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.

Bony turnouts are unusual and may present because of cosmetic deformity. The benign ivory osteoma may be either drilled down or simply excised with the defect being reconstituted by either a split cavarial graft from adjacent bone or filled with an acrylic cranioplasty. Primary malignant growths of the skull are exceedingly rare and more often these lesions are found to be secondary (Fig. 35.7). In childhood, however, lytic lesions within the skull may be as a result of histiocytosis and therefore open biopsy with or without excision or curettage may be indicated