A craniectomy is a major brain surgery in which a surgeon removes a portion of the skull and intentionally leaves it off. That’s the key distinction from the more common craniotomy, where the bone is temporarily lifted, the brain is treated, and the bone is secured back in place during the same operation. In a craniectomy, the missing piece of skull stays off for weeks or months, giving the brain room to swell safely before a second surgery replaces it.
Why a Craniectomy Is Performed
The brain sits inside a rigid box of bone. When the brain swells from injury or disease, pressure builds rapidly inside that box with nowhere to go. This rising intracranial pressure can compress brain tissue, cut off blood flow, and become fatal. Normal pressure inside the skull stays below about 16 mmHg. Current guidelines recommend treating pressure that rises above 22 mmHg, as levels beyond that point are associated with higher mortality. When medications, drainage, and other measures fail to bring pressure down, removing part of the skull is considered a last-resort option to give the brain space to expand outward instead of crushing inward.
The most common reasons for a craniectomy include severe traumatic brain injury (such as from car accidents or falls), large strokes that cause dangerous swelling (called malignant cerebral infarction), bleeding between the brain and skull, and widespread brain swelling from other causes. Less frequently, it may be used for certain brain infections, tumors, or rare conditions in children where the skull bones fuse too early.
What Happens During the Surgery
The procedure is performed under general anesthesia. After shaving and cleaning the area, the surgeon makes an incision through the skin and pulls back muscle and tissue to expose the skull. A surgical drill creates several small holes in the bone, and then cuts are made between those holes to lift out a section of skull. The size of the piece removed depends on how much room the brain needs.
Once the bone is out, the surgeon addresses the underlying problem, whether that’s relieving pressure, removing a blood clot, or treating damaged tissue. The exposed area of the brain is then covered with a protective mesh material, and the skin and muscle are closed over it with staples or sutures. You’re left with a section of your head where only skin, mesh, and soft tissue sit between your brain and the outside world.
What Happens to the Bone
The removed piece of skull (called the bone flap) is carefully preserved so it can potentially be used later to repair the gap. The two most common storage methods are freezing it at around -80°C in a hospital bone bank, or tucking it into a pocket beneath the skin of the patient’s abdomen, where the body keeps it alive with blood supply. Both approaches aim to keep the bone sterile and viable until it’s needed again, typically weeks to months later.
How a Craniectomy Differs From a Craniotomy
In a craniotomy, the surgeon lifts a section of skull, performs the procedure underneath, and reattaches the bone before closing. The patient leaves the operating room with their skull intact. In a craniectomy, the bone stays off. This means the patient lives with a skull defect that requires protection until a second surgery, called a cranioplasty, fills in the gap. Craniotomies are far more common and are used for planned procedures like tumor removal. Craniectomies are typically reserved for emergencies where the brain is already swelling dangerously or is expected to.
Living With a Skull Defect
The period between the craniectomy and the cranioplasty can be challenging. Without bone protecting part of the brain, even minor bumps to the head carry serious risk. Patients are fitted with a custom protective helmet that they wear whenever they’re upright or moving around. In the hospital, staff follow specific protocols: repositioning the head so the unprotected side doesn’t press against surfaces, ensuring at least one person supports the head during any transfer or turning, and marking the patient as a high falls risk. Upon discharge, patients and caregivers receive written instructions to avoid any contact with the craniectomy site.
Some patients develop a complication known as syndrome of the trephined. This happens when the skin over the skull defect begins to sink inward, and patients experience a cluster of symptoms including headaches, dizziness, ringing in the ears, fatigue, cognitive decline, and depression. A hallmark clue is that symptoms improve when lying flat and worsen when sitting or standing upright. The condition can stall neurological recovery and is sometimes mistaken for a lack of progress from the original brain injury. Fortunately, it typically resolves quickly once the skull is repaired, with many patients showing noticeable improvement within four days of their cranioplasty.
The Cranioplasty: Repairing the Skull
The follow-up cranioplasty restores the skull’s protective shell. If the original bone flap was preserved and remains intact, surgeons prefer to use it. Autologous bone (the patient’s own) is considered the first choice because the body recognizes it, it integrates well, and it costs less than alternatives. However, if the stored bone has been damaged, fragmented, infected, or has started to deteriorate, surgeons use a custom-made titanium plate instead. Titanium implants are manufactured to match the exact contours of the skull defect using imaging scans and can be a preferred option when early repair is needed and the original bone isn’t viable.
The timing of the cranioplasty varies. Patients typically spend a considerable waiting period, often several months, before they’re medically stable enough for the reconstruction. During this entire window, the brain remains vulnerable and the protective precautions described above stay in place.
Outcomes and What to Expect
A craniectomy is not a routine procedure. It is performed when brain swelling is life-threatening and other treatments have failed, which means the patients who need it are already critically ill. Outcomes depend heavily on the severity and cause of the original brain injury, not just the surgery itself. One observational study tracking patients who underwent decompressive craniectomy for traumatic brain injury, hemorrhage, and other severe brain conditions found a mortality rate of 67%, with only about 6 to 10% of patients achieving what clinicians consider a favorable functional outcome at follow-up of six months or more.
Those numbers reflect the gravity of the conditions that lead to craniectomy, not the failure of the procedure itself. For many patients, the surgery prevents what would otherwise be certain death from uncontrolled brain pressure. The goal in most cases is survival and the possibility of rehabilitation, even when full recovery is unlikely. Patients who do survive face a long rehabilitation process that may include physical therapy, occupational therapy, speech therapy, and cognitive rehabilitation depending on which areas of the brain were affected.
For patients with large strokes specifically, the evidence for decompressive craniectomy is stronger, with studies showing it can meaningfully improve survival. The decision to operate always involves weighing the potential for survival and quality of life against the risks, and it is one that surgical teams make urgently, often when the patient cannot participate in the decision themselves.