The skull
The skull consists of several bones which are
fused by means of sutures to form the cranium which encases the brain and from
which the face hangs. The normal skull has a remarkable degree of symmetry about
the midline. There is rapid growth of the skull during the first few years of
life, a growth which is driven and shaped by the underlying developing brain and
the development of the sphenoid bone. If the development of the brain is
abnormal, then this can be reflected in the overall skull size. Therefore,
macrocephaly may occur as a result of hydrocephalus (Fig. 35.3).
If
premature closure of any of the cranial sutures occurs, this may result in loss
of midline symmetry and associated developmental abnormalities of the face. The
most common type of synostosis is that of the sagittal suture, which results in
the characteristic keel-shaped head or scaphocephaly (Fig. 35.4 a—c).
Trigonocephaly
is caused by premature fusion of the metopic suture (Fig. 35.5), whereas plagiocephaly will result from unilateral coronal or
lambdoid synostosis. When more than one suture is involved in the synostotic
process, this may result in elevation of the intracranial pressure. This may be
as a result of not only restriction of calvanial growth but also obstruction to
venous drainage at the base of the skull and respiratory problems. These are
commonly associated with syndromic craniosynostosis, such as Crouzon’s and
Apert’s syndrome. Surgery for craniosynostosis is undertaken in specialised
units and because of the associated otolaryngological, dental and
ophthalmological implications, the approach should be multidisciplinary. Surgery
is directed towards increasing the volume of the skull, improving the cosmetic
deformity and overcoming airway problems that may contribute to morbidity.
Congenital
defects of the skull may occur at any point in the midline from the nasion to
the foramen magnum as a result of incomplete fusion. Meningeal prolapses that
occur with these defects may contain cerebral tissue and likewise be associated
with a degree of structural abnormality of the underlying brain (Fig. 35.6).
These lesions are usually situated in the frontonasal region and are not
commonly associated with derangement of the cerebral architecture, whereas
those occurring more towards the occipital region characteristically have more
severe anatomical problems with consequent mental and physical handicaps.
Frontonasal encephalocoeles are more common in Asiatic races and may be
associated with a degree of hypertelonism. Smooth swellings seen in the roof of
the mouth or in the nose in infants and dermal sinuses should be approached
cautiously, as these might harbour underlying skull defects with herniation of
the intracranial contents. Investigation with CT and often MRI is required to
exclude intracranial communication. If this is confirmed, neurosurgical
exploration may be required to prevent the risk of future ascending infection.