IMAGING OF THE HEAD, NECK AND SPINE
Magnetic Resonance Imaging
A) HEAD (SKULL AND BRAIN)
Since the advent of computed tomography and magnetic resonance the need for plain X-rays of the skull has almost disappeared. However, apart from ultrasound, which is of limited value in examining the head, plain X-rays are often the only imaging method available in some countries. Plain films are of limited value in suspected intracranial pathology, especially in the absence of neurological signs.
The standard views are:
AP or PA – usually taken PA unless following trauma.
In some instances the PA view will be substituted by the half axial or Townes view or the latter may be taken as a third view. This is taken with a 30 degree caudal tilt of the tube to project the occipital and petrous bones free of the overlying facial bones.
Indications for skull X-rays
Minor trauma if history of loss of consciousness
Bleeding from the ear or cerebro-spinal fluid leakage indicates a fracture of the base of skull. This will not be seen on skull X-ray due to overlapping structures at the base of the skull but if a lateral film is taken with the patient lying supine other signs may be seen such as fluid in the sphenoid sinus or air in the cranial cavity.
Local bulge, if fixed and not mobile.
Indentation ?bony defect
Suspected skull metastases or myeloma - lateral view only. Additional views are unhelpful.
Persistent headache – seldom helpful unless there are clinical signs such as a neurological abnormality, signs of raised intracranial pressure, or visual abnormality.
Suspected osteomyelitis of the skull, spread from infected sinus
Earache – skull views are seldom helpful. Special views need to be taken for the mastoids & these are difficult to interpret & often unhelpful even in suspected acute mastoiditis
Other views are sometimes taken. These are:
views for optic foramina (suspected optic nerve glioma)
mastoid views ( mastoiditis, chronic middle ear disease)
petrous bone ( internal auditory canals in suspected 8th cranial nerve tumour
coned views for pituitary fossa ( pituitary fossa tumour, raised intracranial pressure)
view of the base of skull – submento-vertical
The skull X-ray is complex. The skull vault is easier to assess than the skull base, which is dense with many superimposed structures. In the skull vault the 2 tables of bone should be seen intact separated by a darker line of marrow.
Little detail can be seen in the skull base unless special views are taken
The pituitary fossa is a rounded depression in the middle of the skull base lying above the sphenoid sinus. It is bounded by the bony anterior & posterior clinoids. Lining the pituitary fossa is a thin white line called the lamina dura.
In the PA skull film taken with 10 degree caudal tilt the petrous ridges are projected through the mid orbits. With a 20 degree tilt they are projected over the inferior orbital margin. The latter projection is needed to assess the orbits.
ascular markings occur due to arteries and veins. The arterial markings are in fairly constant positions and branch becoming smaller in diameter peripherally. They are not as dark as fracture lines & smoother in outline. Veins drain into venous lakes. The vascular markings vary considerably from patient to patient.
The greater wing of the sphenoid should be seen projected through the orbit on the PA 20 film.