THE classical symptoms and signs of increased intracranial pressure may be recognized in the adult with a fair degree of accuracy. They consist, briefly, of headache, vomiting, the appearance of papilledema and a depressed or altered state of consciousness. They appear in the presence of any expanding lesion, be it brain tumor, traumatic hematoma or chronic infection, because of the relatively simple fact that the adult skull may be considered a closed box, incapable of significant expansion in terms of relief of intracranial hypertension.This famous closed box theory upon which almost all the methodology of neurologic surgery depends was presented first by Monro and Kellie and was later modified to include the cerebrospinal fluid by Burrows. In the era of modern neuro-surgery the work of Dr. Lewis H. Weed has further refined this theory to include chiefly the stretch component of the inner confining membrane of the closed box, the dura mater.In essence, the closed box theory of this long list of distinguished investigators states: (1) that the skull, pierced but by minor foramina, may be considered inexpansible, (2) that within the skull, brain tissue, arterial and venous circulating blood and cerebrospinal fluid rest in equilibrium influenced in the normal state only by postural head and body changes, (3) that any change such as that of an expanding brain tumor in the relative volume of these components of the closed box must be compensated for by a change in one or all of the constituents, and (4) that when the limits of this normal compensatory mechanism are attained, since the closed box can no longer expand, signs of increased intracranial pressure will develop (Fig. 1). Normal intracranial pressure in the adult is, in simple terms, a measure of the pulsating arterial systolic pressure, an unimpeded venous outflow, a stable brain volume, the normal production and absorption of cerebrospinal fluid and a solid inexpansible skull.Identical factors operate in the maintenance of normal intracranial pressure in the infant or child although they may be envisaged as progressively changing factors due to the growth of the central nervous system and its envelope, the skull.
展开▼
