Clinical applicability of arterial spin labeling magnetic resonance imaging in patients with possible idiopathic normal pressure hydrocephalus: A prospective preliminary study

Idiopathic Normal Pressure Hydrocephalus (iNPH), first described by Hakim et al. in 1965, is a disorder characterized by slow progressive impairment of gait and balance, cognitive deterioration, and urinary incontinence [1]. The cause of this condition, which is typically characterized by ventricular enlargement and normal intracranial pressure (ICP), is still unknown [2], [3]. The treatment is surgical and consists of Ventriculo-Peritoneal Shunting (VPS) or Ventriculo-Atrial Shunting. This procedure is usually successful with an acceptable complication rate in the majority of cases [4], [5], [6], [7], [8]. Currently, clinicians have two main different invasive tests to select patients who may benefit from surgery: a test measuring the effect on symptoms of temporary drainage of cerebrospinal fluid (Tap Test) and a test measuring the resistance to CSF outflow (Lumbar Infusion Test) referred as Rout. These tests do not have high specificity or sensitivity, especially for excluding patients from surgery [9], and other non-invasive methods to better identify patients that will benefit from surgery are required. Several studies have shown that patients affected by iNPH have a global reduction of cerebral blood flow (CBF) in comparison to healthy subjects, particularly in the periventricular white matter, the thalami, and the basal ganglia region [2], [10], [11]. Furthermore, some Authors demonstrated a positive correlation between the increase of cerebral perfusion in periventricular white matter and in the basal ganglia region after CSF removal or shunt procedure and the clinical improvement [12], [13]. The majority of these studies are based on the estimation of CBF by using different techniques such as Dynamic Susceptibility Contrast (DSC) Magnetic Resonance (MR) or Computed Tomography (CT) perfusion. Nonetheless both these methods require intravenous contrast agent administration.

Arterial Spin Label (ASL) MR is a completely non-invasive imaging perfusion technique with the main advantage of allowing a global evaluation of CBF without the injection of contrast agents [14]. ASL is safe and less time-consuming and it has been widely used for better characterization of neurodegenerative diseases as Alzheimer’s Disease (AD) and Frontotemporal Dementia (FTD) [15], [16]. Currently, to the best of our knowledge, only a few different studies regarding the relationship between CBF measured by ASL and iNPH have been published [17], [18], [19]. However, these studies were mainly focused on the quantitative evaluation of CBF while no evidence of the possible role of visual assessment of ASL perfusion colored maps in the management of iNPH patients has been investigated yet. The purpose of our study was to determine if the brain ASL-MRI technique may be useful in the management of patients affected by probable iNPH by assessing the qualitative evaluation agreement of ASL CBF colored maps between different neuroradiologists and by correlating these data to Tap Test results.

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