Surgery of the middle ear, mastoid and inner earvictorslavutsky.com/wp-content/uploads/2014/10/...Contribution à l'étude de l'anatomie du nerf facial du nouveau-né 2ª et 3ª portions:

Surgery of the middle ear, mastoid and inner ear

A simple mastoidectomy is done once the corticalexposure of the mastoid has been completed.Drilling at the level of the linea temporalis andslightly posterior to the external auditory canalwill mark the beginning of this surgical step(Figure 7.169). The mastoidectomy needs notto be extremely wide or with the intent ofremoving most mastoid air cells. It has to beample enough to be able to comfortably reachthose areas and anatomical pointers relatedwith the second surgical step which is theposterior tympanotomy. In this sense it issuggested to expose the body and short processof the incus in the fossa incudis, the bulge ofthe horizontal semicircular canal and the digastricridge (Figure 7.170). Its size should be largeenough to allow the passage of the cable thatjoins the electrodes and the receiver-stimulator.

It is necessary to open the lateral wall of theaditus and the posterior attic in order toadequately visualize the body and short processof the incus and the horizontal semicircularcanal. It is important to avoid damage to the

incus and to cause a sensorineural hearingdamage by the transmission of vibrations fromthe drill to the cochlea. At this point it issuggested to switch from a cutting to a diamondbur, working at low speed and avoiding contactof the bur with the incus. These suggestionsare within the concept of “atraumatic surgery”for the insertion of a cochlear implant (1).

In order to expose the digastric ridge it issuggested to extend the drilling inferiorly towardsthe mastoid tip. This implies the elimination -bydrilling- of the intersinufacial cells. These surgicalsteps will allow a better drilling angle during thedevelopment of the posterior tympanotomy andthe cochleostomy.

At the same time, during the performance ofthe posterior tympanotomy it is important toavoid an excessive thinning of the posterior wallof the external auditory canal. This can causecontinuity solutions that will eventually end upwith cholesteatomas because of invaginationof the skin of the ear canal.

Mastoidectomy and posteriortympanotomy approach in cochlearimplant surgery.

Surgical technique in an adult patient in whom the air spaces of the middleear have already been fully developed.

Mastoidectomy.

Manuel Manrique, Raquel Manrique Huarte.


CONSIDERATIONS ABOUTMASTOIDECTOMY IN CHILDREN.

Pneumatization of the air spaces of the middleear in children, varies during the developmentperiod. The middle ear and epitympanum endtheir pneumatization during the 33rd and 37thweek of gestation, respectively. The mastoidprocess be comes pneumatized between the34th gestational week and 10 to 14 years ofage. Because of this reason the mastoiddimensions will have a variation of 1cm in depthfrom medial to lateral, 2 cm in its antero posteriorwidth and 3 cm in its superior inferior length.

In a new born the mastoid will be basicallyrepresented by the antrum. When amastoidectomy is done before and during thefirst year, after a brief drilling of the soft mastoidcortex, the antrum is promptly exposed. Thescarce development of the tip will be representedby a non pneumatized spongy tissue that tendsto bleed quite easily during drilling. Thismaneuver is essential in order to create sufficientspace so that an adequate posteriortympanotomy can be done. Bleeding must bestopped with dry drilling with diamond burs orby applying bone wax.

POSTERIOR TYMPANOTOMY.

A posterior tymanotomy -opening of the facialrecess of the posterior wall of the tympaniccavity- provides a direct access to the medialwall of the middle ear during mastoidectomy.This route facilitates an approximation in astraight line to the scala tympani in the basalturn of the cochlea. This is of great value at the

time of insertion of electrodes in the cochlea(Figure 7.171).

When doing a posterior tympanotomy in a middleear without malformations or pathology, onemust take advantage of the anatomical pointersthat lead towards an easier localization of theFallopian canal. In this sense we suggest thereader to review the book of the author of thischapter (2).

Once the mastoidectomy is done and theanatomical pointers such as the short processof the incus, the horizontal semicircular canaland digastric ridge are identified, the mainsurgical maneuvers in doing a posteriortympanotomy are the following:

Thinning of the posterior wall of the externalauditory canal from its lateral most aspect to alevel determined by an imaginary line thattraverses between the incus and the digastricridge. This line represents the stretch throughwhich traverses the third portion of the facialnerve. As the drilling approaches this area it isbest to use a large or medium sized diamondbur, always maintaining a longitudinal drillingin relation to the facial nerve. The Fallopiancanal can even be skeletonized in order to havea better idea of the nerve location. This willprevent facial nerve damage duringcochleostomy and electrode insertion. On theother hand it is important to maintain the heightof the external auditory canal and a thicknessof the canal of two to three millimeters. This willprevent future complications related to thepresence of a continuity solution in the posteriorwall (Figure 7.172).

Once this point is reached, the drilling maneuvers


will be done between the facial and the chordatympani nerves. The bur will always be adiamond bur and the size should be such thatit can pass in between both structures withoutharming them. Drilling will progress mediallyuntil opening the facial recess. The tympanotomymust be widened inferiorly in order to allowadequate exposure of the promontory area,especially of the round window niche, area inwhich the cochleostomy is to be done (Figure7.173). If this widening is not done, one runsthe risk of doing a cochleostomy in a superiorposition, with an opening in the scala vestibuleand with a traumatic electrode insertion. At timesthe chorda tympani is sectioned, especiallywhen it emerges superiorly from the third portionof the Fallopian canal. At the same time, theposterior tympanotomy in its highest portion,must allow visualization of the stapes and itstendon without the elimination of the buttress.In addition to providing anatomical referencesfor the performance of the cochleostomy, thevisual control of the stapes can be useful if thestapedius muscle contraction is to be evaluatedby stimulation with the electrodes. Thisevaluation provides useful information in orderto establish C thresholds in cochlear implantprogramming.

Once the mastoidectomy and posteriortympanotomy are completed, a straightapproximation to the scala tympani and thebasal turn of the cochlea is available and acochleostomy can be done. In other words, withthese surgical steps “a hole, in a hole, in a hole”has been developed (Figure 7.174).

POSTERIOR TYMPANOTOMY IN CHILDREN.

As a consequence of an incompletedevelopment, In the case of children the thirdportion of the facial nerve is localized moresuperficially than in adults. It is important to beaware of this anatomical fact in order to avoiddamaging the facial nerve during mastoidectomyand posterior tympanotomy. It is important toconsider that the second genu of the facial nervehas a wider angle (more open) in children thanin adults. The angle of this second genu isalways over 90 degrees, varying according toBeauvillain (3) between 92° and 125°. Thisauthor describes the width of the Fallopian canalat the level of this genu as identical in childrenand adults, however, this is not true for its length.In the new born and in children, the genu projectsand curls posteriorly.

It is suggested that these surgical steps areconducted with facial nerve monitorization,especially in those cases in which the CAT scansuggests a malformation of the temporal boneor in the craniofacial region.

As it has been already described, doing aposterior tympanotomy requires thinning of theposterior wall of the external auditory canal.This is especially important in the case ofchildren since they have an immature Eustachiantube, and thus it is more frequent for them tohave negative pressures in the middle earspaces for longer periods of time. This willfacilitate the occurrence of skin retractions intothe external auditory canal in case of bonydehiscences of the posterior wall, favoring thedevelopment of cholesteatomas.


Fig. 7.169. Starting the mastoidectomy. The outlines ofthe drilling of the mastoid cortex are shown. These areat the level of the temporal line (linea temporalis) andthe posterior wall of the external auditory canal.

Fig. 7.170. Localization of the three principalanatomical pointers to be identified duringmastoidectomy in order to facilitate theposterior tympanotomy procedure.

Lineatemporalis

Digastric ridge.

CSH

FosaIncudis


Fig.7.171. Histological preparation of a temporal bone which shows the straight approximation to the scala tympaniof the cochlea that is obtained after a mastoidectomy and a posterior tympanotomy.

Scala tympani

Chorda tympani

Facial recess

Facial nerve

Mastoid


Fig.7.174. “A hole. In a hole, in a hole.” Asequence of mastoidectomy, posteriortympanotomy and cochleostomy, which providea direct linear approach to the cochlea incochlear implant surgery.

Fig.7.172. Graphic representation of theanatomical structures that are exposed witha posterior tympanotomy.

Fig.7.173. Graphic representation of theanatomical elements that are visible throughthe opening of the facial recess after a posteriortympanotomy.

Digastric ridge

Facial nerve

Chorda tympani

CSH

Round window

Promontory

Stapes


References.

1. LEHNHARDT E. Intracochleäre plazierungder cochlear-implant elektroden in soft surgerytechnique. HNO 1993; 41: 356-359.

2. MANRIQUE M. Guía para la disección delhueso temporal. Ed. biblio stm, Masson S.A.Barcelona, 1998.

3. BEAUVILLAIN C, SIMON C, LEGENT F.Contribution à l'étude de l'anatomie du nerffacial du nouveau-né 2ª et 3ª portions: aplicationchirurgicale. Ann Otolaryngol, 1982; 99:223-230.


ADVANTAGES

1. Technical simplicity.

2. Involves less bone drilling and tissue removal.

3. Carries almost no risk to the facial nerve.

4. Allows for direct view of and work in the roundwindow niches.

5. Provides a better angle in the basal turn ofthe cochlea for sliding the electrode, makingfull insertion easier.

6. Small postauricular flap carries less risk ofhematoma or infection; requires no drains;makes healing easier.

7. Allows faster recovery and shorterhospitalization.

SURGICAL STEPS

1. Endaural incisions (Lempert I and II) or smallpostauricular incision.

2. Canal incisions at 6 and 2 o'clock.

3. Exposure of the middle ear.

4. Drilling of the round window niche and

visualization of the round window membrane.

5. Small atticotomy.

6. Mastoidotomy.

7. Postauricular incision.

8. Removal of temporal muscle and periosteum.

9. Drilling of a seat for the internal receiver.

10. Introduction of the electrode into the antrumand middle ear.

11. Insertion of the electrode into the cochlea.

12. Securing of the internal receiver.

13. Closure, packing, and a mastoid dressing.

PROCEDURE

The procedure is usually done using a smallpost auricular incision, however, for didacticpurposes -and due to the fact that thepostauricular incision for cochlear implantationis described in this same chapter- endauralincisions will be described.

The first incision (Lempert I) is madesemicircumferentially between 6 and 12 o'clock

Active electrodes by the antrum.

Mastoidotomy/Tympanotomy Approach

Santiago Arauz, Marcos Goycoolea.


on the posterior wall at the bony cartilaginousjunction. The second incision (Lempert II) runsbetween the tragus and helix (at the incisura).The extension of this incision is approximately0.75 cm. The posterior canal skin (cartilaginousportion) is preserved and gently elevated witha small periosteal elevator, clearly exposing theentire posterior bony canal (Fig. 7.175A). Two- prong retractors are used for exposure;occasionally three-prong retractors are needed.

With a scalpel, vertical incisions are made at 6and 2 o'clock. In a completely dry field, a flapis elevated and the middle ear cavity is enteredbeneath the annulus. All anatomic structuresand landmarks are visualized. Using stapescurets, the posterior canal wall is enlarged anda small atticotomy is done (Fig. 7.175B). Specialattention is paid to the round window niche. Theanterosuperior portion is removed with a

small bur and the round window membrane isbrought directly into view (Fig. 7.175C). Anyadditional drilling needed for exposure is delayeduntil the electrode is inserted (see PosteriorTympanotomy [Facial Recess] Approach).

A piece of Gelfoam is used to cover the roundwindow and a large piece of cotton is placedover the ear canal. This avoids contaminationby bone dust and debris from the mastoidotomydrilling.

A mastoidotomy is done by drilling in the fossamastoidea toward the antrum (Fig. 7.175D).The opening should be large enough to visualizethe antrum. The posterior edge is beveled andall sharp bony edges are smoothed. The incusis disarticulated from its stapes and malleusattachments with a joint knife and totally

removed. If desired, a dummy electrode can beinserted through the mastoidotomy opening andinto the niche to verify the adequacy of theexposure. The middle ear and mastoid are thenfilled with an antibiotic solution.

A postauricular incision is needed for the solepurpose of placing the internal receiver; it shouldbe made at or above the linea temporalis,allowing enough space without interfering withthe use of eyeglasses. Lidocaine (Xylocaine)2% with 1:100,000 epinephrine is injected. Thecircumferential incision measures 3 to 3.5 cmand is deepened through the subcutaneoustissues until the temporal muscle is reached(Fig. 7.175E, F). The seat size for the internalreceiver is measured, and the correspondingunderlying temporal muscle and periosteum areremoved. The periosteum is saved for graftingthe round window niche. The bone seat is drilleddown to accommodate the receiver (Fig. 7.176A)and, depending upon the type of receiver,additional holes are drilled either for sutures orfor screw placement (see Poster iorTympanotomy [Facial Recess] Approach).

An electrode guide is passed from the endauralto the postauricular incision by tunneling itbeneath the temporal muscle. An electrodeguide, which is similar to an antrum trocar, isspecially curved and has a blunt distal openingto avoid damaging the electrode (Fig. 7.176B).The obturator is removed and the electrodeintroduced into the guide; the guide is thenwithdrawn and, with it, the electrode is carriedinto the mastoidotomy opening. It is then passedto the antrum and into the middle ear. Theexposed round window membrane is detachedwith an angled pick, and the electrode isintroduced with a nonserrated baby alligator


forceps in an angle pointing toward the basalturn of the cochlea, immediately past the hook(Fig. 7.176D). The opening of the round windowis sealed with temporalis fascia or periosteumwrapped around the electrode (Fig. 7.177A).Small pieces of Gelfoam are then placed lateralto the periosteum graft.

With a postauricular approach the electrodearray is introduced directly into the antrum andinto the middle ear, without the need of anelectrode guide.

The internal receiver is then secured in placewith sutures, the ground electrode is placedunder the temporal muscle, and the rest of thefascia or periosteum is used to seal the antrum.

The canal flap is repositioned. Gelfoam and anantibiotic ointment are used in the distal twothirds of the ear canal, and gauze is embeddedin antibiotic ointment in the distal one third.Incisions are closed with subcutaneous 3-0chromic catgut or 3-0 Vycril rapid and skinsutures of 4-0 silk or nylon, and a mastoiddressing is applied.


Figure 7.175.


Figure 7.176A, B,D.

Figure 7.177.


The usual technique for cochlear implantation (CI) involves anantromastoidectomy and a posterior tympanotomy (PT) through the facialrecess (1). The endomeatal approach (EMA) is a surgical technique thatuses a direct approach through two natural pathways: the external auditorycanal (EAC) and the round window (RW) (18, 19).

Our purpose is to describe the advantages of this approach; not only inconventional cochlear implant surgery, but in all those cases in which theposterior tympanotomy approach is difficult to perform.

Highligts.OPTIMAL INSERTION PLANE.

The scala tympani (ST) starts its basal turnimmediately alter the round window (RW),describing from its onset a spiral curve centeredin the modiolus. Therefore, in its way to thecochlear apex the ST longitudinal axis ischanging its direction continuously, going initiallydownward and forward, after a few milimiterstakes a horizontal, to the front and inwarddirection, and after that an inward and upwarddirection. The RW and its membrane are likean oblique base for the ST cylinder, with itsvisible face looking outward and backward.

The safest site for positioning of the electrodearray is the floor of the scala tympani (21). The

The endomeatal approach.

projection of the axis of the basal spira passesbetween the posterior border of the oval windowand the pyramidal process, and inferiorly by theinternal aspect of the crista fenestra. Therefore,in order to avoid damage to the neurosensorystructures, the direction of an optimal imaginaryinsertion plane must be from postero-superiorto antero-inferior (Figs. 7.178, 7.179, 7.180).

Fig.7.178. Optimal insertion plane (red line). Dissectedleft temporal bone, courtesy of Rodrigo Posada, MD.

Purpose.

Víctor Slavutsky, Luis Nicenboim, RodrigoPosada Trujillo.

Hook.

oval window posterior rimoptimalinsertion plane

pyramid

Facial nerve


Fig.7.179 Left temporal bone dissection with the groovelandmarks.

Fig. 7.180. Schematic groove´s cut, showing the overhangthat retains EL.

Depending on anatomical variability, thisprojection can coincide with the posterior wallof the external auditory canal or pass in frontof it. This is an anatomical fact to have in mindduring surgery in order to achieve goodpositioning of the electrode array.

THE GROOVE

EMA requires making a bony EAC groove forelectrode lead (EL) lodging, in order to avoidcontact between the skin and the EL that couldlead to i ts extrusion (Figure 7.179).

A safe anatomic area to perform the groovewith no risk for adjacent structures like facialnerve, chorda tympani, eardrum and ossicularchain were studied and finally established withthese landmarks: the incus and pyramidalprocess in the inner EAC side, and the outerborder of tympano-squamous suture in the outerside. This -groove placement is also on line withthe axis of the more basal segment of ST, sothe EL does not suffer any degree of bendingafter it is finally positioned in the ST.

From the pyramidal process in up, there isenough room to drill a groove with a 0.5 mmcutting burr. An overhang is left in the superiorgroove's edge, in order to retain the electrodelead and avoid its contact with the EAC skin,therefore preventing extrusion (Figs. 7.179,7.180).l mm wide and 2 mm depth is enoughto cross the fallopian canal at a safe distanceand lodge the EL. It is convenient to leave anoverhang that retains the EL (Fig. 7.180).

The pyramid level is the best place for thefollowing reasons:

Chorda tympani

Groove tympanosquamous suture

Incus

- a safe distance to FN even in infants;- good direct control of fallopian canal, visibleat oval window;

- good position for electrode insertion in theplane described before;

- EL does not cross over the incus process inits way to the RW.


Surgical technique.

FIRST STAGE: ENDOMEATAL

a. Anterior tympanotomy and exposure of theRW membrane

This stage is aided with an autostatic earspeculum. It starts with an endomeatalstapedectomy-like but a few millimeters moreexternal-skin incision, in the posterior wall ofthe bony EAC. The skin is carefully elevatedand the tympanic annulus is desinserted. Thetympanomeatal flap is driven forward over theanterior eardrum quadrants, respecting themalleolar eardrum insertion. At this moment theRW and promontory are visualized. Thetympanic bone margin must be lowered with acurette or diamond burr in order to completethe RW visualization-if necessary and to exposethe chorda tympani, the pyramidal process,the incus long process, the stapes, the ovalwindow and the fallopian canal (Fig. 7.181).

With a Skeeter microdrilt the overhang boneprojection that protects the RW is totally removeduntil complete RW membrane exposition. Themembrane is preserved at this stage in orderto prevent perilymph lost and bone dust entranceinto ST

b. Endomeatal groove.

Taking as reference the location of the RW, thepyramidal process, and the incus in the innerborder of the EAC, and the tympano-squamous

suture in the outer border, a 1 mm width and 2mm depth groove is performed in the EACposterior wall from inside to outside, in the EACaxis direction, with a Skeeter microdrill (Fig.7.179). As stated earlier, an overhang is left inorder to retain EL. In order to avoid CT damage,in some cases it is necessary to separate it fromthe tympanic ring. The bone dust is carefullycleansed with suction-irrigation. The TC and thetympanomeatal flap are protected with gelfoam.

SECOND STAGE: RETROAURICULAR

Groove lateral segment. Receiver-stimulatorwell and second well for the remaining EL

A retroauricular skin incision with a small postero-superior extension is performed [4] and themuscle-aponeurotic plane is dissected onecentimeter in both incision lips. The muscle isincised to the bone and the periosteum isdetached creating in a posterior manner a pocketfor the receiver-stimulator, and discovering inan anterior manner the mastoid bony surfaceup to the EAC. The dissection is continued intothe EAC until the endomeatal skin incisionexternal lip is detached from the bone, and theinternal part of the bony EAC is visible, with thegroove carved in the first stage. A classic mastoidretractor can be used or one with a valve thatprotects the skin of the posterior wall (Fig. 7.183).Then the groove drilling is resumed and pro-longed up to the external mastoid surface (Fig.7.182). The receiver-stimulator (RS) well isdrilled and a 2 cm diameter and 3 mm depthflat second well is performed in front of the firstone. This second well is connected forward to


Fig. 7.181. EMA RW cochleostomy. Anatomical relations. Fig. 7.182. The EL inside the groove. Deep insertionthrough the RW. EMA second stage.

Fig. 7.183. Mastoid retractor with a valve. EMA with retroauricular incision.

ScalaTympani

RWmembrane

Perilymph

Pyramid Facial nerve

Groove

Chordatympaniover incus

Round window

Groove

Electrode lead


the groove and backward to the RS well. TheTC Gelfoam protection is removed, and the RWmembrane is incised with a pick from its superioredge to the antero-inferior edge, taking carewith its posterior aspect that is in close relationwith the spiral lamina (Fig. 7.181). The RS isplaced in the pocket and the proximal portionof the electrode array is introduced through theEAC up to the TC.

The tympanotomy is wide open, with thetympanomeatal flap driven forward and protectedwith Gelfoam. It results in a clear RW exposure,since the posterior EAC skin and the eardrumdo not bother any surgical maneuver.

Optimal plane of electrode insertion.

It is necessary to consider that the EMA allowsthe EA to come from a more superior and

anterior position, .without being limited by theposterior wall as it happens in the PT approach.

The insertion is made in an up to down, backto front direction, from the EAC postero-superiorpart up to the superior edge of the round window.That results in an insertion angle approximately30° more anterior, and also 15° more superiorcompared with the PT insertion angle. Thatexplains why EMA avoids to crush modiolarwall, spiral lamina and/or basilar membrane asRoland et al. [3] refer, coming from a morevertical position and with enough space in theEAC to lead the EA to slide over the ST curvedouter wall, in a more inferior posi-tion, farther-from the basilar membrane and spiral laminaand running away from the inner wall.

Once the insertion is done, the EL is gentlyintroduced inside the groove (Fig. 7.182 ) and

Fig. 7.184. Groove. Cochlear implant in postirion. Leftear.

Fig. 7.185. Secondary tympanotomy from the superiorborder of the round window membrane. Left ear.

Superior border of the roundwindow

Groove

Chordatympani


kept in place carefully filling the groove with bone pate [5] (Fig. 7.186).

The RS is sutured in its bony well to the surrounding periosteum. The remaining EL is locatedinside the flat second well that has been performed with undercut edges to prevent extrusion.The ground electrode is located under the periosteum, in contact with the temporal bone, andthe retroauricular incision is sutured by planes.

THIRD STAGE: ENDOMEATAL

RW seal. telemetry measurements. Tympanomeatal flap restoring.

The RW is sealed with connective tissue (Fig. 7.186). The telemetry and electric stapedial reflexmeasures are carried out, the tympanomeatal flap is restored and the skin adapted over thegroove. The final stage ends by carefully dressing with Gelfoam the EAC internal segment andwith gauze in its external part. The retroauricular incision is dressed as usual.

Fig.7.186. The electrode does not contact the ossicular chain. Round window seal and groove obturated.


Ema with endopreaural(lempert) incision.

It is indicated in eras with a previousmastoidectomy in which it is not convenient tohave the cochlear implant in a position that isrelated to the previous procedure (eg.meningocele, fistula, radical surgery, etc.) Figs.7.187, 7.188.

EMA allows us to be less concerned with thestatus of the mastoid, especially in cases ofradical cavities. EMA is an alternative surgerythat allows avoiding the mastoid and respectthe results of the previous surgery. Dependingon the surgeon´s surgical habits It can also besimpler to perform in ears without previousprocedures.

A. INCISION.

A superior and posterior extended endopreauralincision is done (Heermann incision). Theextension will depend on the implant that isbeing used and it should be done in one plain.

B. GROOVE.

The endomeatal groove is extended by drillingthe superior wall of the EAC until reaching the

external surface of the temporal squama. It isa safe anatomical area and the dimensions ofthe groove are similar to those that are done inthe mastoid (1mm wide by 2 mm deep). It is notnecessary to do any extra drilling for the excesscable because thae distance that the electroideguide has to travel is longer due to the abscenseof a mastoidectomy, The electrode guide isplaced subperiostically as if it were a referenceelectrode.

C. ROUND WINDOW.

EMA with a Lempert (endopreaural) incisiónallows theuse o fan autostatic speculum at themoment of insertion of the electrodes and thisfacilitates control in the round window.

D. INSERTION.

The electrode array should be placed first, andthen the referente electrode. Otherwise theelectrode array can end up being short duringthe insertion maneuvers. The referenceelectrode is placed under the inferior lip of theincision and is introduced until the exit of theelectrode guide is approximately at the level ofthe EAC so that the receiver ends up completelycovered by the musculo-cutaneous plane butwithout placing it in its bony bed. The electrodearray is then inserted through the autostaticspeculum, and once it is done the speculum iswithdrawn. Once this is done, the referenceelectrode (RE) is placed in its definite position.


Fig. 7.187. Left ear with a previous mastoidectomy with labyrinthectomy. EMA with Lempert incisión avoids mastoidcompromiso and risk to the facial nerve.


E. POSITIONING OF THE RE.

The RE will have a morehorizontal position compared tothe retroauricular approachbecause the electrode guidemust be directed to the superiorwall of the EAC and not to thefacial recess. Fig 7.189.

F. FIXATION.

Fibrin glue can be used in themiddle ear and the groove andat the level of the RE. It helps tofix the implant in tese cases andavoids unwanted displacementsduring the surgical maneuversat the same time that it providesisolation. The surgical stages aresimilar to thos of EMA withretroauricular incision.

Fig. 7.188. Control CAT scan. EMA with endopreaural incisión (Lempert) with previousmastoidectomy in the left ear.

Fig 7.189. EMA with endopreaural (Lempert) incision.


MODIFIED EMA TECHNIQUE FORPEDIATRIC SURGERY.

In children the mastoid fossa(anterior well) is replaced by adeeper mastoid cavity that requiresthinning of the posterior wall of theEAC in its external 2/3rds but withoutopening the mastoid antrum (17).

The external portion of the grooveis communicated with the mastoidcavity, transforming the groove in anarrow open cleft that will allow thepassage of the electrode array intothe bottom of the cavity. The grooveis limited to the internal third of theosseous EAC, thus avoiding tensionand displacement during thedevelopment of the osseous canal.Fig 9. The cleft and short grooveare obturated with bone paté. Theexcess cable adopts a position thatis similar to the transmastoidapproach but limiting the drilling ofhealthy tissues without exposingthe mastoid antrum. Fig. 7.191.

Fig.7.190. EMAC. Pediatric mastoidectomy withoutantrostomy. Modified technique for children.

Fig. 7.191. EMAC. Electrode guide incide the smallmastoidectomy. The cleft and groove have been obturatedwith bone paté.


intraoperative radiology is not available.Figs.7.196, 7.198, 7.199.

If the insertion of the electrode guide would notbe posible from the basal turn, a reversedinsertion can be done from the cochleostomyof the medial turn, in direction towards the roundwindow. It is not necessary to sacrifice theossicular chain which serves as an anatomicallandmark. Double cochleostomy allows a safeinsertion when it is done from the basal turn.Magnetic resonance imaging is essential inthesecases. Figs. 7.192, 7.193.

b. Total ossification.

EMA allows a circunmodiolar technique in orderto completely expose the basal turn. This impliesthe elimination of the medial tur and apical turns,conserving the posterior wall of the EAC. Theossicular chain must be sacrificed in order toplace the tympano meatal flap as anterior aspossible. The tensor tympani muscle is sectionedas well as the malleus head maintaining itshandle, since this allows stabilization of thetympanic membrane once the flap has beenreplaced.

EMA IN TEMPORAL BONEMALFORMATIONS.

The potential benefit of EMA is maximized whenthere are malformations with a bifurcated facialnerve or a facial nerve with an anomalous tract.In these cases the risk of damaging the nerveby a posterior tympanotomy approach is high,

EMA in ossified cochleas.CONCEPT.

The anatomical location of the cochlea is anteriorto the posterior wall of the EAC. EMA allows usto maintain this wall and to have access to anyarea in the cochlear turns. The maintenance ofthe spaces that are free of ossification allowsadequate stimulation. An alternative that ispossible with EMA is to do a doublecochleostomy with the intention of maintainingthese spaces and confirm an adequate insertion.

SISTREMATIZATION OF THE TECHNIQUE.

a. Partial ossification and double cochleostomy.

Usually the ossification is located in the basalturn, near the round window (Figs. 7.194, 7.195).In these cases the drilling is initiated from theround window in an anterior - inferior directiontowards the beginning of the turn of the basalturn. It is possible to find non ossified spacesIn this area and to do a cochleostomy. A secondcochleostomy can be done with a 1 mm bur atthe side of the first one, under the cochleariformprocess, at the level of the medial spira (turn)Fig. 7.197.

If a basal cochleostomy can be done, theelectrode guide is inserted and then checkedthrough the medial cochleostomy, thus makingsure that the electrodes are correctly positioned.This maneuver is particularly useful when


Fig 7.192. Otosclerosis.Cochlea with permeable scalas.Inst. Rx Dra Guirado, Barcelona.

Fig 7.193. Otosclerosis. Labyrinthitis ossificans postsptapedectomy. Only the scala tympani can be observed.Inst Rx Dra Guirado, Barcelona.

Fig 7.194. CAT Scan. Stapedectomy prostheses andotospongiosis.Inst. Rx Dra Guirado, Barcelona.

Fig 7.195. CAT scan. Otospongiosis that involves thebasal turn and allows the CI (Figs 7.197. and 7.198).Inst Rx Dra Guirado, Barcelona.


whereas in the approach by the ear canalthe risk is significantly diminished. Incongenital malformations identified withan adequate CAT scan, a cochleostomyvia an endomeatal approach can be donewithout the risk of damaging the facialnerve.

Hidden dangers.

Cochlear implant surgery is not withoutsome risks, and these are more relatedto the surgical technique than to thepathology. Cochlear implant surgery isusually done in an anatomically normalear, therefore, the surgical risks shouldbe minimal. What matters most is not howit is positioned but how it works over timeafter it has been adequately positioned.

Fig.7.196. EMA. Technique for partial ossification.Dissection of a left temporal bone. The middle turn hasbeen completely exposed in order to observe the finalposition of the electrode array.

Fig. 7.197. EMA. Technique for partial ossification. Doublecochleostomy: basal and middle turn.

Fig 7.198. EMA. Technique for partial ossification. The electrodesare inserted by the basal turn and their position is checked inthe middle turn.

Basal cochleostomy.

Middle turncochleostomy.


FACIAL NERVE LESION.

The main risk of this surgery is damaging thefacial nerve. EMA significantly reduces thischance, since its approach to the middle ear isthrough the EAC and through this naturalopening the intratympanic portion of the facialnerve can be identified without any drilling. Thisis one of the main advantages of EMA sincethe best way to avoid damage of the facial nerveis to identify exactly its location.

Posterior tympanotomy requires skeletonizationand at times exposure of the facial nerve. Alesion can thus be caused by direct damage orby heat produced by the bur near the Falopiancanal. Fayad et al (8), described 0.7% delayed

onset of facial paralysis in a retrospective studyof over 700 cases. The cause of this paralysisis not clear, however, it is likely that thisrepresents an inflammatorey post surgicalprocess or a reactivation of a viral processrelated to microtrauma over the fallopian canalor chorda tympani. In EMA, the facial canaland chorda tympani can be easily identified

EMA does not require searching for the nerve;it identifies it without drilling. As a differencefrom posterior tympanotomy, the nerve is notan anatomical reference for EMA. Facial nervemonitorization is unnecessary in normal ears.The only anatomical reference to the facial nervein normal ears for EMA is its branch chordatympani which can be preserved with EMA since

Fig 7.199. EMA technique for partial ossification. Post op control with CAT scan.


this technique intends to be the least destructivethat is possible.

INTERNAL CAROTID ARTERY.

The carotid artery is very close to the basal turn.This proximity has to be considered as well asits anatomical variations (see anatomy chapters)Figs 7.200, 7.201.

Practical suggestions.

POSTERIOR WALL.

Regardless of the surgical approach, cochlearimplant surgery is subjected to limited anatomicalspaces. In the case of posterior tympanotomythe opening of the facial recess is not alwayssufficient in order to expose the round windowadequately. At times extensive drilling is required.EMA uses the EAC which is anatomically lesslimited than posterior tympanotomy. The naturalaccess to the area of the windows is via theEAC. That is why stapes surgery is done by anendomeatal and not a posterior tympanotomyapproach. Exposure of the round window isalways possible through the endomeatalapproach. This is not the case with posteriortympanotomy. Posterior tympanotomy is notfeasible in cases of a low tegmen or a prominentlateral sinus. In these cases removal of theposterior wall and closure of the EAC is required.Fig. 7.202.

Fig. 7.200. Relationship of the basal turn of the cochleaand the carotid artery Inst Rx Dra Guirado, Barcelona.

Fig 7.201. Temporal bone dissection. Anatomicalrelationship of the basal turn and he carotid artery.Courtesy of Prof. Dr Rodrigo Posada Trujillo. CentroAsociado de la FIMF in Pereira, Colombia.


EMA can position the electrode array in thesame plane of insertion than the posteriortympanotomy, without damaging functionalstructure, whereas this is not possible withposterior tympanotomy.

ROUND WINDOW.

The round window has gradually acquired morerelevante as the insertion site for the electrodearray, since it is the natural ostium where thescala tympani starts. The same as the ovalwindow, it has anatomical variabilities. Moreover,the niche is usually covered by a mucous layer(false round window membrane) that has to beidentified and removed.

Fig. 7.202. Prominent lateral sinus that does not allowa posterior tympanotomy. Inst Rx Dra Guirado, Barcelona.

Procedure.

MASTOID AIR CELL SYSTEM (MACS).

EMA preserves healthy tisúes and does notdestroy the MACS (18) which allows gasdiffusion and contributes to maintaining thepressure of the middle ear. MACS acts as acompensation element for the ventilation of themiddle ear (17) and this helps in avoidinginflammatory processes and in the developmentof a mastoid aereation system for a neumo-sufficient tympanomastoid complex (20).

More alterations of ventilation of the middle ear

seem to occur with tympanomastoidectomy thanwith tympanoplasty alone (22). Electro acousticstimulation with a hybrid implant requires notonly of residual hearing but also a correctfunction of the middle ear. Mastoidectomy couldhave a negative influence in the functional resultsoriginating an additional conductive loss (23).EMA has less blood loss, and in addition EMAallows maintenance of the MACS (Fig. 7.203).

Beyond the consequences that such destructionimplies, a surgical approach should alwaysintend to maintain healthy tissues, not onlybecause it simplifies surgical technique butbecause it minimizes surgical aggression to thepatient.


Fig. 7.202. Bilateral cochlear implantation. Comparing EMA and posterior tympanotomy. Note the mastoidectomyin PT compared to mastoid preservation with EMA.

ANGLE OF INSERTION THROUGH THEROUND WINDOW.

EMA has a better angle of insertion that thefacial recess, which is a narrow anatomicalwindow which requires drilling of margins or toperform a promontorial cochleostomy (15), andeven then it does not avoid -in all cases- damageto the spiral lamina, basilar membrane or striavascularis (3, 4, 21). In EMA the electrode guideis introduced through the EAC in front of itsposterior wall, instead of introducing them behindthis wall, following an insertion line that from amore anterior and superior position. Thisinsertion line is directed toward the floor of thebasal turn, avoiding trauma to the spiral lamina

making its introduction easier (Figs. 7.204,7.205). Insertion is soft and generally there isno need to drill the margins of the round window,thus avoiding the introduction of bone dustand/or blood in the scala tympani. EMA is anadequate approach for the preservation ofresidual hearing (EAS-"soft surgery") (11).

ALSE ROUTES.

EMA avoids false routes because it allows easyrecognition of the round window ans scalatympani. This adequate view avoids confusionwith hypotympanic air cells.


BETTER STIMULATION.

Insertion through the round window allowsbetter stimulation of the neuronal populationbecause the position of the electrode array isdone exactly at the beginning of the scalatympani.

TYMPANOTOMY.

Adequte visualization of the round window isnot posible in one third of the cases throughposterior tympanotomy. For this reasonGoycoolea and Lavinsky (12, 13) in addition toa limited posterior tyumpanotomy do an anteriortympanotomy. Anterior tympanotomy is inherentto EMA, therefore, both tympanotomies are notnecessary.

CONTRAINDICATIONS.

There are no absolute contraindications. Thosecases with a small EAC or with prominentosteomas can require a previous surgicalprocedure. Dermatologic pathologies thatinvolve the ear canal have to be considered.

Results.SURGICAL.

Follow upfor over 3 years of patients subjectedto EMA has shown no complications. Healingof the EAC and retroauricular incision wasadequate. There have been no electrodeextrusions in the EAC and the skin is normal.Two of 30 cases required a marginalcochleostomy (3).

Annual radiologic controls show stability of thesystem over time (Figs 7.208, 7.209).

Fig 7.204. Dissection. Endocochlear view of the naturalprojection of the basal turn (red line). Courtesy of Prof.Rodrigo Posada Trujillo. Centro Asociado de la FIMF inPereira, Colombia.

Fig. 7.205. Dissection. Angle of insertion for EMA andposterior tympanotomy (pt). Courtesy of Prof Dr RodrigoPosada Trujillo. Centro Asociado de la FIMF in Pereira,Colombia.

EMA

pt


Fig 7.206. CAT scan. Insertion plane for EMA.

Fig 7.208. EMA. Rx Stenvers. The electrode array canbe observed traversing the EAC and inserted in thecochlea.

Fig 7.207. CAT scan. Stress points of the insertion planeof the posterior tympanotomy. Circle indicatespromontorial cochleostomy.


Fig 7.209. EMA. Patient was implanted at 18 months of age. Control at 3 years that shows stability of the implantand adequate position of the electrode array.


Potential complications andhow to avoid them.ExtrusionThe main objections to the approaches that usethe EAC for CI is the possibility of extrusion ofthe electrode guide through the skin of the EAC.This complication was described in previousattempts of approach through the EAC (14, 15).This possibility is avoided with EMA becauseof the lip that is left over the groove and thebone paté that isolates the electrode guide fromthe skin.

Postoperative management.Retroauricular sutures and EAC packing areremoved 7 to 10 days after surgery. The patientis checked on a weekly basis and the hook upis done at 4 weeks.

Conclusions.The purpose of this technique is to avoidantromastoidectomy, posterior tympanotomyand promontorial cochleostomy, since theseare replaced by the groove and insertion throughthe round window. This is s fast and safetechnique that avoids osseous demolition andavoids damage to the facial nerve. The ossicularchain and chorda tympani are preserved andthe endomeatal exposure of the round windowfacilitates the insertion of the electrode arrayinto the scala tympani. It can replace thetransmastoid approach in normal cochleas and

in previously operated patients. It can also beused in malformed cochleas, ossified c ochleasand even in cases with anatomical variations.It is also a surgical option when posteriortympanotomy cannot be done.

EMA reduces surgical time with the samefunctional result. It is an alternative techniquethat can also be a first choice.

Acknowledgements.Our thanks to Dr Carmen Guirado and Dr PedroMartínez of the Institutes of Rx and RM DraGuirado de Barcelona (España) for theircollaboration.


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