Incidence and Magnetic Resonance Imaging

Abstract

Holoprocencephaly (HPE) is a developmental anomaly featured by a failure in differentiation and cleavage of the prosencephaly resulting in incomplete separation of the two hemispheres. In almost 80% of individuals it is accompanied by specific craniofacial anomalies. Both genetic and teratogen factors are responsible for the development of HPE [1]. Rare in absolute terms, HPE is the most common brain abnormality and is seen in 1 per 8000-16,000 live births [2-4]. In an analysis of 21 HPE epidemiologic articles Orioli IM and Castilla EE [5] found that the pregnancy outcomes had relevant impact on the incident rate of HPE, being lower than 1 per 10,000 in live and stillbirth and between 40-50 per 10000 in aborted embryos. In a large series of 4,157,224 births, the same authors observed 370 infants with suspected holoprosencephaly (0,009%) stressing that isolated HPE was homogeneous among the 11 sampled countries, increasing from 0.5/10,000 births to 1/10,000 births between 1967 and 2000% [6]. The early embryonic occurrence may be even higher with prevalence of 1:250 in embryos [7] but may not be detected due to most fetuses aborting in early gestation [2]. In our small series of 4000 MRI explorations in children of different ages (from newborns to 15 years old) only three cases harboring HPE were diagnosed, accounting for almost 0.05%. Even though, the holoprosencephaly has been divided into three categories (alobar, semilobar and lobar) and a clear distinction between them does not exist. However, another two categories have been added to the previous one: the middle interhemispheric fusion variant (MIHF/MIHV or syntelencephaly [8] and a septopreoptic type [9]. Alobar HPE is a rare and the most severe congenital malformation, usually diagnosed by prenatal ultrasound, rarely postnattally by CT or MRI, because the infant is most often stillborn. There is no separation of cerebral hemisphere with only one large ventricle and failure of transverse cleavage into diencephalon and telencephalon. Semilobar HPE, less dysmorphic then alobar (HPE), has both the frontal and parietal lobes completely fused and interhemispheric fissure exist posteriorly. The concomitant anomalies might be microcephaly, macrocephaly, motor abnormalities such as choreoathetosis or lower extremity spasticity.