This system drains into the internal jugular vein. Notably, the bridging veins of the superior sagittal sinus are vulnerable to rupture upon impact, leading to subdural haematoma (Fig. 13.2).

The meninges are a trio of connective tissue layers covering the central nervous system named the dura mater, arachnoid mater and pia mater. The pia mater lies the deepest, immediately surrounding the brain, whereas the dura mater is the most superficial, lying just deep to the bones of the skull. Between the dura and arachnoid mater lies the subdural space. Between the arachnoid mater and pia mater lies the cerebrospinal fluid-filled subarachnoid space. The understanding of these anatomical structures is key to the understanding of various pathological processes including subdural, subarachnoid and extradural haemorrhage.

Folds of dura mater also make up the falx cerebri and tentorium cerebelli. The falx cerebri runs between the left and right hemispheres in the longitudinal fissure. The tentorium cerebelli overlies the superior aspect of the cerebellum and separates it from the inferior aspect of the occipital lobes.

Intracranial pressure (ICP) is normally 7–15 mm Hg in the supine position; at 20–25 mm Hg, the upper limit of normal, treatment to reduce ICP may be needed. It varies in children from adults.

Under normal conditions, the blood flow to the brain is auto-regulated to remain within homeostatic limits. This is maintained physiologically at cerebral perfusion pressures between 50–150 mmHg (mean arterial pressure). The mean cerebral blood flow is 750 ml/min. If perfusion pressure deviates from these values, decompensation can occur with increases or decreases in cerebral blood flow (Fig. 13.3).

It is also important to appreciate the physiological relationship between intracranial pressure and volume. Increasing volume, for example as a result of a tumour or an expanding intracranial haematoma, can result in drastically rising ICP. An increasing ICP can eventually exceed the cerebral perfusion pressure, resulting in critically reduced brain perfusion.

Certain neurosurgical conditions require an emergent intervention to interrupt this sequence of events before catastrophic consequences to brain function; e.g. craniotomy for evacuation of a traumatic extradural or subdural haematoma; external ventricular drainage with diversion of CSF in acute hydrocephalus (Figs. 13.4 and 13.5).

The Glasgow Coma Scale (GCS) is a tool allowing an objective assessment of the conscious state of a patient (see Table 13.1). It originated in the assessment of trauma patients but is widely used in all brain surgery conditions. The score takes into account eye opening, motor and verbal responses to various stimuli. A total score of 15 is possible. A score of 8 or below is considered to be indicative of a comatose patient and the minimum score possible, 3, indicates a totally unresponsive patient. Notably, a different version of the scale is used in paediatric practice.

The paediatric scale features a modified verbal response scale (Table 13.2):

This condition is characterised by dilatation of the ventricular system due to an obstruction to cerebrospinal fluid flow. This can be classified as communicating hydrocephalus (due to no obvious obstruction of the ventricular system, but presumed reabsorption deficit), or non-communicating hydrocephalus (due to an obstruction within the ventricular system). Many conditions can lead to hydrocephalus, including congenital malformations, subarachnoid haemorrhage, trauma, abscesses and tumours.

This condition usually results from tearing and bleeding of the bridging veins of the superior sagittal sinus or other trauma to the brain or skull. A haematoma accumulates in the subdural space, raising intracranial pressure and potentially precipitating rapid neurological decline (Fig. 13.6).

Chronic subdural haematomas have a similar aetiological mechanism to acute subdural haematomas but develop insidiously. They are more common in the elderly and often the insulting trauma is minor and never identified.

Traumatic brain injury describes a spectrum of clinical states categorised by GCS. They are a significant cause of mortality and morbidity in young people and range from concussion to comatose state. Pathologies requiring neurosurgical attention may result from traumatic brain injury, including subdural haematoma.

Adjacent vertebrae are separated by intervertebral discs. These consist of the annulus fibrosus, a series of concentric fibrocartilaginous layers; and the nucleus pulposus, a water-based gelatinous core. Age-related changes in the annulus fibrosus allow the herniation of the nucleus pulposus through it, placing pressure on surrounding structures, including nerve roots, the cauda equina and the spinal cord above its termination point which is usually at L1/2 in adults (Fig. 13.7).

Cauda equina syndrome is a relatively rare condition usually associated with a space-occupying lesion in the lumbosacral spine, most often a disc prolapse. It presents with pain, motor and sensory loss and bowel and bladder dysfunction. Symptoms and signs can be subtle and a high index of suspicion is necessary given the need for urgent treatment by surgical decompression of spinal canal.

Some of the most common neurosurgical operations are described briefly below. The aim is to provide a basic understanding and to cultivate the curiosity to delve into detailed texts.