The effect of total-brain irradiation on cerebrospinal fluid pressure.

Abstract

After fifty years of clinical and experi-A mental brain irradiation the etiology of its complications is still not well understood. Headache, vomiting, coma, respiratory arrest, and death after irradiation are commonly attributed to increased cerebrospinal fluid pressure (1). As a result, large doses of therapeutic irradiation are fractionated to small daily doses“to avoid increasing the intracranial pressure” (4, 7, 15, 18). While this practice is almost universal, experimental documentation of the pressure increases is scarce and inconclusive (10, 13, 16, 17). The impracticality and presumed dangers of high single-dose irradiation studies in patients have led to extensive animal experimentation on the effects of brain irradiation. Most researchers have concentrated on histological, biochemical, morphological, and functional effects of irradiation while merely assuming that pressure increases occurred. Specific investigation of irradiation-induced pressure changes in animals, however, is not recorded in the literature. The absence of such basic data prompted the following study of the effect of total brain x irradiation on the CSF (cerebrospinal fluid) pressure of normal dogs. Materials and Methods Permanent cervical subarachnoid catheters were placed in healthy mongrel dogs to facilitate numerous pressure readings without the disadvantages of multiple punctures (9). Each dog was anesthetized with sodium pentobarbital, and an 18-gauge, thin-walled Tuohy spinal needle was inserted through the atlanto-occipital membrane. When fluid appeared in the needle, a 0.020-in. vinyl catheter was inserted and advanced caudally for approximately 12 cm in the subarachnoid space (6). The tubing was closed with a three-way stopcock attached to a protective device taped around the dog's neck. The procedure was accomplished without signs or symptoms of spinal cord damage, and the dog's postsurgical activities were not impaired. Measurements of CSF pressure were obtainable repeatedly without anesthesia or struggling, using a spinal manometer or a strain gauge (Fig. 1). Sensitivity of the apparatus to pressure changes within the CSF system was verified by recordings of normal variations of 4–10 mm H2O with each respiration (2, 5) (Fig. 2). Increased venous pressure from abdominal compression and flexion of the head produced expected increases in CSF pressures (2, 3, 9, 17). The large variability in CSF pressures, even in the same animal, was minimized by identical physical conditions and pressure measurement by the same individual.