Turkish Neurosurgery 9: 105 - 112, 1999 Ziyai: Varialioiis of ELA

The Surgical Anatomy of Six Variations ofThe Extreme Lateral Approach

Uzak Lateral Yaklasimin Alti Varyasyonunun Cerrahi Anatomisi

IBRAHIM M. ZIYAL, EDUARDO SALAS, LALIGAM N. SEKHAR

The Abant Izzet Baysal University, Medical School of Düzce, Deparhnent of Neurosurgey, (IMZ) Düzce, TürkiyeThe George Washington University Medical Center, Department of Neurological Surgery, (ES,LNS) Washington OC, USA

Gelis Tarihi: 15.1.1998 ç:> Kabul Tarihi: 4.3.1999

Abstract: The extreme lateral transcondylar approach(ELA) is used to access lesions that are located or extendsuperior to the middle elivus, inferior to the upper cervicalspine, and lateral to the foramina jugulare. Differentcombinations of drilling of several bone structures,ineluding the occipital candyle, the CL and C2 facets andlaminae, and the jugular tuberele and process, coupledwith suboccipital craniotomy, equip the surgeon withdifferent ways of approaching the region of interest. Inorder to fully understand the options for ELA, it is usefulto clarify the variations of this approach. This studyinvolved the bilateral use of 10 complete cadaveric headspecimens and ineludes the description and discussion ofsix different variations of ELA relative to lesion locatian

and the need for subsequent occipito-cervical fusion. TheELA options are as follows:1. Retrocondylar approach (RCA)2. Partial transcondylar approach (PTCA)3.Transtubercular approach (TTA)4. Transcondylar approach (TCA)5. Transjugular approach (TJA)6. Transfacetal approach (TFA)

Key Words: elivus, cranio-cervical junction, extremelateral approach, foramen magnum, tuberculumjugulare, transcondylar approach

INTRODUCTION

The extreme lateral transcondylar approach(ELA) is use d to access the ventral surface of the

cervicomedullary junction, lower eliyus, and foramen

Özet: Uzak lateral yaklasim (ELA), yukarida orta elivus,asagida üst servikal spinal bölge ve yanlarda da foramenjugulareye uzanan lezyonlar için kullanilmaktadir.Occipital candyle, CL ve C2 faset ve laminalari,tuberculum jugulare ve processus jugularis gibi farklikemik olusumlarin alinmasinin degisikkombinasyonlarina suboksipital kranyotomininde eklenmesi ile birlikte uygun bölgelere farkliyaklasimlar yapmak mümkündür. Bu çalismada,ELA'nin modifikasyonlarinin daha iyi kavranmasi amaciile, on kadavra (çift tarafli) kullanilmak ve lezyonununyeri ve uzanimi da göz önünde bulundurulmak sureti ilealti farkli varyasyon, oksipital-servikal füzyonendikasyonlari ile birlikte tarif edilmekte vetartisilmaktadir:1. Retrokondüler yaklasim (RCA)2. Kismi transkondülar yaklasim (PTCA)3.Transruberküler yaklasim (TTA)4. Transkondüler yaklasim (TCA)5. Transjuguler yaklasim (TJA)6. Transfasetal yaklasim (TFA)

Anahtar Kelimeler: elivus, foramen magnum, kranyo­servikal bileske, transkondüler yaklasim, tuberculumjugulare, uzak lateral yaklasim

magnum, and is the preferred technique ofnumerous authors 0,2,3,4,5,8,10,11,12,13,14,16,17,18,

19). This approach is useful for managing aneurysmsof the vertebrobasilar junction and vertebral artery,meningiomas and hypoglossal neurilemomas at the

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MATERIALS AND METHOD S

Af ter positioning the head specimen andmaking an inverted U-shaped incision on theoccipital region (Figure lA), the skin flap was

foramen magnum, and chordomas of the lower eliyus(2,17,18). Drilling of different combinations of bonestructures, ineluding the jugular tuberele and process,the occipital condyle, and the articular facets andlaminae of CL andi or C2, allows optimal surgicalexposure of normal anatomical structures andpathologicallesions (2,3,5,6,7,14). The purpose of thisstudy was to impart a better understanding of theindications for, and surgical anatomy involved in,six variations of ELA. The need for occipito-cervicalfusion relative to each option is also discussed.

For this study, we used 10 complete cadaverichead specimens that were fixed with Formalin andinjected with Microfil. We made an inverted U-shapedincision on the occipital region and then dissectedand reflected the museles layer by layer. The vertebralartery was exposed in the suboccipital triangle. Afterremoving the bone tissue from the lateral process andhemilaminectomy of CL, we performed a suboccipitalcraniotomy and drilled the appropriate bonestructures. The dura was opened, either leaving a cuffaround the vertebral ar tery or in linear fashion. Wethen exposed the normal anatomical structuresaround the lower eliyus, the foramen magnum, andthe anterior part of the upper cervical spine.

reflected posteriorly to expose the bone landmarksand museles. The important bone landmarks for theextreme lateral transcondylar approach are themastoid tip and the mastoid body, the asterion, andthe superior nuchalline. The transverse process ofCL is inferior to the mastoid tip, and no more than 10to 15 mm away. The location and bone insertions ofthe lateral ne ek museles are easily recognized, andthese should be separated and reflected to allowadequate surgical exposure. The museles are group edin three layers. The superficial musc1e layer containsthe sternoeleidomastoideus and trapezius musc1es.The sternoeleidomastoideus covers the CL transverse

process, and is the only musele group that should bereflected anteriorly. All the other museles should bereflected posteriorly or inferiorly. The spleniuscapitis, splenius cervicis, and longissimus capitismuseles constitute the middle layer. The semispinaliscapitis musc1e is located posterior to the spleniuscapitis (Figure 1B). The occipital ar tery can beidentified in apiane deep to the splenius capitis butsuperficial to the longissimus capitis and semispinaliscapitis museles. The splenius cervicis musele is oneof the important landmarks for exposing the vertebralartery (VA). This artery courses between thetransverse processes of CL and C2 close to thismuscle. The levator scapulae muscle is anotherimportant landmark for locating the VA. The deepmusele layer contains the superior obliquus capitis,the inferior obliquus capitis, the rectus capitis major,and the rectus capitis minor muscles. The first threemuseles constitute the suboccipital triangle, wherethe extradural VA can be safely exposed (Figures2A&B). The ar tery is covered with fat tissue and a

Anatomical Disseetion andSurgiealDeseription

~7-----i'iii\

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..,

Figure lA: The schematic drawing shows the position ofthe head specimen and the inverted U-shapedincision for ELA on the occipital region.

Figure lB: The middle muscle layer was exposed beneaththe sternocleidomastoideus and trapeziusmuscles, which constitute the superficial musclelayer. (Abb: SCM: sternocleidomastoideus T:trapezius, SC:splenius capitis, SSC:semispinaliscapitis).

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'J'f

Figure 2A: After reflection of the musdes in the superficialand middle layers, the deep musdes wereexposed. The superior obliquus capitis, theinferior obliquus capitis, and the rectus capitismajor musdes constitute the suboccipitaltriangle. (Abb: LS:levator scapulae, SC:spleniuscervicis, SCM: sternodeidomastoideus, SO:superior obliquus capitis, 10: the inferiorobliquus capitis, RCM: rectus capitis majori.

dense venous plexus in this triangle. The rectuscapitis lateralis muscle extends from the transverseprocess of the atlas to the jugular process. This muscleis a good landmark for identifying the posterior

Table i: Variations of the Extreme Lateral Approach.

Figure 28: The extradural vertebral artery was exposed inthe suboccipital triangle (double arrow) andbetween CI-C2 (x). (Abb: oa: ocdpital artery SO:superior obliquus capitis, 10: the inferiorobliquus capitis, RCM: rectus capitis majori.

portian of the jugular bulb. The VA courses underthe lamina of Cl from medial to lateral in an L shape(Figure 3). We removed the transverse process andlamina of Cl, and performed a suboccipitalcraniotomy. The vertebral artery was transposedposteromedially, and then the occipital candyle wasexposed for parti al or total resection. We then studiedsix variations of the extreme lateral transcondylarapproach (Table 1).

Variations of ELA lndications

1. Retrocondylar Approach (RCA)

Lateraiiy located lesions above the atlanto-occipital joint2. Partial Transcondylar Approach (PTCA)

Midline intradural lesions located above the at1anto-occipital joint3. Transtubercular Approach (TTA)

Large and giant aneurysms of the VA and vertebrobasilar junction4. Transcondylar Approach (TCA)

Extradural lesions involving the ocdpital condyle5. Transjugular Approach (TJA)

Extensive lesions involving the jugular foramen6. Transfacetal Approach (TFA)

Lesions below the atlanto-ocdpital joint

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Figure 3: The extradural vertebral artery courses under thelamina of CLfrom medial to lateral in an L shape.The CLdorsal root and ventral root are superior,and the C2 ganglion is inferior to the lamina(Abb: VA: vertebral artery, ClL: lamina of Cl,eid: CLdorsal root, civ: CLventral root, C2g: C2ganglion)

Six Different Variations of ELA:

1. Retrocondylar approach (RCA): Theretrocondylar approach is the method of choice forintradurallesions that are located anterolateral to the

craniocervical junction. Removal of the transverseprocess and the lamina of CL, and suboccipitalcraniotomy without drilling the occipital condyleachieve the desired exposure (Figure 4). The durashould be opened in linear fashion.

2. Partial transcondylar approach (PTCA):Midline intradurallesions that are located anterior

and above the atlanto-occipital joint can be exposedusing this approach. Af ter the VA is movedposteromedially, the posterior third of the occipital

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Figure 4: Retrocondylar Approach (RCA): The transverseprocess and the lamina of Cl were removed, anda suboccipital craniotomy was performed. Theoccipital condyle was not drilled. (Abb: VA:vertebral artery, OC: occipital condyle, cid: CLdorsal root, clv: CL ventral root, C2g: C2ganglion).

condyle and the superior facet of CL are drilled. Thelandmark for the limit of condyle drilling is thehypoglossal cana!. The dura should be openedleaving a cuff around the VA (Figure 5).

3. Transtubercular approach (TTA): Large andgiant aneurysms of the VA and the vertebrobasilarjunction are exposed using the TT A. The bone abovethe hypoglossal canal corresponds to the jugulartuberele, and drilling this provides access to themiddle eliyus. The posteromedial third or half of theoccipital condyle-CI facet joint is drilled. The jugulartuberele is removed extradurally to allow enoughspace for intradural exposure (Figure 6). The deepestpart of the tuberele should be drilled intradurally andthe dura should be opened leaving a cuff around theVA.

4. Transcondylar approach (TCA): Thetranscondylar approach is usually used forextradurallesions that involve the occipital condyleand lower eliyus. The posterior half of the occipitalcondyle is drilled, and the hypoglossal cana i isexposed (Figure 7). Depending on the extent of theextradurallesion, the whole condyle may have to bedrilled. it is usually not necessary to open the duraduring this approach. Occipito-cervical fusion isnecessary af ter this procedure.

5. Transjugular approach (TJA): This method ispreferred for extensive extradurallesions that involvethe jugular foramen and for simple glomus jugulare

Turkish NeliroslIrgery 9: 105 - 112, 1999

Figure 5: Partial Transcondylar Approach (PTCA): Thevertebral artery was mobilized posteromedially.The posterior third of the occipital condyle andthe superior facet of CL were driiied. Thelandmark for the condyle drilling limit is thehypoglossal canal. The dura should be openedleaving a cuH around the VA (dotted lines).(Abb: VA: vertebral artery, OC: occipitalcondyle, he: hypoglossal canal, CL:CLroots, C2:C2 roots).

Figure 6: Transtubercular Approach (TTA): After drillingthe posterior third or half of the occipitalcondyle-Cl facet joint, the hypoglossal canal wasexposed. The jugular tuberde (white arrow) isabove the hypoglossal canal and medial to thejugular foramen. it was removed extradurallyto allow adequate space for intradural exposure.Limited (A) and extensive (B) drilJing of thejugular tuberde is shown. The deepest part ofthe tuberde should be driIJed intradurally. Thedura should be opened leaving a cuff aroundthe vertebral artery. (Abb: he: hypoglossal canal,va: vertebral artery).

tumorsoThis approach requires total mastoidectomywith anterior mobilization of the mastoid segmentof the facial nerve from the fallopian canal, and the

Ziyai: Variatioiis of ELA

Figure 7:Transcondylar Approach (TCA):The posterior halfof the occipital condyle was drilled, and thehypoglossal canal was exposed. Depending onthe extent of the extradural lesion, the wholecondyle may need to be drilled. Usually, thedura does not need to be opened during thisapproach. Occipito-cervical fusion is necessaryafter this procedure. (Abb: he: hypoglossol canal,va: vertebral artery, eiv: CLventral root, cid: CLdorsal root).

Figure 8: Transjugular Approach (TJA): This approachrequires total mastoidectomy, with anteriormobilization of the mastoid segment of the facialnerve from the fallopian canal and exposure ofthe lateral aspect of the jugular bulb and jugularvein. The jugular process of the occipital bone,which forms the posterior and inferior wall ofthe jugular bulb, was then driIJed away. (Abb:va: vertebral artery, he: hypoglossal canal, VII:facial nerve, IX: glossopharyngeal nerve, jb:jugular bulb).

exposure of the lateral aspect of the jugular bulb andjugular vein. This allows dissection of the lesion fromthe internal carotid artery. The jugular process of theoccipital bone, which forms the posterior and inferiorwall of the jugular bulb, is drilled away (Figure 8).

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The sigmoid sinus may be ligated to achieve widerexposure with the TJA. Af ter umoofing the CNs IX,X, Xi, and XII extradurally, a lower clival tumor canbe removed superior to the internal auditory canaland inferior to C2. The removal of the posterolateralthird of the occipital condyle exposes the entirehypoglossal cana i. Drilling the lateral portion of thejugular tubercle, which is above the hypoglossal canaland medial to the jugular foramen, exposes themedial wall of the jugular bulb. CN IX coursesanterior to the connection of the inferior petrosalsinus with the jugular bulb, and CNs X and XIposteriorly. A linear dural incision should bemade approximately 1 cm posterior to the sigmoidsinus.

6. Transfacetal approach (TFA): Lesions locatedanterior or anterolateral to the upper cervical spineare exposed via the TFA. The first step is CL and C2hemilaminectomy without a mastoidectomy. The VAis mobilized posteromedially. The posterior half ofthe CL and C2 facet joint and the occipital condyleare drilled until the CL and C2 nerve roots are

exposed. The dura should be opened in linear fashionanterior to the cervical nerve roots, and should be

divided posteriorly as two flaps. Occipito-cervicalfusion is of ten necessary following this approach(Figure 9).

Through the use of these six approaches, theintradural VA, the posterior inferior cerebellar artery

Figure 9: Transfacetal Approach (TFA): After CL and C2hemilaminectomy without a mastoidectomy, thevertebral artery was mobilized posteromedially.The posterior half of the CL and C2 facet jointand the occipital condyle were drilled until theCL roots and C2 roots were exposed. Occipito­cervical fusion is often necessary following thisapproach. (Abb: LCl: cl hemilaminectomy,LC2:C2 hemilaminectomy, VA: vertebral artery,OC: occipital condyle, C2: C2 roots)

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(PICA), the lower cranial nerves, and the brainstem

can all be safely exposed (Figure 10).

DISCUSSION

Since the first attempt of Hammon and Kempe,who described a suboccipital craniotomy foraneurysms of the vertebral and basilar arteriesincluding removal of the posterior rim of the foramenmagnum (9), other authors have added new ways ofapproaching the lower clivus and the occipito­cervical junction. Partial resection of the occipitalcondyle (3), drilling of the jugular tubercle (14), andmedial mobilization of the VA (5) have be en

described by several authors. ELA involving medialmobilization of the VA from C2 to the dural entrypoint, and partial or total resection of the occipitalcondyle and lateral mass of CL have als o be endescribed (3,5,6,7,17,18,19). Sen and Sekhar described

an ELA variation for anteriorly located extra- andintradural lesions (17,18). This approach exposes themiddle clivus superiorly, the upper cervical spineinferiorly, and the jugular foramen laterally. Thevarious ELA techniques involve single or combinedremoval or drilling of several bone structures,including the occipital condyle, jugular tubercle,jugular foramen, occipito-cervical joint, and bonesof the C1-C2 joint (2,3,5,6,10,13,14,17,18,19). Salas andSekhar have recognized six variations of ELA whichare very useful inpractive (16).

Figure 10: The dura was opened leaving a cuH around thevertebral artery. The intradural vertebralartery, the lower cranial nerves, and thebrainstem were exposed. The posterior inferiorcerebellar arteryarises from the intradural VAand courses between the rootlets of cranial

nerve XII. (Abb: VA: vertebral artery, IX, X, XIand XII: lower cranial nerves, pica: posteriorinferior cerebellar artery)

Turkish Neiirosurgery 9: 105 - 112, 1999

In this paper, we describe and discuss these sixvariations of ELA that equip the neurosurgeon withspecific and practical anatomical knowledge andsurgical technique. For the RCA, a lateral suboccipital(retrosigmoid) craniotomy with resection of theforamen magnum provides adequate exposure. Toreach ventral lesions of the foramen magnum andthe craniocervical junction, Sen and Sekhar adviseddrilling the posterior third of the occipital condyle(17,18). To visualize the ventral part of the lowerbrainstem, Bertalanffy preferred to use the PTCA,drilling the posteromedial third of the condylewithout a mastoidectomy (3). The removal of theposterior third or half of the condyle allows wide­angle visualization of the anterior aspect of the lowerbrainstem. We prefer to drill the posterior third ofthe condyle and the mastoid process, which exposesthe contralateral VA and the hypoglossal nerve.Hosoda et aL.also prefer to drill the posterior thirdof the condyle, and combine this with partialmastoidectomy (11).

The TTA is useful for accessing large and giantaneurysms of the VA and the vertebrobasilar junction(4,12).In this approach, it is very important to keepunder control the VA through medial transpositionafter drilling the jugular tubercle. The transpositionof the proximal VA clears the accessory nerve, thePICA, and the spinal and perforating arteries fromthe surgical corridor. This also makes it possible tointerpose a vascular graft or reimplant the PICA. Invertebrobasilar aneurysms that are in higherlocations and if a proximal-distal VA anastomosis isnecessary, the combination of TTA and aretrolabyrinthine approach should be done. Thedivision and reanastomosis of the sigmoid sinus maybe required (2).

Al- Mefty et aL. pointed out that the TCAprovides access to lesions located lateral to thehypoglossal canal, and they used this approach in aseries of eight patients with extradural nonneoplasticlesions of the craniocervical junction (1). Thisapproach is also useful for radical resection ofchordomas. The resection of the inferior wall of the

jugular foramen for TJA may require drilling of thelateral part of the condyle. Drilling the bone abovethe condyle, which corresponds to the posteromedialside of the jugular foramen, is also usefuI. Thesuperior wall should be drilled once the mas toidsegment of the facial nerve is exposed (5,6) whichrequires a mastoidectomy. Wen et aL.also pointedout the need for mastoidectomy and anteriormobilization of the facial nerve during TCA. They

Ziyai: Variatioiis of ELA

reported using a paracondylar approach to exposethe jugular foramen, without drilling the condyle (20).The opening of the hypoglossal canal and drilling ofthe medial wall of the jugular foramen is veryimportant when removing CN X and XIIschwannomas (8).When the tumor extends anteriorlythrough the carotid canal, it is necessary to combinethis approach with a subtemporal infratemporalapproach (2). if the tumor has a large intracranialextension, combination TJA with a transpetrosalretrolabyrinthine approach may be necessary. Thisapproach can be also combined with division of thenondominant sigmoid sinus.

George et aL.reported the TFA, dividing thisapproach into the three subgroups of anterolateral,posterolateral, and posterior (6). They opened thedura posterior to the cervical roots using varioustypes of dural flaps. We preferred to make the duralopening anterior to the cervical roots, in order to beable to retract the neural structures and expose theanterior aspect of the spinal cord.

Midline meningiomas originating from the duraof the clivus or the foramen magnum extendbilaterally. In these cases, the surgical site should beon the side where the tumor is largest. Drilling of theposterior third or half of the condyle is very importantto achieve good exposure of the contralateral side.To expose and remove the dural attachment ofmidline meningiomas that also extend into themiddle divus, it is important to drill the jugulartuberde. To remove lesions that originate in the boneitself, such as chordomas, chondrosarcomas, ormetastatic carcinomas, it is essential to totally removethe condyle. In ord er to drill the condyle safely, theextradural segment of the VA should be reflectedposteromedially. An anatomical variation, theextradural PICA, should always be kept in mind (15).

After removing the bone in each approach, thedura is opened, either leaving a dural cuff aroundthe VA or in linear fashion. The form er preventsinjury to the branches of the VA that are close to thedural opening. Medial mobilization of the intraduralsegment of the VA exposes the vertebrobasilarjunction and the anterior aspect of the foramenmagnum. The rootlets of the hypoglossal nerve arethe only neural structures that cross the surgicalcorridor. if the VA is encased by the tumor, workingaround the artery will help mobilize the artery.

The ELA may require occipito-cervical fusion,depending on the extent of bone removal that is

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required 0,3,18). The most important element ofpreventing occipito-cervical junction instability ispreservation of the portian of the candyle that liesanterior to the hypoglossal canal. if more extensivebone removal is needed, occipito-cervical fusian mustbe done to maintain adequate stability. The TCA andTFAusually require fusian. if unilateral TCA isperformed, the fusian may be done either during thesame surgeryar the following day. if both condylesare invaded by the tumor, fusian should be done atthe end of the first stage of tumor removal to stabilizethe craniocervical junction and avoid sigmoid sinusthrombosis (2,17,18). The RCA, PTCA, TJA, and TTA

do not require occipito-cervical fusian. Themaximum bone removal that can be done without

occipito-cervical fusian is drilling of the posteriorthird, and sametimes even half, of the candyle.

In conclusian, the ELA has been described forlesions located anterior and anterolateral to the

foramen magnum. Each variatian of the ELA shouldbe chosen in accordance with the exact locatian and

nature of the pathology involved. The appropriatechoice will help the surgeon achieve completeremoval of the tum or with minimal complications,morbidity, and mortality.

Correspondence: Ibrahim M. Ziyai, MDAbant Izzet Baysal ÜniversitesiDüzce Tip FakültesiNörosirürji AnaBilim DaliDüzce - Bolu, TürkiyePhone: 216 384 7955Fax: 2122454608

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