IMPORTANCE OF ANTI-SIPHON DEVICES IN THE TREATMENT OF PEDIATRIC HYDROCEPHALUS

The effects of an antisiphon device (ASD) on shunt flow and intracrani al pressure (ICP) in 16 children with hypertensive hydrocephalus were examined using quantitative radionuclide shuntography (Tc-99m) with th e children in supine and sitting positions. The average age of these p atients was 9.5 years. Results were compared with those recorded in 36 patients with adult normal-pressure hydrocephalus (NPH). The closing pressure levels of shunt valve used were low in 8 cases, medium in 7 a nd high in 1. Half the children (8) had shunt systems with, and the ot her 8 without, ASD. In the children who had the shunt system without A SD, sitting shunt flow was significantly greater than supine shunt flo w, which indicated overdrainage. Conversely, in children who had the s hunt system with ASD, supine shunt flow was greater than sitting shunt flow. Because ASD prevented overdrainage, ICP was higher with the shu nt system with ASD than with the shunt system without ASD. Without ASD , sitting shunt flow of children was lower than that of adult patients with NPH because of the lower hydrostatic pressure, which correlated with their height. Conversely, in the presence of a shunt system with ASD, sitting shunt flow of children was greater than that of adults, b ecause of the higher ICP and lower hydrostatic pressure. The effect of ASD was smaller in children than in adults, because positive pressure over the ASD was greater (hypertension vs normal pressure) and negati ve pressure under the ASD was less (short vs tall) in children than in adults. Thus, in children the ASD was effective in preventing overdra inage. An overfunction of the ASD, which has sometimes been observed i n adult patients with NPH, was not encountered. The relationships amon g the function of the ASD and ICP, height and position of the ASD are discussed.