Ross & Wilson Anatomy and Physiology in Health and Illness (84 page)

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Authors: Anne Waugh,Allison Grant

Tags: #Medical, #Nursing, #General, #Anatomy

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Figure 7.53
Spina bifida.

Occult spina bifida

In this ‘hidden’ condition the skin over the defect is intact and excessive growth of hair over the site may be the only sign of abnormality. This is sometimes associated with minor nerve defects that commonly affect the bladder.

Meningocele

The skin over the defect is very thin and may rupture after birth. There is dilation of the subarachnoid space posteriorly. The spinal cord is correctly positioned.

Meningomyelocele

The meninges and spinal cord are grossly abnormal. The skin may be absent or rupture. In either case there is leakage of CSF, and the meninges may become infected. Serious nerve defects result in paraplegia and lack of sphincter control causing incontinence of urine and faeces. There may also be mental impairment.

Hydrocephalus (see
p. 173
)

Tumours of the nervous system

Learning outcome

After studying this section you should be able to:

outline the effects of tumours of the nervous system.

Primary tumours of the nervous system usually arise from the neuroglia, meninges or blood vessels. Neurones are rarely involved because they do not normally multiply. Metastases of nervous tissue tumours are rare. Because of this, the rate of growth of a tumour is more important than the likelihood of spread outside the nervous system. In this context, ‘benign’ means slow growing and ‘malignant’ rapid growing. Early signs are typically headache, vomiting, visual disturbances and
papilloedema
(swelling of the optic disc seen by ophthalmoscopy). Signs of raised ICP appear after the limits of compensation have been reached (see
p. 172
).

Within the confined space of the skull, haemorrhage within a tumour exacerbates the increased ICP caused by the tumour.

Slow-growing tumours

These allow time for compensation for increasing intracranial pressure, so the tumour may be quite large before its effects are evident. This involves gradual reduction in the volume of cerebrospinal fluid and circulating blood.

Rapidly growing tumours

These do not allow time for adjustment to compensate for the rapidly increasing ICP, so the effects quickly become apparent (
Fig. 7.49C
). Complications include:

•
neurological impairment, depending on tumour site and size

•
effects of increased ICP (
p. 172
)

•
necrosis of the tumour, causing haemorrhage and oedema.

Specific tumours

Brain tumours typically arise from different cells in adults and children, and may range from benign to highly malignant. The most common tumours in adults are
gliobastomas
and
meningiomas
, which are usually benign and originate from arachnoid granulations.
Astrocytomas
are commonest in children.

Metastases in the brain

The most common primary sites that metastasise to the brain are the breast, lungs and colon. The prognosis of this condition is poor and the effects depend on the site(s) and rate of growth of metastases. There are two forms: discrete multiple tumours, mainly in the cerebrum, and diffuse tumours in the arachnoid mater.