The suboccipital craniotomy has been the “standard” approach to lesions within the posterior fossa. This remains an excellent approach to lesions of the cerebellum, posterior and lateral brainstem, and medial face of the petrous bone. In this chapter, we outline a refinement of the retrosigmoid approach. The retrosigmoid is divided into three zones each approached in a slightly different fashion. This refinement makes the surgery less invasive. These approaches can be employed to treat trigeminal neuralgia, hemifacial spasm, trigeminal schwannomas confined to the posterior fossa, vestibular schwannomas, intradural jugular foramen schwannomas and cerebellopontine angle meningiomas.
20.1 Superior Cerebellopontine Angle Approach for Trigeminal Neuralgia and Paratrigeminal Lesions
Step 6. Dissection around trigeminal nerve root (Fig. 20.15)
Step 7. Dislocation of offending artery (Fig. 20.17)
Illustrated Steps with Commentary
Fig. 20.1 (Step 1) Skin incision.An “S” shaped incision is made over the depression that lies behind the body of the mastoid. This depression in the bone is often visible and almost always palpable. The body of the mastoid and the projected inferior edge of the transverse sinus are mapped out on this photo as a dashed line. (EOP, external occipital protuberance; MT, mastoid tip)Fig. 20.2 Exposing the fibrous soft tissue under the skin.The superficial layer of fibrous tissue is split, leaving a small rim of tissue attached to the skin. This rim of tissue is crucial for anchoring sutures during the skin closure.Fig. 20.3 Harvesting the fibrous tissue graft.The superficial layer of fibrous tissue is circumscribed. It will be used to obtain a watertight dural closure at the end of the surgery.Fig. 20.4 Dissecting the fibrous tissue graft.The tissue is harvested as a contiguous graft with a sharp scalpel.Fig. 20.5 Cutting the sternocleidomastoid and splenius capitus muscles.The sternocleidomastoid is incised to expose the splenius capitus muscles.Fig. 20.6 Identifying the sutures.The asterion is a most important landmark. It usually lies over the inferior corner of the lateral and sigmoid sinus junction, although there is some variation. (As, asterion; Lam, lambdoid suture; OMS, occipitomastoid suture; PMS, parietomastoid suture)Fig. 20.7 (Step 2) Performing a craniectomy.A small craniectomy is made exposing the inferior one-third of the lateral sinus and the posterior one-third of the sigmoid sinus. (LS, lateral sinus; SS, sigmoid sinus)Fig. 20.8 (Step 3) Dural incision.An inversed “T” shaped dural incision is made to maximize exposure along the transverse and the sigmoid sinuses. (LS, lateral sinus; SS, sigmoid sinus)Fig. 20.9 Exposing the cerebellar surface.The dural opening will demonstrate the lateral corner of the cerebellar hemisphere. The supracerebellar cistern is opened and cerebrospinal fluid is patiently drained. Pressing on a tense cerebellum will lead to contusion, hemorrhage, and postoperative brain swelling.Fig. 20.10 Inspecting the tentorial surface for bridging veins.Bridging veins are rarely seen over the lateral portion of the cerebellar hemisphere, but the veins do not have an absolute predetermined pattern. Tearing an unexpected vein will obscure the operative eld with blood and can cause a venous infarction. (T, tentorium)Fig. 20.11 (Step 4) Exploration of the tentorial surface of the cerebellum.At first the surgeon explores the upper surface of the cerebellum to identify the trochlear nerve under the edge of the tentorial incisura. (IV, trochlear nerve; SCA, superior cerebellar artery; T, tentorium)Fig. 20.12 (Step 5) Identification of the petrosal veins.Looking laterally over the corner of the cerebellum, the surgeon should expose the petrosal veins entering the superior petrosal sinus. (PV, petrosal vein)Fig. 20.13 Exposing the petrosal veins.The arachnoid membrane that encases the petrosal veins is cut along the veins to release tension from the veins. An attempt should be made to preserve the veins; however, if the veins obstruct the surgeon’s view, a portion of the veins can usually be sacrificed. The entrance of the veins into the superior petrosal sinus can be reinforced with absorbable hemostatic agent and fibrin glue in cases where the veins are under some tension or when a small amount of hemorrhage occurs from the venous– sinus junction. (PV, petrosal vein)Fig. 20.14 Identifying the distal superior cerebellar artery.Loops of the superior cerebellar artery are seen to compress the trigeminal nerve. Generally the superior cerebellar artery has bifurcated before reaching the trigeminal nerve. (IV, trochlear nerve; PV, petrosal vein; SCA, superior cerebellar artery; V, trigeminal nerve)Fig. 20.15 (Step 6) Inspection of the trigeminal root.The superior petrosal vein is fed by a confluence of veins draining the petrosal and lateral tentorial surfaces of the cerebellum. Once freed of arachnoid, these veins usually become mobile enough to be retracted out of the surgeon’s line of sight. (IV, trochlear nerve; PV, petrosal vein; SCA, superior cerebellar artery; V, trigeminal nerve)Fig. 20.16 Inspecting the trigeminal nerve.The petrosal veins can usually be simply pushed aside when approaching the trigeminal nerve. If the petrosal vein is tethered anteriorly by a trigeminal vein, the trigeminal vein can be coagulated and cut. The offending artery found compressing the trigeminal nerve, a branch of the superior cerebellar artery, is translocated toward the tentorium to separate it from the nerve. Note the difference between Figs. 20.16 and 20.17. (IV, trochlear nerve; PV, petrosal vein; SCA, superior cerebellar artery; V, trigeminal nerve)Fig. 20.17 (Step 7) Translocation of superior cerebellar artery.A translocation of the superior cerebellar artery has been performed. The artery is displaced toward the tentorium. (PV, petrosal vein; SCA, superior cerebellar artery; V, trigeminal nerve)Fig. 20.18 Supporting the superior cerebellar artery with Tefion bers and brin glue.In surgery, the superior cerebellar artery is translocated toward the tentorium and is held in place with Teflon bers and brin glue. In this photo, oxidized cellulose was used to hold the artery in place. (PV, petrosal vein; V, trigeminal nerve)
20.2 Middle Cerebellopontine Angle Approach for Acoustic Nerve and Tumors
Step 6. Exposure of meatal segment of facial nerve (Fig. 20.51)
Illustrated Steps with Commentary
Fig. 20.19 (Step 1) Skin incision.The seventh and eighth cranial nerves are approached through a craniotomy centered on the mid-sigmoid sinus. Traditionally a “C” shaped incision is made in the skin, although an “S” shaped incision centered 0.5 cm behind the posterior border of the lower body of the mastoid will work. Because this exposure is most often made for tumors, the craniotomy will be larger. (EOP, external occipital protuberance; MT, mastoid tip)Fig. 20.20 Skin flap.The skin flap is raised along with a thin layer of brous tissue. Most of the brous tissue is left attached to the suboccipital muscles.Fig. 20.21 Dural graft.The remainder of the fibrous tissue is raised as a dural graft. This graft may include some of the covering of the sternocleidomastoid muscle.Fig. 20.22 Fibrous dural graft.The fibrous tissue graft allows the dura to be closed in a water-tight fashion with autologous tissue at the end of the case. (PAM, posterior auricular muscle; SCM, sternocleidomastoid muscle)Fig. 20.23 Raising the muscle flap.The muscle is raised as a ap. The initial cut through the splenius capitus and sternocleidomastoid reveals the deep fascia overlying the occipital artery. That artery is ligated and then the superior oblique muscle is cut. The full thickness muscle ap is re ected medially. (DG, digastric muscle; MEV, mastoid emissary vein)Fig. 20.24 Planning the craniotomy.The asterion usually is close to the inferior junction of the transverse and sigmoid sinuses. A prominent emissary vein is usually found 5 mm posterior to the sigmoid sinus. Although opening the bone just above the medial edge of the sigmoid sinus makes anatomical sense, adhesions between a thin-walled sinus and the bone makes this a dangerous practice. (As, asterion; DG, digastric muscle; Lam, lambdoid suture; MEV, mastoid emissary vein; OMS, occipitomastoid suture; PMS, parietomastoid suture)Fig. 20.25 (Step 2) Performing the craniotomy.The initial perforation of the skull is made through the asterion. It is enlarged until the transverse sinus is localized. (LS, lateral sinus)Fig. 20.26 Making a retrosigmoid groove.A groove is drilled in the bone adjacent to the sigmoid sinus. Especially in older patients, this groove should not be made over the medial edge of the sigmoid sinus, as the sinus may be torn when the bone flap is lifted. An incision just anterior to the exit of the emissary vein will put the surgeon a few millimeters behind the sigmoid sinus. The bone over the posterior edge of the sigmoid sinus can be removed with an extra coarse diamond drill. (LS, lateral sinus; SS, sigmoid sinus)Fig. 20.27 Making a suboccipital groove.Because it is difficult to use a craniotomy through the inferior occipital bone, it is easier to extend the retrosigmoid groove along the inferior limb of the craniotomy. (LS, lateral sinus; SS, sigmoid sinus)Fig. 20.28 Performing the craniotomy.If the bone is not absolutely stuck to the dura, the craniotomy can be completed with a craniotome. (LS, lateral sinus; SS, sigmoid sinus)Fig. 20.29 Exposing the dura.At the end of the craniotomy, additional bone may be removed to expose the inferior edge of the transverse sinus and the posterior edge of the sigmoid sinus. The anterior inferior edge of the craniotomy may be extended to give the surgeon better access to the medullary cistern. (LS, lateral sinus; SS, sigmoid sinus)Fig. 20.30 (Step 3) Opening the dura.If a lumbar drain has not been placed, an opening is made in the anterior inferior edge of the dura so that the medullary cistern can be opened. This affords a release of cerebrospinal fluid and lowers the pressure on the cerebellum. The dura is opened in a “C” shaped fashion. (LS, lateral sinus; SS, sigmoid sinus)Fig. 20.31 Opening the dura.Dural tenting sutures are placed adjacent to the sigmoid sinus to maximize the lateral exposure. If the dura is kept moist, it will contract less and make for an easier dural closure.Fig. 20.32 Retraction of the petrosal surface of the cerebellum.Cottonoid paddies or other protective pads are placed in a “V” over the petrosal surface of the cerebellum.Fig. 20.33 Exploring the petrosal surface of the temporal bone.If the surgeon is trying to preserve hearing, the cerebellar hemisphere is not retracted straight laterally as it is in this photo. In such cases the superior petrosal surface is first exposed.Fig. 20.34 (Step 4) Exploring the seventh and eighth nerve complexes.A large branch of anterior inferior cerebellar artery is seen below the seventh and eighth nerve complex. The seventh nerve originates ventral to the eighth nerve but then rotates rostrally to assume its position anterior to the superior vestibular nerve. (AICA, anterior inferior cerebellar artery; IX, glossopharyngeal nerve; JT, jugular tubercle; PV, petrosal vein; V, trigeminal nerve; VII, facial nerve; VIII, cochlear nerve; X, vagus nerve)Fig. 20.35 Exploring the petrosal surface of the temporal bone.The operculum of the temporal bone is seen between the trigeminal and seven-eight complex. The ventral portion of this bone obstructs the surgeon’s view of the trigeminal nerve entering Meckel’s cave. (AICA, anterior inferior cerebellar artery; PV, petrosal vein; V, trigeminal nerve; VII, facial nerve; VIII, cochlear nerve)Fig. 20.36 Upper extent of the exposure.The superior cerebellar surface, the petrosal veins, and the superior cerebellar arteries are all seen by tilting the microscope upward. (AICA, anterior inferior cerebellar artery; IV, trochlear nerve; PV, petrosal vein; SCA, superior cerebellar artery; V, trigeminal nerve; VII, facial nerve; VIII, cochlear nerve)Fig. 20.37 Finding the origin of the eighth nerve.The choroid plexus is a good landmark for the foramen of Luschka. The approximate location of this foramen can also be found by following the ninth nerve to its exit from the brainstem. Because the dorsal cochlear nucleus lies in the floor of the foramen of Luschka, the eighth nerve is seen to exit the brainstem just anterior to the foramen. (CP, choroid plexus; IX, glossopharyngeal nerve; JT, jugular tubercle; VIII, cochlear nerve; X, vagus nerve; XI, accessory nerve)Fig. 20.38 The lower end of the exposure.Tilting the microscope inferiorly, the spinal accessory nerve is seen at the lower edge of the lower cranial nerve bundle. The hypoglossal nerve is seen to exit below the jugular tubercle close to the posterior inferior cerebellar artery. (CP, choroid plexus; IX, glossopharyngeal nerve; PICA, posterior inferior cerebellar artery; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)Fig. 20.39 The inferior exposure.The posterior inferior cerebellar artery is seen passing below the three fascicles of the hypoglossal nerve. (IX, glossopharyngeal nerve; PICA, posterior inferior cerebellar artery; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)Fig. 20.40 Demonstrating the cranial nerves exposed by this approach.An anatomical relationship is well demonstrated in this photo. (AICA, anterior inferior cerebellar artery; IX, glossopharyngeal nerve; JT, jugular tubercle; PV, petrosal vein; V, trigeminal nerve; VII, facial nerve; VIII, cochlear nerve; X, vagus nerve; XI, accessory nerve)Fig. 20.41 Identifying the fovea created by the endolymphatic sac.A bony depression (arrow) created by the endolymphatic sac is a good landmark for the lateral extent of the meatal drilling. (Fo, fovea; VII, facial nerve; VIII, cochlear nerve)Fig. 20.42 (Step 5) Preparing to open the internal auditory canal.Cottonoids, oxidized cellulose, and even Gelfoam (Pflzer Inc., NY, NY) can become caught in the surgeon’s drill. It is safest to protect the brain with a attened strip of bone wax.Fig. 20.43 Cerebellar protection.The bone wax plate is placed under the retractor blade.Fig. 20.44 Raising a dural flap.A dural ap is turned with its apex at the fovea of the temporal bone. This is the approximate apex of the endolymphatic sac and marks the position of the posterior semicircular canal.Fig. 20.45 Preparing to open the internal auditory canal.The dural flap is held under the bone wax to protect the seventh and eighth cranial nerves.Fig. 20.46 Opening the internal auditory canal.Drilling begins with a 4 mm coarse diamond drill at the porus acusticus. In hearing preserving operations, the depth at which the vestibule lies can be determined from preoperative imaging. The surgeon must be very cautious at depths greater than 6 mm. With the patient in the lateral position, the vestibule lies super- cial to the internal auditory canal.Fig. 20.47 Opening the internal auditory canal.The bone is rst removed at the porus acusticus. The internal auditory canal is gradually exposed laterally. (IAC, internal auditory canal)Fig. 20.48 Opening the internal auditory canal.The opening should be widened to expose at least 180 degrees of the porus acusticus. The shoulders of the opening are removed using progressively smaller sizes of diamond bits. Care must be taken when drilling caudally of the eighth nerve and rostrally of the seventh cranial nerve. Air cells may be encountered and should be filled with bone wax. The dome of the jugular bulb may be encountered caudally. The dome can be shrunk using a bipolar cautery. (ML, meatal loop of the anterior inferior cerebellar artery)Fig. 20.49 Identifying the meatal loop of the anterior inferior cerebellar artery.The posterior dura of the internal auditory canal is opened using a sharp scissors or hook knife. This dura is usually very thin. A loop of vessel is seen branching from anterior inferior cerebellar artery and entering the internal auditory canal. (AICA, anterior inferior cerebellar artery; IX, glossopharyngeal nerve; ML, meatal loop of the anterior inferior cerebellar artery; PV, petrosal vein; V, trigeminal nerve; VII, facial nerve; VIII, cochlear nerve; X, vagus nerve; XI, accessory nerve)Fig. 20.50 Identifying the superior and inferior vestibular nerves.Further opening of the dura reveals the internal auditory artery. The superior and inferior vestibular nerves are seen from this posterior approach. (IAA, internal auditory artery; IVN, inferior vestibular nerve; ML, meatal loop of the anterior inferior cerebellar artery; SV, superior vestibular nerve)Fig. 20.51 (Step 6) Removing the superior and inferior vestibular nerves and the cochlear nerve.The internal auditory artery can be seen branching off of a loop of the anterior inferior cerebellar artery after removing the superior and inferior vestibular nerves and the cochlear nerve. In hearing preservation surgery for vestibular schwannomas, preservation of the cochlear nerve and the internal auditory artery is essential. The meatal segment of the facial nerve is demonstrated. (IAA, internal auditory artery; ML, meatal loop of the anterior inferior cerebellar artery; M-VII, meatal segment of the facial nerve)Fig. 20.52 Final view of this approach after removing the superior and inferior vestibular nerves and the cochlear nerve.The meatal segment of the facial nerve and the internal auditory artery are preserved. (AICA, anterior inferior cerebellar artery; IAA, internal auditory artery; IX, glossopharyngeal nerve; JT, jugular tubercle; ML, meatal loop of the anterior inferior cerebellar artery; M-VII, meatal segment of the facial nerve; PV, petrosal vein; V, trigeminal nerve; X, vagus nerve; XI, accessory nerve)
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Jul 19, 2020 | Posted by drzezo in NEUROSURGERY | Comments Off on 20 Lateral Suboccipital Approach: Superior, Middle, and Inferior Cerebellopontine Angle Approach
18 Anatomy for Posterior Skull Base Surgery
19 Transcondylar Transtubercular Approach
3 Transfacial Transmaxillary Approach
7 Orbital Approach
12 Middle Fossa Rhomboid Approach (Anterior Petrosectomy)
11 Preauricular Transzygomatic Approach to the Anterior Infratemporal Fossa and Middle Infratemporal Fossa
