Craniotomy

The term "craniotomy" refers broadly to the surgical removal of a section of the skull in order to access the intracranial compartment. The portion of skull temporarily removed is called a bone flap, and it is placed back in its original position after the operation is completed, typically fastened into place with low-profile titanium plates and screws. "Craniectomy" refers to an operation wherein the bone flap is removed but not replaced.

A craniotomy is named for the specific region of the skull where the bone is removed. For example, if the craniotomy is opened in the frontal bone, it is called a frontal craniotomy. Among the more common craniotomies in addition to the frontal include the parietal, temporal, occipital, and suboccipital. One of, if not the most common craniotomy site is referred to as "pterional." The pterional craniotomy is named for the pterion, the junctional point of 4 bones within the skull (frontal, temporal, greater wing of sphenoid, parietal).

If a craniotomy involves 2 contiguous regions of the skull, it is named for both regions (eg, frontotemporal craniotomy, also rendered as fronto-temporal craniotomy); if 3 regions are involved, all names are included in the description (eg, a frontotemporoparietal craniotomy).

Craniotomies that involve the use of MRI-based navigational software, which has become standard in nearly all planned craniotomy operations, are referred to as “stereotactic” craniotomies. "Stereotactic" is a generic term and does not specify the location of the craniotomy site.

Smaller craniotomies are often referred to as "keyhole” craniotomies and are used in situations that require less bone removal. As the accuracy of navigational software has improved, along with advances in surgical technique and visualization, these keyhole craniotomy approaches have become more commonplace.[1] An example of such a minimally invasive craniotomy is the supraorbital craniotomy, also more coloquially known as an "eyebrow" craniotomy, in which the incision and bone flap are placed in the region of the patient's eyebrow.  

The smallest type of craniotomy is technically a “burr hole,” also known as trephination. This is less regarded as a true craniotomy and more so as its own category of surgical approach, since it provides an extremely limited view of the underlying brain. However, with the advent of the endoscope, a long and thin high-definition camera, the burr hole serves as the entry port for the endoscope in a variety of intracranial approaches. Creating a burr hole involves drilling a small hole into the skull, revealing the underlying dura mater, the outermost of the 3 meninges covering the brain. The dura can then be opened to allow further exploration of the underlying brain.

The craniotomy is a fundamental tool in the armamentarium of the neurosurgeon. It represents the primary means by which a neurosurgeon enters the intracranial space. Diseases that affect the brain and its elements, including the brain parenchyma (the brain matter itself), vasculature (arteries, veins, capillaries), meninges (3 membranes covering the brain), and bone, all require an opening in the skull as the initial step. The craniotomy, therefore, is the first step in operations that target elements within the intracranial compartment. The following is a list of many basic indications for a craniotomy:

• Clipping of cerebral aneurysm (both ruptured and unruptured)

• Resection of arteriovenous malformation (AVM)

• Resection of brain tumor

• Biopsy of abnormal brain tissue

• Removal of brain abscess

• Evacuation of hematoma (eg, epidural, subdural, and intracerebral)

• Insertion of implantable hardware (eg, ventriculoperitoneal shunt [VPS], deep brain stimulators [DBS], subdural electrodes for seziure monitoring, Ommaya reservoir)

• Resection of epileptogenic focus/tissue

• Microvascular decompression (eg, for trigeminal neuralgia)

• Relieving elevated intracranial pressure (craniectomy)

There are no discrete contraindications to a craniotomy itself, but a spectrum of medical conditions may render craniotomy a high-risk intervention. It is up to the treating physicians to determine whether the risk of a craniotomy outweighs the risk of exacerbating other concomitant medical conditions. The following is a list of conditions that increase the risks associated with a craniotomy[2] , but are not rigid contraindications when taken singly:

• Advanced age

• Poor functional status

• Severe cardiopulmonary disease

• Severe systemic collapse requiring intensive care support (eg, sepsis, multiorgan failure)[3]

In addition, a craniotomy may be performed in order to treat an intracranial lesion that either directly involves or is located adjacent to critical nervous tissue, or what is often called “eloquent” brain. Such brain tissue may be responsible for vision, speech, memory, muscle strength and mobility, swallowing, coordination and balance, and even breathing. In these situations, it is the responsibility of the neurosurgeon, often in consultation with a neurologist, to determine whether the risk of operating in and around this eloquent tissue outweighs the risk of conservative (nonsurgical) management. This can be considered a type of intrinsic “contraindication,” and the final decision is left to the judgment of the treating neurosurgeon.

As noted above, craniotomy is a means to an end, the end being an intracranial operation. Therefore, the postprocedural complications that result from a craniotomy depend more on the type of surgery performed. However, some complications apply generally to all types of craniotomy. These complications differ from those that result from any prolonged surgery with a patient under general anesthesia (eg, deep venous thrombosis, pulmonary embolism, atelectasis/pneumonia, myocardial infarction).

Postoperative craniotomy complications can be divided into early and late categories and are listed with descriptions below.[4] Of note is that each of these complications leads to a change in neurologic status that is initially assessed with a neurologic examination followed by an urgent CT scan of the head.

Early complications

Bleeding/hematoma: A hematoma may form in the region of the surgery for multiple reasons (eg, poorly controlled blood pressure postoperatively, residual tumor, incomplete hemostasis). Symptoms may manifest as a depressed level of consciousness or a focal neurologic deficit (eg, new onset or worsening weakness) and can present within a few hours following surgery. A reoperation for hematoma evacuation is the standard treatment.

Seizures: Disruption of normal brain tissue can precipitate seizures postoperatively. The patient may present with classic signs of a seizure or simply with depressed level of consciousness. Patients are monitored with continuous electroencephalography (EEG). Treatment is medical if no underlying structural problem is found (eg, parenchymal hemorrhage).

Cerebrospinal fluid (CSF) leak: This can result from poor wound closure (eg, improperly sealed dura, poorly situated bone flap, loosely stitched fascial layers), infection, violation of mastoid air cells. It presents as clear drainage from the incision site, often with a palpable collection underlying the incision. Treatment may include reoperation for wound inspection and closure, spinal drain placement, overstitching the incision, and/or CSF shunting.

Cerebral infarct: This is stroke caused by damage to a major artery or vein and can be caused by the craniotomy itself, especially if a major sinus is damaged (venous infarct). It manifests as a new deficit (eg, altered mental status, aphasia, weakness, numbness, visual deficit). Evaluation is with MRI, specifically diffusion-weighted imaging (DWI). Treatment is supportive, and a thromboembolic source is investigated.

Pneumocephalus: This is air within the cranium introduced through the craniotomy site. It may manifest as confusion, lethargy, headache, seizures, and nausea/vomiting. Treatment is inhalation of 100% oxygen through a nonrebreather mask.

Late complications

Infection: This results from the introduction of some form of contamination into the surgical site (brain, subdural/epidural space, incision). It can manifest as fevers, rigors/chills, and other systemic symptoms. Most reliably, the wound itself appears erythematous, indurated, and/or expressing pus. Treatment can be antibiotic therapy alone but typically involves surgery for washout of the wound followed by long-term antibiotic therapy[5, 6]

Late seizure: An epileptic focus may develop secondary to scarring (gliosis).

Informed consent is the process of explaining the risks, benefits, and alternatives of the planned craniotomy to the patient. This is done by the neurosurgeon and can be supplemented with teaching materials at the neurosurgeon's discretion. Patients nowadays have more access to information through multiple online resources, which can help to prepare the patient for the planned procedure. The informed consent is typically conducted in the neurosurgeon's office prior to the planned procedure, or in the hospital if the patient has developed an acute issue. There are occasions where the patient is incapacitated by the brain pathology so that consent must be obtained through a designated health care proxy, spouse or sibling, and rarely in emergency cases, by means of two attending physicians, one of whom is the operating neurosurgeon.

Prior to undergoing craniotomy, all patients will have undergone some type of brain imaging.

Computed tomography (CT) of the head is the most widely used and accessible form of brain imaging, and along with CT angiography (abbreviated as CTA, useful for vascular pathology such as aneurysms and AVMs), they continue to play a major role in operative planning.

Magnetic resonance imaging (MRI) has largely replaced CT scanning in the delineation of brain tumors while continuing to expand its role in stereotactic neurosurgery (image guidance). Its application remains vast and has become standard in nearly all planned craniotomy operations.

In certain circumstances, diagnostic cerebral angiography may be the primary mode of imaging, although a patient nearly always undergoes angiography based on a finding initially identified on CT or MRI.

In addition to brain imaging, a patient’s preoperative assessment may include a recent set of basic blood tests, electrocardiogram (ECG), and chest radiography, depending on the patient’s medical history and recommendations of the treating physician. These studies are generally grouped into the pre-admission testing category done for nearly any scheduled craniotomy.

A few fundamental tools are required to accomplish a standard craniotomy or craniectomy. The setting for a craniotomy is a controlled, sterile environment in a designated operating room. The basic objective is to remove the bone flap as safely as possible, taking great pains to minimize blood loss, to reduce the potential for infection, and to limit damage to the underlying brain. The essential instruments for performing a craniotomy are as follows:

• Skin knife (scalpel): No. 10 blade is typically used to make the skin incision

• Suction tips and tubing (eg, Frazier tip): For clearing blood from the surgical field to maintain visibility; microsuction and variable suction devices are typically utilized when the brain itself is entered

• Raney clips and tissue retractors (Adson cerebellar, Weitlaner, Jansen): The clips are placed on the scalp edges to stop bleeding, while the retractors serve to keep the incision open

• Leyla bar and fish hooks: An optional setup that allows retraction of scalp and muscle for the duration of the operation, most often used for a pterional craniotomy

• Monopolar electrosurgical unit (eg, Valleylab, Covidien): Often referred to as a Bovie, this instrument offers two functions (cut and coagulation) for dissection through subcutaneous tissue, fascia, and muscle while preserving hemostasis

• Bipolar electrosurgical unit (eg, Codman, Malis): Provides focused electrocautery of blood vessels as a means of stopping bleeding; can also be used to safely coagulate dura and to dissect both normal and abnormal brain tissue

• Periosteal elevator: Used to lift the periosteum off the skull prior to drilling

• High-speed air drill (eg, Midas Rex, Zimmer): Accommodates various drill bits, including burrs and perforators (used to penetrate the skull and form a burr hole), as well as the craniotome with foot plate (used to carve out a bone flap from the initial burr hole)

• Flap elevator and Penfield dissector no. 3: Both used to lift the bone flap after the craniotome has drilled out a window of bone

• Craniotomy miniplate and screw set (eg, Lorenz, Codman): Titanium low-profile plating system used for replacing the bone flap after the intracranial surgery is complete[7]

Given the importance of minimizing blood loss during a craniotomy and the subsequent intracranial surgery, medications that are considered "blood thinners" should be discontinued prior to surgery. These include nonsteroidal anti-inflammatory medications (NSAIDs, eg, aspirin and ibuprofen), antiplatelet agents (eg, clopidogrel [Plavix]), and anticoagulant medications (eg, warfarin [Coumadin]). With the proliferation of newer age blood-thinning agents (eg pradaxa, eliquis), some of which may be unfamiliar to the treating neurosurgeon, more attention must be paid to the patients' mediation list. Patients should also be counseled to stop smoking and drinking alcohol prior to a craniotomy.

The treating neurosurgeon may also initiate preoperative steroid therapy (eg, with dexamethasone [decadron]) to reduce cerebral edema due to an intracranial mass lesion, as well as antiepileptic therapy (phenytoin [Dilantin] or levetiracetam [Keppra]) if there is a significant concern for potential seizures. If the craniotomy is part of an operation that will involve manipulation of brain tissue, an additional steroid dose is typically given in the operating room prior to incision (10-20 mg IV dexamethasone). Likewise, a loading dose of an antiepileptic drug is given for the same circumstance (eg, 1 gram of fosphenytoin or phenytoin [15-18 mg/kg body weight], 1000-1500 mg of levetiracetam).

It has now become standard practice for an intravenous antibiotic to be administered in the operating room approximately 30 minutes prior to the surgery (eg, cefazolin [Ancef], vancomycin, clindamycin) with the goal of reducing the likelihood of wound infection from neighboring bacterial skin flora (most commonly Staphylococcus aureus). For some craniotomies, typically those involving a large mass lesion with significant underlying edema and brain shift, a diuretic (mannitol) is administered during skin incision for additional brain relaxation at a dose of 0.5-1 g/kg body weight.[3]

Two broad categories of anesthesia are used for a craniotomy: local and general. Most craniotomies involve both methods of anesthesia; local anesthetic is injected into the incision site for superifical hemostasis and postoperative pain control, while general endotracheal anesthesia (GETA) is administered for the duration of the operation.

In certain circumstances, an awake craniotomy is performed so that the patient can be awoken and interact during the critical portions of the case, and this requires greater emphasis on local anesthesia and intravenous administration of sedatives during the operation.[8, 9, 10] An awake craniotomy involves a combination of local and general anesthesia via intravenous agents, but does not involve insertion of an endotracheal (ET) tube. This type of anesthesia is commonly referred to as monitored anesthesia care (MAC), which is marked by the absence of an ET tube and the lack of inhalational agents. MAC is used for awake craniotomies and smaller, shorter operations such as the drilling of burr holes. The advent of more advanced anesthetic agents (eg, precedex and remifentanil) and higher-definiton navigational software (including functional MRI) for eloquent region mass lesions have expanded the use of MAC and awake craniotomy approaches. In particular, this is being done with increasing frequency in the case of tumors that were once considered unresectable.

The local anesthetic agent used for craniotomies is typically characterized by a rapid onset of action and intermediate duration of action. Lidocaine (0.5%-2%) is the most commonly used medication. Additionally, the local anesthetic is mixed with a dilution of epinephrine (1:100,000-1:400,000), which confers local hemostatic control via vasoconstriction. This vasoconstrictive effect also counteracts the vasodilatory effect of the anesthetic agent, thus prolonging its duration of action at the injection site.

GETA for craniotomies, commonly referred to as neuroanesthesia, involves two categories of medications: inhalational agents and intravenous agents. There are a number of factors of special concern to the neuroanesthesiologist before and during a craniotomy. These parameters and a brief description of their importance to the operation are as follows:

• Blood pressure: May have to be raised or lowered depending on the operation; its control is paramount to the anesthesiologist, as it affects cerebral perfusion pressure (CPP) and bleeding; monitored continuously via arterial line

• Arterial CO2 tension (PaCO2): As a potent vasodilator, CO2 must be closely monitored and can be manipulated by the anesthesiologist, as hyperventilation reduces PaCO2 and leads to vasoconstriction and less cerebral blood flow (CBF); the goal during and immediately after a craniotomy is an end-tidal CO2 (ETCO2) of 25-30 mm Hg, which correlates to a PaCO2 of 30-35 mm Hg

• Hematocrit: Monitoring blood loss intraoperatively and transfusing blood as necessary is a critical aspect of maintaining the patient's circulatory status during the operation

• Temperature: Mild hypothermia has demonstrated protection against cerebral ischemia and is used in certain neurosurgical procedures[11]

Inhalational drugs in use today tend to be halogenated agents that have in common the properties of suppressing EEG activity and offering some element of cerebral protection. Included in this category are isoflurane, desflurane, and sevoflurane. Intravenous agents of choice include propofol, which is often used because of its short half-life, for induction of general anesthesia, as well as a continuous infusion for total intravenous anesthesia (TIVA). Less often used in this latter category are barbiturates, etomidate, and ketamine. Narcotics are also used as intravenous agents during general anesthesia for a craniotomy; remifentanil and fentanyl are more commonly administered, particularly in awake craniotomies as noted above.[11]

In many ways, the positioning of the patient is the most critical step in performing an effective operation. It begins with the choice of how to situate the patient’s head, or head fixation.

Head position

There are two basic ways of positioning the head: unfixed and fixed.

The unfixed approach is typically used when rapid access is necessary or stabilization of the head is not essential. This involves placing the head on a head-holding apparatus, often a padded cerebellar headrest (also called a horseshoe) or a simple "doughnut" (a circular foam with the middle portion cut out). In children younger than 3 years, pins are not recommended owing to increased risk of depressed skull fractures, so a cerebellar head rest is used. In children aged 3-10 years, special pediatric pins are recommended.

Head fixation is achieved with 3 skull pins that are situated in a head clamp (eg, Mayfield head-holder). The location of the craniotomy dictates where the pins are placed in the patient’s skull. Some basic principles include placement of pins above the orbits and pinna; avoidance of thin areas of the skull, such as the temporal squamosa and the frontal sinus; placement of the single pin anteriorly when the patient is positioned supine; and placement of the single pin on the same side of the craniotomy when the patient is positioned prone for a posterior fossa approach.[11]

When the desired pin positioning is achieved, the clamp is squeezed together, thereby seating the pins in the skull. The knob that houses the tension spring is screwed tightly until 60 pounds of pressure is registered. In pediatric patients, 30-40 pounds is the recommended limit. The clamp is then locked into the Mayfield adaptor, which is a series of joints extending from the head of the operating table. Care should be taken to avoid hyperflexion of the neck, which could lead to obstruction of the ventilated airway, and to avoid compression of the neck or jugular venous outflow, which could increase intraoperative bleeding. Other vulnerable areas include the ulnar nerves and the axilla, both of which require careful padding, especially in the lateral position.

Body position

Depending on the location of the intracranial lesion, there are various methods of positioning the patient on the operating table in order to maximize visualization and to improve ease of access to the target. There are 4 fundamental positions for a craniotomy: supine, prone, lateral, and sitting (see image below).

The following is a list describing these positions in greater detail, including a variation on the sitting position (semi-sitting)[12] :

• Supine position: The most common position; can involve the head in the neutral position or turned; allows access to the frontal, parietal, and temporal lobes; associated with craniotomies in all of these regions, as well as with the pterional craniotomy for Circle of Willis aneurysms; also used for transsphenoidal approaches to the pituitary region; can also be used for certain lesions of the posterior fossa such as cerebellopontine angle (CPA) masses, but this approach requires a significant head turn (nearly horizontal) and the aid of a shoulder roll

• Prone position: More narrow application; head is pinned in the neutral position; associated with occipital craniotomy and suboccipital craniotomy/craniectomy to access the posterior fossa

• Lateral position: Associated with suboccipital craniotomies for access to posterior fossa lesions, including retrosigmoid, far lateral and extreme far lateral approaches; can also be used for posteriorly situated lesions of the parietal lobe and lesions of the occipital lobe; modifications include the "park bench" position, a more exaggerated head turn that is used in certain approaches (eg, occipital trans-tentorial); another use is for deep-seated lesions, often in the ventricular system of the brain, where an interhemispheric approach is utilized; this approach develops a corridor between one frontal lobe and the falx cerebri, a large dural fold in the midline separating the frontal and parietal lobes of the brain

• Sitting position: Rarely used; used for access to the posterior fossa and pineal region; associated with a higher risk of venous air embolism, which is a potentially fatal complication

• Semi-sitting position: Associated with surgeries involving the pineal region, namely the supracerebellar infratentorial approach; can also include approaches to the posterior parietal region and occipital lobes; less risk of air embolism than a pure sitting position, but still higher risk than that of the recumbent positions

Operating room layout

Depending on the craniotomy, the patient’s physical positioning in the operating room varies. The key elements of the operating room include the patient on the operating room table, anesthesiology team, operating neurosurgeon and assistant, scrub tech, and intraoperative microscope. Other equipment fits into the room based on where these elements are situated (see image below).

Immediate postcraniotomy care

For nearly all types of craniotomy, the patient is observed for at least the first 24 hours in a neurological intensive care unit (NICU) or general surgical ICU. Basic laboratory tests are sent (complete blood cell count and basic metabolic panel). Neurological examinations are performed by the nursing staff every 1-2 hours, and any changes in neurologic status (eg, confusion, lethargy, aphasia, cranial nerve deficit, weakness, numbness) are immediately conveyed to the neurosurgical team.

In addition, the patient’s systolic blood pressure is kept between 90-140 mm Hg, since pressures above this range place the patient at risk for hemorrhage into the operative site, while pressures too low may compromise cerebral perfusion pressure and lead to possible infarcts. If necessary, an intravenous antihypertensive medication is administered (eg, intravenous nicardipine).

Antibiotics are continued for a total of 24 hours following the craniotomy. Dexamethasone is tapered depending on the surgery; a straightforward supratentorial craniotomy requires a shorter taper, over one week, while operations for malignant mass lesions (gliomas, metastases) and posterior fossa craniotomies receive a longer taper, over two weeks. Patients with malignant lesions are typically tapered down to and then maintained on a low dose of decadron that is subsequently managed by the treating radiation oncologist, neuro-oncologist, or general oncologist.

Antiepileptics are administered postoperatively at the discretion of the neurosurgeon; if the use of these drugs extends beyond a month, they are often managed in consultation with a neurologist.

Long-term monitoring

After the acute postoperative phase (24-48 hours of observation in an ICU setting), the patient is transferred to a hospital floor bed, where the recovery continues. For most craniotomies, on the first postoperative day, the patient’s blood pressure parameters are liberalized, Intraoperative monitoring devices are removed (arterial line, Foley bladder catheter), and the patient is encouraged to ambulate.

From the first postoperative day onward, functional needs are assessed by an assortment of therapists, if necessary (eg, physical therapy, occupational therapy, speech therapy), and plans for further care are implemented, such as an inpatient rehabilitation stay or outpatient physical therapy.

All dressings are removed on the second postoperative day, and the staples or sutures used to close the most superficial skin layer can be removed 5-10 days following surgery. Absorable sutures are being more commonly utilized due to the use of more minimally invasive incisions and approaches.

If the recovery proceeds without complication, patients can be discharged as soon as the first postoperative day, though more commonly on the second or third postoperative day. Hospitalizations can exceed this duration depending on the specifics of the surgery.

Routine postoperative follow-up includes an office visit to the treating neurosurgeon within 1-2 weeks after hospital discharge. For benign lesions (eg, meningiomas, pituitary adenomas) the neurosurgeon typically conducts the long-term followup with surveillance MRIs. For malignant lesions, a neuro-oncologist in the case of primary brain neoplasms (eg, glioblastoma) and oncologist in the case of metastatic tumors conduct the long-term followup, also with surveillance MRIs along with adjuvant treatment as well.

Patient education

Upon discharge, the patient and family are given specific instructions. If the patient notes clear leakage from the craniotomy incision, which could indicate CSF egress, an immediate call to the neurosurgeon is made. Bleeding from the incision site for the first few days following surgery is common and not concerning. If the wound itself is noted to be tender, red, or not healing well or the patient develops fevers and chills, the patient should contact the neurosurgeon. If the patient feels nauseous, vomits, notices visual changes (blurriness, field cuts), experiences increasing headaches, has word-finding difficulties, experiences cognitive slowing, has newly onset weakness and/or numbness, or is noted to be lethargic, confused, or difficult to arouse by family, an urgent call should be placed to the neurosurgeon.

In terms of wound care, the patient is allowed to shower on the third postoperative day but typically discouraged from a bath until 1–2 weeks later. Hair products other than baby shampoo are also discouraged for at least 2 weeks. Also, the patient is cautioned against picking and manipulating the incision. Most patients who undergo craniotomy are considered fit to return to most occupations 2–6 weeks following the operation.

Patients may also be cautioned against flying for 1–4 weeks given the possibility of exacerbating air pockets (pneumocephalus) that are introduced into the intracranial space during the craniotomy. Changes in cabin pressure may induce severe headaches.

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.

The goals of pharmacotherapy are to reduce morbidity and to prevent complications.

Preoperative and postoperative medications include the following:

• Steroids (dexamethasone): For brain edema and inflammation

• Antiepileptics (phenytoin, levetiracetam): Seizure prophylaxis or treatment

• Osmotic diuretics (mannitol): Given intraoperatively to reduce brain bulk

• Prophylactic antibiotics (cefazolin, vancomycin, clindamycin): Gram-positive coverage reduces the incidence of infection from scalp flora

• Local anesthetic (lidocaine with epinephrine): Local pain relief with vasoconstrictive agent for hemostasis

• Intravenous sedatives: Propofol, remifentanil, fentanyl

• Inhalational anesthetics: Isoflurane, desflurane, sevoflurane

• Intravenous antihypertensive (nicardipine): For postoperative systolic blood pressure control

Class Summary

Corticosteroids have anti-inflammatory properties and cause profound and varied metabolic effects. Corticosteroids modify the body’s immune response to diverse stimuli.

Dexamethasone (Baycadron)

Dexamethasone has many pharmacologic benefits, but also significant adverse effects. It stabilizes cell and lysosomal membranes, increases surfactant synthesis, increases serum vitamin A concentrations, and inhibits prostaglandin and proinflammatory cytokines.

Class Summary

These agents prevent seizure recurrence and terminate clinical and electrical seizure activity.

Phenytoin (Dilantin, Phenytek)

Used for seizure prophylaxis or treatment. Phenytoin works for tonic-clonic seizures and is often used because it can be administered once a day. Long-term side effects of osteopenia and cerebellar ataxia now temper its use by neurologists. This agent is one of the most difficult antiepileptic drugs to use because of its zero-order kinetics and narrow therapeutic index. In addition, it can have significant bidirectional drug interactions.

Levetiracetam (Keppra, Keppra XR)

Used for seizure prophylaxis or treatment. Administered as adjunct therapy for partial seizures and myoclonic seizures. Also indicated for primary generalized tonic-clonic seizures. Mechanism of action is unknown.

Class Summary

These agents are used in an attempt to lower ICP and cerebral edema by creating an osmotic gradient across an intact blood-brain barrier; as water diffuses from the brain into the intravascular compartment, ICP decreases.

Mannitol (Osmitrol, Aridol)

Mannitol may reduce pressure within the subarachnoid space by creating an osmotic gradient between the CSF in the arachnoid space and the plasma. This agent is not for long-term use.

Class Summary

Empiric antimicrobial therapy must be comprehensive and should cover all likely pathogens in the context of the clinical setting.

Cefazolin

First-generation semisynthetic cephalosporin that, by binding to one or more penicillin-binding proteins, arrests bacterial cell wall synthesis and inhibits bacterial replication. Poor capacity to cross blood-brain barrier. Primarily active against skin flora, including S aureus. Regimens for IV and IM dosing are similar.

Clindamycin (Cleocin, Cleocin Pediatric)

A lincosamide semisynthetic antibiotic produced by 7(S)-chloro-substitution of 7(R)-hydroxyl group of parent compound lincomycin. Inhibits bacterial growth, possibly by blocking dissociation of peptidyl tRNA from ribosomes, causing RNA-dependent protein synthesis to arrest. Widely distributes in the body without penetration of CNS. Protein bound and excreted by liver and kidneys.

Available in parenteral form (ie, clindamycin phosphate) and oral form (ie, clindamycin hydrochloride). Oral clindamycin is absorbed rapidly and almost completely and is not appreciably altered by presence of food in stomach. Appropriate serum levels reached and sustained for at least 6 h following oral dose. No significant levels attained in cerebrospinal fluid. Also effective against aerobic and anaerobic streptococci (except enterococci).

Vancomycin

This is a potent antibiotic that is directed against gram-positive organisms and is active against enterococcal species. It is useful in septicemia and skin structure infections. Vancomycin is used in conjunction with gentamicin for prophylaxis in penicillin-allergic patients undergoing a craniotomy. Dose adjustment may be necessary in patients with renal impairment.

Class Summary

Local anesthetic agents are used to increase patient comfort during the procedure.

Lidocaine and Epinephrine (Lignospan, Xylocaine with Epinephrine)

Lidocaine is an amide local anesthetic used in a 1%-2% concentration. This agent inhibits depolarization of type C sensory neurons by blocking sodium channels. Epinephrine prolongs the effect and enhances hemostasis (maximum epinephrine dose, 4.5-7 mg/kg).

Class Summary

After standard monitoring equipment is attached and peripheral venous access achieved but before the arterial line is inserted, the midazolam dose is administered. Before placement of the arterial line, it should be ensured that a radial artery graft will not be used for CABG.

Propofol (Diprivan)

Propofol is a phenolic compound unrelated to other types of anticonvulsants. It has general anesthetic properties when administered intravenously. Propofol IV produces rapid hypnosis, usually within 40 seconds. The effects are reversed within 30 minutes, following the discontinuation of infusion. Propofol has also been shown to have anticonvulsant properties.

Isoflurane (Forane, Terrell)

Isoflurane is an inhalation anesthetic. It may have a myocardial protective effect and therefore is especially useful in off-pump surgery. Isoflurane potentiates the effects of muscle relaxants. Small doses of muscle relaxants can achieve complete paralysis when administered concomitantly with isoflurane.

Desflurane (Suprane)

Desflurane is an inhalation anesthetic. It may have a myocardial protective by depressing myocardial contractility. Induces general anesthesia by enhancing inhibitory postsynaptic channel activity and inhibiting excitatory synaptic activity.

Sevoflurane (Sojourn, Ultane)

Sevoflurane is an inhalation anesthetic. May decrease blood pressure through a decrease in sympathetic activity. It may have a myocardial protective effect by depressing myocardial contractility.

Class Summary

Induction of anesthesia is accomplished by using high doses of opioid (usually fentanyl or remifentanil) to minimize the dose of propofol, etomidate, or thiopental and thereby maximize cardiovascular stability.

Fentanyl citrate (Duragesic, Abstral, Actiq, Fentora, Onsolis)

Fentanyl citrate is a synthetic opioid that has 75-200 times more potency and a much shorter half-life than morphine sulfate. It has fewer hypotensive effects than morphine and is safer in patients with hyperactive airway disease because of minimal or no associated histamine release. By itself, fentanyl citrate causes little cardiovascular compromise, although the addition of benzodiazepines or other sedatives may result in decreased cardiac output and blood pressure.

Fentanyl citrate is highly lipophilic and protein-bound. Prolonged exposure to it leads to accumulation of the drug in fat and delays the weaning process. Consider continuous infusion because of the medication's short half-life.

Remifentanil (Ultiva)

Remifentanil binds mu-opioid receptors at various sites within the CNS.

Class Summary

Antihypertensive agents are used to reduce blood pressure.

Nicardipine (Cardene)

Nicardipine is a calcium channel blocker that has a potent and rapid onset of action, is easy to titrate, and lacks toxic metabolites. It appears to be effective in hypertensive encephalopathy, but the reported experience is limited.