The role of MRI-CSF flowmetry in the diagnosis of idiopathic normal pressure hydrocephalus

Abstract

Background: Normal pressure hydrocephalus is a gloomy entity with no definite cause known till date.The classical clinical triad includes gait apraxia, urinary incontinence and different grades of cognitive dysfunction as dementia.NPH is considered the first treatable type of dementia as it differs from other dementias in that the symptoms can show clinical recovery & regression with CSF diversion.Many tests have been employed in the diagnosis of idiopathic NPH, including invasive methods which may lead to serious complications.That is why; non-invasive techniques are required to increase the sensitivity and specificity of routinely used imaging methods.Flow sensitive cardiac gated phase contrast MR imaging techniques have been increasingly applied recently providing the potential for non-invasive study of CSF flow dynamics, as it can be used to discriminate between different types of hydrocephalus & to provide significant information in preoperative evaluation of NPH and the prediction of the benefit from surgery.The aim of this study: is to evaluate the role of MRI-CSF flowmetry using its various flow indices for the diagnosis of INPH. Patients and methods:In our prospective study conducted at radiology department in our institute including thirty cases: 25 patients with clinically suspected NPH & ventriculomegaly & 5 normal elderly control cases.Two protocols of PC MRI CSF flowmetry examination were used, one assessing CSF flow dynamics qualitatively using a sagittal plane and one quantitatively using an axial plane perpendicular to the aqueduct.Results: Among the 25 patients involved in the study, 19 patients (76%) were diagnosed as NPH based on the clinical & radiological findings as well as the hyper dynamic CSF flow across the aqueduct in the PC MRI study & 6 patients (24%) were diagnosed as atrophic dilatation with hypo dynamic CSF flow across the aqueduct in the PC MRI study.In our study, we found that normal CSF flow throughout the cardiac cycle show free aqueductal pulsatile CSF flow as a cranial flow during CSF diastole (hyper intense signal) and caudal flow during systole (hypo intense signal).In our study, we found that at a cut off value for aqueductal SV of about 42 ul/cycle.Aqueductal stroke volume (> 42) shows sensitivity of about (93.3%) & specificity of about (75%) with total accuracy of about (89.5%) in predicting shunt responsiveness in NPH patients. Conclusion:Phase contrast MRI CSF Flowmetry was found to be of high sensitivity and specificity in diagnosing NPH & differentiating it from atrophic dilatation.It is simple, fast and non-invasive effective method that adds more to the total accuracy of the conventional MRI examination as it provide valuable additional information & reducing rates of complications and predicting shunt responsiveness.