The central nervous system (CNS) consists of two parts: the brain and spinal cord. The brain consists of four lobes (frontal, temporal, parietal and occipital), the midbrain, pons, medulla oblongata and cerebellum. Each has individual and joint roles, and interconnects with the others via a complex system of pathways producing automatic and volitional movement and cognitive function. These connect with every part of the body via the peripheral nervous system, consisting of cranial and spinal nerves which carry motor (efferent) and sensory (afferent) fibres (refer to Chapter c14: Observations).

Many neurological complications caused either by primary brain cancer or secondary malignancy SOL result from a rise in ICP. This may result directly from the mechanical forces generated by the tumour mass or from cerebral oedema caused by altered capillary permeability. As the tumour infiltrates normal brain tissue, obstruction of venous drainage in the brain or obstruction of cerebrospinal fluid may contribute to elevation in ICP. Changes in blood supply due to the pressure caused by the growing tumour cause brain tissue necrosis. This and haemorrhage into the tumour may also elevate ICP (Behin et al. [16]). The skull can be viewed as a rigid box which the brain sits inside. Rapidly growing tumours cause the greatest dysfunction and it is when masses grow larger than 3 cm that they compress brain tissue, its blood supply and adjacent neuronal pathways (Lefebvre [140]).

The impaired arterial blood supply generally manifests as an acute loss of function and may be confused with primary cerebrovascular disorders. Seizures, as a manifestation of neurosensitivity changes, may be associated with compression due to SOL invasion thus impairing blood supply to the brain tissue. Some SOLs form cysts that can also suppress the surrounding brain parenchyma causing focal neurological disorders.