Brain imaging provides essential diagnostic information and is very useful for research on the brain. Images of the skull, the brain and its vessels, and spaces in the brain containing cerebrospinal fluid can aid immeasurably in the localization of lesions. In concert with physical examination and history, imaging studies can provide important clues to diagnosis. In emergency cases, images of unconscious patients may be the only diagnostic information available.
Computed tomography (CT), magnetic resonance imaging (MRI), and other similar imaging methods are usually displayed to show sections of the head; the sagittal, coronal (frontal), and horizontal (axial) planes are commonly used (Fig 22-1).
Planes used in modern imaging procedures.
It is essential for the clinician to understand the various imaging modalities that are available and to order the most useful tests. It is also essential to correlate results of imaging with the clinical picture, that is, with the history and neurological examination.
Skull x-rays provide a simple method for imaging calcium and its distribution in and around the brain when more precise methods are unavailable. Plain films of the skull can define the extent of a skull fracture and a possible depression or determine the presence of calcified brain lesions, foreign bodies, or tumors involving the skull. They can provide images of the bony structures and foramens at the base of the skull and of the sinuses. Skull x-ray films can also provide evidence for chronically increased intracranial pressure, accompanied by thinning of the dorsum sellae, and abnormalities in the size and shape of sella turcica, which suggest large pituitary tumors. Skull films are sometimes used to screen for metal objects before beginning MRI of the head.
Angiography (arteriography) of the head and neck is a neurodiagnostic procedure used when a vessel abnormality such as occlusion, malformation, or aneurysm is suspected (Figs 22–2 to 22–12; see also Chapter 12). Angiography can also be used to determine whether the position of the vessels in relation to intracranial structures is normal or pathologically changed. Aneurysms, arteriovenous fistulas, or vascular malformations can be treated by interventional angiography using balloons, a quickly coagulating solution that acts as a glue, or small, inert pellets that act like emboli.
Angiogram of the aortic arch and stem vessels. Normal image. 1: Brachiocephalic artery; 2: common carotid artery; 3: left subclavian artery; 4: right vertebral artery. (Reproduced with permission from Peele TL: The Neuroanatomical Basis for Clinical Neurology. New York, NY: McGraw-Hill Education; 1954.)
Left internal carotid angiogram, early arterial phase, lateral view. Normal image (compare ...