the far-lateral approach and its transcondylar, supracondylar, and paracondylar extensions

CHAPTER 7

The Far-lateral Approach and Its Transcondylar,Supracondylar, and Paracondylar Extensions

Albert L. Rhoton, Jr., M.D.Department of Neurological Surgery, University of Florida, Gainesville, Florida

Key words: Cranial base, Cranial nerve, Craniocervical junction, Foramen magnum, Microsurgical anatomy, Occipital bone, Occipital condyle,Skull base, Surgical approach, Temporal bone, Vertebral artery

The basic far-lateral exposure is carried up to but doesnot include removal of the posterior part of the occipitalcondyle. It includes 1) dissection of the muscles along

the posterolateral aspect of the craniocervical junction to per-mit an adequate exposure of the C1 transverse process and thesuboccipital triangle; 2) early identification of the vertebralartery either above the posterior arch of the atlas or in itsascending course between the transverse processes of the atlasand axis; and 3) a suboccipital craniectomy or craniotomywith removal of at least half of the posterior arch of the atlas(5, 19, 20). It provides access for the following three ap-proaches: the transcondylar approach directed through theoccipital condyle or the atlanto-occipital joint and adjoiningparts of the condyle; the supracondylar approach directedthrough the area above the occipital condyle; and the para-condylar exposure directed through the area lateral to theoccipital condyle (Fig. 7.1). The transcondylar extension ac-companied by drilling the condyles allows a more lateralapproach and provides access to the lower clivus and pre-medullary area. The supracondylar approach provides accessto the region of and medial to the hypoglossal canal andjugular tubercle. The paracondylar approach, which includesdrilling of the jugular process of the occipital bone in the arealateral to the occipital condyle, accesses the posterior part ofthe jugular foramen, and the posterior aspect of the facialnerve and mastoid on the lateral side of the jugular foramen.In the standard posterior and posterolateral approaches, anunderstanding of the individual suboccipital muscles is notessential. However, these muscles provide important land-marks for the far-lateral approach and its modifications. Im-portant considerations include the relationship of the occipitalcondyle to the foramen magnum, hypoglossal canal, jugulartubercle, the jugular process of the occipital bone, the mastoid,and the facial canal (1–3, 6, 7, 10, 12, 15–17).

STAGES OF APPROACH

The approach is divided into three anatomic stages (Fig.7.2). The first stage, the muscular dissection, includes the skinincision, reflection of muscles, including those forming the

suboccipital triangle, and examination of the relationship ofthe muscles to the occipital and vertebral arteries, the verte-bral venous plexus, the transverse process of the atlas, and theupper cervical nerves. The second stage, the extradural dis-section, examines landmarks for the suboccipital craniectomy,the extent of occipital condyle removal, and the exposure andidentification of the hypoglossal canal, jugular process, jugu-lar tubercle, and facial nerve. The final stage, the intraduralexposure, reviews the relationships of the intradural segmentof the vertebral artery and its branches, including the postero-inferior cerebellar artery (PICA), the lower cranial and uppercervical nerves, and the dentate ligament.

Muscular stage

For our study of the region, the exposure was done using ahorseshoe scalp flap because it provided a better display ofthe muscular layers and their relationships to the neural andvascular structures (Fig. 7.2A). The incision began in the mid-line, approximately 5 cm below the external occipital protu-berance, and was directed upward to just above the externaloccipital protuberance, turned laterally just above the supe-rior nuchal line, reached the mastoid, and turned downwardin front of the posterior border of the sternocleidomastoidmuscle onto the lateral aspect of the neck to approximately 5cm below the mastoid tip and below where the transverseprocess of the atlas can be palpated through the skin. The skinflap was reflected downward and medially to expose the mostsuperficial layer of muscles formed by the sternocleidomas-toid and splenius capitis muscles laterally and the trapeziusand the semispinalis capitis muscles medially. In this descrip-tion, the muscles are reflected separately but at an operation,the scalp and muscles superficial to the suboccipital triangleare reflected from the suboccipital area in a single layer,leaving a musculofascial cuff attached along the superiornuchal line for closure.

Muscular dissectionThe sternocleidomastoid and trapezius are in the first layer

encountered (Fig. 7.2, B--H). Dividing the sternocleidomastoid

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FIGURE 7.1. Osseous relationships. A, inferior view of the occipital condyles and foramen magnum. The occipital condyles areovoid structures located along the lateral margin of the anterior half of the foramen magnum. Their articular surfaces are convex,face downward and laterally, and articulate with the superior facet of C1. A probe inserted through the hypoglossal canal passesforward approximately 45 degrees from the midsagittal plane in an anterolateral direction. The hypoglossal canal is located abovethe middle third of the occipital condyle and is directed from posterior to anterior and from medial to lateral. The intracranial endof the hypoglossal canal (small oval ) is located approximately 5 mm above the junction of the posterior and middle third of theoccipital condyle and approximately 8 mm from the posterior edge of the condyle. The extracranial end of the canal is locatedapproximately 5 mm above the junction of the anterior and middle third of the condyle. The average length of the longest axis ofthe condyle is 21 mm. The large arrow shows the direction of the transcondylar approach and the cross-hatched area shows theportion of the occipital condyle that can be removed without exposing the hypoglossal nerve in the hypoglossal canal. The condy-lar fossa is frequently the site of a canal, the condylar canal, which transmits the posterior condylar emissary vein that connects thevertebral venous plexus with the sigmoid sinus just proximal to the jugular bulb. The condylar canal passes above and usually doesnot communicate with the hypoglossal canal. The jugular process of the occipital bone extends laterally from the posterior half ofthe occipital condyle to form the posterior margin of the jugular foramen. The portion of the jugular process located immediatelybehind the jugular foramen serves as the site of attachment for the rectus capitis lateralis muscle. The stylomastoid foramen is situ-ated lateral to the jugular foramen. The styloid process is located anterior and slightly medial to the stylomastoid foramen. B,inferolateral view. A probe has been passed through the hypoglossal canal, which passes above occipital condyle. From its intracra-nial to its extracranial end it is directed forward, lateral, and slightly upward. C, superior view. The occipital condyle projectsdownward from the lateral margin of the anterior half of the foramen magnum. The intracranial entrance of the hypoglossal canalis located above the condyle. The jugular tubercles are located above and anterior to the hypoglossal canals. The jugular process ofthe occipital bone extends laterally from the condyles to form the posterior margin of the jugular foramen. The sigmoid sinuscrosses the occipitomastoid suture and turns in a hooklike groove on the upper surface of the jugular process to reach the jugularforamen. Drilling the occipital condyle increases access to the anterolateral margin of the foramen magnum. Drilling in a supracon-dylar location below the hypoglossal canal accesses the lateral edge of the clivus. Drilling in the supracondylar location above thehypoglossal canal accesses the jugular tubercle, which projects upward and often blocks visualization of the junction of the middleand lower clivus and the region of the pontomedullary junction during the far-lateral approach. Drilling the jugular process in a

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just below and with preservation of its upper attachment forclosure and reflecting it laterally exposes the upper extensionof the splenius capitis. Detaching the trapezius and spleniuscapitis muscles, while preserving a cuff of their upper attach-ments for closure, and reflecting them medially exposes thelongissimus capitis muscle. Reflecting the longissimus capitisdownward exposes the semispinalis capitis and the superiorand inferior oblique muscles as well as the transverse processof the atlas, which has a prominent apex palpable through theskin between the mastoid process and mandibular angle. Thesemispinalis capitis is reflected medially to expose the suboc-cipital triangle, which is limited by three muscles; above andmedially by the rectus capitis posterior major, above andlaterally by the superior oblique, and below and laterally bythe inferior oblique (Fig. 7.2G).

The triangle deep to these muscles is covered by a layer ofdense fibrofatty tissue. The floor in the depth of the triangle isformed by the posterior atlanto-occipital membrane and theposterior arch of the atlas (Fig. 7.2H). The structures in thetriangle are the vertebral artery and the C1 nerve, both of whichlie in a groove on the upper surface of the lateral part of theposterior arch of the atlas. The suboccipital triangle is opened byreflecting the rectus capitis posterior major inferiorly and medi-ally, the superior oblique laterally, and the inferior oblique me-dially. Opening the triangle exposes the portion of the vertebralvenous plexus that surrounds the vertebral artery as it passesbehind the atlanto-occipital joint and across the upper edge ofthe posterior arch of the atlas (Fig. 7.2I). Reflecting the superioroblique muscle, as described earlier, exposes the rectus capitislateralis, a short, flat muscle that is an important landmark inidentifying the jugular foramen (Figs. 7.2, K and L, and 7.3). Itarises from the upper surface of the transverse process of theatlas and attaches above to the rough, lower surface of thejugular process of the occipital bone behind the jugular foramen.The jugular process is a plate of occipital bone extending later-ally from the posterior half of the occipital condyle. It is indentedin front at the site of the jugular notch, which forms the posterioredge of the jugular foramen (Fig. 7.1). The rectus capitis lateralis,because it is attached to the jugular process at the posterior edgeof the jugular foramen, provides a landmark for estimating theposition of the jugular foramen and the facial nerve, which exitsthe stylomastoid foramen just lateral to the jugular foramen.

Vascular structures

Reflecting the muscles forming the suboccipital triangle, asdescribed earlier, exposes the vertebral artery, which is sur-rounded by a rich venous plexus that must be obliterated andpartially removed if the vertebral artery is to be exposed ortransposed (Fig. 7.2, H and I).

The vertebral artery, above the transverse foramen of the axis,veers laterally to reach the transverse foramen of the atlas, whichis situated further lateral than the transverse foramen of theaxis. The artery, after ascending through the transverse pro-cess of the atlas, is located on the medial side of the rectuscapitis lateralis muscle. From here it turns medially behindthe lateral mass of the atlas and the atlanto-occipital joint andis pressed into the groove on the upper surface of the poste-rior arch of the atlas, where it courses in the floor of thesuboccipital triangle and is covered behind the triangle bythe semispinalis capitis muscle. The first cervical nervecourses on the lower surface of the artery between the arteryand the posterior arch of the atlas (Fig. 7.2, K–M). Afterpassing medially above the lateral part of the posterior arch ofthe atlas, the artery enters the vertebral canal by passingbelow the lower, arched border of the posterior atlanto-occipital membrane, which transforms the sulcus in which theartery courses on the upper edge of the posterior arch ofthe atlas into an osseofibrous casing that may ossify, trans-forming it into a complete or incomplete bony canal sur-rounding the artery (Fig. 7.2H) (5).

The third segment of the vertebral artery, the segmentlocated between the C1 transverse process and the duralentrance, gives rise to muscular branches and the posteriormeningeal arteries. The muscular branches arise as the arteryexits the transverse foramen of C1 and courses around thelateral mass of the atlas to supply the deep muscles andanastomose with the occipital and ascending and deep cervi-cal arteries (Fig. 7.2I). Some of the muscular branches mayneed to be divided to mobilize and transpose the vertebralartery. The posterior meningeal artery arises from the poste-rior surface of the vertebral artery as it passes behind thelateral mass or above the posterior arch of the atlas or justbefore penetrating the dura in the region of the foramenmagnum, but it may also have an intradural origin from the

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paracondylar location accesses the posterior margin of the jugular bulb, which is situated in the sigmoid portion of the jugu-lar foramen. D, medial aspect of the occipital condyle and supracondylar region. The inner surface of the mastoid portion ofthe temporal bone is grooved by the sulcus of the sigmoid sinus. The asterion, the site of the junction of the lambdoid, pari-etomastoid, and the occipitomastoid sutures, is an important landmark used to define the transition between the transverseand sigmoid sinuses. The sigmoid sulcus crosses the occipitomastoid suture just behind the jugular foramen. The intracranialend of the hypoglossal canal is located above the junction of the posterior and middle thirds of the occipital condyle. Theexternal occipital protuberance is located an average of 2 cm below the apex of the internal occipital protuberance and 1 cmbelow the lower margin of the torcular herophili. The parietal notch, located at the junction of the squamosal and parieto-mastoid sutures, defines the upper limit of the petrous portion of the temporal bone and the floor of the posterior portion ofthe middle fossa. The midportion of the parietomastoid suture approximates the anterior edge of the junction of the trans-verse and sigmoid sinuses. Ac., acoustic; Artic., articular; Car., carotid; Cond., condyle; Fiss., fissure; For., foramen; Hypogl.,hypoglossal; Int., internal; Jug., jugular; Mast., mastoid; Med., medial; Occip., occipital; Parietomast., parietomastoid; Petro-cliv., petroclival; Proc., process; Protub., protuberance; Sig., sigmoid; Squam., squamosal; Stylomast., stylomastoid; Tymp.,tympanic.

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FIGURE 7.2. A–D. Far-lateral and transcondylar approach. A, a suboccipital scalp flap is commonly selected for the far-lateral exposure. The medial limb extends downward in the midline so that a wide upper cervical laminectomy can be com-pleted if needed. The lateral limb extends below the C1 transverse process, which can be palpated between the mastoid tipand the angle of the jaw to access the vertebral artery as it ascends through the C1 transverse process. In this dissection, themuscles are reflected separately to show their anatomy; however, at an operation, the muscles superficial to the suboccipitaltriangle can be reflected from the suboccipital area in a single layer with the scalp flap, leaving a cuff of suboccipital muscleand fascia attached along the superior nuchal line to aid in closure. B, the scalp flap has been reflected to expose the sterno-cleidomastoid and trapezius, the edges of which form the margins of the posterior triangle of the neck. The splenius andsemispinalis capitis are in the floor of the triangle. C, the sternocleidomastoid has been detached from the lateral part of thesuperior nuchal line and reflected laterally to expose the splenius capitis, which is attached just below the line. The asterion,located at the junction of the lambdoid, occipitomastoid, and parietomastoid sutures, most commonly overlies the lower halfof the junction of the transverse and sigmoid sinuses. D, the splenius capitis has been reflected to expose the longissimuscapitis and deep cervical fascia. The occipital artery may pass superficial or deep to the longissimus capitis. A., artery; Atl.,atlanto; Br., branch; Cap., capitis; CN, cranial nerve; Dent., dentate; Digast., digastric; Dors., dorsal; Gang., ganglion;Hypogl., hypoglossal; Inf., inferior; Lat., lateralis; Lev., levator; Lig., ligament; Long., longissimus; M., muscle; Maj., major;Mas., mastoid; Memb., membrane; Men., meningeal; Min., minor; Musc., muscular; Obl., oblique; Occip., occipital; P.I.C.A.,posteroinferior cerebellar artery; Plex., plexus; Post., posterior; Proc., process; Rec., rectus; Scap., scapula; Semispin., semispi-nalis; Splen., splenius; Suboccip., suboccipital; Sup., superior; Trans., transverse; Vent., ventral; Vert., vertebral.

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FIGURE 7.2. E–J. Far-lateral and transcondylar approach. E, the fascia has been removed to expose the occipital arterypassing behind the superior oblique and semispinalis. F, the longissimus capitis has been reflected to expose the attach-ment of the superior and inferior oblique muscles to the C1 transverse process. G, the suboccipital triangle, in thedepths of which the vertebral artery courses behind the atlanto-occipital joint and across the posterior arch of C1, issituated in the depths of the area between the superior and inferior oblique and the rectus capitis posterior major. H,the superior oblique muscle has been reflected laterally and the rectus capitis posterior major muscle inferomedially.The floor of the suboccipital triangle is formed by the posterior atlanto-occipital membrane and the posterior arch ofthe atlas. The vertebral artery and the C1 nerve root, which are surrounded by the vertebral venous plexus, coursealong the upper surface of the posterior arch of the atlas. I, the muscles forming the margins of the suboccipital trianglehave been reflected to expose the vertebral artery ascending through the C1 transverse process and behind the atlanto-occipital joint and the surrounding venous plexus. J, the venous plexus around the vertebral artery has been removed.The vertebral artery gives off muscular branches, passes medially behind the atlanto-occipital joint and above the poste-rior arch of C1, and turns upward and anterior to penetrate the dura.



FIGURE 7.2. K–O. Far-lateral and transcondylar approach. K, a suboccipital craniectomy has been completed and the righthalf of the posterior arch of C1 has been removed. The posterior root of the transverse foramen of the atlas has beenremoved while preserving the portion of the tip of the transverse process of the atlas to which the rectus capitis lateralis,levator scapulae, and the superior oblique attach. The atlanto-occipital joint and the posterior condylar emissary vein areexposed. The ventral rami of the C1 and C2 nerve roots pass behind the vertebral artery. The dorsal ramus of C2 gives rise tothe greater occipital nerve, which passes through the semispinalis capitis to reach the posterior scalp. L, the area above theoccipital condyle has been drilled to the depth of the cortical bone surrounding the hypoglossal canal. The change from can-cellous to cortical bone indicates that the hypoglossal canal has been reached. M, the hypoglossal canal has been opened toexpose the venous plexus, which surrounds the hypoglossal nerve in the canal and connects the basilar venous plexus with themarginal sinus, which encircles the foramen magnum. The dorsal ramus of the C1 nerve root, also termed the suboccipital

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vertebral artery, in which case it pierces the arachnoid overthe cisterna magna to reach the dura (Fig. 7.2L) (20).

The occipital artery is also exposed as the superficial anddeep muscles in the region are reflected (Fig. 7.2, C--G). Itoriginates from the posterior wall of the external carotid ar-tery at the level of the angle of the mandible, ascends paralleland medial to the external carotid artery and lateral to theinternal jugular vein to reach the area posteromedial to thestyloid process. At that point, it changes its course to posteriorand lateral, passing first between the rectus capitis lateralisand the posterior belly of the digastric and then between thesuperior oblique and the posterior belly of the digastric whereit courses in the occipital groove medial to the mastoid notch,in which the posterior belly of the digastric muscle arises.After exiting the area between the superior oblique muscleand the posterior belly of the digastric, it courses medially,being related to the longissimus capitis and semispinalis ca-pitis. If the occipital groove is present, the occipital artery willcourse deep to the longissimus capitis muscle, but if thegroove is absent, the artery will course superficial to thelongissimus capitis muscle (Fig. 7.2E). It courses mediallybehind the semispinalis capitis just below the superior nuchalline in the upper part of the posterior triangle to pass betweenthe upper attachment of trapezius and the semispinalis capi-tis, where it pierces the attachment of the trapezius muscle tothe superior nuchal line and ascends in the superficial fasciaof the posterior scalp.

Osseous structures

The transverse process of the atlas, an important landmarkin these approaches, projects further lateral than the trans-verse processes on the adjacent cervical vertebrae and has anapex that can be felt through the skin in the area between themastoid process and angle of the mandible (Fig. 7.2A). Severalmuscles important in completing the exposure attach to thetransverse process of the atlas (Fig. 7.2G). The rectus capitislateralis arises from the anterior portion, and the superioroblique arises from the posterior portion of the upper surfaceof the transverse process. The inferior oblique muscle insertson the lateral tip of the transverse process. The levator scap-ulae, splenius cervicis, and the scalenus medius attach to theinferior and lateral surface of the transverse process. Thelevator scapulae is also attached by tendinous slips to theposterior tubercles of the transverse processes of C2 to C4 (Fig.7.2, F and G).

Neural structuresThe neural structures encountered during the muscle dis-

section arise predominantly from the C1 and C2, and to alesser extent from the C3 spinal nerves that are formed by theunited dorsal and ventral roots and are described in thechapter on the foramen magnum (Fig. 7.2, J–M).

Extradural stage

The extradural stage begins with a suboccipital craniec-tomy or craniotomy, identification of the occipital condyle,and removal of at least half of the posterior arch of the atlasand possibly the posterior root of the transverse foramen, ifmobilization of the vertebral artery is needed (Fig. 7.2K). Twoosseous landmarks important in planning the suboccipitalcraniotomy are the asterion located along the lower half of thegroove on the inner table of the cranium near the point wherethe transverse sinus empties into the sigmoid sinus, and theinion (external occipital protuberance) located an average of 1cm below the apex of the internal occipital protuberance andthe inferior margin of the confluence of the sagittal and trans-verse sinuses. In completing the removal of the posterior archof the atlas, the tip of the transverse process is preserved alongwith the attachment of the superior oblique, which is reflectedlaterally while preserving the attachment of the rectus capitislateralis.

At this stage, the segment of the vertebral artery extendingfrom the transverse foramen of C2 to its entrance to the durais exposed. Removal of the posterior root of the transverseforamen will permit the artery to be displaced downward andmedially away from the atlanto-occipital joint to expose theoccipital condyle (Fig. 7.2, L--N). The occipital condylesproject downward along the lateral edges of the anterior halfof the foramen magnum (Figs. 7.1 and 7.3). The articularsurfaces, which are ovoid with the long axis in the AP direc-tion, are located on the lower-lateral margin of the condyles.They face downward and laterally to articulate with the su-perior facets of the atlas, which face upward and medially.

The intracranial end of the hypoglossal canal is locatedapproximately 5 mm above the junction of the posterior andmiddle third of the occipital condyle and appropriately 5 mmbelow the jugular tubercle (Fig. 7.1). The canal is directedforward and laterally at a 45-degree angle with the sagittalplane. The extracranial end of the hypoglossal canal is locatedimmediately above the junction of the anterior and middlethird of the occipital condyle and medial to the jugular fora-men. The average length of the longest axis of the condyle is

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nerve, passes backward between the posterior arch of the atlas and the vertebral artery, supplies the muscles bordering thesuboccipital triangle, and sends fibers to the rectus capitis posterior minor and the semispinalis capitis muscles. N, an uppercervical laminectomy has been completed and the dura opened. The dural incision completely encircles the vertebral artery,leaving a narrow dural cuff on the artery so that the artery can be mobilized. The drilling in the supracondylar area exposesthe hypoglossal nerve in the hypoglossal canal, and can be extended extradurally to the level of the jugular tubercle toincrease access to the front of the brainstem. O, enlarged view of the site of dural penetration by the vertebral artery inanother specimen. The rostral end of the dentate ligament ascends behind the vertebral artery with the accessory nerve andattaches to the dura along the lateral margin of the foramen magnum.



21 mm (range, 18–24 mm) and the average distance betweenthe posterior edge of the occipital condyle and the posteriorborder of the intracranial end of the hypoglossal canal is 8.4mm (range, 6–10 mm) (20). The hypoglossal canal is sur-rounded by cortical bone. The contents of the hypoglossalcanal are the hypoglossal nerve, a meningeal branch of theascending pharyngeal artery, and the venous plexus of the

hypoglossal canal, which communicates the basilar venousplexus with the marginal sinus that encircles the foramenmagnum (Figs. 7.2M, 7.3B, and 7.4, C and D). Posterior to theoccipital condyle, a depression, the condylar fossa, may bepierced by the condylar canal, which transmits the posteriorcondylar emissary vein, a communication between the verte-bral venous plexus and the sigmoid sinus (Fig. 7.3). The canal

FIGURE 7.3. Relationships in the transcondylar,supracondylar, and paracondylar exposures. A, rightside. The segment of the vertebral artery coursingbehind the superior articular process of C1 has beenremoved. The posterior condylar emissary veinpasses through the posterior condylar canal and joinsthe sigmoid sinus. The rectus capitis lateralisattaches below to the transverse process of C1 andabove to the jugular process of the occipital bonethat forms the posterior edge of the jugular foramen.The internal jugular vein descends on the anteriorside of the rectus capitis lateralis and the C1transverse process. B, the cancellous bone within theoccipital condyle has been drilled away whilepreserving the cortical and articular surfaces toexpose the hypoglossal nerve in the hypoglossalcanal. The posterior condylar vein passes above theoccipital condyle and hypoglossal canal to emptyinto the sigmoid sinus. The transition between thesigmoid sinus and jugular bulb is located lateral tothe occipital condyle in front of the jugular processof the occipital bone. The posterior third of theoccipital condyle can be removed without entering

the hypoglossal canal. The extracranial end of the hypoglossal canal is located medial to the jugular foramen. C, the portionof the rectus capitis lateralis that attaches to the jugular process of the occipital bone has been removed to expose theinternal jugular vein, and the jugular process of the occipital bone has been removed to expose the jugular bulb. The facialnerve is exposed laterally at the stylomastoid foramen. Several meningeal branches of the occipital artery ascend to passthrough the jugular foramen. An emissary vein passes from the jugular bulb to the vertebral venous plexus. A., artery; Atl.,atlanto; Cap., capitis; CN, cranial nerve; Cond., condyle; Dent., dentate; Emiss., emissary; Int., internal; Jug., jugular; Lat.,lateralis; Lig., ligament; M., muscle; Men., meningeal; Occip., occipital; P.I.C.A., posteroinferior cerebellar artery; Post.,posterior; Proc., process; Rec., rectus; Sig., sigmoid; V., vein; Vert., vertebral.

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is directed slightly upward as it proceeds anteriorly to join thesigmoid sinus at the hook-like turn immediately proximal towhere the sinus empties into the jugular bulb. The condylarcanal does not communicate with the hypoglossal canal.

The jugular process of the occipital bone serves as a bridgebetween the condylar and squamosal parts of the occipitalbone and forms the posterior margin of the jugular foramen(Fig. 7.1). It extends laterally from the posterior half of thecondyle. The jugular process also serves as the site of attach-ment of the rectus capitis lateralis muscle behind the jugularforamen. The stylomastoid foramen, which transmits the fa-cial nerve, is situated lateral to the jugular foramen at theanterior end of the mastoid notch (Figs. 7.3C and 7.4C). Thestyloid process is located anterior to the stylomastoid foramenand anterolateral to the jugular foramen.

After removing the superficial layer of cortical bone cover-ing the occipital condyle, soft cancellous bone will be encoun-tered. Further drilling of the cancellous bone in and above theposterior third of the condyle exposes the second layer ofhard, cortical bone that surrounds the hypoglossal canal (Figs.7.2N and 7.3–7.6). Subsequent drilling of this cortical boneexposes the venous plexus of the hypoglossal canal. The lat-eral aspect of the intracranial end of the hypoglossal canal isreached with removal of approximately the posterior third ofthe occipital condyle (8.4 mm of 21 mm) (Fig. 7.1) (20). Furtherdrilling of the occipital condyle can be done after reaching thelateral aspect of the intracranial end of the hypoglossal canal,as the canal is directed anteriorly and laterally, permitting thelateral part of the posterior two-thirds of the condyle to beremoved without entering the hypoglossal canal. The distancebetween the upper surface of the hypoglossal nerve and theroof of the hypoglossal canal averages 4.4 mm. Extensivedrilling around the canal may allow the nerve to be trans-posed from its normal course (Fig. 7.6).

After exposing the hypoglossal canal above the occipitalcondyle, the bone of the jugular tubercle situated above thehypoglossal canal can be removed extradurally to gain addi-tional exposure (1–3, 9, 10, 13). The jugular tubercle is arounded prominence located at the junction of the basilar andcondylar parts of the occipital bone (Figs. 7.1, 7.4, C and D,and 7.5, A–C). It is situated above the hypoglossal canal andmedial to the lower half of the intracranial end of the jugularforamen. The average distance from the posterior edge of thejugular tubercle (the site of the groove in which the lowercranial nerves course) to the upper border of the hypoglossalcanal is 4.5 mm (20). The glossopharyngeal, vagus, and acces-sory nerves cross the posterior portion of the jugular tuberclein passing from the brainstem to the jugular foramen, some-times coursing in a shallow groove on the surface of thetubercle (Figs. 7.4 and 7.5).

The prominence of the jugular tubercle blocks access to thebasal cisterns and clivus anterior to the lower cranial nerves.As the jugular tubercle is removed extradurally the cranialnerves, which course along the back margin of the tubercleand are intradural, will not be visualized. As the drillingproceeds, bone will be removed from below the cisternalsegment of the accessory and the vagus nerves that courseabove the tubercle just inside the dura. Caution is required in

removing the jugular tubercle to avoid damaging the lowercranial nerves, either by direct trauma, by stretching the dura,or by the heat generated by the drilling (Fig. 7.5, A–C). Thelateral margin of the jugular tubercle is situated just medial toand below the medial edge of the jugular bulb. If a morelateral exposure is needed, or the jugular foramen is to beopened from posteriorly, the jugular process of the occipitalbone, which extends laterally from the occipital condyle, canbe removed after detaching the rectus capitis lateralis musclefrom its lower surface (Figs. 7.3 and 7.4). Removing the jugularprocess, which forms the posterior margin of the jugular fo-ramen, will expose the transition between the sigmoid sinus,jugular bulb, and internal jugular vein. Care is required toavoid damaging the vertebral artery, because it passes up-ward through the transverse process of the atlas and turnsmedially in the area directly below the jugular process. For aneven more lateral exposure, the posterior belly of the digastricmuscle can be separated from the mastoid notch to expose thefacial nerve just distal to the stylomastoid foramen (Figs. 7.3C,7.4, B and C, and 7.6). A partial mastoidectomy can be per-formed to expose the mastoid segment of the facial nerve inthe facial canal at this stage.

Intradural stage

The dural incision begins behind the sigmoid sinus andextends behind the vertebral artery into the upper cervicalarea. The upper extent of the dural opening depends on howmuch of the cerebellopontine angle is to be exposed. Possiblesources of bleeding during the dural opening are the marginalsinus that encircles the foramen magnum and the posteriormeningeal artery, which usually originates from the vertebralartery extradurally, but may infrequently originate intra-durally, in which case it crosses the lateral medullary cisternand pierces the arachnoid to reach the dura. Opening the duraexposes the intradural segment of the vertebral artery. As theartery pierces the dura, it is encased in a fibrous tunnel thatbinds the posterior spinal artery, dentate ligament, first cer-vical nerve, and the spinal accessory nerve to the vertebralartery (Figs. 7.2, N and O, 7.3) (14). Care should be taken topreserve the posterior spinal artery during the dural openingand mobilization of the vertebral artery because it may beincorporated into the dural cuff around the vertebral artery.

At the craniocervical junction, the dentate ligament is lo-cated between the vertebral artery and ventral roots of C1anteriorly and the branches of the posterior spinal artery andspinal accessory nerve posteriorly, and is often incorporatedinto the dural cuff around the vertebral artery (Figs. 7.2O, 7.3,and 7.5). The most rostral attachment of the dentate ligamentis located at the level of the foramen magnum above wherethe vertebral artery pierces the dura and behind the accessorynerve, although the dentate ligament is located anterior to theaccessory nerve at lower levels. Section of the upper twotriangular processes will increase access anterior to the spinalcord. The first cervical nerve courses along the posteroinferiorsurface of the vertebral artery as it pierces the dura. Theventral root is located anterior to the dentate ligament, andthe dorsal root, which is infrequently present, passes posterior



FIGURE 7.4. Relationships in the transcondylar, supracondylar, and paracondylar exposures. A, a left suboccipital craniectomy has beencompleted and the dura opened. The nerves entering the jugular foramen have been exposed. Bone has been removed above the occipi-tal condyle to expose the hypoglossal nerve entering the hypoglossal canal. A bridging vein passes from the lateral aspect of the medullato the jugular bulb. B, the rectus capitis lateralis has been detached from the cranial base and the jugular process of the occipital bone,which forms the posterior margin of the jugular foramen, has been removed to expose the jugular bulb. The posterior belly of the digas-tric muscle has been reflected forward and a mastoidectomy completed to expose the mastoid segment of the facial nerve. C, the jugularbulb and adjoining segment of the internal jugular vein have been removed to expose the glossopharyngeal, vagus, and accessory nervespassing through the jugular foramen and descending behind the internal carotid artery. The cortical bone lining the hypoglossal canal hasbeen removed to expose the hypoglossal nerve and the venous plexus in the canal. The hypoglossal nerve joins the nerves exiting the jug-ular foramen to descend in the carotid sheath. A mastoidectomy has been completed to expose the bony capsule of the semicircularcanals and the mastoid segment of the facial nerve. D, enlarged view of the nerves passing through the hypoglossal canal and jugularforamen in the supracondylar and paracondylar areas. A., artery; Bridg., bridging; Car., carotid; CN, cranial nerve; Cond., condyle; For.,foramen; Gl., gland; Hypogl., hypoglossal; Int., internal; Jug., jugular; Lat., lateral, lateralis; Occip., occipital; P.I.C.A., posteroinferior cere-bellar artery; Post., posterior; Seg., segment; Sig., sigmoid; Stylomast., stylomastoid; Vert., vertebral.

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FIGURE 7.5. Posterior view of the left cerebellopontine angle. A, the glossopharyngeal, vagus, accessory, and hypoglossalnerves arise from the medulla. The hypoglossal canal has been exposed by drilling the cancellous bone above the occipitalcondyle. The posterior root of the transverse process of C1 has been removed. The accessory nerve crosses the jugular tuber-cle, the latter acting as a trochlea around which the accessory nerve courses to reach the jugular foramen. B, enlarged view.The area above the occipital condyle has been drilled to further expose the cortical bone around the hypoglossal canal. Theatlanto-occipital joint has been preserved. C, the cortical bone lining the hypoglossal canal has been opened to expose thehypoglossal nerve and the hypoglossal venous plexus in the canal. D, anterior view. The anterior surface of the posteriorfossa and the anterior wall of the hypoglossal canal have been removed to expose the hypoglossal nerve in its canal. Therootlets of the hypoglossal nerve originate ventral to the inferior olive and join before exiting the hypoglossal canal. The glos-sopharyngeal, vagus, and accessory nerves penetrate the dura on the medial side of the jugular bulb. The hypoglossal nerveexits the hypoglossal canal on the medial side of the jugular foramen. A., artery; A.I.C.A., anteroinferior cerebellar artery;Atl., atlanto; Bas., basilar; CN, cranial nerve; Cond., condyle; Dent., dentate; For., foramen; Hypogl., hypoglossal; Jug., jugu-lar; Lig., ligament; Occip., occipital; P.I.C.A., posteroinferior cerebellar artery; Vert., vertebral.



to the dentate ligament. The rootlets forming the spinal por-tion of the accessory nerve, which arise from the cervicalportion of the spinal cord midway between the dorsal andventral rootlets as far caudally as C5, unite to form a trunkthat ascends through the foramen magnum between the den-tate ligament and the dorsal roots and enters the posteriorfossa behind the vertebral artery (5).

The intradural segment of the vertebral artery, after emerg-ing from the fibrous dural tunnel, ascends in front of therootlets of the hypoglossal nerve to reach the front of the me-dulla oblongata where it unites near the junction of pons and

medulla with its mate to form the basilar artery (Fig. 7.2,N and O). Before reaching the lower border of pons, thevertebral artery gives off the PICA, which courses backwardaround the lateral surface of the medulla and between therootlets of glossopharyngeal, vagus, and accessory nerves.The anterior, lateral, and tonsillomedullary PICA segmentsand the intradural segment of the glossopharyngeal, vagus, andaccessory nerves, which may be exposed in this approach, aredescribed in greater detail in this issue in the chapters on thecerebellar arteries and cerebellopontine angle (Figs. 7.2, N andO, and 7.3-7.5) (11).

FIGURE 7.6. A, axial section extending through the occipital condyle and internal jugular vein below the right jugular fora-men. The internal jugular vein descends just in front of the rectus capitis lateralis and behind the carotid artery. The occipitalcondyle is located on the medial side of the jugular foramen, and the styloid process, facial nerve, and parotid gland are on thelateral side. The nerves passing through the jugular foramen and hypoglossal canal collect together on the medial side of the inter-nal jugular vein in an area just below the jugular foramen. B, the parotid gland has been removed. The facial nerve exits the stylo-mastoid foramen on the lateral side of the internal jugular vein. The styloid process is located along the anterolateral margin of theinternal jugular vein. The central third of the occipital condyle has been removed to expose the hypoglossal nerve as it passesthrough the hypoglossal canal and joins the nerves exiting the jugular foramen on the medial side of the internal jugular vein. Therectus capitis lateralis and some of the jugular process of the occipital bone have been removed to expose the terminal part of thesigmoid sinus. C–D. Transposition of the hypoglossal nerve. C, the vertebral artery has been displaced medially. The occipital con-dyle, jugular tubercle, and the bone around and in front of the hypoglossal canal have been removed to expose the edge of thelower clivus. The dura ostium of the hypoglossal nerve has been opened so that the nerve can be mobilized. D, enlarged view ofthe mobilized hypoglossal nerve. A., artery; Atl., atlanto; Cap., capitis; Car., carotid; CN, cranial nerve; Cond., condyle; For., fora-men; Gl., gland; Hypogl., hypoglossal; Int., internal; Jug., jugular; Lat., lateralis; M., muscle; Occip., occipital; P.I.C.A., posteroinfe-rior cerebellar artery; Proc., process; Rec., rectus; Sig., sigmoid; Stylomast., stylomastoid; V., vein; Vert., vertebral.

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DISCUSSION

The basic far-lateral approach without drilling of the occip-ital condyle may be all that is required to reach some lesionslocated along the anterolateral margin of the foramen mag-num. However, it also provides a route through which thetranscondylar, supracondylar, and paracondylar approachesand several modifications of these approaches can be com-pleted. The transcondylar exposures can be categorized intoseveral variants. An atlanto-occipital transarticular approach,in which the adjacent posterior parts of the occipital condyleand the superior articular facet of C1 are removed to facilitatecompletion of a circular dural incision, permitting the verte-bral artery with the surrounding cuff of dura to be mobilized.A more extensive removal of the articular surfaces and con-dyles can be done to gain access to extradural lesions situatedalong the anterior and lateral margins of the foramen mag-num. Another variant, the occipital transcondylar variant, isdirected above the atlanto-occipital joint through the occipitalcondyle and below the hypoglossal canal to access the lowerclivus and the area in front of the medulla. The supracondylarapproach directed above the occipital condyle can also bevaried, depending on the pathology to be exposed. The su-pracondylar exposure can be directed above the occipitalcondyle to the hypoglossal canal or both above and below thehypoglossal canal to the lateral side of the clivus. In the transtu-bercular variant of the supracondylar approach, the prominenceof the jugular tubercle that blocks access to the area in front of theglossopharyngeal, vagus, and accessory nerves is removed ex-tradurally to increase visualization of the area in front of thebrainstem and to expose the origin of a PICA that arises fromthe distal part of the vertebral artery near the midline. Theparacondylar approach also has several variants. In the trans-jugular variant, the exposure is directed lateral to the condylethrough the jugular process of the occipital bone to the pos-terior surface of the jugular bulb. The approach can also beextended lateral to the jugular foramen into the posterioraspect of the mastoid to access the mastoid segment of thefacial nerve and the stylomastoid foramen.

Many suboccipital operations are completed without re-quiring that each individual muscle be identified. However,identification of selective muscles is an essential part of com-pleting the transcondylar, supracondylar, and paracondylarapproaches. Muscles that are especially significant in identi-fying the neural, vascular, and osseous structures involved inthese exposures are the three muscles forming the suboccip-ital triangle and the levator scapulae, rectus capitis lateralis,and the posterior belly of the digastric. Identification of theindividual muscles is also helpful in exposing and preservingthe occipital artery if it is needed for a bypass procedure andin preserving the peripheral branches of the upper cervicalnerves. The levator scapulae muscle provides an excellentlandmark for localizing the vertebral artery as it ascendsbetween the transverse foramina of the atlas and axis wherethe artery is located medial to the upper attachments of themuscle. The main risk in this area is related to a tortuousvertebral artery that loops posteriorly as it ascends betweenthe transverse processes of the axis and atlas, making it vul-

nerable to injury when one expects the artery to be passingstraight upward from the lower to the upper transverse fora-men. The artery is also susceptible to damage as it passesbehind the superior articular facet of the atlas. The arterynormally hugs the posterior surface of the superior articularfacet of the atlas, extending upward only to the level of theatlanto-occipital joint. However, if the artery elongates andbecomes tortuous it can loop upward behind the occipitalcondyle, even resting against the occipital bone behind the con-dyle. It also can loop backward and bulge posteriorly betweenthe lips of the suboccipital triangle, which it can damage if oneexpects it to be found in the depth of the suboccipital triangle.

In obliterating and coagulating the venous plexus aroundthe vertebral artery, there is the risk that some of the branchesof the vertebral artery, which arise in an extradural location oreven a hypoplastic vertebral artery, might be occluded ordivided. The posterior spinal artery, and uncommonly thePICA, may arise extradurally in the region of the portion ofthe vertebral venous plexus, which may need to be partiallyexcised or obliterated to gain access to the vertebral artery.

The far-lateral approach, in which the exposure is carriedup to, but does not include, the posterior margin of theoccipital condyle, may be selected for lesions located along thelateral or anterolateral aspect of the foramen magnum. It isfrequently necessary to remove a small portion of both theoccipital condyle and the superior articular facet of the atlas ifthere is a need to complete a circumferential dural incisionaround the site where the artery penetrates the dura, so thatthe artery can be displaced for access to lesions located ventralto the artery and in front of the cervicomedullary junction. Forlesions requiring a greater anterior and superior exposure, theposterior third of the occipital condyle can be removed with-out entering the hypoglossal canal. It is possible to drill thecancellous bone of the occipital condyle to expose the lateralclivus and hypoglossal canal while preserving some of thecortical bone of the condyle and the articular surface so thatthe joint is not disrupted (Figs. 7.3 and 7.5). The corticalsurface around the hypoglossal canal can be preserved if thereis no need to expose the nerve within the canal.

Another key aspect of this approach is the condyle drilling,which requires an understanding of the relationship of thehypoglossal canal to the occipital condyle (Figs. 7.3–7.6). Themaximum extent of the upper portion of occipital condyle thatcould be drilled without exposing the hypoglossal canal is theposterior third of its long axis. The occipital condyle some-times can be covered by a hypertrophic superior articularfacet of C1 that protrudes into the foramen magnum, makingit easy to overlook the upper medial portion of the occipitalcondyle. In exposing lesions located along the anterior portionof the cervical cord, the inferior portion of the occipital con-dyle and the superior facet of C1 can be removed after re-tracting the vertebral artery inferior and medially. In drillingthe upper posterior portion of the condyle, the posterior con-dylar vein may be a source of bleeding, which could bemistaken for bleeding from the venous plexus in the hypo-glossal canal. After exposing the hypoglossal canal, the jugu-lar tubercle, which is located just above and anterior to thecanal, is identified. The drilling can be extended to a supra-



condylar location above the hypoglossal canal for removal ofall or part of the jugular tubercle, so that the dura covering thetubercle can be pushed forward to gain access to the front ofthe medulla and the pontomedullary junction. Removal of thejugular tubercle may yield better visualization of the intra-dural segment of vertebral artery and the origin of the PICA,especially if the PICA originates from the upper part of thevertebral artery. The supracondylar approach, in which thejugular tubercle is removed and the hypoglossal canal isexposed or opened, provides a route for reaching extradurallesions located in the lower lateral part of the clivus in front ofthe hypoglossal canal. The extradural removal of the jugulartubercle should be performed with caution because of the riskof injuring the glossopharyngeal, vagus, and the accessorynerves that hug and often course in a shallow groove at thesite where they cross the tubercle.

The paracondylar exposure, which accesses the posteriormargin of the jugular foramen and the jugular bulb, can becompleted without drilling the occipital condyle (8, 20). Anexcellent landmark for identifying the jugular process is therectus capitis lateralis, which extends upward from the trans-verse process of the atlas to attach to the jugular process justbehind the jugular bulb. The muscle is located medial to thesite where the occipital artery enters the retromastoid area bypassing between the rectus capitis lateralis and posterior bellyof the digastric. The jugular foramen and jugular bulb isaccessed by drilling the jugular process at the posterior mar-gin of the foramen. Drilling lateral to the jugular bulb fromthis posterior exposure risks damaging the facial nerve in thefacial canal at and just above the stylomastoid foramen. Theposterior belly of the digastric muscle, which attaches alongthe digastric groove just posterior to the stylomastoid fora-men, provides a useful landmark for identifying the facialnerve. A limited or more extensive mastoidectomy may becompleted, depending on the length of the mastoid segmentof the facial nerve to be exposed and the extent to which thebone on the lateral aspect of the jugular bulb must be re-moved. A wider exposure of the jugular foramen is obtainedby a retrolabyrinthine transtemporal approach, in which amore extensive mastoidectomy is completed and the mastoidand the tympanic segments of the facial nerve are exposed sothat the facial nerve can be transposed forward to provideaccess to both the lateral and the posterior margin of thejugular foramen.

Several controversies concern the positioning of the patientand the type of skin incision (20). The modified park benchposition that we use offers the main advantage of avoiding airembolism (2, 3, 10, 14). The sitting position recommended byothers is associated with a less distended venous plexus, butthe rich net of veins around the cervical muscles, vertebralartery, and bone in the region offers the risk of air embolism(4, 13). A straight scalp incision has been recommended asbeing easier to open and close (10, 13). However, the thickcervical muscular mass and need for extensive retraction cre-ate a deep surgical field and the lateral position of the incisionmakes it difficult to complete a wide removal of the posteriorC1 arch and C2 lamina, which is especially important if thelesion extends through the foramen magnum. We prefer an

inverted horseshoe incision, with the medial limb extended sothat a wide C1 to C2 laminectomy can be completed, and alateral limb extended below the C1 transverse process so thatthe muscles attaching to the transverse processes are visual-ized (2, 5, 17, 18, 20). A musculofascial cuff is left attachedalong the superior nuchal line for closure. The flap on theupper part of the occipital squama can be reflected as a singlelayer, however it is helpful to identify the muscles forming thesuboccipital triangle as an aid to exposing the vertebral artery.Anatomically, muscle dissection layer by layer offers the bestpreservation of the muscular landmarks. However, reflectionof the superficial muscles individually carries a greater risk offlap dehiscence. Elevating the muscles attached to the upperpart of the occipital squama with the scalp minimizes thisproblem and allows identification of important deep muscu-lar landmarks, such as the suboccipital triangle and levatorscapulae for localizing the vertebral artery and the rectuscapitis lateralis for localizing the posterior portion of thejugular bulb.

Reprint requests: Albert L. Rhoton, Jr., M.D., Department of Neuro-logical Surgery, University of Florida Brain Institute, P.O. Box 100265,100 South Newell Drive, Building 59, L2-100, Gainesville, FL32610-0265.

REFERENCES

1. Arnold H, Sepehrnia A: Extreme lateral transcondylar approach.J Neurosurg 82:313, 1995 (letter).

2. Babu RP, Sekhar LN, Wright DC: Extreme lateral transcondylarapproach: Technical improvements and lessons learned. J Neuro-surg 81:49–59, 1994.

3. Baldwin HZ, Miller CG, van Loveren HR, Keller JT, Daspit CP,Spetzler RF: The far lateral/combined supra- and infratentorialapproach: A human cadaveric prosection model for routes ofaccess to the petroclival region and ventral brainstem. J Neuro-surg 81:60–68, 1994.

4. Bertalanffy H, Seeger W: The dorsolateral, suboccipital, transcon-dylar approach to the lower clivus and anterior portion of thecraniocervical junction. Neurosurgery 29:815–821, 1991.

5. de Oliveira E, Rhoton AL Jr, Peace D: Microsurgical anatomy of theregion of the foramen magnum. Surg Neurol 24:293–352, 1985.

6. Hakuba A, Tsujimoto T: Transcondyle approach for foramenmagnum meningiomas, in Sekhar LN, Janecka IP (eds): Surgery ofCranial Base Tumors. New York, Raven Press, 1993, pp 671–678.

7. Heros RC: Inferolateral suboccipital approach for vertebral andvertebrobasilar aneurysms, in Wilkins RH, Rengachary SS (eds):Neurosurgery Update: Vascular, Spinal, Pediatric, and FunctionalNeurosurgery. New York, McGraw-Hill, 1991, vol II, pp 106–109.

8. Katsuta T, Rhoton AL Jr, Matsushima T: The jugular foramen:Microsurgical anatomy and operative approaches. Neurosurgery41:149–202, 1997.

9. Kratimenos GP, Crockard HA: The far lateral approach for ven-trally placed foramen magnum and upper cervical spine tumors.Br J Neurosurg 7:129–140, 1993.

10. Lang DA, Neil-Dwyer G, Iannotti F: The suboccipital transcondy-lar approach to the clivus and cranio-cervical junction for ven-trally placed pathology at and above the foramen magnum. ActaNeurochir (Wien) 125:132–137, 1993.

11. Lister JR, Rhoton AL Jr, Matsushima T, Peace D: Microsurgicalanatomy of the posterior inferior cerebellar artery. Neurosurgery10:170–199, 1982.

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12. Matsushima T, Ikezaki K, Nagata S, Inoue T, Natori Y, Fukui M,Rhoton AL Jr: Microsurgical anatomy for lateral approaches to theforamen magnum: With special reference to the far lateral ap-proach and the transcondylar approach, in Nakagawa H (ed):Surgical Anatomy for Microneurosurgery: Anatomy and Approaches tothe Craniocervical Junction and Spinal Column [in Japanese]. Tokyo,SciMed, 1994, vol VII, pp 81–89.

13. Perneczky A: The posterolateral approach to the foramen mag-num, in Samii M (ed): Surgery in and around the Brainstem and theThird Ventricle. Berlin, Springer-Verlag, 1986, pp 460–466.

14. Rhoton AL Jr: Meningiomas of the cerebellopontine angle andforamen magnum. Neurosurg Clin N Am 52:349–377, 1994.

15. Sen CN, Sekhar LN: An extreme lateral approach to intradurallesions of the cervical spine and foramen magnum. Neurosurgery27:197–204, 1990.

16. Sen CN, Sekhar LN: Surgical management of anteriorly placedlesions at the cranio-cervical junction: An alternative approach.Acta Neurochir (Wien) 108:70–77, 1991.

17. Sen C, Sekhar LN: Extreme lateral transcondylar and transjugularapproaches, in Sekhar LN, Janecka IP (eds): Surgery of Cranial BaseTumors. New York, Raven Press, 1993, pp 389–411.

18. Spetzler RF, Grahm TW: The far-lateral approach to the inferiorclivus and the upper cervical region: Technical note. BNI Q6:35–38, 1990.

19. Tedeschi H, Rhoton AL Jr: Lateral approaches to the petroclivalregion. Surg Neurol 41:180–216, 1994.

20. Wen HT, Rhoton AL Jr, Katsuta T, de Oliveira E: Microsurgicalanatomy of the transcondylar, supracondylar, and paracondylarextensions of the far-lateral approach. J Neurosurg 87:555–585,1997.

Cranium showing various anatomical structures. Vesalius was so confident that his work would be studied andplagiarized that he obtained the sponsorship and copyright protection of the Emperor, the King of France, and theGrand Council of Venice, the three great powers of his day. From, Andreas Vesalius, De Humani Corporis Fabrica.

Basel, Ex officina Ioannis Oporini, 1543. Courtesy, Rare Book Room, Norris Medical Library, Keck School of Medicine,Los Angeles, California. (Also see pages S27, S68, and S285.)



the far-lateral approach and its transcondylar, supracondylar, and paracondylar extensions

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