Infants have natural defects in the skull called fontanelles through which the brain may be imaged by ultrasound. This in many cases may obviate the necessity for a CT scan. Bone will not transmit sound waves and cannot be used to image the brain in detail once the fontanelles have closed. There is a thin area of bone in the temporal bone through which ultrasound may be used to measure the velocity in the middle cerebral artery. This is being used in children with sickle cell disease to detect the ones most at risk of developing a stroke.
Ultrasound is the first choice of imaging in babies. In neonates ventricular and subependymal haemorrhages are easy to detect with ultrasound. These lead to ventricular dilatation, which is easy to detect. Hydrocephalus can be diagnosed and its progression monitored comparing the ventricular width on follow up scans.
Brain angiography is still performed in specialised units where there is a neurosurgeon available. The main use of cerebral angiography is to localise an aneurysm prior to surgery, or to show the feeding vessels in an AV malformation. This is nowadays performed via the femoral artery with selective catheterisation of the ICA or VA.
It may also be used in the assessment of ICA stenosis when ultrasound is doubtful. An arch aortogram may be performed if stenosis at the origin of one of the vessels arising from the arch is suspected.
MRA – magnetic resonance angiography is now taking over from conventional angiography. It is used to detect berry aneurysms and to confirm the ultrasound findings in the carotid vessels prior to surgery.
CT ANGIOGRAPHY – is now possible with the advent of spiral CT. Reconstructed images can be obtained in the sagittal plane and a picture very similar to an angiogram produced.
B) PARANASAL SINUSES
Although the frontal sinuses are seen well on skull X-rays the maxillary antra cannot be assessed accurately without special views to show them more clearly.
These are not fully developed in childhood and plain films are seldom helpful below the age of 3 years. The frontal sinuses may not develop at all or be rudimentary.
The standard projection is an occipito-mental view (OM) or Waters view This is adequate in many cases but a second view may be needed to show the frontal sinuses. This is the occipito-frontal or OF view. Usually the OM view is taken with the patients mouth open. This projects the sphenoid sinus through the open mouth however disease of this sinus alone is unusual.
A lateral view used to be a standard projection but seldom adds any useful information and is not taken routinely. It is needed to assess the posterior wall of the maxillary antrum
Indications for plain films:
Sinusitis – this is a clinical diagnosis and plain films are generally not necessary unless surgery is planned. In which case computed tomography is preferred to map out the anatomy of the drainage ostia.
The commonest abnormalities seen on plain films are: