What Clinical Signs Can Be Associated With Benign External Hydrocephalus?

Patient Presentation
A 6-month-old female was seen by a pediatrician for macrocephaly. The parents had normal head circumferences. The head circumference velocity had been increasing so a head magnetic resonance imaging study was completed and was normal. The infant was acting normal and did not have any developmental delays reported other than having more problems getting into a sitting position or staying there if placed because of balance with her head. The parents said the infant was without illness and was not taking any medications or supplements in addition to her normal breastfeeding and oatmeal cereal. The family history was negative for any neurological, developmental or growth problems.

The pertinent physical exam showed a smiley infant with weight in the 50%, length in the 75% and a head circumference > 95% and growing at 2 cm/month growth velocity. The vital signs were normal including a normal temperature. The anterior fontanele was open, bulging when palpated in a seated position without pulsations and was ballottable. Her neurological examination was normal.

The diagnosis of macrocephaly in a healthy appearing infant with normal imaging but with a bulging fontanele was made. The pediatrician was concerned about the bulging fontanele and asked a colleague about the follow-up that might be recommended. He was reassured when the other pediatrician felt that as the child did not appear ill that a spinal tap for meningoencephalitis was not indicated at this time. “I think that because there is increased pressure the fontanele is going to be bulging as this is the pop-off valve for the fluid. You could just talk with neurosurgery but usually if the child isn’t having any problems they are certainly not going to do any procedures. You could monitor the child closer with the parent doing weekly head circumferences and sending those to you and in that way you have close follow up and can also talk with the parent about the baby’s development too,” the colleague offered. The pediatrician talked with the colleague the next week and said that neurosurgeon had agreed that close follow-up would be good to make sure there weren’t developing problems but that they would not do any procedures at this time.

Hydrocephalus is an abnormal accumulation of cerebrospinal fluid (CSF) in the ventricles and/or subarachnoid spaces. External hydrocephalus is a communicating hydrocephalus often defined as the patient having a rapidly enlarging head circumference (HC) and enlargement of the subarachnoid spaces especially over the frontal lobes with normal or moderately enlarged ventricles. Benign external hydrocephalus (BEH) is a self-limited external hydrocephalus that occurs during infancy and resolves spontaneously in childhood, usually by age 2 years, that is felt to not cause significant problems. It was first described by W.E. Dandy 1947 and there have been other terms used to describe this entity that indicate further understanding of the entity and the presumed pathophysiology.

A recent study in Norway reported the incidence to be 0.4 per 1000 live births. Some patients seem to have a genetic propensity to BEH.

The cause of BEH is debated but is most commonly felt to be because of immature arachnoid villi. Arachnoid granulations become visible between 6-18 months and then gradually develop in size over years. It is felt that there is a delay in maturation of this process where the villi are not able to reabsorb the CSF that is being produced, thus the CSF accumulates externally in the subarachnoid spaces.

An evaluation for macrocephaly is a common reason a child has neuroimaging which can include transfontanele ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI). Cerebral atrophy and subdural fluid collections should be differentiated from external hydrocephalus. The “cortical vein sign” where cortical veins are visualized within fluid collections in the cerebral convexities suggests that the fluid is not caused by subdural fluid collections that would compress the subarachnoid space and the veins within it. Intracranial pressure measurements show normal to slightly elevated pressures (6-16 mm Hg) and the fluid analysis has been reported as normal or with slight xanthochromia or slight elevated protein.

BEH is usually felt to have a “benign” prognosis but there can be problems. External hydrocephalus has an increased risk of subdural hematomas after minimal or no head trauma. Developmental delays, especially motor delays, are often seen for some time in infancy and toddlerhood. There are few long-term studies and those generally find that children overall seem to do well, but there can be some subtle changes. A recently study of at least 7 years follow-up of children with BEH showed subtle long-term neurocognitive problems. This was true for both children who received shunting or were treated conservatively. The authors acknowledge that there may be a selection bias as the group came from a neurosurgery population. The authors found even in non-operated children, children performed significantly poorer in attention span, psychomotor speed and executive functioning. BEH treatment is usually conservative with observation of the condition, or use of acetazolamide. Intervention with needle aspiration or shunting procedures is usually for patients with clinical signs and symptoms of increased intracranial pressure.

The differential diagnosis of a bulging anterior fontanele can be found here.

Learning Point
According to a comprehensive literature review, the clinical signs and symptoms of BEH include:

“The large or enlarging head appear indistinguishable from those seen in other hydrocephalus cases (…). A relatively common sign is a tense anterior fontanel (…). Other early symptoms and signs have also been reported occasionally: dilated scalp veins (…), frontal bossing (an unusually prominent forehead) (…), irritability (…), hypotonia (…), vomiting (…), gross motor delay (…), ataxia (…), poor head control (…), seizures (…), fever (…), and mental retardation (…). We have not found any articles reporting sunset gaze.”

Questions for Further Discussion
1. What are indications for ventriculoperitoneal or similar neurological shunt placements?
2. What causes macrocephaly?
3. When should the anterior fontanele close? Learn more here.

Related Cases

To Learn More
To view pediatric review articles on this topic from the past year check PubMed.

Evidence-based medicine information on this topic can be found at SearchingPediatrics.com, the National Guideline Clearinghouse and the Cochrane Database of Systematic Reviews.

Information prescriptions for patients can be found at MedlinePlus for this topic: Hydrocephalus

To view current news articles on this topic check Google News.

To view images related to this topic check Google Images.

To view videos related to this topic check YouTube Videos.

Zahl SM, Egge A, Helseth E, Wester K.
Benign external hydrocephalus: a review, with emphasis on management. Neurosurg Rev. 2011 Oct;34(4):417-32.

Marino MA, Morabito R, Vinci S, et.al. Benign external hydrocephalus in infants. A single centre experience and literature review. Neuroradiol J. 2014 Apr;27(2):245-50.

Mikkelsen R, Rodevand LN, Wiig US, et.al. Neurocognitive and psychosocial function in children with benign external hydrocephalus (BEH)-a long-term follow-up study. Childs Nerv Syst. 2017 Jan;33(1):91-99.

Wiig US, Zahl SM, Egge A, Helseth E, Wester K. Epidemiology of Benign External Hydrocephalus in Norway-A Population-Based Study. Pediatr Neurol. 2017 Aug;73:36-41.

Donna M. D’Alessandro, MD
Professor of Pediatrics, University of Iowa