The combined petrosal approach affords the surgeon a view of the petroclival region extending from the posterior cavernous sinus to the lower cranial nerves, and preserves the patient’s hearing. Preserving the cochlea and semicircular canals limits the surgeon’s access across the midline. The view of the anterior brainstem is at a steeper angle with the preservation of the neuro-otologic structures. This view affords an excellent view of unilateral extensive posterior fossa lesions without significant retraction of the cerebellum. The amount of bone resected is customized for each case. This procedure is useful for approaching petroclival meningiomas, giant and partially thrombosed basilar artery aneurysms, chordomas, and chondrosarcomas.
This approach affords the surgeon a lateral view of the posterior fossa and preserves hearing. A key part of this procedure is the removal of the operculum of the temporal bone medial to the posterior and superior semicircular canals.
Step 12. Identification of the cranial nerves and arteries and opening of the Meckel’s cave (Fig. 15.35)
Illustrated Steps with Commentary
Fig. 15.1 Positioning the patient.The patient is put in a lateral position. A lumbar drain is placed. The pelvis is tilted posteriorly to facilitate the harvesting of abdominal fat and fascia. The neck is laterally flexed so the vertex is positioned closer to the opposite shoulder. The mastoid tip and zygomatic arch are identi ed. (MT, mastoid tip; Zy, zygoma)Fig. 15.2 (Step 1) Incising the scalp.A modifled “U” shaped incision is made around the ear. The incision starts over the zygomatic root 10 mm anterior to the tragus and travels superiorly behind the hairline for 6-7 cm. It continues posteriorly parallel to the temporal line and turns inferiorly to pass through a point 2-2.5 cm dorsal to the asterion (asterisk). The incision terminates just below the level of the mastoid tip. (As, asterion; MT, mastoid tip; Zy, zygoma)Fig. 15.3 “C” or “L” shaped skin incision (can be used if a less anterior exposure is needed).A “C” or “L” shaped skin incision is used for tumors in the posterior cavernous sinus or dumbbell shaped tumors that reside mostly in the posterior fossa. This skin incision is useful when a second stage frontotemporal craniotomy is planned. (MT, mastoid tip; Zy, zygoma)Fig. 15.4 (Step 2) Elevating the flap in two layers.The skin ap is raised with the galea and parietotemporal fascia. When the patient’s pericranium is thin, the subgaleal loose areolar tissue is left attached to the pericranium to add to the thickness of the vascularized pericranial ap. (DTF, deep temporal fascia; PC, pericranium; SCM, sternocleidomastoid muscle)Fig. 15.5 Enlarging the pericranial flap.The galeal layer should be separated from the pericranium along the periphery of the flap to enlarge the size of the pericranial graft. (DTF, deep temporal fascia; PC, pericranium; SCM, sterno-cleidomastoid muscle)Fig. 15.6 Elevating the myofascial pericranial flap.To provide vascularized tissue to ll the cranial defect and to protect against infection postoperatively, the deep temporal fascia, the pericranium, and the upper part of the sternocleidomastoid muscle should be harvested in a “U” shape fashion, maintaining a wide vascularized pedicle. (DTF, deep temporal fascia; PC, pericranium)Fig. 15.7 Reflecting the vascularized myofascial pericranial flap.The vascularized pericranial flap has a wide pedicle. (SpM, splenius capitis muscle; TM, tympanic membrane)Fig. 15.8 Elevating the temporalis muscle.The temporalis muscle is retracted anteriorly exposing the squamosal portion of the temporal bone, the root of the zygomatic arch, and the pterion. The zygomatic process of the frontal bone does not need to be exposed in this approach. The splenius capitis muscle comes into view when the sternocleidomastoid muscle is partially removed with the myofascial pericranial flap. (EAC, external auditory canal; P, parietal bone; SpM, splenius capitis muscle; Sq, squamosal suture)Fig. 15.9 Exposing the body of the mastoid and adjacent occipital bone by reflecting the posterior neck muscles.The splenius capitis, semispinalis capitis, and the upper part of the superior oblique muscles are reflected posteriorly to expose the body of the mastoid and the lateral occipital bone. A monopolar coagulator should be used to separate the posterior neck muscles from the occipital bone. (EAC, external auditory canal; MEV, mastoid emissary brain; O, occipital bone; P, parietal bone; Sq, squamosal suture)Fig. 15.10 (Step 3) Performing a super cial mastoidectomy.A cosmetic mastoidectomy in which the cortical bone overlying the mastoid is removed along with the craniotomy flap is an option. This option has a greater risk of injuring the sigmoid sinus. The cosmetic defect produced by a standard mastoidectomy can be hidden with a titanium plate. The thin shell of bone that is left covering the sigmoid sinus after a standard piecemeal super cial mastoidectomy should be carefully removed. The free sinus can be compressed posteriorly to improve the surgeon’s view of the posterior fossa. (JB, jugular bulb; MEV, mastoid emissary brain; SCs, semicircular canals; SS, sphenoid sinus)Fig. 15.11 Operculum medial to the posterior semicircular canal.The bone that lies medial to the posterior semicircular canal limits the surgeon’s view of the posterior fossa. This is referred to as the operculum (arrowheads) and should be thinned to improve the exposure. The sharp bone notch that lies between the inferoanterior border of the sigmoid sinus and the posterior border of the jugular bulb should be thinned, but if stuck should not be removed. The surgeon may encounter remarkable bleeding from tears in the wall of the sinus adjacent to this bone’s ridge. (JB, jugular bulb; LSC, lateral semicircular canal; PSC, posterior semicircular canal; SS, sphenoid sinus; SSC, superior semicircular canal; V-VII, vertical segment of the facial nerve)Fig. 15.12 Drilling the operculum.The operculum can be removed medial to the yellow bone of the posterior semicircular canal with an extra coarse diamond drill under a constant stream of irrigation. The endolymphatic sac is cut to free the posterior fossa dura from the posterior semicircular canal. The mastoidectomy exposes the posterior fossa dura inferior to the posterior semicircular canal, extending down to the jugular bulb. (JB, jugular bulb; LSC, lateral semicircular canal; PSC, posterior semicircular canal; SS, sphenoid sinus; SSC, superior semicircular canal; V-VII, vertical segment of the facial nerve)Fig. 15.13 (Step 4) Drilling a groove in the inferior temporal bone.After the mastoidectomy is complete, a groove (arrowheads) is drilled along the floor of the middle fossa in line with the root of the zygoma using a 4 mm diamond bur. This helps to minimize bone loss when turning a craniotomy. This groove is extended superiorly along the temporalis muscle to the pterion. After a groove is made in the bone, bone wax is inserted between the bone and the dura. This will protect the dura during drilling of the overlying bone.Fig. 15.14 (Step 5) Drilling a suboccipital groove.It is difficult to use a craniotome at the base of the skull. Drilling a groove (arrowheads) along the under surface of the occipital bone maximizes the size of the suboccipital bone ap. A 4 mm diamond bur is used to “eggshell” the bone over the dura. This thin shell of bone is removed with a small bone curette.Fig. 15.15 Creating bur holes.At least two bur holes should be made with a 4 mm diamond bur. One is made 1-1.5 cm above the highest point of the squamosal suture. The other is made 2 cm behind the asterion over the transverse sinus to avoid injury to the sinus during the craniotomy. If the dura is tightly adherent to the bone, additional holes should be made, and the dura is separated from the bone between the bur holes.Fig. 15.16 (Step 6) Cutting the craniotomy.A craniotome is used to connect the ends of the subtemporal and suboccipital grooves and the bur holes. The occipital side of the bone ap is short and the temporoparietal side is long.Fig. 15.17 Exposing the dura.A craniotomy is turned with caution to avoid injury to the dural and venous sinuses. To control the dural venous bleeding the surgeon coagulates the dura through an overlying layer of absorbable hemostatic agent. Epidural venous bleeding from the dural edges is controlled by placing absorbable hemostatic agent under dural tacking sutures. (SCs, semicircular canals; SS, sphenoid sinus; TS, transverse sinus)Fig. 15.18 Placing self-retaining retractors.Two self-retaining retractors are used to expose the petrous apex. (SCs, semicircular canals; SS, sphenoid sinus; TS, transverse sinus)Fig. 15.19 (Step 7) Removal of irregularities in the bony floor of the middle fossa.The bony protrusions (arrowheads) from the floor of the middle fossa that impede the surgeon’s line of sight are removed. (EAC, external auditory canal; SCs, semicircular canals)Fig. 15.20 Drilling the inner plate of the middle fossa.The bulging of the temporomandibular joint (arrowheads) into the operative fleld should not be drilled to avoid the postoperative ankylosis of this joint. Similarly, care should be taken not to enter the middle ear through the tegmen tympani or open the superior semicircular canal. The two retractors are just posterior to the mid-subtemporal ridge. (EAC, external auditory canal; SCs, semicircular canals)Fig. 15.21 (Step 8) Identification of middle fossa rhomboid.The rhomboid is defined by the medial edge of the petrous bone, posterior edge of the third division of the trigeminal nerve, the eminentia arcuata (superior semicircular canal), and the greater superficial petrosal nerve. The superior semicircular canal has already been identifled through the mastoidectomy. The dura propria is separated from the maxillary nerve and the mandibular nerve to expose the fibrous ring through which the trigeminal nerve enters the posterior fossa. The foramen ovale does not need to be opened to translocate the mandibular nerve anteriorly with the combined petrosectomy approach. The fibrous ring around the trigeminal nerve and the tentorial attachment of Meckel’s cave is opened to allow the surgeon to shift the mandibular nerve anteriorly without opening the foramen ovale. (GSPN, greater superficial petrosal nerve; LSC, lateral semicircular canal; PE, petrosal edge; SSC, superior semicircular canal; V3, mandibular nerve )Fig. 15.22 Drilling the rhomboid portion of the petrous bone.The rhomboid portion of the petrous bone is removed as demonstrated in chapter 12. The middle meningeal artery is coagulated and cut. Absorbable hemostatic fiber is packed into the foramen spinosum as added protection against bleeding from the middle meningeal artery. (Co, cochlea; GSPN, greater superficial petrosal nerve; IAC, internal auditory canal; LSC, lateral semicircular canal; MMA, middle meningeal artery; PSC, posterior semicircular canal; SSC, superior semicircular canal; T-VII, tympanic segment of the facial nerve; V3, mandibular nerve )Fig. 15.23 Exposing the presigmoid and basal temporal dura.Two self-retaining retractors are used to support the dura. One retractor supports the infratemporal dura and a second supports the presigmoid dura.Fig. 15.24 (Step 9) Dural incision at the base of the middle fossa.An incision is made parallel and just lateral to the tentorium (arrowheads). The dural . ap protects the temporal lobe. A careful search is made for veins that drain the lateral and inferior temporal lobe and enter the sigmoid sinus. These veins are carefully protected. The veins may be adherent to the dura before they enter the sinus. (JB, jugular bulb; SCs, semicircular canals; SS, sphenoid sinus; TS, transverse sinus)Fig. 15.25 Exposing the inferior temporal lobe.Once the dura is incised (arrowheads) the inferior temporal lobe is exposed. (JB, jugular bulb; SCs, semicircular canals; SS, sphenoid sinus)Fig. 15.26 Incising the presigmoid dura.The presigmoid posterior fossa dura is incised between the endolymphatic sac and the sigmoid sinus (arrowheads). This provides a substantial dural flap that will aid in the postoperative dural closure. By opening the dura in this fashion the endolymphatic sac is preserved. The literature is unclear as to the bene ts of preserving the sac. (SCs, semicircular canals; SS, sphenoid sinus)Fig. 15.27 Identifying the tentorium and the superior petrosal sinus.In most cases the exposure obtained with an anterior petrosectomy is enlarged by simultaneously opening the tentorium, which constitutes the posterior floor of the middle fossa. Usually the posterior and middle fossa openings are connected by ligating the superior petrosal sinus. (SPS, superior petrosal sinus; TE, tentorial edge)Fig. 15.28 Identifying the trochlear nerve.The trochlear nerve pierces the inferior surface of a free margin of the tentorium cerebelli. (IV, trochlear nerve; TE, tentorial edge)Fig. 15.29 Incising the tentorium along the trochlear nerve.The tentorium cerebelli is obliquely cut about 10 mm along the trochlear nerve to expose the extracavernous portion of the nerve. (IV, trochlear nerve; TE, tentorial edge)Fig. 15.30 Incising the tentorium toward the trigeminal fibrous ring.The tentorial incision is extended laterally to reach the trigeminal fibrous ring. Opening the trigeminal fibrous ring allows for maximal exposure of the trigeminal nerve and frees the nerve completely. (IV, trochlear nerve; TE, tentorial edge)Fig. 15.31 Identifying the superior petrosal sinus.Opening the superior petrosal sinus causes profuse bleeding. (IV, trochlear nerve; PCA, posterior cerebral artery; SCA, superior cerebellar artery; SPS, superior petrosal sinus; TE, tentorial edge)Fig. 15.32 Controlling bleeding from the superior petrosal sinus.Venous bleeding from the superior petrosal sinus is controlled by packing absorbable hemostatic fibers into the sinus or the posterior cavernous sinus, or both. (IV, trochlear nerve; PCA, posterior cerebral artery; SCA, superior cerebellar artery; TE, tentorial edge)Fig. 15.33 (Step 10) Completing the tentorial division.The superior petrosal sinus is ligated, coagulated, and cut. A 4-0 suture passes around the tentorium and through the presigmoid posterior fossa dura to ligate the superior petrosal sinus. The stitch is passed around the sinus twice to secure ligation of the venous sinus. The tentorium cerebelli is completely divided. An arrow demonstrates an entrance of the posterior cavernous sinus. In the case of petroclival or petrotentorial meningioma, this technique of detaching the posterior cavernous sinus results in the ligation of the feeding arteries from the internal carotid artery to the tumor. (IV, trochlear nerve; LSC, lateral semicircular canal; PCA, posterior cerebral artery; Po, pons; SCA, superior cerebellar artery; SSC, superior semicircular canal; TE, tentorial edge; V, trigeminal nerve)Fig. 15.34 (Step 11) Tacking up the tentorial edge.The cut edge of the tentorium cerebelli is sutured posteriorly to expand the surgical fleld. (IV, trochlear nerve; LSC, lateral semicircular canal; PCA, posterior cerebral artery; Po, pons; SCA, superior cerebellar artery; SSC, superior semicircular canal; V, trigeminal nerve)Fig. 15.35 (Step 12) Identification of fourth and fifth cranial nerves.After incising the arachnoid of the lateral potomesencephalic cistern, the trochlear nerve and the trigeminal nerve root are freed. (IV, trochlear nerve; SCA, superior cerebellar artery; Vm, motor division of the trigeminal nerve; Vs, sensory division of the trigeminal nerve)Fig. 15.36 Identifying cranial nerves VII, VIII, IX, X, XI, and XII.Incising the arachnoid of the lateral pontine and medullary cistern frees the facial, cochlear, and lower cranial nerves along with the vertebral artery and the anterior inferior cerebellar artery. (AICA, anterior inferior cerebellar artery; IX, glossopharyngeal nerve; VII, facial nerve; VIII, cochlear nerve; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)Fig. 15.37 Identifying cranial nerve XII.When the microscope is angled inferiorly, the hypoglossal nerves can be seen behind the vagus nerve rootlets. (AICA, anterior inferior cerebellar artery; IX, glossopharyngeal nerve; VII, facial nerve; VIII, cochlear nerve; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)Fig. 15.38 Opening Meckel’s cave and cutting the trigeminal fibrous ring (posterior cavernous detachment).The tentorium is removed from the roof of Meckel’s cave to expose the trigeminal nerve root and gasserian ganglion. Bleeding from the superior petrosal sinus and veins within the roof of Meckel’s cave is controlled with absorbable hemostatic fibers and sutures. The petrosal vein cannot be preserved. The cautery is used sparingly to minimize the risk of postoperative dysesthesias in the trigeminal distribution. The trochlear nerve should be freed from its canal within the tentorium to maximize the resection of a meningioma. The canal can be opened approximately 1 cm. An incision between the fibrous ring of the trigeminal nerve and the posterior edge of the freed trochlear nerve will remove additional tumor filtrated into the tentorium. Extending the trochlear canal opening more than 1 cm risks considerable venous bleeding. From our experience the risks of following the tumor into the cavernous sinus outweigh the benefits. (GG, gasserian ganglion; IV, trochlear nerve; LSC, lateral semicircular canal; SSC, superior semicircular canal; Vm, motor division of the trigeminal nerve; Vs, sensory division of the trigeminal nerve)Fig. 15.39 Following the course of the trigeminal nerve.After Meckel’s cave is opened the tentorium is resected. The trigeminal nerve can be followed from the gasserian ganglion to its entrance into the pons. The motor division of the trigeminal nerve (arrowheads) runs along the medial border of the sensory nerve root. (GG, gasserian ganglion; IV, trochlear nerve; LSC, lateral semicircular canal; SSC, superior semicircular canal; VII, facial nerve; VIII, cochlear nerve; Vm, motor division of the trigeminal nerve; Vs, sensory division of the trigeminal nerve)Fig. 15.40 Finding cranial nerve VI.The distal end of abducens nerve may be buried in a meningioma arising from the nerve’s entrance into Dorello’s canal. It is usually easiest to find the abducens nerve on the underside of the pons close to the branching of anterior inferior cerebellar artery from the basilar artery. (GG, gasserian ganglion; LSC, lateral semicircular canal; SSC, superior semicircular canal; VI, abducens nerve; Vm, motor division of the trigeminal nerve; Vs, sensory division of the trigeminal nerve)Fig. 15.41 Following cranial nerve IV.The trochlear nerve enters into the tentorium medial to Meckel’s cave. The trochlear nerve will continue in the lateral wall of the cavernous sinus passing over the oculomotor nerve. (III, oculomotor nerve; IV, trochlear nerve)Fig. 15.42 Finding cranial nerve III.The oculomotor nerve can be seen passing between the superior cerebellar artery and the P1 segment of the posterior cerebral artery. (BA, basilar artery; III, oculomotor nerve; IV, trochlear nerve)Fig. 15.43 Viewing the olfactory nerve.The olfactory nerve is seen on the undersurface of the frontal lobe. (AntChol, anterior choroidal artery; I, incus; ICA, internal carotid artery; II, optic nerve; Pcom, posterior communicating artery; St, stalk)Fig. 15.44 Identifying the internal carotid artery.The internal carotid, anterior choroidal, and posterior communicating arteries and the perforators can be seen easily with minimal retraction of the temporal lobe. (AntChol, anterior choroidal artery; BA, basilar artery; I, incus; ICA, internal carotid artery; II, optic nerve; III, oculomotor nerve; Pcom, posterior communicating artery; St, stalk)Fig. 15.45 Viewing the optic nerve and pituitary stalk.The caudal optic nerve contiguous with the optic tract and the stalk to the pituitary gland entering the diaphragm sellae just anterior to the dorsum sellae can be seen well. (AntChol, anterior choroidal artery; BA, basilar artery; ICA, internal carotid artery; II, optic nerve; Pcom, posterior communicating artery; St, stalk)Fig. 15.46 Identifying the superior cerebellar and posterior cerebral arteries.In the lateral pontomesencephalic and premesencephalic cistern, the upper portion of the basilar artery and the superior cerebellar and posterior cerebral arteries can be identifled. The oculomotor nerve can be followed into its tentorial canal for a distance of 6-7 mm. The tentorium can be cut between the liberated third and fourth nerves to further detach the tumor from the posterior cavernous sinus. (BA, basilar artery; GG, gasserian ganglion; III, oculomotor nerve; IV, trochlear nerve; MB, midbrain; P2, P2 segment of the posterior cerebral artery; Pcom, posterior communicating artery; Po, pons; SCA, superior cerebellar artery; V, trigeminal nerve)Fig. 15.47 Viewing the basilar tip and P1 segment of the posterior cerebral artery.The basilar tip and the hypoplastic P1 segment can be identifled under the temporal lobe. (BA, basilar artery; III, oculomotor nerve; P1, P1 segment of the posterior cerebral artery; P2, P2 segment of the posterior cerebral artery)Fig. 15.48 Viewing the mesencephalon and pons.The upper portion of the brainstem can be seen from an anteromedial trajectory. Intramedullary cavernomas of the anterolateral pons are ideally exposed from this trajectory. (BA, basilar artery; III, oculomotor nerve; IV, trochlear nerve; MB, midbrain; P2, P2 segment of the posterior cerebral artery; SCA, superior cerebellar artery)Fig. 15.49 An overview of intradural structures seen by viewing over the petrous bone.Cranial nerves V through XII in the posterior fossa can be seen. By tipping the microscope the surgeon will see completely different perspectives of the posterior fossa structures. (AICA, anterior inferior cerebellar artery; BA, basilar artery; GG, gasserian ganglion; IX, glossopharyngeal nerve; LSC, lateral semicircular canal; PSC, posterior semicircular canal; SSC, superior semicircular canal; VI, abducens nerve; VII, facial nerve; VIII, cochlear nerve; Vm, motor division of the trigeminal nerve; Vs, sensory division of the trigeminal nerve; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)Fig. 15.50 An overview of intradural exposure seen posteriorly by looking over the petrous bone.The cranial nerves within the posterior fossa can be seen. (AICA, anterior inferior cerebellar artery; BA, basilar artery; GG, gasserian ganglion; IV, trochlear nerve; IX, glossopharyngeal nerve; LSC, lateral semicircular canal; PSC, posterior semicircular canal; SCA, superior cerebellar artery; SSC, superior semicircular canal; VI, abducens nerve; VII, facial nerve; VIII, cochlear nerve; Vm, motor division of the trigeminal nerve; Vs, sensory division of the trigeminal nerve; X, vagus nerve)Fig. 15.51 An overview of intradural structures seen viewing anteriorly along the petrous bone.The trochlear, trigeminal, and abducens nerves can be identifled over the petrous bone. (GG, gasserian ganglion; IV, trochlear nerve; LSC, lateral semicircular canal; Po, pons; PSC, posterior semicircular canal; SSC, superior semicircular canal; V3, mandibular nerve ; VI, abducens nerve; Vm, motor division of the trigeminal nerve; Vs, sensory division of the trigeminal nerve)Fig. 15.52 Motor root of the trigeminal nerve from the subtemporal view.The motor root (arrowheads) of the trigeminal nerve can be identifled at the medial border of the nerve. The dura should be repaired by incorporating a fascial graft if an edge of dura under the temporal lobe is hard to find after the meningioma is removed. To obtain a reasonable dural closure, the graft is sewn along the lateral edge of the middle fossa dura. If there is no place to sew the graft along the base of the middle fossa, the graft is secured to the temporal bone with titanium plates and screws. It is not possible to get a perfectly watertight closure, as the trigeminal nerve must pass under the graft. The fascial closure is reinforced with a free fat graft. After the bone ap is secured, the mastoid area is covered with a triangular titanium plate. (GG, gasserian ganglion; IV, trochlear nerve; LSC, lateral semicircular canal; SCA, superior cerebellar artery; SSC, superior semicircular canal; V3, mandibular nerve ; Vm, motor division of the trigeminal nerve; Vs, sensory division of the trigeminal nerve)
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14 Transmastoid Approach: Retrolabyrinthine, Translabyrinthine, and Transcochlear Approaches
13 Anatomy for Posterolateral Skull Base Surgery
17 Total Petrosectomy with Partial Clivectomy
3 Transfacial Transmaxillary Approach
18 Anatomy for Posterior Skull Base Surgery
12 Middle Fossa Rhomboid Approach (Anterior Petrosectomy)
