If this condition is left untreated, the pupils eventually dilate symmetrically, the eyes no longer respond to oculocephalic maneuvers, and the limbs become flaccid. Or, there is an unanticipated cardiac or respiratory arrest, even at an early stage of evolution of the hydrocephalus; this complication is seen particularly in children with masses, particularly at the foramen magnum, and may be presaged by brain compression at the level of the perimesencephalic cisterns, detectable by imaging studies.
Treatment is by drainage of CSF, usually effected by a ventricular catheter or, if there is undoubted communication between all the CSF compartments, by lumbar puncture. The latter may pose some risk if spinal fluid is withdrawn rapidly or there is a sizeable leak of fluid through the spinal dura at the site of the puncture, thereby creating a pressure gradient between the cerebral and spinal regions.
Neuropathologic Effects of Hydrocephalus
Expansion of the lateral ventricles tends to be maximal in the frontal horns, explaining the hydrocephalic impairment of frontal lobe functions and of basal ganglionic–frontal motor and gait activity in many forms of hydrocephalus. The central white matter yields to pressure, while the cortical gray matter, thalami, basal ganglia, and brainstem structures remain relatively unaffected. There is an increase in the content of interstitial fluid in the tissue adjacent to the lateral ventricles (transependymal flow), readily detected by MRI (see Fig. 29-3). Myelinated fibers and axons are injured, but not to the extent that one might expect from the degree of compression; minor degrees of astrocytic gliosis and loss of oligodendrocytes in the affected tissue are present to a decreasing extent away from the ventricles and represent a chronic hydrocephalic atrophy of the brain. The ventricles are characteristically denuded of ependyma, and the choroid plexuses are flattened and fibrotic. The lumens of cerebral capillaries in biopsy preparations are said to be narrowed—a finding that is difficult to evaluate.
In meningeal and ependymal diseases, hydrocephalus may develop and reach a stable state. It is then said to be “compensated” in the sense that formation of CSF equilibrates with absorption. Once equilibrium is attained, the ICP gradually falls, though it still maintains a gradient from ventricle to basal cistern to cerebral subarachnoid space. A stage is reached where the CSF pressure reaches a high normal level of 150 to 200 mm H2O, but the patient nonetheless eventually manifests the cerebral effects of the hydrocephalic state. The name given to this condition by Adams and colleagues and Hakim and Adams was normal-pressure hydrocephalus (NPH).
There continues to be controversy regarding the frequency of this condition in older adults, and there have even been reasonable arguments questioning the existence of the entity as a coherent disorder or syndrome and, in response to guidelines for treatment issued by the American Academy of Neurology (see Halperin et al) there has certainly been divergence of opinion (Saper). As to the frequency of the disorder, estimates vary widely and depend on the age group studied but Jaraj and colleagues using four cohorts, estimated the prevalence as 0.2 percent of those aged 70 to 79 and 5.9 percent of those over 80.
A triad of clinical findings is characteristic of NPH: a slowly progressive gait disorder is usually the earliest feature, followed by impairment of mental function and later, sphincter incontinence. The reader should be alerted to the fact that the fully developed triad is not usually present in the early stages of the process. Grasp reflexes in the feet and falling attacks may also occur, but there are no Babinski signs. Headaches are infrequently a complaint, and there is no papilledema.