The transcavernous approach widens the exposure afforded by a standard pterional craniotomy. This procedure is not only useful in approaching lesions within the cavernous sinus, but is useful in approaching the interpeduncular and the prepontine cisterns.
Key Steps
Position: Supine with head turned 45 degrees away from the side of the surgery
Step 1. Skin incision, question mark shape (Fig. 9.1)
Step 2. Scalp elevation (one, one and a half, or two layers) (Fig. 9.3)
Fig. 9.1 (Step 1) Skin incision.(A, routine incision for a pterional approach; B, incision for a large frontotemporal exposure; C, extended incision for frontotemporal, orbitobasal, and middle fossa exposure)Fig. 9.2 Layers to be elevated.The surgeon cuts through the subcutaneous fat and the temporoparietal fascia before reaching the muscle fibers of the temporalis muscle. (DTF, deep temporal fascia; LAT, loose areolar tissue; TPM, temporoparietal muscle)Fig. 9.3 (Step 2) One layer scalp and temporalis muscle elevation.The zygomatic arch only should be removed when the surgeon will be looking under the temporal lobe. Removing the orbital rim facilitates the surgeon looking up under the frontal lobe. When an orbital, but not orbitozygomatic, osteotomy is planned, the muscle does not need to be separated from the scalp. Care is taken to separate the origin of the temporalis muscle from the frontal zygomatic process and adjacent greater wing of the sphenoid.Fig. 9.4 One and a half layer scalp elevation.The skin, galea, periosteum, temporoparietal fascia, and superficial layer of the deep temporal fascia are elevated together when an orbitozygomatic osteotomy is planned. The temporalis muscle and true temporal fascia (deep layer of the deep temporal fascia) is left in place. The deep and superficial layers of the deep temporal fascia are separated by the deep temporal fat pad. The superficial layer is contiguous with the periosteum on the lateral surface of the zygoma. (dDTF, deep layer of the deep temporal fascia; IFF, interfascial fat pad; sDTF, superficial layer of the deep temporal fascia)Fig. 9.5 One and a half layer scalp elevation (orbitozygomatic exposure).The superficial layer of the temporal fascia and the pericranium are raised along with the skin flap to expose the supraorbital bar and the contiguous zygomatic arch. The frontalis branch of the facial nerve is thus protected. The muscle and fascia are elevated as a second layer. This procedure is indicated for an extended orbitozygomatic craniotomy. Care is taken not to injure the supraorbital nerve. (dDTF, deep layer of the deep temporal fascia; sDTF, superficial layer of the deep temporal fascia)Fig. 9.6 Two layer scalp elevation.This two layer method is used when a large vascularized pericranial flap will be needed for closure. The skin galea, temporoparietal fascia, and superficial layer of the deep temporal fascia are elevated. The periosteum, temporalis muscle, and true temporal fascia (deep layer of the deep temporal fascia) are left attached to the bone. The posterior skin edge should be separated from the periosteum to expose a large pericranial flap. This procedure results in a vascularized pericranial flap that can be used to close the wound. If the pericranial flap is thin, a myofascial or galeal flap can be used. In cases where the galea is separated from the skin, care should be taken to protect the vasculature that runs in the subcutaneous fat. (dDTF, deep layer of the deep temporal fascia; FM, frontalis muscle), (G, galea aponeurotica; IFF, interfascial fat pad; PO, periosteum; sDTF, superficial layer of the deep temporal fascia)Fig. 9.7 Two layer scalp elevation (pericranial flap elevation).The periosteum should be separated from under the posterior scalp edge to enlarge the periosteal flap. The loose connective tissue under the galea should be left attached to the periosteum to thicken the periosteal flap. However, the loose connective tissue on the deep temporal fascia can be elevated with parietotemporal fascia toward the skin flap. The pericranial flap is elevated with its blood supply intact. (dDTF, deep layer of the deep temporal fascia; PO, periosteum; sDTF, superficial layer of the deep temporal fascia)Fig. 9.8 Two layer scalp elevation (elongation of the pericranial flap).The pericranial flap can be elongated by back cutting the pericranium. The pedicle of the flap must be kept broad enough to maintain an adequate blood supply to the tip of the flap. The flap should be kept moist during the surgery. (dDTF, deep layer of the deep temporal fascia; FM, frontalis muscle; G, galea aponeurotica; PO, periosteum; sDTF, superficial layer of the deep temporal fascia)Fig. 9.9 (Step 3) “Golf club” drilling (frontoorbital detachment).A bur hole is drilled crossing the lateral surface of the greater wing of the sphenoid bone as close to the frontal process as possible. This key bur hole, called the “golf club head,” exposes the lateral dura of the anterior and middle fossae on the sides of the sphenoid wing. (FZS, frontozygomatic suture; LOW, lateral orbital wall; MP, marginal process; TD, temporal dura)Fig. 9.10 “Golf club” drilling (frontoorbital detachment).The cortical bone of the lateral orbital wall and the dura of the frontal base and temporal tip are exposed by drilling across the greater wing of the sphenoid bone. The meningoorbital band, which marks the lateral edge of the superior orbital fissure, can be seen through this key hole. (FD, frontal dura; LOW, lateral orbital wall; TD, temporal dura)Fig. 9.11 “Golf club” drilling (drilling the subtemporal groove).Because it is difficult to use a craniotome under the temporalis muscle, a groove is drilled into the bone of the middle fossa as anterior and inferior as possible. This groove connects with our “golf club head.” (FZS, frontozygomatic suture; LOW, lateral orbital wall)Fig. 9.12 Frontotemporal craniotomy.Additional holes are made along the route of the proposed bone flap. The number of holes made depends on how attached the dura is to the bone. The bony flap is outlined with a craniotome.Fig. 9.13 (Step 4) Frontotemporal craniotomyThe craniotomy is raised.Fig. 9.14 Separation of periorbita.A curved sharp dissector is used to separate the periorbita from the orbital roof. The lacrimal gland is encountered laterally. This gland is dissected down with the periorbita.Fig. 9.15 Separation of periorbita.Gelfoam (Pfizer Inc., NY, NY) is placed between the periorbita and the bony orbit to avoid injury of the periorbita at the time of the osteotomy. (GS, gelatin sponge)Fig. 9.16 Separation of periorbita.The periorbita is kept intact by placing the Gelfoam between the periorbita and the superior orbital wall. The supraorbital nerve is protected. (SON, supraorbital nerve)Fig. 9.17 (Step 5) Limited supraorbital bar osteotomy.The osteotomy on the medial side of the orbit is made lateral to the supraorbital foramen or notch. Usually there is no advantage to carrying the osteotomy medial to the supraorbital notch. The lateral side of the osteotomy is made just lateral to the frontozygomatic suture. This limited orbital osteotomy allows the surgeon to look up under the frontal lobe. With a standard pterional approach, the orbital roof forces the surgeon’s line of sight inferiorly. (FZS, frontozygomatic suture)Fig. 9.18 Limited supraorbital bar osteotomy.The osteotomy is completed by drilling the lateral and superior orbital walls 10 mm deep to the inner table of the craniotomy edge with a diamond drill.Fig. 9.19 Limited supraorbital bar osteotomy.If the periorbita is injured, the intraorbital fat is exposed. Because the fat obstructs the surgeon’s view, the torn periorbita should be sutured with a 6-0 suture to hold the fat out of the surgeon’s line of sight.Fig. 9.20 Supraorbital bar and superior wall of the orbit are removed.Fig. 9.21 Extended orbitozygomatic osteotomy.The supraorbital bar, the frontal process of the zygoma, and the zygomatic arch are removed as one piece. The three black lines indicate the location of the osteotomies. (TM, temporalis muscle; Zy, zygomatic arch)Fig. 9.22 Extended orbitozygomatic osteotomy.The extended orbitozygomatic osteotomy is completed by drilling the superior and lateral orbital walls 10 mm deep to the inner table of the craniotomy edge with a diamond drill. (TM, temporalis muscle)Fig. 9.23 Extended orbitozygomatic osteotomy.After the supraorbital bar and the zygomatic arch are removed as one piece, the orbit and the insertion of the temporalis muscle are exposed. (TM, temporalis muscle)Fig. 9.24 Raising the temporalis muscle.Raising the temporalis muscle exposes the temporal base.Fig. 9.25 Midsubtemporal ridge over lateral loop.There is a characteristic protrusion of bone between the mandibular and maxillary branches of the trigeminal nerve. This bony protrusion is usually seen over the lateral loop, which is another name for the dural bridge between V2 and V3. We named this bony protrusion the mid-subtemporal ridge. The ridge serves as a landmark for the identification of V2 and V3 (See Figs. 8.3–8.6 and Figs. 11.1–11.24, and 11.26).Fig. 9.26 Drilling the inner bony table.Bony protrusions including the mid-subtemporal ridge emanating from the inner plate of the middle fossa should be removed with a diamond drill to flatten the base of the middle fossa. Removal of the bony protrusions and the inner plate allows the surgeon to view the base of the middle fossa without obstruction.Fig. 9.27 Meningoorbital band.The meningoorbital band marks the lateral edge of the superior orbital fissure. (MOB, meningoorbital band)Fig. 9.28 Superior orbital fissure.A recurrent branch of the lacrimal artery may pass back through the superior orbital fissure to anastomose with the middle meningeal artery. (MOB, meningoorbital band)Fig. 9.29 Division of the meningoorbital band.The lateral edge of the meningoorbital band can be divided 5–7 mm medially without risking injury to the oculomotor nerve. The division of the band frees the dura propria from the inner layer of the cavernous sinus dura, which houses the cranial nerves.Fig. 9.30 Beginning the osteal dura elevation from the superior orbital fissure.After the meningoorbital band is cut, the dural covering the temporal lobe can be separated from the inner layer of the cavernous sinus. (SOF, superior orbital fissure)Fig. 9.31 Osteal dura elevation from the superior orbital fissure.A sharp dissector is used to dissect the osteal dura from the dura propria. There is a loose connection in between these two layers. This plane may be obliterated by an infiltrating process such as a meningioma. (TCM, true cavernous membrane = osteal dura covering the lateral cavernous wall)Fig. 9.32 Skeletonization of cranial nerves III, IV, V1, V2, and the superior orbital vein.Elevation of the dura propria reveals cranial nerve III, IV, V1 and V2. (III, oculomotor nerve; IV, trochlear nerve; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve])Fig. 9.33 Elevation of the dura from the floor of the anterior fossa to the ethmoidal band (posterior ethmoidal nerve and artery).The ethmoidal band marks the medial border of the anterior fossa dural elevation. (EB, ethmoidal band = posterior ethmoidal artery and nerve)Fig. 9.34 Magnified view of the ethmoidal band.The posterior ethmoidal nerve and artery form the ethmoidal band. (EB, ethmoidal band = posterior ethmoidal artery and nerve)Fig. 9.35 (Step 6 A) Exposure of the base of the anterior clinoid process.The dura medial to the superior orbital fissure is often thin, but with a sharp dissector it can usually be elevated from the lesser wing of the sphenoid until the shadow of the optic nerve can be seen through the thin bone of the orbital apex and the falciform ligament. (III, oculomotor nerve; IV, trochlear nerve; ON, optic nerve; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve])Fig. 9.36 (Step 6B) First step of removing of the anterior clinoid process.Coring of the anterior clinoid process. The anterior clinoid is removed in steps. First, the anterior clinoid is freed from the lesser wing of the sphenoid anteriorly. The optic strut attachment to the anterior clinoid is preserved, as it will secure the anterior clinoid during the remainder of the drilling. The third nerve runs in the fibrous tissue lateral to the anterior clinoid. Thus, the lateral wall of the clinoid is thinned and peeled off the fibrous tissue with a thin dissector. All drilling of the optic strut and optic canal is done under copious irrigation to avoid heat damage. This photo shows the first step. The anterior clinoid is hollowed in the beginning. (III, oculomotor nerve; IV, trochlear nerve; ON, optic nerve; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve])Fig. 9.37 (Step 6B) Removing the lateral half of the anterior clinoid process.The second step is to remove the lateral half of the anterior clinoid process preserving the medial half of the clinoid and its attachment to the optic strut. The microscope is tilted laterally. The oculomotor nerve runs just under the lateral half of the process. (COM, carotico-oculomotor membrane; III, oculomotor nerve; IV, trochlear nerve; ON, optic nerve; T, tip of the anterior clinoid process; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve])Fig. 9.38 Tilting the microscope medially.The microscope is tilted medially in preparation for removing the medial anterior clinoid. (COM, carotico-oculomotor membrane; III, oculomotor nerve; IV, trochlear nerve; OC, optic canal; ON, optic nerve; T, tip of the anterior clinoid process; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve])Fig. 9.39 (Step 6C) Removal of medial half of the anterior clinoid process.The bone over the optic canal is thinned and lifted off the nerve with a dissector. (COM, carotico-oculomotor membrane; III, oculomotor nerve; IV, trochlear nerve; ON, optic nerve; T, tip of the anterior clinoid process; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve])Fig. 9.40 (Step 6C) Partial removal of the optic strut.The optic strut is partially removed with a diamond drill. The surgeon should be aware that the sphenoid sinus may extend into the optic strut. (III, oculomotor nerve; IV, trochlear nerve; ON, optic nerve; OS, optic strut; T, tip of the anterior clinoid process; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve])Fig. 9.41 Observation of carotico-oculomotor membrane.A microscope is returned to a neutral position. The base of the anterior clinoid process has been removed. The carotico-oculomotor membrane that covers the C3 portion of the internal carotid artery is observed after the base is detached. When this membrane is completely preserved, venous bleeding from the medial triangle of the cavernous sinus is not encountered. More frequently, cavernous sinus bleeding is controlled with small bits of oxidized cellulose. (COM, carotico-oculomotor membrane; III, oculomotor nerve; IV, trochlear nerve; ON, optic nerve; T, tip of the anterior clinoid process; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve])Fig. 9.42 (Step 6D) Removal of the tip of the anterior clinoid process.The anterior clinoid tip is held in a forceps and freed from the interclinoid attachment with a sharp dissector. (COM, caroticooculomotor membrane; III, oculomotor nerve; IV, trochlear nerve; ON, optic nerve; T, tip of the anterior clinoid process; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve])Fig. 9.43 Completion of removal of the anterior clinoid process.The anterior clinoid process is completely removed. An anatomical relationship of the cavity created by removing the anterior clinoid process and adjacent structures is well demonstrated. (COM, carotico-oculomotor membrane; EB, ethmoidal band = posterior ethmoidal artery and nerve; III, oculomotor nerve; IV, trochlear nerve; ON, optic nerve; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve])Fig. 9.44 Removal of the orbital roof.The remainder of the roof and the lateral wall of the orbit are partially removed. The purpose of the removal of this roof is to make the anterior skull base flat.Fig. 9.45 Identifying the C3 portion of the internal carotid artery covered by the carotico-oculomotor membrane.The C3 portion of the internal carotid artery is exposed when the anterior clinoid is removed. The artery is covered by the carotico-oculomotor membrane (true cavernous membrane). (COM, carotico-oculomotor membrane; III, oculomotor nerve; IV, trochlear nerve; ON, optic nerve; V1, ophthalmic nerve [first division of the trigeminal nerve])Fig. 9.46 (Step 7) Mobilization of the membrane covering the oculomotor nerve.The relationship between V2, V1, CN III, CN IV, and the carotid artery is demonstrated. The caritico-oculomotor membrane has been removed from the carotid artery. The oculomotor nerve is covered by a thin membrane. (C3, C3 portion of the internal carotid artery; III, oculomotor nerve; IV, trochlear nerve; ON, optic nerve; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve])Fig. 9.47 Removing the true cavernous membrane.The membrane has been removed to expose the nerves that reside in the lateral wall of the cavernous sinus. In clinical cases, the true cavernous membrane is not removed. (C3, C3 portion of the internal carotid artery; III, oculomotor nerve; IV, trochlear nerve; ON, optic nerve; SOV, superior ophthalmic vein; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve]; VI, abducens nerve)Fig. 9.48 (Step 8) Opening the dura.The dura is incised in a semilunar fashion at first.Fig. 9.49 Opening the dura.The dura’s opening is extended in a “crossbow” fashion. A cuff of the dura, including the external carotid ring, is preserved. This cuff serves as an anchor for dural sutures at the time of closure.Fig. 9.50 Opening the sylvian fissure.The sylvian fissure is opened to expose the internal carotid, middle cerebral, and anterior cerebral arteries. (A1, A1 segment of the anterior cerebral artery; C1, C1 portion of the internal carotid artery; C2, C2 portion of the internal carotid artery; M1, M1 segment of the middle cerebral artery; ON, optic nerve)Fig. 9.51 Opening the dura.The dural opening is continued laterally and medially at the base. (C2, C2 portion of the internal carotid artery; COM, caroticooculomotor membrane; DR, dural ring; ON, optic nerve)Fig. 9.52 Magnified view.The external and internal carotid dural rings and the intervening clinoid space are well demonstrated. (C2, C2 portion of the internal carotid artery; COM, carotico-oculomotor membrane; DR, dural ring; ON, optic nerve; PCP, posterior clinoid process)Fig. 9.53 Initial incision of the dural ring.The medial side of the dural ring is incised at first. (C2, C2 portion of the internal carotid artery; COM, carotico-oculomotor membrane; DR, dural ring; ON, optic nerve; PCP, posterior clinoid process)Fig. 9.54 Releasing the internal carotid artery from the dural ring.The dural ring is dissected from the inside out. The oculomotor canal is opened. A blunt hook tents up the dural cuff that surrounds the oculomotor nerve and the dura is cut with a pointed knife. Bothersome bleeding from the medial triangle of the cavernous sinus may be encountered (arrowheads). (C2, C2 portion of the internal carotid artery; COM, carotico-oculomotor membrane; III, oculomotor nerve; ON, optic nerve)Fig. 9.55 Removing the carotico-oculomotor membrane.The carotico-oculomotor membrane is held in a forceps or by a blunt hook. (C2, C2 portion of the internal carotid artery; COM, carotico-oculomotor membrane; III, oculomotor nerve; ON, optic nerve)Fig. 9.56 Opening the carotico-oculomotor membrane.The membrane is incised by scissors or a sharp knife. (C2, C2 portion of the internal carotid artery; C3, C3 portion of the internal carotid artery; COM, carotico-oculomotor membrane; III, oculo-motor nerve; ON, optic nerve)Fig. 9.57 Opening the carotico-oculomotor membrane.Bleeding from the dural venous complex, which drains into the posterior cavernous sinus and the connection of the posterior cavernous sinus with the basal sinus, is controlled by packing the bleeding points with small pieces of a oxidized cellulose held in place by gentle pressure. Large slabs of hemostatic agents will only obstruct the surgeon’s view and are no more effective in stopping hemorrhage from discrete bleeding points. The carotico-oculomotor membrane is raised laterally and pushed into the cavernous sinus with a piece of oxidized cellulose. (C2, C2 portion of the internal carotid artery; C3, C3 portion of the internal carotid artery; COM, carotico-oculomotor membrane; III, oculomotor nerve; ON, optic nerve)Fig. 9.58 Exposing the C3 portion of the internal carotid artery.After the carotico-oculomotor membrane has been removed, the relationship between V1, CN II, CN III, CN IV, and the intra- and extradural carotid arteries is demonstrated. (C2, C2 portion of the internal carotid artery; C3, C3 portion of the internal carotid artery; III, oculomotor nerve; IV, trochlear nerve; ON, optic nerve; PCP, posterior clinoid process; V1, ophthalmic nerve [first division of the trigeminal nerve])Fig. 9.59 Viewing the top of the basilar artery.The anterior inferior portion of the sylvian fissure is opened and the internal carotid artery is followed to its bifurcation. The opening between the oculomotor nerve and the carotid artery makes a corridor to the distal basilar artery. The posterior communicating artery is divided in this specimen. (BA, basilar artery; C2, C2 portion of the internal carotid artery; III, oculomotor nerve; IV, trochlear nerve; ON, optic nerve; P1, P1 segment of the posterior cerebral artery; PC, posterior communicating artery; V1, ophthalmic nerve [first division of the trigeminal nerve])Fig. 9.60 Viewing the top of the basilar artery.The two proximal posterior cerebral arteries (P 1) segments and the left superior cerebellar artery are clearly seen. (BA, basilar artery), (C2, C2 portion of the internal carotid artery; III, oculo-motor nerve; ON, optic nerve; P1, P1 segment of the posterior cerebral artery; SCA, superior cerebral artery)Fig. 9.61 Viewing the top of the basilar artery.The basilar artery proximal to the superior cerebellar artery can be occluded with a temporary clip. A well-developed posterior clinoid process may disturb surgical access to the mid-basilar artery. (BA, basilar artery; C2, C2 portion of the internal carotid artery; C3, C3 portion of the internal carotid artery; III, oculomotor nerve; ON, optic nerve; P1, P1 segment of the posterior cerebral artery; PCP, posterior clinoid process; SCA, superior cerebral artery)Fig. 9.62 Viewing the ipsilateral posterior communication artery.The ipsilateral posterior communicating artery is seen anastomosing with the left posterior cerebral artery. (III, oculomotor nerve; P1, P1 segment of the posterior cerebral artery; P2, P2 segment of the posterior cerebral artery; PC, posterior communicating artery; PCP, posterior clinoid process)
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