The mandibular swing-transcervical approach to the skull base: anatomical study

Transcription

1 J Neurosurg 78: , 1993 The mandibular swing-transcervical approach to the skull base: anatomical study Technical note MARIO AMMIRATI, M.D., JIANYA MA, M.D., MELVIN L. CHEATHAM, M.D., ZHONG TAO MEI, M.D., JOSEPH BLOCR, B.F.A., AND DONALD P. BECKER, M.D. Division ~f Neurosurgery, University ~f California, Los Angeles, California ~" This report describes in a stepwise fashion the surgical anatomy of an approach to the midline and lateral compartments of the skull base (clivus, infralabyrinthine/infratemporal regions). ]-he salient features of this procedure are represented by a mandibulotomy and by detachment of the pharynx from the skull base through a combined oral and cervical approach. There is full neurovascular control of the internal carotid artery and lower cranial nerves with the possibility of complete exposure of the intrapetrous and intracavernous segments of the internal carotid artery on the side of the exposure. This approach, which may be regarded as an expansion of the original work of Krespi, should be considered when dealing aggressively with extensive skullbase lesions invading the midline and lateral compartments of the skull base. KEY WORDS 9 clivus 9 labyrinthine fossa intratemporal fossa 9 skull base 9 mandibular splitting anatomical study I N 1981, Spiro, et al., 15 reported on a mandibular swing approach to oral and oropharyngeal tumors. Later, Biller, et al., 1 described an expansion of this technique to expose the skull base of the basal aspect of the clivus and of the infralabyrinthine and infratemporal areas. Despite the seemingly significant advantages of such an approach (wide field/multiangled exposure, carotid vascular control, and expansibility), it has never gained popularity among neurosurgeons. A lack of detailed description of the intra- and extracranial areas that were approachable and a perceived complexity of this surgical procedure are possibly some of the reasons that have limited its more widespread use. This approach merits broader recognition among neurosurgeons in view of its applicability to extensive skullbase lesions. The purpose of this paper is to describe the surgical anatomy of a modification of this surgical avenue and to individuate the intra- and extracranial areas that may be exposed by this method. Surgical Technique The procedure was carried out in 10 embalmed cadaveric heads. The cephalic vascular system in each had been injected with colored material. The skin incision starts at the lower lip, extends inferiorly in the midline to the hyoid bone, then curves laterally over the sternocleidomastoid muscle to reach the mastoid tip (Fig. 1). A myocutaneous flap is elevated superiorly, deep to the platysma, ending at the lower border of the mandibular body. The skin flap remains FIG. 1. The skin incision is shown. It starts at the lower lip, extends infefiorly in the midline to the hyoid bone, then curves laterally over the sternocleidomastoid muscle to reach the mastoid tip. J. Neurosurg. / Volume 78/April

2 M. Ammirati, et al. FIG. 2. The skin flap has been raised. The flap is superficial to the parotid and submandibular glands. The mandibular body and ramus, the muscles of the floor of the mouth, the stylohyoid muscle, and the anterior portion of the sternocleidomastoid muscle are exposed at this stage of the dissection. The facial artery is seen crossing the field. superficial to the submandibular gland (Fig. 2). After posterior retraction of the sternocleidomastoid muscle, it is possible to identify the common carotid artery, the internal carotid artery, the external carotid artery, and the internal jugular vein. The 10lh through 12th cranial nerves are also exposed and freed in a cranial direction as much as possible. The superior thyroid, lingual, facial, and occipital branches of the external carotid artery are also identified (Fig. 3). The intermediate tendon of the digastric muscle is transected; the posterior and anterior belly of the muscles are retracted posteriorly and superiorly, respectively. The mylohyoid FIG. 3. The common carotid artery, its bifurcation, and the internal jugular vein are exposed in the neck after posterior retraction of the sternocleidomastoid muscle. The spinal accessory (XI) and hypoglossal (XII) nerves are seen crossing the internal jugular vein and the carotid bifurcation, respectively. muscle is released from the hyoid bone as well as from the midline and retracted superiorly, while the geniohyoid muscle is detached from the mandibular symphysis and retracted inferiorly (Fig. 4). FIG. 4. Transection of the dlgastnc, genlohyold, and mylohyoldmuscles, revealing the deep muscles of the floor of the mouth. When transecting the mylohyoid muscle, care must be taken not to injure the hypoglossal nerve that runs just underneath the mylohyoid muscle. 674 d. Neurosurg. / Volume 78/April, 1993

3 Mandibular swing-transcervical approach to the clivus The mandibular periosteum is incised and freed for 2 cm on each side of the midline. The mandibular incision is executed in a staircase fashion using the Gigli saw. The lower incisor tooth should be removed. Holes are placed on either side of the vertical limb of the mandibular incision for placement of stabilizing wires at the conclusion of the procedure (Fig. 6 inset). After superolateral retraction of the tongue, a mucosal incision is executed in the floor of the mouth starting between the orifices of Wharton's ducts and extending posterolaterally to the anterior tonsillary pillar (Fig. 5). The lingual nerve is divided and separated from the tongue. The purpose of this incision is to enter the prestyloid segment of the mandibulopharyngeal space between the pharynx medially and the inner aspect of the mandibular ramus laterally. The mandible is swung laterally to enlarge the mandibulopharyngeal space. The facial artery is cut and the inner pterygoid muscle is transected from its attachment on the lateral pterygoid plate to further enhance entry into the prestyloid segment of the mandibulopharyngeal space (Fig. 6). The styloid process is identified by palpation. The stylohyoid, stylopharyngeal, and styloglossus muscles are detached from the styloid process, which may need Flr 5. The incision in the floor of the mouth is shown. I hc incision starts between the orifices of Wharton's ducts and exlcnds posterolaterally to the anlerior tonsillary pillar. FIG. 6. After midline mandibulotomy, the mandible is swung laterally. This maneuver, together with the previously executed incision of the floor of the mouth, allows wide exposure of the space between the mandibular ramus laterally and the pharynx medially (mandibulopharyngeal space). The lingual nerve, the facial artery, and the medial Nerygoid muscle have been transected at this stage. Inset: The staircase technique of mandibulotomy is shown. J. Neurosurg. / Volume 78/April,

4 M. Ammirati, et al. FiG. 7. The stylohyoid, styloglossus, and stylopharyngeal muscles have been released from the styloid process. Transection of the external carotid artery allows untethered retraction of the soft tissues, permitting unhindered tracing toward the skull base of the internal carotid artery, internal jugular vein, and lower cranial nerves. to be shortened. These muscles are retracted inferiorly. The ninth cranial nerve is identified at this stage (Fig. 7). The external carotid artery is cut at the level of the facial artery, and the occipital artery is also cut. Transection of these vessels permits wider retraction of the soft tissues allowing entry into the retrostyloid portion of the mandibulopharyngeal space and facilitating tracing of the internal carotid artery, internal jugular vein, and ninth through 12th cranial nerves to the skull base (Fig. 7). The mucosal incision on the floor of the mouth is extended posteriorly to the maxillary luberosity, then turned medially and anteriorly on the hard palate 1 cm from the gingival margin to end on the opposite side just past the midline. The mucoperiosteal flap is retracted contralaterally. The greater palatine artery and nerve are transected (Fig. 8). The posterior portion of the hard palate is rongeured away exposing the nasal mucosa that is cut in a 13 fashion with its attachment lateral, on the medial pterygoid plate. This maneuver is necessary when there is tumor in the nasal cavity or in the anterior cranial fossa. The pharynx is retracted contralaterally. At this stage FIG. 8. The mucosal incision on the floor of the mouth has been extended to the hard palate, the posterior portion of which has been removed on the side of the exposure. At this stage, the pharynx is tethered to the skull base only through the eustachian tube and the tensor and levator patatini muscles. The dotted lines show the incision in these structures. Inset: The pharynx is retracted contralaterally after transection of the tensor and levator palatini muscles and the eustachian tube. The anterior elements of the atlas and of the axis start to come into view at this stage. 676 J. Neurosurg. / Volume 78/April, 1993

5 Mandibular swing-transcervical approach to the clivus the nasopharynx is tethered to the skull base only through the eustachian tube and the tensor and the levator palatini muscles (Fig. 8). These structures are divided just before they cross the free edge of the superior constrictor pharyngeal muscle (Fig. 8 inset). The whole pharynx can now be retracted to the opposite side, exposing the entire length of the clivus and the upper cervical spine covered by the longus capitis muscles/prevertebral fascia. These muscles are retracted inferiorly to expose the occipito-atlas junction and the upper cervical spine (Fig. 9). Inferior retraction of the longus capitis muscles allows later exposure of the intrapetrous internal carotid artery; if this exposure is not needed, the muscles may be laterally retracted. The clivus may be drilled to expose the epidural space. The infralabyrinthine space ipsilateral to the skin incision is also fully exposed from the carotid canal onward to the basal aspect of the petrous apex. The intrapetrous internal carotid artery may be completely exposed in its vertical and horizontal portions with full control; the intracavernous internal carotid artery may be exposed as well (Fig. 10). This approach may be further extended to expose the infratemporal fossa by removing the lateral pterygoid plate after detachment of both pterygoid muscles that are inferiorly retracted. The pterygopalatine fossa may also be exposed by removing the lateral and posterior walls of the maxillary tuberosity after removal of the pterygoid plate. The sphenoid sinus, and hence the sellar floor, may be reached by removing the vomer (Fig. 11). At each level of desired exposure the dura Fz(,. 9. The midline compartment of the skull base is exposed. The lower clivus and anterior margin of the foramen magnum are well visualized. The pins are in the Cl-2 joint. FIG. 10. Left: Exposure of the midline and lateral compartments (infralabyrinthine space) of the skull base. The intrapetrous internal carotid artery (ICA) covered by its venous plexus is demonstrated from the foramen caroticum to the foramen lacerum. Exposure of the intrapetrous internal carotid artery is executed from the outside of the skull base, thus not interfering with the bony labyrinth located above the carotid artery. Right: Overview of the exposure. The clivus has been removed all the way to the body of the sphennid. The infralabyrinthine and infratemporal spaces are exposed. The intrapetrous internal carotid artery is well visualized in its entirety with good control. The jugular bulb and the anterior element of the C-1 and C-2 vertebrae are evident. J. Neurosurg. / Volume 78/April,

6 M. Ammirati, et al. FIG. 11. The sphenoid sinus has been opened. Left. The mucosa of the sphenoid sinus is shown after removal of the sphenoid sinus floor. Ri(Tht: The floor of the sella turcica has been removed exposing the sellar dura. FIG. 12. Left: The dura over the pons, medulla, and craniocervical junction has been opened. The vertebral arteries are demonstrated from their point of dural penetration to the basilar artery. The lower and middle portion of the basilar trunk is also exposed. At this stage, there is good exposure of the anterior cervical cord, anterior medulla, and anterior pons; the proximal segments of the abducens and hypoglossal nerves are well visualized. AICA = anterior inferior cerebellar artery; PICA = posterior inferior cerebellar artery. Roman numerals indicate cranial nerves. Right: The dura covering the interpeduncular fossa has been opened. The basilar tip, the proximal segment of the superior cerebellar arteries, and the P1 segment of the posterior cerebral arteries (PCA's) are well exposed. The oculomotor nerve is seen between the superior cerebellar artery and the PCA. 678 J. Neurosurg. / Volume 78/April, 1993

7 Mandibular swing-transcervical approach to the clivus may be opened to expose the base of the brain (Figs. 12 and 13). Closure is achieved by reattaching the superior constrictor muscle to the base of the skull. The floor of the mouth, the palate, and the lip incision are closed as usual. The mandible may be reapproximated using wires. A posterior nasal pack and a palatal stent are applied for 2 weeks. In case major reconstruction is needed, the temporalis muscle or the sternocleidomastoid muscle is readily accessible. Ventilation is maintained for about 1 week through a tracheostomy performed at the very beginning of the operation. A nasogastric tube is left in place for i0 to 14 days. t'6'7 This approach allows unhindered exposure of the skull base from the ipsilateral infratemporal fossa to the contralateral medial pterygoid plate. Anteroposteriorly, it allows exposure of the skull base from the anterior cranial fossa to the lower border of the clivus and to the anterior aspect of the cervical spine. There is full neurovascular control on the side of the exposure (Fig. 14). Discussion Simple Approaches to the Clivus Limited exposure of the clivus may be obtained through a variety of intracranial approaches, essentially revolving around the ptefional, subtemporal, and suboccipital avenues. 14 These approaches expose mainly the unilateral clivus in its upper (pterional, subtemporal) or middle-lower (suboccipital) portions. These surgical avenues have generally been used for the treatment of exclusively or predominantly intradural lesions; the indications for the use of each are well established. ~3 Combinations of some of the these approaches may somehow increase the exposure. 5<2 The upper-mid clivus may also be reached through the paranasal cavities via the transethmoidal-transsphenoidal, 9 transseptal-transsphenoidal, 8 or simple lransmaxillary route? ~ These approaches offer good exposure of the upper-mid clivus mainly limited to the midline and have been generally used to access extradural pathology. The transcervical j6 and transoral '~ routes have also been used to reach the lower clivusupper cervical spine in the midline. Each of these approaches has its own merits in dealing with limited extradural clival lesions or when only a limited procedure is indicated in an otherwise extensive lesion. Derome 3 combined the transsphenoidal and subfrontal approaches in the transbasal approach to the base of the skull, allowing exposure of the anterior and part of the middle cranial fossa, together with exposure of the midline nasal-paranasal cavities (nose, ethmoid, and sphenoid sinus) and of the entire length of the clivus FiG. 13. Left: The dura of the anterior cranial fossa has been opened, yielding a good view of the basal aspect of the optic chiasm and of the gyrus rectus with the fronto-orbital artery. The pituitary gland is at the posterior limit of the field. Center: The gyrus rectus has been partially removed to show the anterior communicating artery (Ant. comm. a.) and the A2 segment of the anterior cerebral artery. Right: The dura covering the anterior aspect of the brain stem has been opened and the structures of the left prepontine, cerebellopontine angle, and lateral cerebellomedullary cisterns are exposed. This tangential view shows the distal vertebral arteries and the proximal and midbasilar artery. The origin of the anterior inferior cerebellar artery (AICA) is well shown. Note that the proximal AICA splits the abducens nerve (VI). Roman numerals denote cranial nerves; PICA = posterior inferior cerebellar artery. J. Neurosurg. / Volume 78/April,

8 M. Ammirati, et al. FIG. 14. Overviewof the intra- and extradural exposure. The intradural exposure extends from the upper cervical cord inferiorly to the gyrus rectus anteriorly. The pituitary gland and the optic ehiasm are located in the middle of the intradural exposure. The basal aspect of the intrapetrous and intracavernous segments of the internal carotid artery (ICA) is well exposed on the side of the approach. The infratemporal fossa on the side of the approach is also well visualized. Broken line~ indicate overlyingstructures. with the exception of the dorsum sellae. Derome used this approach for intra- and extradural tumors, variably invading the anterior and middle cranial fossae, the posterior extension of which was strictly limited to the clivus. Surgical Requirements of Extensive Clival Lesions When dealing aggressively with an extensive clival lesion, a more complex approach is needed. In fact, extensive clival lesions often span the whole length of the clivus and invade adjacent areas such as the infralabyrinthine space and infratemporal space laterally, the sphenoid sinus and nasal cavity anterosuperiorly, and the upper cervical spine inferiorly. From a surgical standpoint, the skull base may be divided by the intrapetrous internal carotid artery into one midline and two lateral compartments. 7 The midline compartment corresponds to the body of the sphenoid, to the clivus, and to the occipital condyles.~ The lateral compartment is formed by the undersurface of the petrous pyramid (infralabyrinthine space) and by the greater wing of the sphenoid (infratemporal fossa), J The intrapetrous internal carotid artery runs in the infralabyrinthine space. An approach that deals effectively with extensive clival lesions must provide wide, multiangled exposure of the clivus with the possibility of affording adequate access to the bordering areas (midline and lateral compartments). In addition, due to the proximity of the 680 intrapetrous and intracavernous segments of the internal carotid artery, carotid vascular control is desirable to protect the artery or to perform vascular bypass procedures. Moreover, in cases where the tumor extends laterally into the infralabyrinthine space, exposure of the internal jugular vein and ninth through 12th cranial nerves is mandatory. Also desirable is a short working distance. Complex Approaches to the Clivus Among the extensive approaches to the clivus, the median labiomandibulotomy with glossotomy and variable degrees of palatal incision affords excellent visualization of the entire length of the clivus, which is, however, limited to the midline. There is no neurovascular control, and access to the surrounding areas, other than the upper cervical spine, is lacking. The morbidity associated with this procedure is limited to a temporary tracheostomy and gastrostomy.~7 The infratemporal fossa approach (Type B) offers excellent exposure of the infratemporal fossa and of the infralabyrinthine space. 4 The exposure of the clivus is mainly lateral; inferior extension is lacking. There is good control of the carotid artery, the internal jugular vein, and the ninth through 12th cranial nerves. Morbidity is represented by conductive hearing loss, section of the fifth nerve, and various degrees of seventh nerve compromise, at times permanent. The subtotal maxillectomy offers excellent exposure J. Neurosurg. / Volume 78/April, 1993

9 Mandibular swing-transcervical approach to the clivus of the entire length of the clivus and of the undersurfacc of the pyramis from one eustachian tube to the other. The upper cervical spine can also be exposed. Control of the carotid artery is absent. The morbidity includes temporal tracheostomy, gastrostomy, and partial removal of the maxilla requiring oral prosthesis. The distance to the target is long. 2 The Mandibular Swing-Transcervical Approach to the Skull Base The approach we describe here differs from the original description of Krespi 1'67 because of the sacrifice of the lingual nerve which we believe necessary in order to enhance exposure and for the skeletonization of the intrapetrous and intracavernous segments of the internal carotid artery that may be required for safe removal of tumors from these areas or for bypass procedures. This approach, which we call the "mandibular swingtranscervical approach to the skull base," offers extensive exposure of the midline and lateral (ipsilateral to the exposure) compartments of the skull base with full carotid vascular control as well as internal jugular vein and control of the ninth through 12th cranial nerves. In addition, other adjacent areas, such as the infratemporal and pterygopalatine fossae, the sphenoid sinus, the cavernous sinus, the anterior cranial fossa, and the upper anterior cervical spine, may be readily accessible. The morbidity of this technique is represented by temporary tracheostomy and gastrostomy, temporary swallowing difficulties and decreased tongue motility, decreased sensation in the presulcal tongue area, serous otitis media requiring tympanostomy tubes, and oral prosthesis. 6,7 Conclusions The mandibular swing-transcervical approach to the skull base has several unique features: 1) simultaneous exposure of the midline and lateral compartments of the skull base with the possibility of expansion to the surrounding areas; 2) excellent neurovascular control; and 3) a short distance to the target. Due to the development of plastic reconstructive techniques, the routine use of spinal drainage, and the use of fibrin glue, this approach may be considered not only for extradural lesions but also for intradural pathology involving these areas. As with all complex skullbase procedures, this approach should only be used by a specialist team that has extensively familiarized itself with the complex anatomy after laboratory dissections. This approach, like all other complex skull-base exposures, has built-in morbidity; consequently, the indications for its use should be carefully considered and it should probably be reserved only for those cases when a surgical cure or a significant palliation may be achieved (for example, in cases of meningioma, chemodectoma, or chordoma). References 1. Biller HF, Shugar JMA, Krespi YP: A new technique for wide-field exposure of the base of the skull. Arch Otolaryngol 107: , Cocke EW Jr, Robertson JH, Robertson JT, et al: The extended maxillotomy and subtotal maxillectomy for excision of skull base tumors. Arch Otolaryngol Head Neck Surg 116:92-104, Derome PJ: The transbasal approach to tumors invading the base of the skull, in Schmidek HH, Sweet WH (eds): Operative Neurosurgical Techniques. Indications, Methods, and Results. New York: Grune & Stratton, 1982, Vol 2, pp Fisch U, Pillsbury HC: lnfratemporal fossa approach to lesions in the temporal bone and base of the skull. Arch Otolaryngol 105:99-107, Hakuba A, Nishimura S, Jang B J: A combined retroauricular and preauricular transpetrosal-transtentorial approach to clivus meningiomas. Surg Neurol 30: , Krespi YP, Har-E1 G: Surgery, of the clivus and anterior cervical spine. Arch Otolaryngoi Head Neck Surg 114: 73-78, Krespi YP, Sisson GA: Transmandibular exposure of the skull base. Am J Surg 148: , Laws ER Jr: Transsphenoidal surgery for tumors of the clivus. Otolaryngol Head Neck Surg 92: , Papel ID, Kennedy DW, Cohn E: Sublabial transseptal transphenoidal approach to the skull base. Ear Nose Throat J 65: , Pfistzor E: Transoral approach for epidural craniocervical pathological processes. Adv Tech Stand Neurosurg 12: , Price JC, Holliday MJ, Johns ME, et al: The versatile midface degloving approach. Laryngoscope 98: , Samii M, Ammirati M: The combined supra-infratentorial pre-sigmoid sinus avenue to the petro-clival region. Surgical technique and clinical applications. Acta Neurochir 95:6-12, Samii M, Ammirati M, Mahran A, et al: Surgery of petroclival meningiomas: report of 24 cases. Neurosurgery 24:12-17, Samii M, Draf W: Surgery of the Skull Base. An Interdisciplinary Approach. Berlin: Springer-Verlag, 1989, pp Spiro RH, Gerold FP, Strong EW: Mandibular "swing" approach for oral and oropharyngeal tumors. Head Neck Surg 3: , Stevenson GC, Stoney R J, Perkins RK, et al: A transcervieal transclival approach to the ventral surface of the brain stem for removal of a clivus chordoma. J Neurosurg 24: , Wood BG, Sadar ES, Levine HL, et al: Surgical problems of the base of the skull. Arch Otolaryngol 106:1-5, 1980 Manuscript received June 15, Accepted in final form September 3, Address reprint requests to. Mario Ammirati, M.D., Division of Neurosurgery, Room CHS, University of California, Le Conte Avenue, Los Angeles, California l. J. Neurosurg. / Volume 78/April,