PURPOSE: Benign external hydrocephalus (BEH) is characterized by enlarged subarachnoid spaces in infants. The underlying pathophysiology of BEH remains unclear and the term “benign” reflects the common view that this is an idiopathic, self-limiting condition that resolves spontaneously. We sought to describe the development of BEH based on quantitative MRI analysis.
MATERIAL & METHODS: T2-weighted and venography images from age-matched 27 BEH patients and 21 controls were acquired on 1.5T MRI. Age-related dynamics of a number of neuroimaging biomarkers were investigated using a set of specially developed quantification techniques.
RESULTS: BEH patients demonstrated a significantly increased volume of SAS at birth, while the initial size of the ventricular system was not significantly different. The frontal SAS width was substantially widened in BEH at all ages. Thus, an average value of the frontal SAS width above 3 mm may establish a criterion for diagnosis of BEH. The parietooccipital SAS width was similar between the groups at birth, and remained almost unchanged in BEH patients, contrasting with a dramatic reduction in controls. In both groups, the inter-hemispheric fissure width underwent some resolution and decreased from initially excessive to normal values by the age of about 2 years. The AG volumetric measurement showed no difference between the groups, indicating low impact of this parameter. The cerebral venous volume was decreased in the early life of BEH patients. However, by the age of two years, the cerebral venous volume of the BEH patients normalized to values of the control group. BEH patients demonstrated substantially wider and tortuous optic nerve (ON) and enlarged Meckel’s cave compared to controls.
CONCLUSION: We proposed a neuroimaging technique for quantification of the intracranial venous system, CSF redistribution within SAS spaces and the ventricular system, and additional imaging signs of increased intracranial pressure, including enlargement of Meckel’s caves and deformed ON. From this work, we suggested biomarkers that may contribute to definitive diagnosis of BEH. Integrating the diagnosis into an artificial intelligence program may promote rapid identification of the disorder. We proposed that abnormalities of sinus narrowing cause elevated intracranial pressure and might be an initial step in the development of BEH. We thus suggested that BEH is a type of early age idiopathic intracranial hypertension that occurs in infants with open fontanelles. The presence of elevated intracranial pressure raises doubt regarding the benign nature of BEH and explains the relatively high prevalence of neurological deficits in the BEH population.
