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).