Craniotomy is a cut that opens the cranium. During this surgical procedure, a section of the skull, called a bone flap, is removed to access the brain underneath. The bone flap is usually replaced after the procedure with tiny plates and screws. A craniotomy may be small or large depending on the problem. It may be performed during surgery for various neurological diseases, injuries, or conditions such as brain tumors, hematomas (blood clots), aneurysms or AVMs, and skull fractures. Other reasons for a craniotomy may include foreign objects (bullets), swelling of the brain, or infection. Depending on the reason for the craniotomy, this surgery requires a hospital stay that ranges from a few days to a few weeks. Typically the bone flap is replaced. If the bone flap is not replaced, the procedure is called a craniectomy. 

Craniotomies are often named for the bone being removed. Some common craniotomies include frontotemporal, parietal, temporal, and suboccipital. Craniotomies are also named according to their size and complexity. Small dime-sized craniotomies are called burr holes or keyhole craniotomies. Sometimes stereotactic frames, image-guided computer systems, or endoscopes are used to precisely direct instruments through these small holes. Burr holes or keyhole craniotomies are used for minimally invasive procedures to: insert a shunt into the ventricles to drain cerebrospinal fluid (hydrocephalus) insert a deep brain stimulator to treat Parkinson Disease insert an intracranial pressure (ICP) monitor remove a small sample of abnormal tissue (needle biopsy) drain a blood clot (stereotactic hematoma aspiration) insert an endoscope to remove small tumors and clip aneurysms Large or complex craniotomies are often called skull base surgery. These craniotomies involve the removal of a portion of the skull that supports the bottom of the brain where delicate cranial nerves, arteries, and veins exit the skull. Reconstruction of the skull base is often necessary and may require the additional expertise of head-and-neck, otologic, or plastic surgeons. Surgeons often use sophisticated computers to plan these craniotomies and locate the lesion. 

Skull base craniotomies can be used to: remove or treat large brain tumors, aneurysms, or AVMs treat the brain following a skull fracture or injury (e.g., gunshot wound) remove tumors that invade the bony skull Risks No surgery is without risks. General complications of any surgery include bleeding, infection, blood clots, and reactions to anesthesia. Specific complications related to a craniotomy may include: stroke seizures swelling of the brain, which may require a second craniotomy nerve damage, which may cause muscle paralysis or weakness CSF leak, which may require repair loss of mental functions permanent brain damage with associated disabilities