Cerebrospinal fluid (CSF) is a clear, watery fluid that fills the ventricles of the brain and the subarachnoid space around the brain and spinal cord. CSF plays an important role in supporting the brain growth during evolution and protecting it against external trauma [1]. The normal CSF pressure is between 5 and 15 mmHg (65–195 mm H2O) in adults. In children younger than 6 years, normal CSF pressure ranges between 10 and 100 mm H2O [2]. CSF flows through the aqueduct of Sylvius and the foramen magnum is of a pulsatile “to and fro” nature. During systole, CSF flows through the aqueduct and foramen magnum in caudal direction which is reversed in diastole. It is this pulsatile flow which is detected and measured by phase-contrast MRI [3]. For CSF flow evaluation, two series of phase-contrast imaging techniques are applied. One in the axial plane with through-plane velocity encoding for flow quantification, and the other is in the sagittal plane, with in-plane velocity encoding for qualitative assessment. Through-plane evaluation is performed in axial oblique plane perpendicular to the long axis of the aqueduct, and it is more accurate for quantitative analysis because the partial volume effects are minimized [4].
Qualitative assessment is most beneficial in assessment of communication between the arachnoid cyst and subarachnoid CSF spaces. The plane of imaging is adjusted according to the expected point of communication; it may be in axial, sagittal, or coronal planes for detection pulsatile flow (black and white shades) at the neck of the cyst in phase images as evidence of communication with the subarachnoid spaces, as the pulsatile movement of the CSF in the subarachnoid spaces is transmitted to the neck of the cyst through the point of communication. Absence of such signal is an indicator of non-communication [5]. Finally, images obtained from phase-contrast (PC) MRI can be displayed in closed loop cine format or displayed as separate images. Post processing technique starts with manual drawing of a circular region of interest (ROI) on the phase images to include the whole pixels that represents the flow at the aqueduct. Direct measure of the velocity (cm/s) and volume flow rate (ml/min) of the moving spins can be extracted from velocity-time curves and flow-time curve [6, 7].
Phase-contrast MRI also can detect if there is communication with CSF or not in cases with arachnoid cysts which in turn provide the clinician with valuable data that allow him to choose the suitable method of treatment [5]. This imaging method can also help in determination of the severity of CSF flow abnormality that results from tonsillar herniation in Chiari 1 malformation. This may be guidance for the clinician to follow-up those patients after treatment [8, 9].
Normal pressure hydrocephalus (NPH) is a clinical syndrome characterized by gait disturbance, urinary incontinence, and dementia with normal CSF pressure. Hydrocephalus is a main finding in imaging. It is a rare disease but a treatable cause of dementia. Brain atrophy (BA) is a common feature of many diseases affecting the brain, which results in symptoms close to that of NPH; PC MRI is believed to be a reliable method in the diagnosis of NPH and differentiating it from brain atrophy [10].
Idiopathic intracranial hypertension (IIH) is a clinical syndrome characterized by raised intracranial pressure (ICP), in absence of a detectable cause and absence of hydrocephalus [11]. It leads to headache, papilledema, and visual disturbance that may ends with blindness in 10% of cases, without any lateralizing findings in the neurological examination, and normal CSF composition [12]. CSF flow by PC MRI in (IIH) patients, there was difference between the IIH groups and controls in mean rate and flow parameters; this difference suggests that CSF flow analysis by PC MRI may be a marker to follow-up IIH patients [13].
Chiari malformation type I (CM-I) is a condition characterized by downward displacement of the cerebellar tonsils through the foramen magnum and may be associated with or without syringomyelia. CSF flow studies using PC MRI are routinely used nowadays to determine the severity of CSF flow disturbance. The degree of CSF flow disturbance has been shown to correlate with severity and development of clinical symptoms [14].
Ventricular dilatation is the main finding in brain atrophy. It is always mild but symmetrical. Ventricular dilatation is proportional to the widening of the subarachnoid spaces; this change is better assessed on T1 WI MRI; abnormal high signal intensity white matter progressively increases with age as it results from ischemic changes. It may be seen in both deep and periventricular white matter [15]. CSF flow parameters are extracted in one cardiac cycle. Forward flow volume (ml) that represents the CSF flow volume in the encoding direction, while backward flow volume (ml) represents CSF flow volume moving in the opposite direction. Regurgitation fraction ratio is the ratio of the smaller to the larger volume between the backward flow volume and the forward flow volume. The most important parameter calculated from these parameters is stroke volume (ml) which is defined as the mean volume of CSF passing through the aqueduct in craniocaudal and caudocranial direction (Fig. 1) [16]. CSF flow velocity parameters quantify from velocity-time curve; in this curve, the area above the base line is the diastolic velocity, while the area below the base line is the systolic velocity. The curve is analyzed by the following parameters, peak diastolic velocity (PDV) (cm/sec), and peak systolic velocity (PSV) (cm/sec). Maximum CSF flow velocity (Vmax) in the aqueduct is calculated as the average of the absolute values of PDV and PSV (Fig. 2) [17].
For flow volume, maximum flow (cm3/sec) is calculated by multiplying ROI area (cm2) with maximum velocity (Vmax) (cm/sec). Stroke volume represents the average of the volume flowing through aqueduct during systole and diastole, calculated by summation of forward flow volume and backward flow volume then multiply by two [6]. In the current work, MRI CSF flowmetry will be assessed in the different neurological diseases that may cause CSF flow abnormalities.