Extra-axial cerebrospinal fluid spaces in children with benign external hydrocephalus: A case-control study

Background The distinction between normal and pathological extra-axial cerebrospinal fluid (CSF) spaces is unclear, with the use of the term benign external hydrocephalus (BEH) not being well defined in clinical practice. This study aimed to establish a distribution of metrics of the subarachnoid space in a population of children diagnosed as normal, and investigate the clinical use of the term BEH. Methods A retrospective case-control study on magnetic resonance image scans was performed on 150 children diagnosed as normal and 10 children diagnosed with BEH. Measurements were taken in the axial plane for CSF width (CSFW), and interhemispheric width (IHW). Results Normal controls had a mean age of 11.1 ± 7.6 months (78 male, 72 female) and the BEH sample had a mean age of 10.6 ± 7.8 months (six male, four female). Mean CSFW was 7.96 ± 4.79 mm in the BEH sample compared to 4.58 ± 2.25 mm in the normal sample ( p < 0.05). Mean IHW was 6.30 ± 2.79 mm in the BEH sample compared to 3.89 ± 1.83 mm in the normal sample ( p < 0.05). However, a substantial overlap between the two distributions of CSFW was found, with 50% of BEH patients lying within a single standard deviation of the mean of normal individuals. Conclusion The absence of diagnostic criteria for BEH means reporting is variable. Patients being diagnosed with BEH who have no other clinical defects may represent the extreme of the normal population rather than a distinct clinical entity.