Benign external hydrocephalus.

Dear Sir,

A 25-month-old child presented with relatively large head since birth. He was born prematurely. However the perinatal period was uneventful. His growth and development were normal. His head circumference chart is given in Figure 1. He never had tense fontanels. He underwent serial head scans, which showed bilateral frontal subdural cerebrospinal fluid (CSF) collections [Figure 2]. A formal ophthalmological assessment revealed normal vision and fundus. Detailed psychological assessment was normal. He was at par for self-help, communication, locomotion, and socialization. His social quotient as measured on Vineland social maturity scale was 130, which was above average. A final diagnosis of benign external hydrocephalus (BEH) was made, and parents were counseled.

Figure 1

Magnetic resonance imaging (a) at 7 months of age and computed tomography scan (b) at 25 months of age showing enlarged subarachnoid spaces over bilateral frontal lobes without ventriculomegaly

Figure 2

Head circumference chart showing macrocephaly

Benign external hydrocephalus in infants is characterized by macrocephaly and typical neuroimaging findings of enlarged subarachnoid spaces especially overlying the frontal lobes, and normal or only moderately enlarged ventricles. It is considered as a self-limiting condition and does not require any treatment.[1] The actual incidence of BEH in children with macrocephaly is not known. The BEH was seen in 0.6% of the children as incidental finding on magnetic resonance imaging.[2] The exact etiology of BEH is not known. The possible hypothesis is an impairment of CSF absorption through the arachnoid villi and pronounced increase in CSF production during the 1st year of life. The other hypothesis is that external hydrocephalus may be an arrested form of internal communicating hydrocephalus.[1] The clinical features are macrocephaly with nontense fontanels. There may be history of familial macrocephaly or premature birth.[13] The “cortical vein sign” that is visualization of cortical veins across the CSF provides a reliable means of differentiating between enlarged subarachnoid spaces and hypodense subdural fluid collections, which compress the subarachnoid space, approximating the cortical veins to surface of the brain.[4] Most children with BEH seem to do well both initially and in the long term, however a number of children show psychomotor delay.[1] A study of long-term health status of 99 children with BEH showed that the developmental delay was present in 21% of patients (4% verbal, 20% gross motor, 4% fine motor delay). Gross motor delay resolved in 15/20 and fine motor delay in 4/4 patients. Verbal delay resolved in 2/4 patients, but interestingly, was newly detected in 6 other children.[3] The BEH does not require specific treatment. Though surgical and medical treatment is described, the results are good irrespective of treatment modality (observation, medical, or surgical), hence the value of treatment is questioned.[1]