Epidemiology of Atretic Encephaloceles in Children

Incidence and Prevalence

• 1 – 5 per 100,000 births: Encephaloceles in general occur in approximately 1 per 10,000 births in the United States and Europe (18, 21, 28). The atretic variety accounts for 10–50% of all encephaloceles (18, 21, 23, 28, 33). The exact incidence and prevalence of atretic encephalocele are presently unknown due to the scarcity of large series with significant data on this entity (18, 21, 23, 28, 33).
• Sometimes not identified at birth: Although easily discovered after birth, atretic encephaloceles may go unnoticed or ignored until adolescence or adulthood (20).

Age Distribution

• Usually diagnosed at birth: Atretic encephaloceles are lesions of congenital origin and are usually discovered at the neonatal examination (21, 28). In 38 instances of atretic encephalocele, 24 patients were 1 year or younger at the time of diagnosis while only 1 patient was aged 38 years (21).
• Occasionally found on prenatal ultrasound: Atretic encephaloceles may even be diagnosed prenatally in the routine ultrasound assessment performed during pregnancy (15, 18, 28).

Sex Predilection

• Most report no difference: Most reports on atretic encephaloceles suggest no differences in sex distribution (11, 21, 26, 28, 33). In the series from the author’s institution, males outnumbered females (M: F=22:16).

Geographic Distribution

• Not clear: Most probably, atretic encephaloceles occur in patients of all countries and races, although no reliable data were found on the geographical distribution of this anomaly in the literature search for this chapter. The majority of reports on atretic encephaloceles come from developed countries, especially from the United States, Europe, and Japan (21, 28, 33).

Risk Factors

• Teratogens and x-ray exposure: Encephaloceles have been experimentally induced by administration of diverse teratogens such as sodium arsenate, clofibrate, excess of vitamin A, and Trypan blue, and by x-ray exposure (14, 21, 28).
• Other factors: Maternal diabetes, hyperthermia, antimitotic drugs, nitrous oxide anesthetics, clordiazepoxide, amytriptyline, triamcinolone, some antiepileptic drugs (primidone, etosuxamide) and passive smoking have been implicated in the origin of human encephaloceles (18, 21, 28).
• Consanguinity: In the author’s series, an excess of syndromic atretic encephalocele was found to be related to ethnic isolation or consanguinity, mainly seen in the Spanish gypsy population (16, 17, 21).

Relationships to Other Disease States and Syndromes

• Syndromes: Cohen and Lemire and others have reported the association of encephaloceles with known syndromes, including aberrant tissue band, Chemke and cryptophthalmos syndromes, dyssegmental dwarfism, frontonasal dysplasia, and several conditions such as Knobloch, Meckel and pseudo-Meckel, von Voss, Joubert, and warfarin syndromes (8, 21, 28). Atretic encephaloceles have also been reported as forming part of the Walker-Warburg syndrome (15, 17, 31).
• Associated developmental anomalies: A wide spectrum of anomalies may occur in association with encephaloceles. Some of these abnormalities are secondary to encephalocele development; others represent primary noncontiguous embryonic malformations (8). Associated anomalies include hydrocephalus, arachnoid cysts, absent corpus callosum, orofacial clefting, craniosynostosis, Dandy-Walker and Chiari malformations, ectrodactyly, hemifacial microsomia, hypothalamic-pituitary dysfunction, Klippel-Feil anomaly, iniencephaly, and myelomeningocele (8, 18, 21, 23, 28, 32, 33). In addition, cases of atretic encephalocele have been reported with associated extra- or intracranial teratomas or lipomas (1, 6, 30).