Abstract
BackgroundIdiopathic normal pressure hydrocephalus (iNPH) and late-onset idiopathic aqueductal stenosis (LIAS) are two forms of chronic adult hydrocephalus of different aetiology. We analysed overnight intracranial pressure (ICP) monitoring to elucidate ICP waveform changes characteristic for iNPH and LIAS to better understand pathophysiological processes of both diseases.Methods 98 patients with iNPH and 14 patients with LIAS from two neurosurgical centres were included. All patients underwent diagnostic overnight computerised ICP monitoring with calculation of mean ICP, ICP heartbeat related pulse wave amplitude calculated in the frequency domain (AMP) and the time domain (MWA), index of cerebrospinal compensatory reserve (RAP) and power of slow vasogenic waves (SLOW).ResultsICP was higher in LIAS than iNPH patients (9.3 ± 3.0 mmHg versus 5.4 ± 4.2 mmHg, p = 0.001). AMP and MWA were higher in iNPH versus LIAS (2.36 ± 0.91 mmHg versus 1.81 ± 0.59 mmHg for AMP, p = 0.012; 6.0 ± 2.0 mmHg versus 4.9 ± 1.2 mmHg for MWA, p = 0.049). RAP and SLOW indicated impaired reserve capacity and compliance in both diseases, but did not differ between groups. INPH patients were older than LIAS patients (77 ± 6 years versus 54 ± 14 years, p < 0.001).ConclusionsICP is higher in LIAS than in iNPH patients, likely due to the chronically obstructed CSF flow through the aqueduct, but still in a range considered normal. Interestingly, AMP/MWA was higher in iNPH patients, suggesting a possible role of high ICP pulse pressure amplitudes in iNPH pathophysiology. Cerebrospinal reserve capacity and intracranial compliance is impaired in both groups and the pressure-volume relationship might be shifted towards lower ICP values in iNPH. The physiological influence of age on ICP and AMP/MWA requires further research.
Highlights
Idiopathic normal pressure hydrocephalus and late-onset idiopathic aqueductal stenosis (LIAS) are two forms of chronic adult hydrocephalus of different aetiology
The median preoperative Oslo-score was 11 and the median postoperative Oslo-score was 13. They showed a median of 2 points of improvement after shunt surgery. 14 patients with LIAS showing neurological improvement after VPShunt (n = 9) or endoscopic third ventriculostomy (ETV) (n = 5) were included. patients had improvement in gait, 8 in cognitive function, 7 in incontinence, and 7 reported better headache control. patients had improvement in more than one domain
intracranial pressure (ICP) waveform characteristics Figure 3 shows an individual example of 10 h overnight ICP monitoring and the waveform derived parameters amplitude calculated in the frequency domain (AMP), reserve capacity (RAP), respiration induced waves (RESP) and slow vasogenic waves (SLOW)
Summary
Idiopathic normal pressure hydrocephalus (iNPH) and late-onset idiopathic aqueductal stenosis (LIAS) are two forms of chronic adult hydrocephalus of different aetiology. We analysed overnight intracranial pressure (ICP) monitoring to elucidate ICP waveform changes characteristic for iNPH and LIAS to better understand pathophysiological processes of both diseases. Idiopathic normal pressure hydrocephalus (iNPH) is part of the large group of neurodegenerative diseases. Green et al Fluids Barriers CNS (2021) 18:25 in selected patients and makes iNPH one of the few potentially treatable forms of dementia. The pathophysiological processes of iNPH remain incompletely understood, resulting in a lack of clear diagnostic criteria. This makes selection of patients for surgical treatment and differentiation from other neurodegenerative diseases a challenge. There is a need for better understanding of the pathophysiology of iNPH [4]
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