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Stroke Volume Through Aqueduct of Sylvius Changes Over Time in Normal Pressure Hydrocephalus

January 29, 2008
Written by: , Filed in: Neuroradiology
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Background
Normal pressure hydrocephalus (NPH) is characterized clinically by the triad of urinary retention, ataxia, and dementia. Treatment is with ventricular shunting. Prior studies have demonstrated that patients with a stroke volume (SV) of 42 mcL through the aqueduct of Sylvius, as measured on phase-contrast cine MR (PC-CMR) flow studies, have a greater likelihood of responding to shunt therapy. It is also felt that if patients are not treated within a certain time frame, the abnormality becomes irreversible and they don’t respond to treatment.

The objective of a recent study was to determine the evolution of cerebral spinal fluid (CSF) SV over time in patients with NPH.
The study has concluded that in patients presenting initially with normal pressure hydrocephalus, symptoms worsen and aqueductal stroke volume can be expected to increase over time and then decrease again.
Participants
9 patients with symptoms and findings suggestive of NPH who refused treatment.

Methodology
Patients were followed every 6 months clinically and by MRI for up to 2 years. Cardiac-gated PC-CMR in the axial plane across the aqueduct was used. Total volume of CSF passing though during systole and diastole was calculated and averaged. Patient clinical data were obtained at each visit, including scales of urinary incontinence, ataxia, and mental status.

Results
2 patients were followed for 12 months, 2 for 18 months, and 5 for 24 months. Initially, all patients demonstrated gait disturbance. After 12 months, gait worsened in 3, in 2 more after 18 months, and in 4 of 5 patients evaluated after 24 months. One patient did not change from initial presentation throughout the 24 months.

Cognitive impairment, based on Mini-Mental State Evaluation, was impaired in 5 of 9 initially and worsened in 8 of 9 by 12 months, with a mean decrease of 2.6 points. At 24 months, mean decrease was 7.8 points in 5 evaluated patients.

Originally, 6 patients had urinary dysfunction and all did by 12 months. Two patients presented with SV <42 mcL. All patients initially increased their SV over time, and in 7 patients followed for >12 months, only 1 never demonstrated a decrease in SV by the last visit. Evaluation of SV was normalized relative to onset of symptoms and demonstrated that SV increased in these patients from onset of symptoms over 18 to 20 months, and then plateaued. Following this period, SV dropped significantly over the next 12 months.

Conclusions
In patients presenting initially with NPH, symptoms worsen and aqueductal SV can be expected to increase over time and then decrease again. This means that an initial low SV may not represent the end stage; but rather, in the beginning, and following an increase, the patient would be a candidate for shunting.

Reviewer’s Comments
This article sheds light on the progression of NPH. The authors provide an interesting discussion of proposed mechanisms of NPH and how they relate to the findings.

Author: Yaron Lebovitz, MD
Reference:

Scollato A, Tenenbaum R, et al. Changes in Aqueductal CSF Stroke Volume and Progression of Symptoms in Patients With Unshunted Idiopathic Normal Pressure Hydrocephalus. AJNR; 2008; 29 (January): 192-197

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