The anterior petrosectomy is a versatile exposure. It is often combined with a subtemporal exposure to increase the surgical corridor. Variations of the anterior petrous approach are used to approach small acoustic neuromas or lesions of the petrous apex such as a cholesterol granuloma. This approach can open a corridor into the posterior fossa when operating a trigeminal schwannoma or an epidermoid tumor lying lateral to the midbrain. The exposure can be used for small high-riding petrous apex meningiomas. The exposure affords a face-on view of the anterior lateral pons for removing cavernomas. The anterior petrosectomy may be combined with a posterior petrosectomy for lesions that lie below the seventh and eighth cranial nerves.
Key Steps
Position: Supine with head turned or lateral position with head laterally flexed
Step 3. Dura propria elevation to identify the lateral loop (Fig. 12.21)
Step 4. Exposure of the middle fossa rhomboid with anterior translocation of V3 (Fig. 12.24)
Step 5. Drilling of the foramen ovale to shift the mandibular nerve (V3) anteriorly (Fig. 12.27)
Step 6. Drilling of the middle fossa rhomboid (anterior petrosectomy) (Fig. 12.30)
Step 7. Identification of the inferior petrosal sinus and the abducens nerve (Fig. 12.36)
Step 8. Exposure of the facial nerve at the fundus of the internal auditory canal (Fig. 12.40)
Step 9. Inferior translocation of the internal carotid artery and drilling of the clivus (Fig. 12.55)
Step 10. Opening of dura and division of the tentorium (Fig. 12.56)
Step 11. Identification of the intradural structures (Fig. 12.58)
Illustrated Steps with Commentary
Fig. 12.1 (Step 1) Skin incision.The head is placed in the lateral position with the neck laterally flexed toward the floor. (The patient is in the lateral or supine position with the head in the lateral position.) A. This sickle shaped skin incision is made for the treatment of a small tumor such as a vestibular schwannoma. B. This question mark shaped skin incision is for an expansive subtemporal middle fossa rhomboid approach. C. This large question mark shaped skin incision is made for extended subtemporal middle fossa rhomboid approach and for harvesting a vascularized galeofascial pericranial flap.The skin incision should start at the preauricular zygomatic point that is located 10 mm anterior to the tragus on the root of the zygoma. The incision extends along the posterior border of the sideburn. If possible, the incision extending below the hairline follows a skin crease. (PZP, posterior zygomatic point; STL, superior temporal line; Zy, zygoma)Fig. 12.2 Soft tissue opening.Basic: When employing a one-layer exposure, the incision is made through the skin and temporalis muscle. The pericranium, galea, temporoparietal fascia, or deep temporal fascia can be used for dural plasty at the end of the case. (DTF, deep temporal fascia)Fig. 12.3 Mid-temporal bone exposure using the one-layer exposure.The muscle is retracted along with the skin. The roots of the zygoma and squamosal suture are exposed. (Sq, squamosal suture)Fig. 12.4 Two-layer exposure with preparation of a vascularized graft.To prepare a vascularized flap for closure, a two-layer exposure is needed. The periosteal-fascial pericranial flap is used to reinforce the dural closure to avoid a postoperative cerebrospinal fluid leak and infection. (DTF, deep temporal fascia; PO, periosteum)Fig. 12.5 Preparing the vascularized flap.To harvest as much tissue as is possible, the skin and galea are undermined around the circumference of the flap. (DTF, deep temporal fascia; PO, periosteum)Fig. 12.6 Periosteal-fascial flap.The edges of the skin are undermined so the vascularized flap is larger than the area exposed by the skin incision.Fig. 12.7 Preparing the vascularized galeaofascial pericranial flap.The vascularized flap can be back cut lengthwise so that the tip of the flap can reach the petrous apex.Fig. 12.8 Elongation of the vascularized galeaofascial pericranial flap.The pedicle of the flap must be wide enough to maintain the flap’s blood supply. The temporalis muscle must be left intact to avoid a cosmetic deformity.Fig. 12.9 Exposure of the root of zygoma.The zygomatic root has an inclination of 20 degrees and is 20 mm in length. (Sq, squamosal suture; Zy, zygoma)Fig. 12.10 Relationship between the zygomatic root and structures in the middle fossa.The foramen ovale is medial to the anterior edge of the zygomatic root, the foramen spinosum is medial to the midpoint of the zygomatic root, and the geniculate ganglion is medial to the posterior edge of the zygomatic root.Fig. 12.11 Relationship between the middle cranial base structures and the root of zygoma.The boundary between the foramen ovale and the spinosum corresponds to the point just anterior to the midpoint of the root of the zygomatic artery. (GG, gasserian ganglion; MMA, middle meningeal artery; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve )Fig. 12.12 (Step 2) Craniotomy for approaching the internal auditory canal.The trajectory for surgery centered in the vicinity of the internal auditory canal is optimal when the surgeon is viewing anterior to posterior. Starting from the midpoint of the zygomatic root, the bone flap should extend twice as far anteriorly as it does posteriorly to facilitate this view.Fig. 12.13 Craniotomy for approaching the posterior cavernous sinus, gasserian ganglion, and petrous apex.On the other hand, because the surgical trajectory is posterior to anterior for operations approaching the posterior cavernous sinus, gasserian ganglion, or petrous apex, the posterior portion of the craniotomy should be made equal to or larger than the anterior portion. The ratio of the anterior to the posterior is 1:1â1:2.Fig. 12.14 Drilling the subtemporal groove.A groove (arrowheads) is drilled through the bone above the root of the zygoma so that the craniotomy will extend down to the floor of the middle fossa. A second bur hole is placed approximately 10 to 15 mm above the squamosal suture. If the dura is tenaciously adherent to the bone, additional holes are made to facilitate stripping the dura from the bone before turning the craniotomy flap. (Sq, squamosal suture)Fig. 12.15 Outlining the craniotomy.The subtemporal groove and the bur hole are connected using an osteotome.Fig. 12.16 Elevation of the craniotomy.A craniotomy is elevated.Fig. 12.17 Dural elevation.The dura is elevated from the floor of the middle fossa toward the middle meningeal artery and the foramen spinosum.Fig. 12.18 Flattening of the floor of the middle fossa.The inner plate of the floor of the middle fossa should be drilled flat so that the surgeon’s line of vision is unobstructed by bony protrusions. Care must be taken not to flatten the arcuate eminence and open into the superior semicircular canal. The geniculate ganglion can be localized by stimulating the adjacent facial nerve through the bone.Fig. 12.19 Identifying the middle meningeal artery.The middle meningeal artery should be followed proximally to identify the foramen spinosum. (MMA, middle meningeal artery)Fig. 12.20 Identifying the foramen spinosum.The foramen spinosum can be found by following the middle meningeal artery to its exit from the cranium. The foramen is often obscured by a bony overhang that can be removed with a diamond drill. The foramen ovale is seen medial and anterior to the foramen spinosum. (FO, foramen ovale; FS, foramen spinosum; MMA, middle meningeal artery)Fig. 12.21 (Step 3) Dura propria elevation.The middle meningeal artery is coagulated by bipolar coagulation and interrupted using a No. 11 or 15 blade knife. The dura propria elevation is begun by making an incision between the dura covering the temporal lobe and the fibrous tissue covering V3. (FO, foramen ovale; MMA, middle meningeal artery)Fig. 12.22 Identifying the mandibular nerve and greater superficial petrosal nerve.The dura propria is gradually elevated over the mandibular branch of the trigeminal nerve. The greater superficial petrosal nerve (GSPN) is frequently found in its groove along with a branch of the middle meningeal artery, which passes medial to the foramen spinosum and under the mandibular nerve into the vidian canal. The GSPN is sharply separated from the temporal dura. Traction on the nerve can injure the geniculate ganglion and the facial nerve. The foramen ovale emissary vein connecting the pterygoid plexus with the cavernous sinus is seen passing through the foramen ovale. Bleeding from this vein should be controlled using an absorbable hemostatic agent. Bipolar coagulation should be kept to a minimum. (AE, arcuate eminence; FOEV, foramen ovale emissary vein; GSPN, greater superficial petrosal nerve; MMA, middle meningeal artery; V3, mandibular nerve )Fig. 12.23 Identifying the lateral loop.The foramen rotundum can be found by following the dura anteriorly from the foramen ovale toward the superior orbital fissure. The lateral loop formed by the anterior border of the mandibular nerve and the inferior border of the maxillary nerve should be identified. (GG, gasserian ganglion; GSPN, greater superficial petrosal nerve; MMA, middle meningeal artery; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve )Fig. 12.24 (Step 4) Rhomboid exposure.Working down along the petrous ridge from lateral to medial, the arcuate eminence (AE) is encountered on the superior surface of the petrous bone. The medial edge of the AE lies approximately at the level of the geniculate ganglia. The rhomboid space is delineated by the petrous ridge, the AE, the greater superficial petrosal nerve, and the posterior border of the mandibular nerve. This includes Kawase’s and Glasscock’s triangles. (AE, arcuate eminence; GG, gasserian ganglion; GSPN, greater superficial petrosal nerve; MMA, middle meningeal artery; Rbd, rhomboid; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve )Fig. 12.25 Identifying the two petrosal ridges.The petrous ridge is notched by a groove that cradles the superior petrosal sinus. The surgeon needs to strip the dura over two humps to completely expose the petrous ridge. (1st R, first ridge of the petrous bone; 2nd R, second ridge of the petrous bone; AE, arcuate eminence; GG, gasserian ganglion; GSPN, greater superficial petrosal nerve; Rbd, rhomboid; V3, mandibular nerve )Fig. 12.26 Opening the foramen ovale.The foramen ovale should be opened so that V3 can be translocated anteriorly without kinking the nerve. The tip of the petrous bone lies under the Gasserian ganglion. Compare with Fig. 12.27. (FO, foramen ovale; GG, gasserian ganglion; GSPN, greater superficial petrosal nerve; MMA, middle meningeal artery; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve )Fig. 12.27 (Step 5) Opening the foramen ovale.The foramen ovale is unroofed using a diamond drill. The drill is constantly cooled to avoid heat injury to the mandibular nerve. Opening the foramen ovale allows the mandibular nerve to be mobilized anteriorly to expose the tip of the petrous bone. (GG, gasserian ganglion; GSPN, greater superficial petrosal nerve; MMA, middle meningeal artery; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve )Fig. 12.28 Exposing the eustachian tube.Drilling through the bone posterior to the foramen ovale and medial to the foramen spinosum results in the exposure of the cartigenous portion of the eustachian tube. This is not done in a standard approach. The eustachian tube can be viewed as running deep to the tensor tympani muscle and lateral to the carotid artery. If the eustachian tube is opened at the time of surgery, it must be closed to avoid a CSF leak. If the eustachian tube is closed, the patient’s tympanic membrane may need to be opened to drain the middle ear and mastoid sinus. (ET (C), cartilaginous part of the eustachian tube; GG, gasserian ganglion; GSPN, greater superficial petrosal nerve; V3, mandibular nerve )Fig. 12.29 Anterior Translocation of the mandibular nerve and gasserian ganglion.Anterior translocation of the freed mandibular nerve allows the petrous tip and the trigeminal impression (Meckel’s cave) to be exposed. Two spatulas are usually used to expose the anterior petrous bone. One is wedged under the petrous ridge. The other holds the anteriorly translocated trigeminal nerve. (1st R, first ridge of the petrous bone; 2nd R, second ridge of the petrous bone; AE, arcuate eminence; GSPN, greater superficial petrosal nerve; MMA, middle meningeal artery; Rbd, rhomboid; TI, trigeminal impression; V3, mandibular nerve )Fig. 12.30 (Step 6) Drilling in the rhomboid space.Drilling along the petrous ridge between the arcuate eminence and the mandibular nerve will expose the dura lining the porus acousticus. It is safest to expose the internal auditory canal medially away from the cochlea and the superior semicircular canal. (AE, arcuate eminence; Co, cochlea; GSPN, greater superficial petrosal nerve; MMA, middle meningeal artery; V3, mandibular nerve )Fig. 12.31 Skeletonizing the internal auditory canal.The internal auditory canal (IAC) is found by bisecting the angle between the greater superficial petrosal nerve and the arcuate eminence. The cortex and the cancellous bone over the rhomboid are removed. Laterally the internal carotid artery is found inferior to the greater superficial petrosal nerve. The hard bone surrounding the cochlea is found medial to the gena of the carotid artery. The IAC is most extensively drilled at the meatus where it can be exposed 270 degrees circumferentially. As we drill laterally the bony opening must lie directly over the IAC as the semicircular canal lays posterior and the cochlea lies anterior to the IAC. (AE, arcuate eminence; C6, C6 portion of the internal carotid artery; Co, cochlea; GSPN, greater superficial petrosal nerve; IAC, internal auditory canal; MMA, middle meningeal artery; V3, mandibular nerve Fig. 12.32 Exposing the posterior fossa dura and inferior petrosal sinus.Drilling anterior to the internal auditory canal will expose the posterior fossa dura up to the inferior petrosal sinus. The inferior petrosal sinus marks the junction of the petrous bone and the clivus. Medially the abducens nerve passes through the inferior petrosal sinus into Dorello’s tube. The cochlea lies 5 mm medial to the geniculate ganglion, 9 mm medial to the malleus head, and 1â2 mm medial to the genu of the internal carotid artery at the boundary between the vertical C7 and horizontal C6 portion of the artery. Because no defined bony landmarks identify the cochlea, the surgeon should imagine its location based on the surrounding structures. An average length of the bony canal that contains the GSPN from the geniculate ganglion to the facial hiatus is approximately 9 mm. (AE, arcuate eminence; C6, C6 portion of the internal carotid artery; Co, cochlea; ET (C), cartilaginous part of the eustachian tube; GSPN, greater superficial petrosal nerve; IAC, internal auditory canal; IPS, inferior petrosal sinus; PD, posterior fossa dura; V3, mandibular nerve )Fig. 12.33 Exposing the petrous tip.The tip of the petrous bone (T) lies under the gasserian ganglion. Anterior translocation of the mandibular nerve is necessary to expose the petrous apex. (AE, arcuate eminence; C6, C6 portion of the internal carotid artery; Co, cochlea; GSPN, greater superficial petrosal nerve; MMA, middle meningeal artery; PD, posterior fossa dura; T, tip of the petrous bone; V3, mandibular nerve )Fig. 12.34 Removing the petrous tip.The tip of the petrous bone is hard to remove because the petroclival and petrosphenoidal ligaments hold it firmly in place. Similar to removing the tip of the anterior clinoid, the tip is drilled until it is a small sliver of bone that can be stripped from its ligamentous attachments. (C6, C6 portion of the internal carotid artery; GG, gasserian ganglion; GSPN, greater superficial petrosal nerve; PD, posterior fossa dura; T, tip of the petrous bone; V3, mandibular nerve )Fig. 12.35 Complete removal of the rhomboid.The greater superficial petrosal nerve (GSPN) lies over the horizontal C6 portion of the internal carotid artery (C6 ICA). Retraction of the GSPN can damage the facial nerve. If the GSPN cannot be easily preserved, it should be cut. Drilling under the GSPN will expose the C6 ICA. The eustachian tube lies lateral to the C6 ICA. (AE, arcuate eminence; C6, C6 portion of the internal carotid artery; Co, cochlea; GSPN, greater superficial petrosal nerve; IAC, internal auditory canal; IPS, inferior petrosal sinus; MMA, middle meningeal artery; PD, posterior fossa dura; V3, mandibular nerve Fig. 12.36 (Step 7) Identification of abducens nerve on floor of inferior petrosal sinus.The abducens nerve exits the posterior fossa passing through the inferior petrosal sinus (IPS). At the time of surgery, the IPS is opened and packed with absorbable hemostatic agent lateral to the nerve. The nerve is found on the floor of the IPS. (AE, arcuate eminence; C6, C6 portion of the internal carotid artery; Co, cochlea; GSPN, greater superficial petrosal nerve; IAC, internal auditory canal; IPS, inferior petrosal sinus; MMA, middle meningeal artery; PD, posterior fossa dura; V3, mandibular nerve ; VI, abducens nerve)Fig. 12.37 Identifying the fibrous membrane (Dorello’s tube) around abducens nerve.The abducens nerve is covered by the fibrous capsule (Dorello’s tube) inside the inferior petrosal sinus. (IAC, internal auditory canal; PD, posterior fossa dura; VI, abducens nerve)Fig. 12.38 Relationship between the abducens nerve on the floor of the inferior petrosal sinus and surrounding structures.An overview demonstrates the relationship between the abducens nerve and the surrounding structures. (AE, arcuate eminence; C6, C6 portion of the internal carotid artery; Co, cochlea; GSPN, greater superficial petrosal nerve; IAC, internal auditory canal; IPS, inferior petrosal sinus; MMA, middle meningeal artery; PD, posterior fossa dura; V3, mandibular nerve ; VI, abducens nerve)Fig. 12.39 Identifying the subarcuate artery.Looking posteriorly the relationship between the IAC, superior semicircular canal, and cochlea is demonstrated. The subarcuate artery is seen passing through the center of the superior semicircular canal. (AE, arcuate eminence; C6, C6 portion of the internal carotid artery; Co, cochlea; Gen, geniculate ganglion; GSPN, greater superficial petrosal nerve; IAC, internal auditory canal; SA, subarcuate artery)Fig. 12.40 (Step 8) Exposure of the fundus of internal auditory canal.The fundus of the internal auditory canal (IAC) is wedged between the superior semicircular canal (SSC) and the cochlea. When the surgeon drills the fundus of the canal, it is important to only drill directly above the nerves in the fundus or the cochlea or the SSC will be disrupted. The geniculate isthmus (dotted triangle) is defined by the ampulla of the SSC, the cochlea, and the geniculate ganglion. It lies lateral to the fundus of the IAC. (AmpS, ampulla of the superior semicircular canal; Co, cochlea; Gen, geniculate ganglion; GSPN, greater superficial petrosal nerve; IAC, internal auditory canal; L-VII, labyrinthine segment of the facial nerve; M-VII, meatal segment of the facial nerve; SA, subarcuate artery; SSC, superior semicircular canal; SV, superior vestibular nerve; T-VII, tympanic segment of the facial nerve)Fig. 12.41 Identifying Bill’s bar and the geniculate notch (Fukushima’s bar).The bony notch between the superior vestibular and facial nerve is Bill’s bar. Another bony notch lies between the labyrinthine segment and tympanic segment of the facial nerve, the geniculate notch (Fukushima’s bar). The tympanic segment of the facial nerve enters the fallopian canal. The greater superficial petrosal nerve is seen joining the facial nerve at the geniculate ganglion. (BB, Bill’s bar; Co, cochlea; FB, Fukushima’s bar [geniculate notch]; Gen, geniculate ganglion; GSPN, greater superficial petrosal nerve; IAC, internal auditory canal; L-VII, labyrinthine segment of the facial nerve; SSC, superior semicircular canal; SV, superior vestibular nerve; T-VII, tympanic segment of the facial nerve)Fig. 12.42 Identifying the deep petrosal nerve and greater superficial petrosal nerve.The greater superficial petrosal nerve (GSPN) is seen above and parallel to the internal carotid artery. The GSPN is seen to join the deep petrosal nerve to form the nerve of the vidian canal (vidian nerve) that innervates the pterygopalatine ganglion. The origin of the vidian canal is the anterior wall of the foramen lacerum. The GSPN carries sensory and preganglionic parasympathetic fibers from the facial nerve. The deep petrosal nerve (DPN) carries postganglionic sympathetic fibers that enter the skull along with the internal carotid artery. (C6, C6 portion of the internal carotid artery; Co, cochlea; DPN, deep petrosal nerve; Gen, geniculate ganglion; GSPN, greater superficial petrosal nerve; IAC, internal auditory canal; SA, subarcuate artery; SSC, superior semicircular canal; V3, mandibular nerve )Fig. 12.43 Overview at this stage.An overview of the extradural exposure obtained by the middle fossa rhomboid approach is demonstrated. (AE, arcuate eminence; C6, C6 portion of the internal carotid artery; Co, cochlea; GSPN, greater superficial petrosal nerve; IAC, internal auditory canal; IPS, inferior petrosal sinus; MMA, middle meningeal artery; V3, mandibular nerve ; VII, facial nerve)Fig. 12.44 Exposure of tympanic cavity.The tympanic cavity is usually not opened during the rhomboid approach. The dissection is continued to demonstrate the regional anatomy. The tympanic cavity is exposed by removing the tegmen tympani, which is the roof of the middle ear. (C6, C6 portion of the internal carotid artery; Co, cochlea; CP, cochleariform process; CT, chorda tympani; ET (B), bony part of the eustachian tube; GSPN, greater superficial petrosal nerve; IAC, internal auditory canal; LSC, lateral semicircular canal; M, malleus; MMA, middle meningeal artery; PD, posterior fossa dura; SSC, superior semicircular canal; SV, superior vestibular nerve; TTM, tensor tympanic muscle; T-VII, tympanic segment of the facial nerve)Fig. 12.45 Identifying the chorda tympani and eustachian tube.The chorda tympani enters the tympanum (middle ear) through the posterior wall of the tympanum. It passes medial to the malleus to leave the tympanum through a hole in the anterior wall of the middle ear. (C6, C6 portion of the internal carotid artery; Co, cochlea; CP, cochleariform process; CT, chorda tympani; ET (B), bony part of the eustachian tube; ET (C), cartilaginous part of the eustachian tube; GSPN, greater superficial petrosal nerve; I, incus; IAC, internal auditory canal; LSC, lateral semicircular canal; M, malleus; MMA, middle meningeal artery; SSC, superior semicircular canal; TMJ, temporomandibular joint; TTM, tensor tympanic muscle; T-VII, tympanic segment of the facial nerve; V3, mandibular nerve )Fig. 12.46 Relationship between the incus, malleus, and chorda tympani.The chorda tympani exits anteriorly passing through a canal in the petrotympanic fissure. (Co, cochlea; CP, cochleariform process; CT, chorda tympani; ET (B), bony part of the eustachian tube; Gen, geniculate ganglion; GSPN, greater superficial petrosal nerve; I, incus; IAC, internal auditory canal; LSC, lateral semicircular canal; M, malleus; SSC, superior semicircular canal; TMJ, temporomandibular joint; TTM, tensor tympanic muscle; T-VII, tympanic segment of the facial nerve)Fig. 12.47 Exposing the chorda tympani into the infratemporal fossa toward the lingual nerve (branch of posterior trunk of the mandibular nerve).The chorda tympani exits the cranium just medial to the spine of the sphenoid bone and joins with the lingual nerve, a branch of the posterior trunk of the mandibular nerve (V3), in the infratemporal fossa. The connection of the chorda tympani and the lingual nerve is shown in chapter 11 describing the anterior infratemporal fossa approach (Figs. 11.1â11.58 and 11.1â11.59). (CT, chorda tympani; ET (B), bony part of the eustachian tube; ET (C), cartilaginous part of the eustachian tube; ITF, infratemporal fossa; MMA, middle meningeal artery; TMJ, temporomandibular joint; TTM, tensor tympanic muscle; V3, mandibular nerve )Fig. 12.48 Identification of tensor tympani muscle.The tensor tympani muscle is seen to arise from the cartilaginous portion of the eustachian tube and the adjacent sphenoid bone. It passes above and medial to the eustachian tube before entering the tympanum. The tendon of the muscle turns approximately 90 degrees at the cochleariform process toward the manubrium of the malleus. (C6, C6 portion of the internal carotid artery; Co, cochlea; CP, cochleariform process; CT, chorda tympani; ET (B), bony part of the eustachian tube; ET (C), cartilaginous part of the eustachian tube; GSPN, greater superficial petrosal nerve; I, incus; IAC, internal auditory canal; LSC, lateral semicircular canal; M, malleus; MMA, middle meningeal artery; SSC, superior semicircular canal; TMJ, temporomandibular joint; TTM, tensor tympanic muscle; T-VII, tympanic segment of the facial nerve; V3, mandibular nerve )Fig. 12.49 Identifying the stapes and the tensor tympani tendon.The tensor tympani tendon makes a sharp turn at the cochleari-form process around the edge of the septum of the muscular canal and inserts into the manubrium of the malleus. (AmpS, ampulla of the superior semicircular canal; C7, C7 portion of the carotid artery; CP, cochleariform process; CT, chorda tympani; FB, Fukushima’s bar [geniculate notch]; Gen, geniculate ganglion; I, incus; LSC, lateral semicircular canal; MH, malleus head; MM, manibrium of the malleus; S, stapes; SSC, superior semicircular canal; SV, superior vestibular nerve; T-VII, tympanic segment of the facial nerve)Fig. 12.50 Exposing the vertical (mastoid) segment of the facial nerve.The facial nerve passes between the incus and the lateral semicircular canal and then is referred to the vertical segment of the facial nerve. (AmpS, ampulla of the superior semicircular canal; C7, C7 portion of the internal carotid artery; Co, cochlea; CT, chorda tympani; G, genu [second turn or external genu] of the facial nerve; Gen, geniculate ganglion; I, incus; IAC, internal auditory canal; LSC, lateral semicircular canal; L-VII, labyrinthine segment of the facial nerve; M, malleus; PSC, posterior semicircular canal; S, stapes; SSC, superior semicircular canal; SV, superior vestibular nerve; T-VII, tympanic segment of the facial nerve; V-VII, vertical segment of the facial nerve)Fig. 12.51 Exposing the main trunk of the facial nerve, the greater superficial petrosal nerve, and the chorda tympani.The relationship between the facial nerve, chorda tympani, and greater superficial petrosal nerve are demonstrated. (C6, C6 portion of the internal carotid artery; Co, cochlea; CT, chorda tympani; ET (B), bony part of the eustachian tube; ET (C), cartilaginous part of the eustachian tube; G, genu [second turn or external genu] of the facial nerve; Gen, geniculate ganglion; GSPN, greater superficial petrosal nerve; I, incus; IAC, internal auditory canal; ITF, infratemporal fossa; LSC, lateral semicircular canal; L-VII, labyrinthine segment of the facial nerve; M, malleus; M-VII, meatal segment of the facial nerve; PSC, posterior semicircular canal; SSC, superior semicircular canal; SV, superior vestibular nerve; TMJ, temporomandibular joint; TTM, tensor tympanic muscle; TVII, tympanic segment of the facial nerve; V3, mandibular nerve ; V-VII, vertical segment of the facial nerve)Fig. 12.52 Overview at this step.The anatomical relationship at this step of the dissection is shown. (C6, C6 portion of the internal carotid artery; Co, cochlea; CT, chorda tympani; ET (B), bony part of the eustachian tube; ET (C), cartilaginous part of the eustachian tube; GSPN, greater superficial petrosal nerve; I, incus; IAC, internal auditory canal; IPS, inferior petrosal sinus; LSC, lateral semicircular canal; M, malleus; PD, posterior fossa dura; SSC, superior semicircular canal; TMJ, temporomandibular joint; V3, mandibular nerve ; VI, abducens nerve; V-VII, vertical segment of the facial nerve)Fig. 12.53 Exposing the vertical C7 portion of internal carotid artery.The vertical C7 portion of the internal carotid artery is exposed by drilling through the eustachian tube. Knowledge of this relationship is helpful when performing a temporal bone resection for carcinoma of the middle ear. Drilling through the temporal bone from lateral to medial at the level of the posterior root of the zygoma, the carotid artery will lie medial to the eustachian tube. (C6, C6 portion of the carotid artery; C7, C7 portion of the internal carotid artery; Co, cochlea; orifice of ET, orifice of eustachian tube; ET (C), cartilaginous part of the eustachian tube; Gen, geniculate ganglion; I, incus; IAC, internal auditory canal; LSC, lateral semicircular canal; L-VII, labyrinthine segment of the facial nerve; M, malleus; SSC, superior semicircular canal; SV, superior vestibular nerve; TMJ, temporomandibular joint; T-VII, tympanic segment of the facial nerve; V3, mandibular nerve )Fig. 12.54 Exposing the vertical C7 portion of the internal carotid artery.A more anterior trajectory demonstrates the relationship of the genu of the internal carotid artery and the cochlea. The cochlea lies medial and very close to the artery. (AmpS, ampulla of the superior semicircular canal; C6, C6 portion of the carotid artery; C7, C7 portion of the internal carotid artery; Co, cochlea; orifice of ET, orifice of eustachian tube; ET (C), cartilaginous part of the eustachian tube; Gen, geniculate ganglion; I, incus; IAC, internal auditory canal; LSC, lateral semicircular canal; L-VII, labyrinthine segment of the facial nerve; M, malleus; SA, subarcuate artery; SSC, superior semicircular canal; SV, superior vestibular nerve; TMJ, temporomandibular joint; T-VII, tympanic segment of the facial nerve; V3, mandibular nerve )Fig. 12.55 (Step 9) Inferior translocation of internal carotid artery.The mid-clivus can be exposed more extensively by the anterior translocation of the carotid artery. (C6, C6 portion of the carotid artery; C7, C7 portion of the internal carotid artery; CL, clivus; Co, cochlea; Gen, geniculate ganglion; GG, gasserian ganglion; IAC, internal auditory canal; L-VII, labyrinthine segment of the facial nerve; SV, superior vestibular nerve; T-VII, tympanic segment of the facial nerve; V3, mandibular nerve )Fig. 12.56 (Step 10) Posterior fossa dural incision.The dura of the posterior fossa is incised in an inversed âTâ fashion. (C6, C6 portion of the carotid artery; Co, cochlea; IAC, internal auditory canal; VI, abducens nerve)Fig. 12.57 Dural opening of the internal auditory canal.When opening the dura surrounding the internal auditory canal (IAC), care must be taken not to injure the nerves within. In the surgeon’s mind the IAC is like a funnel. The fundus is shallow and the porus acousticus is deep, so the nerves are most likely to fall away from the dura at the meatus. (C7, C7 portion of the carotid artery; Co, cochlea; Gen, geniculate ganglion; LSC, lateral semicircular canal; L-VII, labyrinthine segment of the facial nerve; MVII, meatal segment of the facial nerve; SSC, superior semicircular canal; SV, superior vestibular nerve; T-VII, tympanic segment of the facial nerve)Fig. 12.58 (Step 11) Identification of intradural abducens nerve.The middle fossa rhomboid approach is ideal for viewing the anterolateral surface of the pons. The abducens nerve is demonstrated at the anterior margin of the intradural exposure. The nerve enters into the inferior petrosal sinus, penetrating the posterior fossa dura medial to the trigeminal nerve. The exit of the nerve into Dorello’s canal is often hidden by the anterior arachnoid of the prepontine cistern. (Po, pons; VI, abducens nerve)Fig. 12.59 Identifying the mid-basilar artery.The abducens nerve appears to cross the mid-portion of the basilar artery from the lateral view. (BA, basilar artery; Co, cochlea; Po, pons; VI, abducens nerve)Fig. 12.60 Identifying the lower basilar artery.By angling the microscope inferiorly the lower portion of the basilar artery can be seen. (BA, basilar artery; Co, cochlea; VI, abducens nerve)Fig. 12.61 Identifying the vertebrobasilar artery junction.By angling the microscope more inferiorly the vertebrobasilar artery junction can be seen. (BA, basilar artery; (Co, cochlea; VA, vertebral artery)Fig. 12.62 Identifying the posterior cerebral and superior cerebellar arteries.The middle fossa dura is opened by a linear incision parallel with the superior petrosal sinus. Above the tentorium cerebelli the surgeon is afforded a lateral view of the pons and the midbrain. The trochlear nerve, the posterior cerebral artery, and the superior cerebellar artery can be seen in the ambient cister. (IV, trochlear nerve; MB, midbrain; P1, P1 segment of the posterior cerebral artery; P2, P2 segment of the posterior cerebral artery; Pcom, posterior communicating artery; SCA, superior cerebellar artery; Tent, tentorium)Fig. 12.63 Identifying the oculomotor nerve.Tilting the microscope anteriorly affords the surgeon a view of the dorsum sellae and the proximal oculomotor nerve that runs between the superior cerebellar artery and the posterior cerebral artery. (III, oculomotor nerve; P1, P1 segment of the posterior cerebral artery; P2, P2 segment of the posterior cerebral artery; Pcom, posterior communicating artery; SCA, superior cerebellar artery; SPS, superior petrosal sinus; Tent, tentorium)Fig. 12.64 Cutting the tentorium and superior petrosal sinus.In most cases the exposure achieved with an anterior petrosectomy is enlarged by simultaneously opening the dura of the middle fossa. Usually the posterior and middle fossa opening are connecting by ligating the superior petrosal sinus. The superior petrosal sinus is ligated between two silk sutures that occlude the sinus. (SPS, superior petrosal sinus; Tent, tentorium)Fig. 12.65 Identifying the trochlear nerve.The trochlear nerve is seen running into the caudal surface of a free margin of the tentorium cerebelli. (IV, trochlear nerve; Tent, tentorium)Fig. 12.66 Opening the tentorial tunnel of the trochlear nerve.The superficial tentorium cerebelli is obliquely cut approximately 10 mm over the trochlear nerve. This exposes the extracavernous portion of the nerve that runs through a tunnel within the tentorium. (IV, trochlear nerve; Tent, tentorium)Fig. 12.67 Second tentorial incision toward the trigeminal fibrous ring.The fibrous ring around the trigeminal nerve is opened. The tentorium is cut from the fibrous ring surrounding the trigeminal nerve to the dural incision made over the trochlear nerve. Opening the trigeminal fibrous ring frees the trigeminal nerve from the dura. The incision in the tentorium is usually made from lateral to medial to facilitate the coagulation of venous channels and tentorial arteries. (TFR, trigeminal fibrous ring)Fig. 12.68 Identifying the superior petrosal sinus.The superior petrosal sinus is often ligated with 4-0 silk sutures before the tentorium is cut. In this dissection it was left intact to demonstrate its relationship to the surrounding structures. (IV, trochlear nerve; P2, P2 segment of the posterior cerebral artery; SCA, superior cerebellar artery; SPS, superior petrosal sinus)Fig. 12.69 Packing oxidized cellulose into the superior petrosal sinus.Venous bleeding can be controlled by packing oxidized cellulose into the superior petrosal sinus or posterior cavernous sinus, or both. (IV, trochlear nerve; P2, P2 segment of the posterior cerebral artery; SCA, superior cerebellar artery)Fig. 12.70 Complete tentorial division.The tentorium cerebelli is completely divided. The arrow demonstrates the entrance into the posterior cavernous sinus. This posterior cut will deprive a meningioma of feeding arteries coming from the intracavernous carotid artery and passing through the tentorium. (GG, gasserian ganglion; IV, trochlear nerve; P2, P2 segment of the posterior cerebral artery; SCA, superior cerebellar artery; V, trigeminal nerve)Fig. 12.71 Tacking the tentorial edge.To expand the surgical field, the edge of the tentorium cerebelli should be tacked up posteriorly. (GG, gasserian ganglion; IV, trochlear nerve; P2, P2 segment of the posterior cerebral artery; Po, pons; SCA, superior cerebellar artery; V, trigeminal nerve)Fig. 12.72 Exposing the trigeminal nerve.The opening between the middle and posterior fossa is enlarged by opening the trigeminal fibrous ring that marks the entrance at the trigeminal nerve into Meckel’s cave. (GG, gasserian ganglion; IV, trochlear nerve; MB, midbrain; Po, pons; SCA, superior cerebellar artery; V, trigeminal nerve; V3, mandibular nerve )Fig. 12.73 Identifying the motor root of the trigeminal nerve.The motor root of the trigeminal nerve runs along the medial edge of the nerve as the nerve emerges from the pons. (GG, gasserian ganglion; IV, trochlear nerve; M-V, motor root of the trigeminal nerve; SCA, superior cerebellar artery; S-V, sensory root of the trigeminal nerve; V3, mandibular nerve )Fig. 12.74 Identifying the abducens nerve under the trigeminal nerve.After the tentorium is divided, the abducens nerve can be seen under the root of the trigeminal nerve. (Po, pons; SCA, superior cerebellar artery; V, trigeminal nerve; VI, abducens nerve; V3, mandibular nerve )Fig. 12.75 Identifying the basilar artery.The exposure affords the surgeon a view of the middle and lower portions of the basilar artery, the lateral pons, the trigeminal nerve, and the abducens nerve. (BA, basilar artery; C6, C6 portion of the internal carotid artery; Co, cochlea; Po, pons; V, trigeminal nerve; VI, abducens nerve)Fig. 12.76 Identifying the oculomotor nerve, the posterior cerebral artery, and the superior cerebellar artery.Superiorly we see the upper basilar artery, posterior cerebral artery, superior cerebellar artery, and oculomotor nerve. The anterolateral surface of the midbrain is also seen. (III, oculomotor nerve; IV, trochlear nerve; P1, P1 segment of the posterior cerebral artery; P2, P2 segment of the posterior cerebral artery; Pcom, posterior communicating artery; SCA, superior cerebellar artery)Fig. 12.77 Exposing the proximal oculomotor nerve by retracting the posterior cerebellar artery.The oculomotor nerve is demonstrated exiting the midbrain between the posterior cerebral artery and the superior cerebellar artery. (BA, basilar artery; III, oculomotor nerve; IV, trochlear nerve; SCA, superior cerebellar artery)Fig. 12.78 Exposing the upper portion of the basilar artery.The upper basilar artery and the thalamoperforating arteries are demonstrated. (BA, basilar artery; III, oculomotor nerve; IV, trochlear nerve; P1, P1 segment of the posterior cerebral artery; Pcom, posterior communicating artery; SCA, superior cerebellar artery; TPA, thalamoperforating arteries)Fig. 12.79 Identifying the oculomotor and trochlear nerves on opposite sides.Looking across the front of the midbrain, the oculomotor and trochlear nerves on the side contralateral to the exposure can be seen. (III, oculomotor nerve; IV, trochlear nerve; Pcom, posterior communicating artery)Fig. 12.80 Identifying the posterior communicating and anterior choroidal arteries.Tilting the microscope more anteriorly improves the surgeon’s view of the oculomotor nerve, the internal carotid artery, and the posterior communicating and anterior choroidal arteries. The optic nerve can be seen over the arteries. (AntCho, anterior choroidal artery; ICA, internal carotid artery; II, optic nerve; III, oculomotor nerve; Pcom, posterior communicating artery)Fig. 12.81 Exposing the optic chiasm.The inferior surface of the optic nerves and the optic chiasm are visible by retracting the posterior communicating and internal carotid arteries. (ICA, internal carotid artery; II, optic nerve; III, oculomotor nerve)Fig. 12.82 Exposing the internal carotid artery and oculomotor nerve on opposite sides.The internal carotid artery and the oculomotor nerve on the opposite sides can be seen. (ICA, internal carotid artery; III, oculomotor nerve; Pcom, posterior communicating artery; PCP, posterior clinoid process)Fig. 12.83 Exposing the eustachian tube to demonstrate the relevant anatomy.The lateral wall of the eustachian tube is opened to demonstrate its course. (C6, C6 portion of the internal carotid artery; Co, cochlea; CT, chorda tympani; ET (C), cartilaginous part of the eustachian tube; GSPN, greater superficial petrosal nerve; I, incus; IAC, internal auditory canal; LSC, lateral semicircular canal; M, malleus; SSC, superior semicircular canal; TMJ, temporomandibular joint; V3, mandibular nerve ; VII, facial nerve)Fig. 12.84 Opening the eustachian tube to demonstrate the relevant anatomy.The metal bar is passed inside the eustachian tube toward the nasopharynx. (C6, C6 portion of the internal carotid artery; Co, cochlea; CT, chorda tympani; GSPN, greater superficial petrosal nerve; I, incus; IAC, internal auditory canal; LSC, lateral semicircular canal; SSC, superior semicircular canal; TMJ, temporomandibular joint; V3, mandibular nerve ; VII, facial nerve)Fig. 12.85 Opening the cochlea, semicircular canals, and vestibule to demonstrate the relevant anatomy.The dissector is put inside the basal turn of the cochlea. The middle turn lies right under the geniculate ganglion. (BT, basal turn of the cochlea; C7, C7 portion of the internal carotid artery; CT, chorda tympani; ET (C), cartilaginous part of the eustachian tube; I, incus; LSC, lateral semicircular canal; M, malleus; MT, middle turn of the cochlea; SSC, superior semicircular canal; TMJ, temporomandibular joint; T-VII, tympanic segment of the facial nerve; V3, mandibular nerve ; Ve, vestibule; V-VII, vertical segment of the facial nerve)Fig. 12.86 Opening the cochlea, semicircular canals, and vestibule to demonstrate the relevant anatomy.Magnified view of Fig. 12.85. (BT, basal turn of the cochlea; C7, C7 portion of the internal carotid artery; CT, chorda tympani; Gen, geniculate ganglion; I, incus; LSC, lateral semicircular canal; M, malleus; MT, middle turn of the cochlea; PSC, posterior semicircular canal; SSC, superior semicircular canal; TMJ, temporomandibular joint; T-VII, tympanic segment of the facial nerve; Ve, vestibule; V-VII, vertical segment of the facial nerve)Fig. 12.87 The promontory is shown indenting the middle ear to demonstrate the relevant anatomy.The promontory can be seen easily after the incus, the malleus, the stapes, and the chorda tympani are removed. (BT, basal turn of the cochlea; C7, C7 portion of the internal carotid artery; G, genu [second turn or external genu] of the facial nerve; Gen, geniculate ganglion; LSC, lateral semicircular canal; MT, middle turn of the cochlea; P, pons; PSC, posterior semicircular canal; SSC, superior semicircular canal; TMJ, temporomandibular joint; T-VII, tympanic segment of the facial nerve; Ve, vestibule; V-VII, vertical segment of the facial nerve)Fig. 12.88 The anatomical dissection demonstrates the relationship between the cochlea, the vestibule, and the semicircular canals.The relationship of the cochlea, the vestibule, and the semicircular canals are outlined in this picture. The relationship of the vestibule to the internal auditory canal (IAC) is relevant to the retrosigmoid and translabyrinth approaches. That relationship is nicely demonstrated in this dissection. (BT, basal turn of the cochlea; C7, C7 portion of the internal carotid artery; LSC, lateral semicircular canal; MT, middle turn of the cochlea; P, pons; SSC, superior semicircular canal; TMJ, temporomandibular joint; Ve, vestibule; VII, facial nerve)Fig. 12.89 The anatomical dissection demonstrates the relationship of the promontory (basilar turn of the cochlea) to the vestibule.The relationship of the vestibule, the promontory, and the cochlea can be easily understood from this dissection. The promontory is opened to demonstrate the relationship between the basal turn of the cochlea and the vestibule. (AT, apical turn of the cochlea; BT, basal turn of the cochlea; C7, C7 portion of the internal carotid artery; LSC, lateral semicircular canal; Mo, modiolus; MT, middle turn of the cochlea; SSC, superior semicircular canal; Ve, vestibule; VII, facial nerve)Fig. 12.90 The anatomical dissection demonstrates the relationship of the vestibule to the cochlea.The basal turn of the cochlea connects with the vestibule and is also very close to the internal carotid artery. (BT, basal turn of the cochlea; C7, C7 portion of the internal carotid artery; LSC, lateral semicircular canal; SSC, superior semicircular canal; Ve, vestibule)
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10 Anatomy for Lateral Skull Base Surgery
11 Preauricular Transzygomatic Approach to the Anterior Infratemporal Fossa and Middle Infratemporal Fossa
3 Transfacial Transmaxillary Approach
7 Orbital Approach
18 Anatomy for Posterior Skull Base Surgery
20 Lateral Suboccipital Approach: Superior, Middle, and Inferior Cerebellopontine Angle Approach
