Does aqueductal stenosis influence the lumbar infusion test in normal-pressure hydrocephalus?

BACKGROUND

Late-onset idiopathic aqueductal stenosis may present with clinical features indistinct from idiopathic normal-pressure hydrocephalus (NPH). Moreover, aqueductal stenosis (AS) is not always detected by conventional magnetic resonance imaging (MRI). The aim of this study was to compare the hydrodynamic pattern among NPH patients according to the patency of the aqueduct.

METHODS

Fifty-six consecutive lumbar infusion tests were performed in patients with NPH syndrome. Precipitating causes of hydrocephalus were excluded, and aqueductal patency was examined through high-resolution, T2-weighted 3D MRI. Patients were classified into two groups: non-patent aqueduct and patent aqueduct. Mean values of pressure and pulse amplitude were obtained from basal and plateau stages of infusion studies.

RESULTS

Twelve of 56 patients with NPH-like symptoms presented with morphological AS (21.4 %). Patent aqueduct and non-patent aqueduct groups had similar values of mean opening lumbar pressure (8.2 vs. 8.1 mmHg), and mean opening pulse amplitude (3.1 vs. 2.9 mmHg). Mean pressure in the plateau stage (28.6 vs. 23.2 mmHg), and mean pulse amplitude in the plateau stage (12.5 vs. 10.6 mmHg) were higher in the patent aqueduct group. These differences were not statistically significant. Only Rout was significantly higher in the patent aqueduct group (13.6 vs. 10.1 mmHg/ml/min). One-third of NPH patients with AS presented Rout >12 mmHg/ml/min.

CONCLUSIONS

No differences in mean pressure or pulse amplitude during basal and plateau epochs of the lumbar infusion test in NPH patients were detected, regardless of aqueductal patency. However, Rout was significantly higher in patients with patent aqueduct.