Fig. 4.1 Overview. Depending on the brain regions the surgeon wishes to access via a midline approach, the positioning of the patient and craniotomy technique have to be adapted accordingly. This diagram gives an overview of the standard approaches commonly used in neurosurgery.
Fig. 4.2 Small bone flaps. Sinus-crossing craniotomies can be performed in various ways. We adhere to the following principles to assure sufficient exposure and avoid sinus injury. In small (<5 cm sagittal dimension) craniotomies, we make two burr holes on the sinus and one burr hole laterally (a or b). The craniotomy starts at the lateral burr hole reaching medially and stopping approximately 1.5 cm lateral to the sinus. From the medial burr holes, the craniotomy is then interconnected from medial to lateral. Depending on the amount of retraction of midline structures to the contralateral side that is necessary (e.g., in superficial tumors), the sinus is crossed 1.5 cm contralaterally (a) or the craniotomy is performed on the sinus in the most contralateral aspect of the burr hole (b). The same procedure may also be performed without a lateral burr hole (c, d, young patients, better cosmesis).Fig. 4.3 Medium and large bone flaps. For larger bone flaps, we make burr holes every 3–4 cm along the sinus (a–d). Again, a lateral burr hole is optional (a, b). In large bone flaps (>9 cm sagittal dimension), we always cross the sinus and cut contralateral to the sinus (a, c). Despite crossing to the contralateral side and not interconnecting all burr holes, the number of burr holes on the sinus may remain the same. They are used to detach the dura mater from the bone flap above the sinus to prevent sinus injury during removal of the bone flap.Fig. 4.4 Frontal or subfrontal approaches. For frontal approaches above the frontal skull base, we do not make an anterior burr hole (cosmesis, lower risk of sinus injury). Whether the sinus is crossed (a) or not (b) depends on the surgical target. Remnant bony structures (frontal sinus) may be resected using a drill. Opening of the frontal sinus should be avoided unless indicated (e.g., frontal skull base fracture).
Fig. 4.5 (a, b) Positioning. The (anterior) frontal midline approach is used to access structures near, in, or via the frontal part of the interhemispheric fissure, frontal skull base, or orbital roof. It can be performed either unilaterally or bilaterally. Normally, the head is positioned straight without any rotation and is slightly elevated. In unilateral approaches, the head may be slightly tilted to the contralateral side to facilitate access to the interhemispheric fissure. The degree of head flexion required depends on the planned surgical trajectory.Fig. 4.6 (a, b) Anatomy overview. Important landmarks are (1) coronal suture, (2) sagittal suture and bregma, (3) superior sagittal sinus, and (4) frontal sinus. Another helpful orientation marker (placement of ventricular catheter) is (5) Kocher’s point (1 cm anterior to the coronal suture, 2.5 cm lateral to the midline).Fig. 4.7 (a, b) Draped position before skin incision. The skin incision for a large bilateral craniotomy runs from tragus to tragus, starting roughly 1 cm anteriorly after locating the main branch of the superficial temporal artery by palpation to avoid injury. The incision should usually cross the midline approximately 1 cm anterior to the bregma. However, the size of the skin flap can be adapted according to the size of the craniotomy. In unilateral craniotomies, the incision may end on the contralateral side 2–3 cm above the tragus. The more anterior the planned access, the larger the incision. It should allow the frontal skin flap to be completely folded over without putting it under too much tension (skin color!). The incision line is made behind the hairline for cosmesis. Usually, we shave the hair at a minimum 1 cm anterior and posteriorly to the incision. We prefer a slightly curved incision in the midline. This avoids asymmetry of the forehead skin after wound healing.Fig. 4.8 (a, b) Skin incision. The skin incision spares the periosteum because in most scenarios using such an approach requires a galeal flap. A long incision should be started on one side first. Especially above the tragus, it is sometimes not possible to preserve small branches of the superficial temporal artery. After careful (sparing the superficial layers of the scalp) coagulation of arterial oozing, bleeding from the scalp is controlled with scalp clips covering the entire length of the incision. To place the scalp clips correctly, the subcutaneous scalp layer should be sharply dissected from the periosteum anterior and posteriorly. Fine white tissue adhesions indicate the correct layer.Fig. 4.9 (a, b) Subgaleal flap preparation. The posterior skin flap is pulled back (e.g., using a clamp). Depending on the planned surgery, the anterior skin flap is then dissected to the desired extent using sharp, and careful blunt, dissection.Fig. 4.10 (a, b) Subgaleal flap preparation. While further dissecting the scalp from the periosteum, the assistant pulls back the skin flap with a retractor and completely folds over the flap in a stepwise manner. Particularly above the temporal muscle fascia, adhesion to the scalp might be very tight.Fig. 4.11 (a, b) Subgaleal flap preparation. The skin flap is then held in position with retractors (e.g., Yasargil spring hooks). Bleeding from the skin flap or periosteum is localized and coagulated. Depending on the extent of dissection toward the frontal base, the supraorbital nerve with its accompanying artery and vein passing the supraorbital foramen should be located and spared.Fig. 4.12 (a, b) Subgaleal flap preparation. Finally, the periosteum is individually incised, staying above the temporal line bilaterally and preserving the frontal stalk of the flap. The flap is then dissected stepwise from the bone using a rasp (supraorbital nerve!).Fig. 4.13 (a, b) Subgaleal flap preparation. After dissection, the periosteum is positioned and kept rostrally. For better conservation, it is covered with wet surgical cottonoids or towels.Fig. 4.14 (a, b) Craniotomy planning. The cranial sutures indicate midline structures and intracranial localization of a target lesion. The planning of burr hole placement and craniotomy depends on various parameters such as the target lesion, age of the patient, previous surgery, etc. In this illustration, a large unilateral craniotomy to the midline was necessary. To allow gentle retraction of the midline structure to the contralateral side, the sinus was crossed and exposed 1.5 cm contralaterally. To prevent wound healing problems, the burr holes should not be directly underneath the skin incision. For beginners, it may be helpful to draw the planned craniotomy on the skull with a surgical pen. If performing an extended frontal craniotomy, the borders of the frontal sinus should be respected (see measurements from CT or using navigation to localize the borders) unless opening of the sinus is desired (e.g., for fractures of the frontal skull base). In these cases, an anterior burr hole on the midline can also be avoided for better cosmesis. The risks of injuring the sagittal sinus are very low in this region.Fig. 4.15 (a, b) Burr holes. The burr hole(s) on the sinus should be drilled with a large trephine (18 mm) which may offer a better protection for injury of the sinus. The direction is strictly perpendicular to the skull. Residual bone chips should then be removed using a blunt dissector. If the dura adheres to the bone, a small punch sometimes helps to detach the structures and provide an entry for the craniotome. The lateral burr holes can be drilled with a smaller trephine.Fig. 4.16 (a, b) Craniotomy. The craniotomy is usually performed starting from a lateral burr hole and stopping 2 cm lateral to the midline. From the burr hole on top of the sinus, we then cut from medially to laterally interconnecting the craniotomy. When no lateral burr hole is present, the craniotomy starts in the midline, cutting away from it and interconnecting the craniotomy laterally. The assistant uses the flush to cool the craniotome and tissue structures and the sucker to provide optimal visibility for the surgeon.Fig. 4.17 (a, b) Craniotomy. After complete circumferential craniotomy, the bone flap is gently elevated with an elevator and the dural layer dissected stepwise from the bone. This is performed with special care in the midline to prevent injury of the sinus. The bone flap should always (!) be secured manually by the assistant or surgeon. During this step, the team should be prepared for a potential sinus laceration. In the case of an injury, the sinus is covered with prepared cottonoids before the injury is sutured or sealed with fibrin glue or a hemostasis patch.Fig. 4.18 (a, b) Situs after craniotomy. Typically, after elevation of the bone flap, some minor venous bleeding occurs in the area of the sagittal sinus from pacchionian granulations. This can normally be controlled by coagulation and compression with cottonoids. Further bleeding from dural vessels more laterally should also be coagulated. The whole site then has to be meticulously cleared of bone dust using irrigation.Fig. 4.19 (a, b) Dura opening. After placing surgical cotton around the circumference to protect the brain tissue, the dura is opened from laterally to medially with the base at the sagittal sinus. It is essential to avoid injury of bridging veins whose position should be known from preoperative imaging. Sometimes, small lacunae of the sinus extend laterally. If injured, these can be easily closed using small clips or sutures. Stitches in the dura lateral to the sinus or in the falx inferior of the sinus can be used to gently retract the falx and sinus contralaterally to allow better access to the interhemispheric fissure.Fig. 4.20 (a, b) Closure: bone flap refixation. The bone flap is fixed to the skull using titanium mini-plates with a distance of roughly 120° between the plates. The bone flap is positioned so that the anterior part adjoins the frontal skull without any gap. If a rostral burr hole is placed within the cosmetically sensitive area of the forehead, it should be covered with a burr hole mini-plate or filled with bone cement.Fig. 4.21 (a, b) Closure: subgaleal flap handling and skin closure. If not used as a patch, the subgaleal flap can be reattached to the periosteum. The skin is closed in typical manner using subcutaneous sutures (each 1 cm distance apart) and running or single skin suture. Usually, a subcutaneous drain is inserted.
Checklist
Position the Mayfield clamp in such a way that it does not obstruct you during opening and closure of the skin.
Try to preserve the whole galeal flap (if needed, also preserve its base).
Make sure (in frontal skull base approaches) to preserve supraorbital nerves.
Make sure not to open the frontal sinus unless it is necessary (neuronavigation may be helpful in difficult cases).
Ligation of the first third of the sagittal superior sinus is normally possible in the case of an injury that cannot otherwise be remedied.
Cosmesis in this area of the skull is very important! Respect the hairline, make a curved incision, avoid (if possible) and cover burr holes, replace the bone flap achieving a minimum gap at the anterior and medial borders, and close the wound very carefully.
Fig. 4.22 (a, b) Positioning. The frontal midline approach is used to access structures near, via, or in the interhemispheric fissure located from 5 cm anterior to the bregma up to the superior parietal lobule. It can be performed in a unilateral or a bilateral way. The patient is in the supine position. Normally, the head is straight, but sometimes (in unilateral approaches) it is slightly tilted to the contralateral side to facilitate access to the midline. The head is elevated and flexed, with the bregma being the highest point. At least a finger’s width space should be left between the chin and jugulum.Fig. 4.23 (a, b) Anatomy overview. Important landmarks are (1) coronal suture, (2) sagittal suture and (3) bregma, the (4) superior sagittal sinus, (5) the superior rolandic point (5 cm posterior to the bregma, indicating the central sulcus), and (6) the posterior coronal point (3 cm lateral to the sagittal suture, 1 cm posterior to the coronal suture, indicating the anterior border of the hand motor cortex). Another helpful orientation aid (for placement of a ventricular catheter) is (7) Kocher’s point (10 mm anterior to the coronal suture, 25 mm lateral to the midline).Fig. 4.24 (a, b) Draped position before skin incision. The skin incision (straight, coronal for a bilateral approach) extends approximately 5 cm bilaterally to the midline, depending on the desired size of the craniotomy. Even in large bone flaps, it should normally not cross the superior temporal line. For unilateral approaches, the incision extends the midline approximately 3 cm on the contralateral side and 5 cm on the ipsilateral side, again depending on the planned size of the craniotomy. An incision that is too small limits the exposure of the midline in the sagittal plane. In very anterior approaches, the incision line may be modified (curved) to respect the hairline for better cosmesis. Usually, we shave the hair 1 cm anterior and posterior to the incision.Fig. 4.25 (a, b) Skin incision. The skin incision spares the periosteum if a galea flap is desired. After careful coagulation of arterial oozing (sparing the superficial layers of the scalp), bleeding from the scalp is controlled with scalp clips covering the entire length of the incision. To place the scalp clips properly, the subcutaneous scalp layer has to be sharply dissected from the periosteum, i.e., the incision needs to extend to the periosteum and the skin–galea flap needs to be mobilized a few millimeters.Fig. 4.26 (a, b) Subgaleal flap preparation. If a subgaleal flap is desired, the periosteum is incised circumferentially after placement of a skin retractor. The flap is carefully dissected from the bone using a raspatorium. The assistant retracts the flap using anatomical forceps. The flap should be preserved in wet cottonoids.Fig. 4.27 (a, b) Craniotomy planning. The cranial sutures indicate midline structures and intracranial localization of a target lesion (x cm anterior/posterior to the coronal suture). The planning of burr hole placement and craniotomy depends on various parameters such as the target lesion, age of the patient, and previous surgery. For the basic principles of the craniotomy, see Chapter 4.1, Sinus-Crossing Craniotomies. In the scenario illustrated here, we made three burr holes on the midline to control the superior sagittal sinus, and one lateral burr hole.Several craniometric points are helpful for orientation. Besides the bregma, the superior rolandic point and posterior coronal point are helpful as indicators of the projection of the motor cortex. When an interhemispheric approach is desired, it is helpful to know that fewer bridging veins are encountered in the zone 5 cm anterior to the bregma. Before making the burr holes, the anterior course of the midline (not indicated by the sagittal suture) has to be traced.Fig. 4.28 (a, b) Burr holes. The burr holes on the sinus should be drilled with a large trephine (18 mm) to ensure sufficient control. The direction is strictly perpendicular to the skull. Residual bone chips should be removed using a blunt dissector. In the case of dural adhesion to the bone, a small punch can sometimes help to detach the structures and provide an entry for the craniotome. The epidural space is then carefully dissected from the sinus surface using a dissector. If the burr holes are located close enough together, the sinus surface can be detached from the bone along the entire border of the craniotomy. Cave: particularly in patients with very thin skin or wound-healing problems, the burr holes should not be made directly beneath the skin incision (dotted line).Fig. 4.29 (a, b) Craniotomy: beginning. The craniotomy starts at the lateral burr hole extending medially and ends approximately 2 cm lateral to the sinus. The craniotomy is then continued from the sinus burr hole in a medial-to-lateral direction. Caution: never cut from a lateral directing toward the sinus and on to the sinus, because this creates a much higher risk of injuring the sinus by slippage into a lateral lacuna. Particularly for beginners, it may be helpful to outline the planned craniotomy on the bone with a surgical pen.Fig. 4.30 (a, b) Craniotomy: completion. The craniotomy is then completed by interconnecting the burr holes on the sinus at its most contralateral aspect, starting at the most anterior burr hole before going dorsally.Fig. 4.31 (a, b) Craniotomy: completion. After complete circumferential craniotomy, the bone flap is gently removed with an elevator and the dural layer is dissected stepwise from the bone. This is performed with special care in the midline to prevent injury of the sinus. The bone flap should always be secured manually by the assistant or surgeon. During this step, the team should be prepared for sinus laceration. If such an injury does occur, the sinus is covered with prepared cottonoids before being sutured or sealed with fibrin glue or a hemostasis patch.Fig. 4.32 (a, b) Situs after craniotomy. Typically after elevation of the bone flap, some minor venous bleeding occurs in the area of the sagittal sinus from pacchionian granulations (very large in this case). Bleeding can normally be controlled by coagulation and compression with cottonoids. Further bleeding from dural vessels situated more laterally should also be coagulated. The whole situs then has to be meticulously cleared of bone dust using irrigation. Particularly in deep-seated lesions or if there is complex bridging vein anatomy, additional verification of the planned trajectory and interhemispheric approach is helpful at this stage of surgery (with neuronavigation or ultrasound).Fig. 4.33 (a, b) Closure: bone flap refixation. The bone flap is positioned so that the anterior part adjoins the frontal skull without any gap. If a rostral burr hole is located within the cosmetically relevant area of the forehead, it should be covered with a burr hole mini-plate device or filled with bone cement.Fig. 4.34 (a, b) Closure: bone flap refixation. Covering the burr holes with, e.g., bone cement or titanium plates for cosmesis is optional. The skin is then closed in a typical two-layer manner. Usually, a subcutaneous drain is inserted.
Checklist
Pinpoint the midline prior to positioning of the patient.
Preserve the galea for a potential flap.
Identify craniometric points for better orientation.
Use a large craniotome to make burr holes on the sinus.
Make sure to detach dural adhesions at the rims of the burr hole before performing the craniotomy.
Never cut toward the sinus.
Be prepared for potential sinus injury before elevating the bone flap.
When closing, take care to avoid bony defects. Cover the burr holes in the forehead area for better cosmesis.
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