I- CRANIOTOMY A.

DESCRIPTION

A craniotomy is a surgical operation in which a bone flap is temporarily removed from the skull to access the brain. Craniotomies are often a critical operation performed on patients recording, brain imaging, and for neurological manipulations such as electrical stimulation and chemical titration. Human craniotomy is usually performed under general anesthesia but can be also done with the patient awake using a local anaesthetic; the procedure generally does not involve significant discomfort for the patient. In general, a craniotomy will be preceded by an MRI scan which provides a picture of thebrain that the surgeon uses to plan the precise location for bone removal and the appropriate angle of access to the relevant brain areas. The amount of skull that needs to be removed depends to a large extent on the type of surgery being performed. The bone flap is then replaced using titanium plates and screws or another form of fixation (wire, suture.etc). Craniotomy is distinguished from craniectomy (in which the skull flap is not immediately replaced, allowing the brain to swell, thus reducing intracranial pressure) and from trepanation, the creation of a burr hole through the cranium in to the dura mater.

B. INDICATION
Brain surgery may be needed to treat:

Brain tumors Bleeding (hemorrhage) or blood clots (hematomas) from injuries (subdural hematoma or epidural hematomas) Weaknesses in blood vessels (cerebral aneurysms) Damage to tissues covering the brain (dura) Pockets of infection in the brain (brain abscesses) Severe nerve or facial pain (such as trigeminal neuralgia or tic douloureux) Epilepsy

C.

ANATOMY

At birth the bones that make up the cranium or skull are separated, allowing the head to pass through the birth canal. (Figure 1) As the individual matures, the bones fuse together so that by late teens the bones form a solid union The various bones of the skull are the frontal, parietal, temporal, occipital, and sphenoid, (Figure 2) The scalp covers the skull Within the skull lie: 1. The brain, which is divided into four major parts- the right and left cerebral hemispheres, the cerebellum and the brainstem (Figure 3). The cerebral hemispheres form the largest portion of the brain and can be regarded as the 'thinking' part of the brain and are involved in movement, sensations, speech and creation of ideas Each cerebral hemisphere is divided into four lobes - frontal, parietal, temporal and occipital The surface of the hemispheres is folded upon itself and presents as various grooves (sulci) and bulges (gyri). The two cerebral hemispheres are connected across the midline by a large band of brain fibers called the corpus callosum that transmit nerve impulses between the hemispheres

The cerebellum lies at the back of the brain under the occipital bone and is involved in fine tuning movement The brainstem lies in front of the cerebellum and is attached above to the cerebral hemispheres, behind to the cerebellum and below to the spinal cord

2.

3. 4.

The meninges (the membranes that line the inside of the skull (dura) and cover the brain (piaarachnoid). A large fold of dura called the falx lies above the corpus callosum and separates the cerebral hemispheres. (Figure 4) Another large fold of dura, the tentorium, separates the cerebral hemispheres from the cerebellum. The brainstem passes through a hole in the front of the tentorium. The space that lies beneath the tentorium, which contains the cerebellum and brainstem, is called the posterior fossa The blood vessels that feed the brain The cerebrospinal fluid (the fluid that bathes the brain) originates within the ventricles (spaces) within the brain

D.PATHOLOGY
There are a variety of lesions (abnormalities) that affect the skull and its contents that require a craniotomy or craniectomy for exposure or removal. Skull. The most common lesions of the skull are benign tumors. Brain. The most common lesions of the brain that require craniotomies are 1. Tumors of the supporting cells of the brain called gliomas 2. Cancers from other organs that have gone (metastasized) to the brain (Figure 5) 3. Abscess (localized infection) Meninges. These tissues give rise to mostly benign tumors called meningiomas that may grow quite large and compress the brain causing damage (Figure 6)

Figure 5 - Two metastatic tumors to the Figure 6 - Large benign tumor brain removed using frameless stereotaxic (meningioma) before and after removal. image guided surgery through small The cavity formed by removal of the tumor craniotomies (4 by 4 cm). Cerebrospinal is filled with cerebrospinal fluid. fluid fills the cavities left by removal of the tumors. The small craniotomies directly over the tumors allowed the patient to be discharged the day after surgery. Blood vessels. The vessels at the base of the brain may give rise to aneurysms (weak areas that form like a blister on the vessel) that may rupture and cause bleeding around the brain (subarachnoid hemorrhage). (Figure 7 and click on Figure 8 for a video) An abnormal tangle of arteries and veins called an arteriovenous malformation (Figure 9) may bleed causing a clot

within the brain (intracerebral hematoma). High blood pressure may rupture of a blood vessel in the brain and cause an intracerebral hematoma Fluid that bathes the brain (cerebrospinal fluid). Obstruction to the flow of cerebrospinal fluid produces hydrocephalus that on occasion requires craniotomy.

II- SURGICAL PROCESS

There are 6 main steps during a craniotomy. Depending on the underlying problem being treated and complexity, the procedure can take 3 to 5 hours or longer. Step 1: prepare the patient No food or drink is permitted past midnight the night before surgery. Patients are admitted to the hospital the morning of the craniotomy. With an intravenous (IV) line placed in your arm, general anesthesia is administered while you lie on the operating table. Once asleep, your head is placed in a 3-pin skull fixation device, which attaches to the table and holds your head in position during the procedure (Fig. 2). Insertion of a lumbar drain in your lower back helps remove cerebrospinal fluid (CSF), thus allowing the brain to relax during surgery. A brain-relaxing drug called mannitol may be given.

Figure 2. The patients head is placed in a three-pin Mayfield skull clamp. The clamp attaches to the operative table and holds the head absolutely still during delicate brain surgery. The skin incision is usually made behind the hairline (dashed line). Step 2: make a skin incision After the scalp is prepped with an antiseptic, a skin incision is made, usually behind the hairline. The surgeon attempts to ensure a good cosmetic result after surgery. Sometimes a hair sparing technique can be used that requires shaving only a 1/4-inch wide area along the proposed incision. Sometimes the entire incision area may be shaved. Step 3: perform a craniotomy, open the skull The skin and muscles are lifted off the bone and folded back. Next, one or more small burr holes are made in the skull with a drill. Inserting a special saw through the burr holes, the surgeon uses this craniotome to cut the outline of a bone flap (Fig. 3). The cut bone flap is lifted and removed to expose the protective covering of the brain called the dura. The bone flap is safely stored until it is replaced at the end of the procedure.

Figure 3. A craniotomy is cut with a special saw called a craniotome. The bone flap is removed to reveal the protective covering of the brain called the dura.

Step 4: exposure the brain After opening the dura with surgical scissors, the surgeon folds it back to expose the brain (Fig. 4). Retractors placed on the brain gently open a corridor to the area needing repair or removal. Neurosurgeons use special magnification glasses, called loupes, or an operating microscope to see the delicate nerves and vessels.

Figure 4. The dura is opened and folded back to expose the brain. Step 5: correct the problem Because the brain is tightly enclosed inside the bony skull, tissues cannot be easily moved aside to access and repair problems. Neurosurgeons use a variety of very small tools and instruments to work deep inside the brain. These include long-handled scissors, dissectors and drills, lasers, ultrasonic aspirators (uses a fine jet of water to break up tumors and suction up the pieces), and computer imageguidance systems. In some cases, evoked potential monitoring is used to stimulate specific cranial nerves while the response is monitored in the brain. This is done to preserve function of the nerve and make sure it is not further damaged during surgery. Step 6: close the craniotomy With the problem removed or repaired, the retractors holding the brain are removed and the dura is closed with sutures. The bone flap is replaced back in its original position and secured to the skull with titanium plates and screws (Fig. 5). The plates and screws remain permanently to support the area; these can sometimes be felt under your skin. In some cases, a drain may be placed under the skin for a couple of days to remove blood or fluid from the surgical area. The muscles and skin are sutured back together. A turban-like or soft adhesive dressing is placed over the incision.

Figure 5. The bone flap is replaced and secured to the skull with tiny plates and screws.

III- IMAGES