J Neurosurg 113:64–73, 2010 64 J Neurosurg / Volume 113 / July 2010 S ince it was frst described in 1964, NPH has chal- lenged the scientifc community mainly with regard to 2 apparently unsolved problems: the physio- pathogenetic mechanism(s) underlying ventricular en- largement and the prediction of outcomes after shunt- ing. 16 The latter problem, in particular, has recently re- ceived considerable attention. Several selection criteria, based on pathogenetic or empirical considerations, have been proposed, but, to date, no single diagnostic tool or combination of tools has proved to be able to reliably predict whether the condition of a patient with suspected NPH will improve after a shunt placement procedure. 7,23 With regard to empirical methods, Marmarou et al. 25 claimed a positive predictive value of 90.5% in NPH pa- tients whose condition improved after ELD, but in his series of 151 patients, 22.3% of patients whose condition was not improved after ELD had a good outcome after a CSF shunting procedure. A similar observation had been already reported by other authors, whose prospective study did not confrm the predictive value of ELD. 40 In effect, they concluded that, in view of the high percent- age of patients whose condition improved after a shunt, Selection of patients with idiopathic normal-pressure hydrocephalus for shunt placement: a single-institution experience Clinical article Carmelo anile, m.D., 1 P asquale De Bonis, m.D., 1 alessio alBanese, m.D., 1 alessanDro Di ChiriCo, m.D., 2 annunziato mangiola, m.D., 1 gianPaolo Petrella, m.D., 3 anD Pietro santini 1 1 Institute of Neurosurgery, Catholic University School of Medicine, Rome; 2 Neurosurgical Department, Ospedale Santo Spirito, Rome; and 3 Neurosurgical Department, Azienda Ospedaliera S. Maria, Terni, Italy Object. The ability to predict outcome after shunt placement in patients with idiopathic normal-pressure hydro- cephalus (NPH) represents a challenge. To date, no single diagnostic tool or combination of tools has proved capable of reliably predicting whether the condition of a patient with suspected NPH will improve after a shunting procedure. In this paper, the authors report their experience with 120 patients with the goal of identifying CSF hydrodynamics criteria capable of selecting patients with idiopathic NPH. Specifcally, they focused on the comparison between CSF-outfow resistance (R-out) and intracranial elastance (IE). Methods. Between January 1977 and December 2005, 120 patients in whom idiopathic NPH had been diagnosed (on the basis of clinical fndings and imaging) underwent CSF hydrodynamics evaluation based on an intraventricular infusion test. Ninety-six patients underwent CSF shunt placement: 32 between 1977 and 1989 (Group I) on the basis of purely clinical and radiological criteria; 44 between 1990 and 2002 (Group II) on the basis of the same criteria as Group I and because they had an IE slope > 0.25; and 20 between 2003 and 2005 (Group III) on the basis of the same criteria as Group II but with an IE slope ≥ 0.30. Outcomes were evaluated by means of both Stein-Langftt and Larsson scores. Patients’ conditions were considered improved when there was a stable decrease (at 6- and 12-month follow-up) of at least 1 point in the Stein-Langftt score and 2 points in the Larsson score. Results. Group I: while no statistically signifcant difference in mean R-out value between improved and unim- proved cases was observed, a clear-cut IE slope value of 0.25 differentiated very sharply between unimproved and improved cases. Group II: R-out values in the 2 unimproved cases were 20 and 47 mm Hg/ml/min, respectively. The mean IE slope in the improved cases was 0.56 (range 0.30–1.4), while the IE slopes in the 2 unimproved cases were 0.26 and 0.27. Group III: the mean IE slope was 0.51 (range 0.31–0.7). The conditions of all patients improved after shunting. A signifcant reduction of the Evans ratio was observed in 34 (40.5%) of the 84 improved cases and in none of the unimproved cases. Conclusions. Our strategy based on the analysis of CSF pulse pressure parameters seems to have a great accu- racy in predicting surgical outcome in clinical practice. (DOI: 10.3171/2010.1.JNS091296) Key WorDs • normal-pressure hydrocephalus • shunt placement • cerebrospinal fuid hydrodynamics • infusion test • elastance • cerebrospinal fuid outfow resistance Abbreviations used in this paper: ELD = external lumbar drain- age; ICP = intracranial pressure; IE = intracranial elastance; NPH = normal-pressure hydrocephalus; R-out = outflow resistance. This article contains some figures that are displayed in color online but in black and white in the print edition.