Craniotomy Technique

Incision planning

After the patient is positioned, the first step is to plan the incision. Some basic principles that govern incisions include the following:

• Continuous lines and curves that remain behind the hairline are preferable for wound healing and cosmesis

• Linear incisions are preferred as they promote better wound healing, improved cosmetic appearance, and can be more readily used in repeat surgery; S-shaped and question-mark incisions can have more compromised blood flow at the curved sites and therfore have more potential for breakdown and infection

• Intersecting incisions should be avoided, as these are less likely to heal well

• Intraoperative navigational software can be used for incision planning and avoiding large underlying veins and major sinuses

• Re-operative craniotomies should make use of prior incisions

• If the incision runs over the superficial temporal artery, take care not to damage the artery or its major branches, as this can risk blood supply to the scalp

• Incisions are not carried beyond the zygomatic arch or more than 1 cm in front of the tragus so as to prevent injury to the facial nerve ^[7]

The fundamental goal is to tailor the incision to the underlying intracranial lesion with the aforementioned principles in mind. A wide variety of intracranial processes must be accessed via craniotomy, with a corresponding variety of incisions. The following are examples of the incisions made for the more common craniotomy types: ^[11]

• Pterional and frontotemporal craniotomy: Extends from the zygomatic arch 1 cm in front of the tragus, curves anteriorly, remains behind the hairline, and ends at widow’s peak; variations on this include the mini-pterional approach, which begins further above the origin of the zygomatic arch and ends well before widow's peak

• Frontal craniotomy (unilateral or bilateral): Unilateral approach uses an incision starting less than 1 cm anterior to the tragus and just above the zygomatic arch, travels superiorly, and ends at the midline frontally; bilateral approach uses an ear-to-ear incision (also known as a bicoronal incision) that is also less than 1 cm anterior to the tragus and terminates on each side just above the zygomatic arches while remaining behind the hairline; variations on these incisions are referred to as modified bicoronal incisions, in particular those that do not extend from ear to ear, and in fact are the most common incision type for frontal lobe lesions

• Temporal craniotomy: May be linear or reverse question-mark depending on the target pathology (more anterior temporal lesions can be accessed through a linear approach whereas posterior temporal lesions might require the reverse question-mark incision); linear incisions stay within the temporalis muscle and begin anterior to the tragus, 1-2 cm above the zygomatic arch, and can extend to 6-8 cm above the arch; reverse question-mark incisions also run anterior to the tragus, begin just above the zygomatic arch, and curve posteriorly at the top of the pinna 6-9 cm, then superiorly to the superior temporal line, then anteriorly toward the forehead, terminating at the hairline

• Suboccipital craniotomy/craniectomy: Involves a few incision types; midline and paramedian incisions are linear; midline incision may extend from 6 cm above the inion to the C2 spinous process, but is typically shorter than this; paramedian incision (includes the retrosigmoid approach) begins 5 mm medial to the mastoid notch and extends 4-6 cm above and below the notch; “hockey-stick” incisions (often utilized for a far lateral approach) are curved and begin in the midline at the C2 spinous process, extend superiorly to just above the inion, and then laterally to mastoid tip with a terminal caudal curve

Surgical field preparation

After the incision is planned, a minimal shave (2–4 cm on either side of the incision) is carried out with a disposable razor. Women institutions shave no hair at all. Various surgical scrubs and preps are acceptable; the fundamental 2 steps involve a lengthier scrub with Betadine detergent (povidone-iodine solution, Purdue Pharma, Stamford, CT) for 5 minutes followed by sterile application of Betadine paint that is allowed to dry. Draping involves initial placement of sterile towels to frame the incision, taking care to keep hair out of the field; placement of a 3M Ioban antimicrobial drape; and then a craniotomy drape with a fluid pouch. The incision is injected with a local anesthetic formulation, as described above, and the equipment is then arranged on and around the field.

Incision, burr holes, craniotomy

The skin is incised with a no. 10 blade down through the galea onto bone. In areas where the temporalis fascia and muscle underlie the incision, the scalpel is carried down to the fascial layer, and the fascia is then typically incised sharply and split with either scissors or Bovie cautery. Raney clips are commonly applied to the scalp edges for hemostasis. The scalp flap is reflected using either periosteal elevators (blunt dissection) or Bovie cautery. Retraction, mainly for pterional approaches, is accomplished by placing temporary sutures, fish hooks, or perforating towel clips through the base of the scalp flap, attaching them to rubber bands, and wrapping the rubber bands around a “Leyla” bar, which is a straight metal attachment situated above the surgical field. Most linear incisions are adequately retracted with self-retaining retractors (cerebellar or Weitlaner retractors).

For suboccipital incisions, the incision is carried down to the fascia and muscles, which are left intact. Raney clips can be more difficult to place for these incisions, so major scalp vessels are cauterized, and self-retaining retractors are placed. The fascia and muscles are then dissected with Bovie cautery until the bone is reached. ^[7]  A fascial cuff might be left behind for reattachment of the fascia at the end of the operation.

The number, size, and location of the burr holes depend on the craniotomy type, and there are many acceptable patterns, as follows: ^[11]

• Pterional and frontotemporal craniotomy: Two burr holes are typically drilled, one at the posterior insertion of the zygomatic arch (the low temporal burr hole) and the second at the intersection of the zygomatic bone, superior temporal line, and supraorbital ridge; if only one burr hole is drilled, it is the temporal burr hole

• Frontal craniotomy (unilateral or bilateral): For the unilateral approach, either 2 or 4 burr holes are drilled, one just medial to the sagittal sinus and as far anterior as possible with the second also just medial to the sagittal sinus and as posterior as possible; the additional two burr holes can be placed at the junction of the superior temporal line and orbital rim, along with another posterior to the depression of the sphenoid wing; for the bilateral approach, two burr holes are made on either side of the superior sagittal sinus (or two slots), and two burr holes are made laterally; drilling over the sagittal sinus is reserved for lesions that are located very medial, otherwise this can be avoided

• Temporal craniotomy: For the linear incision, one burr hole is made at the inferior pole of the incision; for the question-mark incision, one burr hole is made at the posterior insertion of the zygomatic arch, one at the upper anterior portion of the zygomatic bone, and one or two burr holes at the superior and posterior edges of the incision

• Suboccipital craniotomy/craniectomy: For midline incisions, the craniotomy involves a horizontal slot inferior to the inion and laterally placed burr holes on either side of the midline; the midline craniectomy extends down to the foramen magnum; for paramedian incisions, smaller craniectomies may be 4 cm in diameter at the transverse-sigmoid sinus junction, while larger craniectomies are bordered by the transverse sinus superiorly, foramen magnum inferiorly, sigmoid sinus laterally (which may violate mastoid air cells and require packing with bone wax), and midline medially

The burr holes are drilled with either the burr or perforator tip on the pneumatic or electric drill. The bone is drilled until the dura is carefully exposed, at which point a curette and Kerrison rongeur (usually 3 or 4 mm) are used to widen the hole. The dura is then separated from the bone using the Penfiled 3 dissector, footplate attachment, double-ender, nerve hook, or ball-ender (the latter 3 are standard instruments in the craniotomy tray). If the planned craniotomy coincides with a major sinus (eg, superior sagittal sinus), “slots” may be drilled over the sinus as opposed to burr holes or running the footplate through the overlying bone. These slots are longer troughs that allow for the sinus to be visualized through the dura and therefore safely avoided by the craniotome when the flap is being drilled.

The craniotomy is then drawn out with a marker or Bovie. The drill is fitted with the craniotome attachment, which slides between the bone and dura at the bottom of the burr hole. The craniotome is carried through the bone with the footplate angled upward (drill angled back) so as to dissect the underlying dura free from the bone. Each burr hole is connected by the craniotome, or a solitary burr hole can be used as both the starting and ending point for the craniotomy.

Once the complete bone flap is drilled out, a flap elevator is placed underneath the bone and used to lift while a Penfield no. 3 dissector separates the underlying attached dura. The flap is removed and then plated later with the mini-plate and screw system. The dura is irrigated to reveal bleeding vessels with the major vessels, such as the middle meningeal artery, cauterized by the bipolar instrument. Blood coming from bony edges is stopped with bone wax. Epidural bleeding, which tends to be diffuse, can be stopped by application of a hemostatic agent such as FloSeal (Baxter, Deerfield, IL), along with placement of Gelfoam and cottonoids that have been saturated in thrombin solution.

At this point, the craniotomy is complete. Once the bleeding is controlled, the dural opening is planned, and the intracranial surgery can proceed.

In the case of the suboccipital approach, a craniectomy is often performed in lieu of a craniotomy. A craniectomy involves the removal of bone without replacing it. This is typically preferred because postoperative swelling in the suboccipital region (which includes the brainstem) is exacerbated by an inelastic bone flap as opposed to absent bone or a pliable synthetic cranioplasty.

Craniectomies are drilled with the pneumatic drill and burr attachment until the underlying dura is partially exposed; curettes and Kerrison rongeurs complete the bony removal and dural exposure. Great care must be taken to avoid injuring the underlying sinuses in this region (eg, transverse and sigmoid sinuses). Bony landmarks such as the asterion can be used to help localize the sinuses (along with image-guided intraoperative navigational software), and, once enough bone is removed with the craniectomy, the sinus may be directly visualized through the dura.

Stereotactic neurosurgery refers to the process of using image guidance to localize and aid in the resection of an intracranial lesion. Preoperatively, the patient must undergo a dedicated MRI or CT sequence (with a set number of more thin cuts than the standard MRI/CT sequences).

In the operating room, this special sequence is displayed on the navigational system, which is then used to detect either facial bony landmarks on the patient or fiducial markers that were placed on the patient’s skull prior to obtaining the imaging. These fiducials can then be detected in the operating room and interfaced with the displayed imaging (MRI or CT). The interface between the navigational system and the patient’s landmarks allows the neurosurgeon to place a probe on the patient that is displayed on the system monitor in relation to the underlying brain anatomy (including the lesion of interest).

The incision and craniotomy can be planned at this point. This navigational system can then be used throughout the case to help actively locate the lesion of interest, as well as any structures that the neurosurgeon would care to avoid (eg, large draining veins, sinuses).

The use of intraoperative image guidance to plan and execute a craniotomy has grown considerably in recent years because of the availability of state-of-the-art stereotactic navigational systems (BrainLab [Heimstetten, Germany] and Stealth [Medtronic, Louisville, CO]) and the success that these systems have in accurately localizing intracranial lesions. For the practicing neurosurgeon, such stereotactic systems have become quite easy to implement and are regarded as standard adjuncts to nearly all planned craniotomy operations.