnerve injury. Patients with acromegaly or Cushing’s diseasemay be difﬁcult to bag-mask ventilate and intubate.Mallampati classiﬁcation may yield a signiﬁcant number offalse negatives in acromegalic patients ; therefore, clinicalsuspicion should be high and the threshold to perform awakeintubation, low.A recent study found that more than 80% of acromegalicpatients have sleep apnea . In the presence of diagnosedobstructive sleep apnea plans should be made for appropriatepostoperative monitoring. Hoarseness should alert the physi-cian to the possibility of laryngeal stenosis or recurrentlaryngeal nerve injury . Patients with laryngeal nerveinjury may be predisposed to aspiration. Rapid sequenceinduction and extubation after the patient fully regains con-sciousness is prudent. Any combination of these issues maycontribute to perioperative respiratory complications.Intraoperative ConsiderationsOtolaryngologist’s PerspectiveThe importance of the surgical ﬁeld achieved through theappropriate anesthetic technique and adequate control ofintraoperative blood pressure and heart rate cannot be over-emphasized in the setting of endoscopic skull base surgery.The surgeon is operating in an area where visualization is ofparamount importance. In open surgery, palpation of the tis-sue and depth perception are added surgical tools to enhancesafety during the procedure. These two valuable adjuncts,however, are not available in endoscopic procedures. A sur-geon must rely on his vision as well as an acquired skill ofpalpation via surgical instruments to determine safety andproximity to critical structures.There are three main procedures that exemplify intraop-erative management of skull base surgery: CSF leak/enceph-alocele repair, pituitary surgery and extended parasellarapproaches, and anterior cranial fossa tumor resection. Thesethree areas demonstrate the key concepts in skull base sur-gery: (1) approach and resection of the pathology, whether itbe a tumor or an encephalocele; (2) reconstruction of theskull base defect with a free graft or vascularized tissue; andlastly (3) return to a normal functioning sinonasal cavity.Paranasal sinus CSF leaks or encephaloceles most com-monly involve the sphenoid and ethmoid regions . Theendoscopic approach for repair of these leaks has nowevolved to become the standard of care for the initial attemptat closure . The approach to this area is similar to a func-tional endoscopic sinus procedure. The anterior cranial fossalies above the frontal and ethmoid sinuses, thus these areasmust be resected completely in order to expose the skull baseand location of the defect. We incorporate the use of diluteintrathecal ﬂuorescein to help localize the site of the leak.
30518 Neurosurgical Otolarynology II: Endoscopic Skull Base and Pituitary SurgeryIt should be noted that ﬂuorescein is not FDA approved forintrathecal use and the patient must be informed of this fact.The safety proﬁle of the present recommended dilution,however, has been demonstrated in the literature [35, 36].A lumbar drain is placed at the beginning of the procedure;0.1 mL of 10% ﬂuorescein solution is diluted in 10 mL of thepatient’s own CSF obtained during lumber drain placement.This dilute ﬂuorescein is injected through the drain slowlyover 30 min with the patient in a head down position. It iscritical to place topical pledgets with decongestant in thenasal cavity in order to limit vascular engorgement of thesinonasal tissue. The ﬂuorescein is used to help localize thesite of leak during the endoscopic procedure as well as toconﬁrm an adequate closure of the defect (Fig. 18.7). Onewill continue to see ﬂuorescein-stained rhinorrhea aroundthe repair if complete closure is not achieved.If an encephalocele is present, it is reduced with bipolarcautery ﬂush with the skull base defect (Fig. 18.8). This iscritical in order to allow placement of an underlay and over-lay graft. In addition the mucosa around the perimeter of thedefect is removed in order to expose the underlying bone. Iffeasible, an underlay graft is placed in defects larger than5 mm in size to avoid risk of herniation of intracranial con-tents. An overlay graft is then placed over the defect and sta-bilized with ﬁbrin glue and nasal packing. There are multipleoptions for graft placement ranging from autologous tissuessuch as, septal or turbinate mucosa and bone, fascia lata, andtemporalis fascia to allografts such as Alloderm®(LifeCellCorporation, Branchburg, NJ) or Duragen®(IntegraLifeSciences Corporation, Plainsboro, NJ). Mucosa shouldnever be placed as an underlay graft as this creates the risk ofintracranial mucocele formation .Pituitary surgery has undergone multiple evolutions over thepast century due to advances in intraoperative technology .It has evolved from its initial descriptions by Cushing withthe use of a headlight to the present purely endoscopic orendoscopic-assisted technique [38–40]. The use of a microscopeprovides the surgeon with valuable depth perception in anarea with little margin for error; however, there are limita-tions with respect to visualization around the perimeter ofthe sella that the endoscope is able to address. The use of anendoscope provides a panoramic view as well as large visualangles ranging from 0° to 70°. This has created the ability toexamine around corners and access extra-sellar lesions.Endoscopes are not without their limitations. Most notable isthe absence of depth perception and 3D imaging. Duringtumor removal and while working in close proximity to criti-cal structures such as the carotid artery, it is imperative towork in a two-surgeon four-handed technique, using a purelyendoscopic technique.For lesions limited to the sella, a microscopic or endo-scopic approach will result in equal success. In this setting,with limited tumor extension, the microscope provides anadequate ﬁeld of vision and in some cases may be superior tothe endoscope since it provides the added beneﬁt of depthperception. When using a microscope, a posterior verticalincision is made at the bony-cartilaginous junction of thenasal septum and resection of the bony septum to the face ofthe sphenoid sinus. The septum between both sphenoidsinuses is resected which results in exposure of the sella tur-cica. A speculum is used to expand the ﬁeld and allow abimanual technique and the passage of instruments into andout of the nose. In contrast, the endoscopic technique requiresmore dissection; however, this results in a wider ﬁeld ofvision and greater range of motion for instrument dissectionthat is critical for larger, more extensive tumors.The reconstruction of the skull base after pituitary andextended transsphenoidal surgery is performed in multiple ways.Fig. 18.7 Fluorescein can be seen draining from a cribriform platecerebrospinal ﬂuid leak into the nasal cavity. The ﬂuorescein is used tolocalize the site of leak and also to conﬁrm adequate closure Fig. 18.8 An encephalocele has been reduced to the skull base defectand the mucosa around the edges of the defect has been removed toprepare the site for graft placement
306 S.G. Deiner et al.A CSF leak is not always present in these cases; however, theconcepts of reconstruction are the same. We favor a combi-nation underlay–overlay technique with Alloderm®and sep-tal bone, and if there is a CSF leak present, a posteriorlybased nasoseptal ﬂap is placed over this repair (Fig. 18.9).The nasoseptal ﬂap is a vascularized ﬂap within the nasalcavity that is based on the blood supply of the posterior sep-tal branch of the sphenopalatine artery.Anterior cranial fossa surgery for resection of benign andmalignant lesions requires complete clearance and openingof the maxillary, frontal, sphenoid, and ethmoid sinuses. Oncethis is done, one or two nasoseptal ﬂaps may be raised fromthe nasal septum with resection of the bony septum up to theskull base. Once this has been done the roof of the nasal cav-ity is removed exposing the underlying dura and tumor. Theanterior and posterior ethmoid arteries will need to be con-trolled and cauterized during this approach in order to avoidthe risk of intra-orbital bleeding. Reconstruction of a defecthere is a challenge. If dural edges are present a sutured trans-nasal graft can be used (Fig. 18.10). In general, a combinationof underlay and overlay techniques is used with fascia lata orAlloderm as the underlay graft and a large nasoseptal ﬂap asthe ideal overlay choice. After the repair is completed, nasalpacking is placed to support the repair and kept in place for5–7 days. This is usually removed in the ofﬁce.Maintenance of a functional sinonasal cavity after limitedor extensive skull base resections is paramount. Inadequateattention to the sinuses during the resection will result inpostoperative infection, compromise to the reconstruction,and long-term chronic sinusitis for the patient. The sinusessurrounding the area of resection are opened and stentsplaced to maintain patency especially in the case of thefrontal sinus where long-term frontal recess stenosis andmucocele formation is a risk. In the case of pituitary surgery,the sphenoid sinus is the only sinus traversed and an adequatesinusotomy is created during the procedure to avoid long-term sphenoid sinus obstruction. Lastly, in addition to thesinuses, intranasal synechiae may develop and for this reasonsilastic splints are sometimes placed to avoid synechiaebetween the lateral nasal wall and septum. These are alsoremoved in the outpatient setting along with the nasalpacking.Although rare (i.e., approximately 1% of cases), internalcarotid artery (ICA) injury can be a life-threatening intraop-erative complication. Primary management is surgical andFig. 18.9 (a) The ﬁrst layer of closure is a combination bone andAlloderm graft that seals the skull base defect. (b) A nasoseptal ﬂap thatwas harvested as part of the approach is rotated into the sphenoid sinusand covers the initial layer of closure. Packing is placed to support thegraft and is left in place for 5 daysFig. 18.10 An Alloderm graft is being sutured in place with U clipsutures. A nasoseptal ﬂap is placed over this closure and secured withtissue sealant
30718 Neurosurgical Otolarynology II: Endoscopic Skull Base and Pituitary Surgeryinvolves the placement of packing, possible endovascularembolization or ligation of the ICA while a primary repair orgraft is placed. It is critical once recognized that this compli-cation is communicated to the anesthesiology team as theymay choose to manipulate the hemodynamics to eitherdecrease hemorrhage (i.e., controlled hypotensive tech-niques) or maintain adequate intracranial perfusion (i.e.,raise the blood pressure) once the bleeding is under control.Further, they can assure adequate intravenous access, inva-sive blood pressure monitoring, blood product administra-tion, and potentially prepare for transport to an interventionalradiologic suite for ﬂuoroscopically guided embolizationwhere appropriate.Anesthesiologist’s PerspectiveInductionIn the operating room the patient is positioned for intubationin the supine position on the operating table. In addition tostandard ASA monitors, patients with increased intracranialpressure or signiﬁcant heart disease secondary to their tumoror underlying comorbidities may require monitoring of arte-rial blood pressure prior to induction. Often, the ﬁnal posi-tion of the patient’s airway will be away from the machine,so an expandable breathing circuit, extensions on the intrave-nous lines, and sufﬁciently long cables for the monitors maybe required. While two experienced anesthesia providersmay choose to induce the patient with the airway at a dis-tance from the machine, a single provider or patient with adifﬁcult airway should be induced within reach of the anes-thesia machine and equipment cart.If a difﬁcult airway is anticipated, then considerationshould be given to an awake intubation, especially if thepatient may be difﬁcult to ventilate. Certainly in the case ofthe patient with acromegaly, appropriately large oral airways,LMAs, a second provider, and backup intubation devices(e.g., ﬁberoptic bronchoscope) should be readily available. In anticipation of subglottic stenosis, a range of endotra-cheal tube sizes should also be present. Standard endotra-cheal tubes are generally adequate, although some providersprefer oral RAE tubes for their low proﬁle or armored tubesbecause of their resistance to kinking.The choice of induction agent is determined by the pres-ence of cardiac disease, increased intracranial pressure, like-lihood of difﬁcult airway and whether the patient has a fullstomach. With an understanding of the patient’s issues theanesthesiologist performs a risk/beneﬁt analysis and choosesthe most appropriate plan. Maintenance of the airway isalways the most important of these considerations. As such,awake techniques may be indicated. Topicalization of theairway in a patient with a full stomach may be risky,however, as coughing and straining could worsen intracra-nial pressure.Propofol may be the appropriate induction agent forpatients with a preserved ejection fraction. Etomidate maybe chosen for patients with poor cardiac reserve. Ketamineshould generally be avoided as it may raise intracranialpressure.The selection of a paralytic drug is dependent on thepatient’s risk for aspiration, whether they have increasedintracranial pressure, and plans for intraoperative neuromon-itoring. Administration of succinylcholine may worsenincreased intracranial pressure and defasiculating doses ofnondepolarizing agents do not block this phenomenon .However, it has not been shown that the use of succinylcho-line has resulted in brain herniation . Therefore, the anes-thesiologist must weigh the indication for rapid sequenceagainst the theoretical risk of aspiration and choose the mostprudent plan. Prior to the use of nondepolarizing neuromus-cular blockade the anesthesiologist should conﬁrm the intra-operative neuromonitoring plan. The use of facial nervemonitoring, EMG, or motor evoked potentials is not compat-ible with intraoperative paralysis. However, many proceduresmay have an initial prolonged phase of preparation and sur-gical start prior to monitoring. If this is the case, then aninitial dose of intermediate acting paralytic may be appropri-ate so long as it is not re-dosed.If intracranial hypertension is suspected or a real risk forthe patient, premedication should be approached cautiouslyas it may result in hypoventilation and hypercarbia leading toincreased intracranial pressure.MaintenanceThe intraoperative goal of the anesthesiologist is to providean amnestic, immobile patient with stable hemodynamics.Surgical considerations include facilitation of a bloodlessﬁeld (discussed in detail in Chap. 13) by a combination oflower blood pressure, avoidance of vasodilators, and the useof vasoconstrictors and nerve blocks.Maintenance of anesthesia may be achieved with inhala-tional agents, intravenous agents, or both. Inhalational agentscause vasodilation and may contribute to venous oozing.While inhalational agents are not contraindicated, supplemen-tation with intravenous agents including propofol, narcotics,or dexmedetomidine may be helpful. Whichever technique ischosen, the end goal is rapid emergence, extubation, and earlyneurologic evaluation. Therefore, the duration of the proce-dure and kinetics of the drugs must be kept in mind.If the patient is to awaken in a timely fashion at the end ofthe procedure it is extremely important that the anesthesiolo-gist is aware of the context sensitive half-life of the drugsthey are using to maintain amnesia. Context sensitive half-life is the time for the plasma concentration to decrease by
308 S.G. Deiner et al.50% from an infusion that maintains a constant concentra-tion. Context refers to the duration of the infusion. Time to50% decrease in plasma concentration was chosen because a50% reduction in drug concentration roughly appears to benecessary for recovery after the administration of most intra-venous hypnotics at the termination of surgery. During longsurgeries this knowledge must be used to aggressively taperthe intravenous anesthetic at the appropriate time, often40 min prior to surgical ﬁnish in the case of propofol. Duringclosure, inhalational gas can be added if necessary.In general postoperative pain is mild to moderate follow-ing skull base surgery.Although counterintuitive, at least onestudy has shown that the presence of nasal packing is notassociated with postoperative discomfort . Therefore, theanesthesiologist should avoid large doses of long-acting nar-cotics for postoperative pain or to achieve blood pressurecontrol during surgical stimulation. Blood pressure may becontrolled with short-acting narcotics (remifentanil, alfenta-nil) or with antihypertensives. In fact, lingering respiratorydepression from long-acting narcotics may serve to increaseintracranial pressure in the postoperative period.Blood Pressure ManagementA detailed discussion of blood pressure management forendoscopic surgery can be found in Chap. 13) and the sameprinciples should be applied to endoscopic base of skull sur-gery. Acceptable intraoperative blood pressure is a functionof the patient’s preoperative blood pressure and relevantcomorbidities. Obviously, patients with poorly controlledhypertension and known carotid or cerebrovascular diseaseare not appropriate candidates for deliberate hypotension. Ifthese conditions are recognized preoperatively, then a dis-cussion should be had with the surgeon regarding the abilityto provide intraoperative hypotension to facilitate a blood-less ﬁeld. In general, intra-arterial catheters are not manda-tory. However, the real possibility for hemorrhage andpotential rapid changes in blood pressure if the brain is vio-lated lead many to place this monitoring modality in allpatients.Recent studies have suggested that nerve blocks may beuseful adjuncts to inhalational agents during sinus surgery.Higashizawa et al. showed that infraorbital nerve blocks areeffective in reducing halogenated agent consumption, theneed for blood pressure control with antihypertensives, inpatients undergoing endoscopic endonasal maxillary sinussurgery (ESS) under general anesthesia . The block is per-formed by injecting a small (1.0 mL) amount of local anes-thetic in the area of the infraorbital foramen (Fig. 18.11). Theinjection may be approached via the soft tissue that overliesthe foramen, intraorally or via the nares.Fluid ManagementSkull-based tumors which are amenable to endoscopic resec-tion generally are not associated with brisk blood loss.Fig. 18.11 Direct and transoral approach to infraorbital nerve. In both approaches, the anesthesiologist palpates the infraorbital foramen anddirects the needle in that direction
30918 Neurosurgical Otolarynology II: Endoscopic Skull Base and Pituitary SurgeryHowever, there is always the potential for blood loss second-ary to surrounding vascular structures. An example is thepotential for damage to the ICA during transphenoidal pitu-itary surgery. As mentioned above, although exceedingly rare(1%), trauma to the ICA during endoscopic base of skull sur-gery can be life threatening. The treatment of this complica-tion is primarily surgical yet the anesthesiologist must beprepared to assist the surgical team in many ways. In high-riskcases (large tumors in close approximation to the artery) theanesthesiologist must be prepared to acutely lower the bloodpressure (MAP of 40–60) with vasodilator agents (e.g., nitro-glycerin or sodium nitroprusside) or anesthetic agents (e.g.,remifentanil, propofol, inhaled anesthetics) to reduce the riskof exsanguination while providing the surgeon an operativeﬁeld for possible detection and repair. If the carotid is to beligated, clamped, or embolized and if the patient is at high riskfor a cerebrovascular event, the blood pressure may in factneed to be raised. This can be accomplished by lightening theanesthetic or through appropriate vasoactive agents (e.g., phe-nylephrine, ephedrine).More commonly, venous “oozing” observed, and for pro-longed surgeries may be signiﬁcant. However, intraoperativebleeding does tend to be more severe in patients with largertumors and also with suprasellar extension . In higher riskprocedures, it is prudent to have access to an extremity foradditional venous access. At least one 18 g IV should beplaced to start these cases.Maintenance ﬂuids with an isotonic crystalloid are gener-ally adequate for intraoperative ﬂuid replacement. Generally,intraoperative osmotic diuresis is not necessary. Awarenessof previously existing or developing diabetes insipidus isimportant and may be signaled by large volumes of diluteurine without other inciting factors. This would prompt eval-uation of an electrolyte panel, which would show hyperna-tremia and dilute urine (speciﬁc gravity <1.005). Acutemanagement of diabetes insipidus would include conserva-tive treatment, or in the case of rising serum sodium andlarge discrepancy between ﬂuid inputs and outputs, DDAVP. However, endoscopic approaches are less likely to causediabetes insipidus than traditional open craniotomy .EmergenceWhile rapid emergence is desirable to facilitate an early neu-rologic exam, avoidance of coughing and straining isextremely important to avoid contributing to a CSF leak orworsened venous oozing. The anesthesiologist must producea calm, but awake patient who breathes reliably after extuba-tion. Unfortunately, deep extubation is generally not anoption as access to the airway is limited, patients may havean additional tendency to obstruct and it is undesirable toadminister positive pressure with a mask.Awake extubation may be accomplished in a variety ofways. Short-acting narcotics (remifentanil or alfentanil) maybe given by low-level infusion (e.g., 0.02–0.08 mcg/kg/minfor remifentanil) and then supplemented with judicious useof longer acting narcotics while the amnestic agents areallowed to dissipate. Dexmedetomidine infusion may beused for its ability to produce a calm patient with reliablerespiratory drive. Notably, dexmedetomidine does not obvi-ate the need for postoperative narcotics although it mayreduce total requirements .Postoperative nausea and vomiting are very common(23% of patients) in patients undergoing neurosurgical pro-cedures . In addition to patient discomfort, vomiting hasdetrimental effects on ICP and could potentially contributeto a CSF leak. Given this risk, routine prophylaxis seemsreasonable. Common sense dictates that when rapid emer-gence and early neurologic examination of the patient isdesirable, antiemetics associated with sedation (e.g., droperi-dol, scopolamine) should be avoided. Using the ConsensusGuidelines for Postoperative Nausea and vomiting, neuro-surgical patients should be considered high risk . Withconsideration of their underlying medical problems treat-ment with two or more of the antiemetic agents with IIAevidence should be considered. In this author’s practice, dex-amethasone 8 mg and ondansetron 4 mg are commonlyadministered prior to incision.Postoperative ConsiderationsOtolaryngologist’s and Anesthesiologist’sPerspectivesThe level of postoperative care is dictated by the patient’spotential for complications, which may warrant monitoringin the intensive care unit. Major surgical complications(1.5%) include CSF leak, meningitis, ischemic stroke, andvascular injury. Minor complications (6.5%) include sinusdisease, septal perforation, epistaxis, wound infections, andhematomas. Fluid and electrolyte disturbances occur in themajority of patients undergoing transsphenoidal resection ofpituitary adenomas and are usually transient. In a few patients,DI may persist and require therapy with ADH analogs. Mostcommonly, hyponatremia occurs 1 week postoperatively andresolves within 5 days, but may occur up to 10 days later .For a full treatment of the medical management of disordersof water balance, the reader is referred to any of the recentexcellent reviews including Nemergut et al. .From a surgical standpoint, some patients with spontane-ous CSF leaks may require postoperative lumbar drainage[10, 15, 16]. This is usually done for 24–48 h in order to address
310 S.G. Deiner et al.the likely elevation in intracranial pressure seen in thispatient population. In addition, long-term acetazolamide isadministered as a means of prevention of recurrent orde novo CSF leaks. Antibiotic prophylaxis is given topatients while nasal packing is in place in order to prevent asecondary sinusitis. After nasal packing is removed patientsundergo endoscopic debridement of the nasal cavity toremove retained mucus and crusting. It is important to avoidthe area of reconstruction in the early postoperative period.After 4 weeks, more aggressive debridement can be safely doneto avoid synechiae development in the sinonasal cavity.ConclusionThe endoscopic approach to skull-based tumor surgery hasbeen a major advance in otolaryngology and neurosurgery.While catastrophic intraoperative problems like hemor-rhage and venous air embolism have decreased, thereremain signiﬁcant anesthetic considerations. The anesthesi-ologist and surgeon should communicate regarding thepatient’s tumor, planned procedure, and intraoperativeexpectations. With this knowledge both physicians can cre-ate a care plan to achieve a smooth intra and postoperativecourse.Clinical InsightsFor the Otolaryngologist(from the Anesthesiologist)Communication between the surgeon and the anes-•thesiologist is critical for patient safety during endo-scopic skull base tumor surgery. Prior to theprocedure communication regarding the plannedprocedure, type, location, and size of the tumor iscritical. This allows the anesthesiologist to obtainappropriate monitoring and venous access prior tosurgical draping and arrange for availability of bloodand blood products.The need for intraoperative hypotension should be•communicated ahead of time. Agreement of therisk–beneﬁt ratio of this technique is important priorto surgical start. Plans for intraoperative neuromoni-toring will affect anesthetic choice as well.Finally, plans for postoperative neurologic evalua-•tion and need for intensive care monitoring allowsthe anesthesiologist to time their anesthetic regimenand consult with the intensive care team regardingplanned transfer of care.Clinical PearlsFor the Otolaryngologist(from the Otolaryngologist)Discuss with the anesthesiologist the possibility of a•total intravenous anesthetic to improve surgical con-ditions. If there is no medical contraindication, thistechnique will facilitate surgery through hemody-namic means.A separate consent is needed for the use of intrathe-•cal ﬂuorescein and the surgeon must inform thepatient that it is not FDA approved for intrathecaluse.The use of an extended needle tip bovie is an ideal•instrument to elevate the posterior nasoseptal ﬂap. Itprovides a dry ﬁeld and more precise incisions forthe ﬂap.The placement of pledgets in the nasal cavity while•the patient is in a head down position during intrath-ecal ﬂuorescein injection will decrease the vascularengorgement in the nose and bleeding once the sur-gery is begun.For the Anesthesiologist(from the Otolaryngologist)The value of a clear surgical ﬁeld is a critical com-•ponent to the success of endoscopic skull base sur-gery. Adequate visualization permits safer and moreefﬁcient dissection during an endoscopicprocedure.The sphenopalatine and infraorbital blocks are use-•ful in endoscopic skull base surgery as they are insinus surgery. The ability to offer these regionalblocks is an asset.These patients will often have nasal packing in•place and in light of the surgery having intracra-nial communication, nasal cannula oxygen shouldbe contraindicated to avoid the risk ofpeumocephalus.Although it is ideal to have a deep extubation to•avoid the risk of compromise to the skull base recon-struction, this beneﬁt must be weighed against therisk of an oversedated patient that will require maskventilation with subsequent positive pressure beingapplied to the reconstruction.
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