The brain is protected by the rigid bony structure of the skull or cranium. The brain, its blood supply and a regulated amount of cerebrospinal fluid fill the cranium and are usually referred to as the intracranial contents (see Box 10.1 and section on raised intracranial pressure, p. 142).

The brain consists of the cerebrum and the cerebellum, which are separated by a double fold of dura mater known as the tentorium. The area above the tentorium is known as the supratentorial space, and the area below it is the infratentorial space.

The cerebrum is further divided into two cerebral hemispheres by the falx cerebri, which is a double fold of dura mater with a venous sinus, the superior sagittal sinus, in between the two layers of dura mater. The two hemispheres are joined by the corpus callosum. The cerebral cortex, which makes up the outer layer of the brain, comprises neural cell bodies (grey matter). This layer of grey matter plays a most important role in the higher functions of the brain. The cerebral cortex of each hemisphere has four lobes which are not separated physically and are named after the bones that lie above them: i.e. frontal, parietal, temporal and occipital.

The nerve fibres carrying sensory and motor information to and from the cortex and other islands of grey matter, such as the basal ganglia, are known as white matter. The white appearance is caused by the presence of myelin surrounding the neural axons making up the fibres. The myelin provides a protective insulating sheath around the axon.

The brain and spinal cord are covered by the meninges, which are made up of an outer tough layer called the dura mater; a middle layer, the arachnoid mater; and a layer which lies next to the brain and spinal cord, called the pia mater. The arachnoid mater is so-called because its cells have a spider-like appearance. Between the arachnoid mater and pia mater lies the subarachnoid space. The arteries of the brain, known as the circle of Willis, lie in the subarachnoid space of the brain, and cerebrospinal fluid circulates around the brain in the subarachnoid space. It is formed in the choroid plexus in all four ventricles. From the lateral ventricles it flows through the interventricular foramina (foramina of Monro) to the third ventricle. From there it flows through the central aqueduct to the fourth ventricle. The cerebrospinal fluid flows from the fourth ventricle into the subarachnoid space via the foramen of Magendie and the foramina of Luschka. There are also large collections of cerebrospinal fluid to be found in the cisterna magna at the base of the brain.

Cerebrospinal fluid consists of water, glucose, protein and electrolytes. It protects and nourishes the brain, by absorbing a certain amount of shock, bringing nutrients such as glucose to the cells and providing some immunity to infection.

The basal ganglia are masses of grey matter deep in the brain and contain the putamen, caudate nucleus, globus pallidus, subthalamic nucleus and substantia nigra. They are interconnected with the thalamus. The function of the basal ganglia is to coordinate voluntary muscle movement and to maintain the tone of the muscles. Disorders of the basal ganglia result in movement disorders such as chorea, athetosis, hemiballismus, and the increased tone and tremor seen in Parkinson’s disease.

The hypothalamus lies above the pituitary gland and is connected by the pituitary stalk. This area of the brain controls the autonomic nervous system and has links with the limbic system and the pituitary gland. The limbic system is a network of interlinking pathways which are responsible for the emotions, motivation and behaviour. This activity results in the monitoring and control of temperature, appetite and satiety; water regulation and thirst; physical experiences of emotion such as fear, pain, pleasure and rage; and the control of the neuroendocrine system by the production of releasing factors.

Computerized axial tomography (CT) is an X-ray technique which enables the brain to be X-rayed in the coronal or sagittal planes in a series of slices 2–10 mm wide. The computer then processes the information, and the end result is a series of films showing the structure of the brain or spine at various levels. It depicts the structures of the brain and spinal cord at the time the scan was taken, but it cannot demonstrate physiological activity over a period of time.

Positron emission tomography (PET) scanning is a relatively new technique which has been developed in order to demonstrate the functional activity of the brain over a period of time (anything from 20 minutes to 2 hours, depending on the substance used). It involves the production of isotopes that emit positrons, which are then used to label substances which the target organ needs. In the case of the brain, oxygen and glucose are labelled. The resulting scan shows areas of increased local uptake and activity (McCulloch, 1986). It has been used in the study of dementia, schizophrenia and many other neurological and psychiatric disorders; however, it is not used in routine clinical investigations.

Cerebral angiography is useful when it is necessary to demonstrate the state of cerebral arteries and diagnose abnormalities of the blood vessels, such as atheroma, aneurysms and arteriovenous malformations. It is also helpful in the diagnosis of brain tumours, and it is used in the newly developing techniques of embolization of vessels in the treatment of aneurysms.

Digital subtraction angiography is a combination of angiography and computer technology in which the computer can subtract information from the image and expose the vessels of interest more clearly.

Magnetic resonance angiography is used to evaluate blood vessels and detect abnormalities of the lumen of blood vessels (Clifton, 2000).

An electroencephalogram (EEG) is a recording of the electrical activity of the brain and is used in the diagnosis of various neurological conditions, especially epilepsy. It is also useful in the investigation of sleep disorders.

Cortical mapping is carried out during awake craniotomies for patients suffering from lesions that are near vital areas such as the speech and language areas. In this way, patients can tell the surgeon what they are experiencing and enable the surgeon to be more precise and selective in the amount of tissue that is removed (Reinhardt et al, 1996).

Video telemetry is a form of electroencephalography which is linked to a video camera. Patients suffering from epileptic or non-epileptic seizures have video telemetry to enable the medical staff to see clearly the clinical manifestations of the seizure and have the EEG recording during it.

Some diagnoses can be made by stimulating specific sensory pathways and recording the electrical activity of the appropriate area of cerebral cortex and/or brainstem. Visual evoked potentials are useful in the diagnosis of multiple sclerosis. Auditory evoked potentials are useful in the diagnosis of acoustic neuroma and brainstem death.

Lumbar puncture is a procedure carried out by a doctor, during which a spinal needle is inserted into the subarachnoid space between the third and fourth lumbar vertebrae. Cerebrospinal fluid is withdrawn for the following reasons:

• to confirm a diagnosis, e.g. meningitis

• to instil dyes, e.g. as in myelography; or drugs, e.g. intrathecal antibiotics.

It should not be used in patients with raised intracranial pressure, as it can provoke tentorial herniation (see p. 143).

A myelogram is a specialized X-ray of the spine. A water-soluble dye is inserted into the subarachnoid space through a lumbar puncture, and lesions of the spine are highlighted if the cerebrospinal fluid pathway around the spinal cord is impeded in any way by a disc protrusion, tumour or arteriovenous malformation.

Anterior–posterior and lateral radiographs of the skull are usually taken in order to diagnose skull fractures, meningiomas and other bony injuries of the skull. In cases of head injury, the radiograph should include the neck down to and including the seventh and eighth cervical vertebrae, to exclude cervical fracture/dislocation.

Transcranial Doppler studies rely on ultrasound technology. A very low frequency ultrasound wave is passed through the skull and is useful in assessing cerebral blood flow and vasospasm in disorders such as carotid stenosis.

Neurosurgery is performed for two reasons:

Box 10.3 gives a brief résumé of the reasons for neurosurgery.

The rehabilitative process begins with the nurse’s preoperative assessment and care planning. The prevention of common perioperative and postoperative complications is shared with the other disciplines discussed in this book, e.g. wound infection, deep vein thrombosis, haemorrhage and anaesthetic complications. The consequences of raised intracranial pressure (RICP) or ischaemia need to be considered, as outlined later in this chapter.

In addition, however, the results of focal damage to a particular area of the brain must be considered. As we will see with John, who underwent partial removal of a frontoparietal glioma, there were focal problems that resulted from removal of part of the frontal and parietal lobes.

The adult brain is protected by a closed skull. The only openings in the skull are the foramen magnum, the small foramina by which the cranial nerves enter or leave the skull, e.g. optic or auditory nerves, and the sinuses. The contents of the skull are such that there is little room for anything that takes up extra space. The normal intracranial pressure (ICP) is 0–10 mmHg. However, a higher upper limit of 15 mmHg is the more usual level recognized in neurosurgical practice (Garner and Amin, 2007). This margin of 0–15 mmHg enables such activities as coughing, straining and bending to take place without the individual being harmed. If there is a space-occupying lesion in the brain, such as a haematoma, hydrocephalus or a tumour, the brain will compensate until it reaches a point where it cannot do so any longer. This period of autoregulation is known as Cushing’s response, and during this phase the autonomic nervous system responds by slowing the pulse rate and widening the systolic and diastolic blood pressure. This is nature’s attempt to overcome the pressure on the cerebral arteries and ensure cerebral blood flow. If the lesion is supratentorial, the pressure above the tentorium will be greater than that below.

In this way the pressure is funnelled toward the weakest point in the tentorium, causing tentorial herniation of the uncus of the temporal lobe. This funnel-shaped pressure wave is like an ice cream cone and gives rise to the term ‘coning’. At this point there is pressure on the brainstem and the third cranial nerve (oculomotor nerve) on the affected side. This results in a change in the size and reaction of the pupil to light on the same side as the lesion.

If left untreated, the third cranial nerve on the other side becomes compromised and both pupils will become dilated and eventually cease to react to light. A Cheyne–Stokes respiratory pattern will follow, and the continuing pressure on the brainstem will disrupt the stability of the blood pressure and pulse rate, and death will follow. Neurological assessment and observations are essential to detect early signs of rising intracranial pressure and to treat them. The first sign of rising intracranial pressure may be headaches, lethargy or increased drowsiness, depending on the speed at which the intracranial pressure is increasing. Nursing measures to treat raised intracranial pressure will be discussed in the section on postoperative care.

The major difference between neurological assessment and neurological observations is that a neurological assessment is more holistic and covers all the nervous system activity, including cognition, perception and behaviour, when it is possible to assess these aspects of the patient. It also includes neurological observations.

A full neurological assessment is taken on admission to the neurosurgical ward and will provide a baseline for planning care. A further full assessment needs to be carried out at regular intervals during the patient’s stay in the unit, in order to fully evaluate care and to plan for the patient’s discharge or transfer to a general hospital.

The nurse should look closely at the findings made by the doctor in their history and clinical examination at the time of admission, in order to compare the patient’s perception of their problems with the nurse’s own findings. Sometimes, patients and their carers give information to nurses because they believe the information to be of little importance to the doctor, or because they forgot to mention it, or may have been too embarrassed or frightened to talk about it.

An assessment of neurological function should include the following: