Pre- and postoperative cerebrospinal fluid absorption studies in patients with myelomeningocele shunted for hydrocephalus.

Nine infants with myelomeningocele and hydrocephalus had cerebrospinal fluid formation and absorption studies before insertion of a ventriculoperitoneal shunt. Six were also tested postoperatively. The preshunt formation rate varied from 0.21-0.42 ml.min-1 and the cerebrospinal fluid absorption rate or CSF conductance (Ccsf) varied from 0.008 to 0.031 ml.min-1.mm Hg-1. The postoperative formation rate varied from 0.21 to 0.39 ml.min-1. The postoperative CSF conductance (Ct) was calculated as the sum of Ccsf and the shunt conductance (Cs). The relationship between the Ccsf and Cs curves was determined by matching the sum of these curves to the postoperative data points using the method of least-squares. The data suggests that the shunt may work directly or indirectly to establish a new resting pressure; the latter by stabilizing the sagittal sinus pressure which preoperatively increased concomitantly with the CSF pressure and thus enhanced an already-existing absorption deficit.