Benign External Hydrocephalus in a Subgroup of Autistic Children Prior to Autism Diagnosis.
One-third of toddlers who later get an autism label carry extra brain fluid that you can spot before age two.
01Research in Context
What this study did
Ben-Arie et al. (2025) looked at brain scans of toddlers. They wanted to see if extra fluid around the brain shows up before an autism diagnosis.
The team compared kids who later got an autism label with kids who did not. All scans happened before age two.
What they found
One in three toddlers who later received an autism diagnosis had benign external hydrocephalus. Their fluid spaces were clearly larger than those of controls.
The gap vanished in older children. Only the toddler group showed the warning sign.
How this fits with other research
Ozonoff et al. (2008) spotted odd toy play at 12 months in kids who later got an autism label. Gal adds a brain marker that shows up around the same age. Together they give you two cheap flags: watch how the child plays and, if you can, peek at the scan.
Yanai et al. (2025) link viral brain infections to later autism. Both papers say early medical events matter, but BEH is a structural trait while meningitis is an outside illness. Keep both on your radar when you see sudden delays.
Wimberley et al. (2018) found tiny autism risk after ear infections. Their signal was small and maybe due to other factors. Gal’s BEH signal is larger and tied to clear brain changes, so it may be a stronger clue.
Why it matters
If you work with infants at risk, ask the pediatrician about any large head or fast growth. Push for an MRI before age two if you see red flags. When the report mentions extra fluid, track the child closely and start early intervention right away. The window closes after toddlerhood, so act fast.
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02At a glance
03Original abstract
Benign external hydrocephalus (BEH) is evident in < 0.6% of births. It is defined by abnormally large cerebrospinal fluid (CSF) volumes in the subarachnoid space (SAS) and otherwise normal neuroimaging findings before 2 years of age. BEH has not been associated with specific developmental disorders and is not treated because it usually resolves spontaneously. However, quantitative MRI studies have reported that some toddlers with autism exhibit enlarged extra-axial CSF (EA-CSF) volumes. Our objective was to determine whether a subgroup of children with autism exhibits both qualitative BEH and quantitative EA-CSF volume enlargements. We analyzed clinical brain MRI scans in a retrospective sample of 136 children, 5-99 months old, 83 with autism, who were assessed for BEH by neuroradiologists. EA-CSF volume and total cerebral volume (TCV) were quantified in T2-weighted scans by manual labeling. Measures were compared across groups while stratifying participants by age. Neuroradiologists reported BEH findings in 33% of autistic children scanned before the age of 2 years old (i.e., before autism diagnosis). Quantitative MRI analyses demonstrated that autistic children in this age group exhibited significantly larger EA-CSF volumes relative to controls (t (49) = 2.89, p = 0.006, Cohen's d = 0.82) with 30% of autistic children and 9.5% of the controls exhibiting EA-CSF/TCV ratios > 0.14, a previously suggested threshold of potential clinical relevance. EA-CSF differences were not apparent in older children. The prevalence of BEH associated with quantifiable EA-CSF enlargements was remarkably high in toddlers who later developed autism, suggesting a specific autism etiology involving early transient CSF circulation problems with potentially long-lasting neurodevelopmental impact.
Autism research : official journal of the International Society for Autism Research, 2025 · doi:10.1002/aur.70104