Craniotomy

A craniotomy is the surgical removal of a section of bone (bone flap) from the skull for the purpose of operating on the underlying tissues, usually the brain. The bone flap is replaced at the end of the procedure. If the bone flap is not replaced, the procedure is called a craniectomy. A craniotomy is used for many different procedures within the head, for trauma, tumor, infection, aneurysm, etc.

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. The meninges (the membranes that line the inside of the skull (dura) and cover the brain (pia-arachnoid). 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
   
3. The blood vessels that feed the brain
   
4. The cerebrospinal fluid (the fluid that bathes the brain) originates within the ventricles (spaces) within the brain