Abstract

Background

     Alobar holoprosencephaly (HPE) is easily detected during a first-trimester screening examination, conversely, recognizing the lesser varieties may be difficult even in the second trimester.

Objectives

     To describe the imaging findings of a cohort of fetuses with holoprosencephaly (HPE) and to elucidate the appearances of the different anatomical varieties.

Materials and methods

      We reviewed medical records and stored images of pregnant women referred to our clinic because of a diagnosis or the suspicion of various forms of HPE. We reported the imaging characteristics, the presence of other associated anomalies, magnetic resonance findings, karyotype and autoptic examinations when available.

Results

     Alobar forms show great distortion of normal brain anatomy, with a single ventricle detectable during the first trimester of pregnancy. Extracerebral, face and karyotype abnormalities are often associated. In semilobar and lobar forms the septum pellucidum is typically absent in axial planes, with fused frontal horns, while posterior fossa is often normal. At multiplanar neurosonogram, anomalies involving corpus callosum and cortex development can be detected. Face abnormalities are mild in lobar forms: receding forehead, various degrees of hypotelorism and the presence of a single central maxillary incisor are reported.

Conclusions

     The alobar forms are detectable since the first trimester, with a peculiar single ventricle and extremely frequent extracerebral and karyotype abnormalities. The semilobar and lobar forms are more challenging and the diagnosis is easily missed in a mid-trimester screening exam unless a careful evaluation of both cavum septi pellucidi and frontal horns as well is conducted.

Introduction

     Holoprosencephaly (HPE) is a complex brain malformation characterized by variable degrees of incomplete cleavage of the two hemispheres and the development of midline structures [1–۳]. Prognosis is variable but is most frequently dismal. The most severe forms are frequently associated with aneuploidies, trisomy 13 and triploidy in particular, and result in miscarriage or perinatal death; the less severe forms are compatible with postnatal survival but in most cases are associated with delayed neurocognitive and motor development, epilepsy and endocrine disorders due to pituitary deficiency [4–۶].

     HPE encompasses a continuum of brain malformations. Classically, three forms with progressive severity have been described: lobar, semi-lobar and alobar. However, there is a broad spectrum of presentation with overlapping findings [7,8]. Thus far, prenatal studies have insisted on the alobar form, the most severe one, which is characterized by typical and very extreme findings [9]. The experience with less severe forms is more limited and the findings that have been described are variable and much more subtle [10–۱۴].

Results

     During the study period fetal HPE was diagnosed in 15 cases; of these 10 (67%) were of the alobar type and 5 of less severe varieties. One case has been previously reported [19].

Alobar HPE Most cases were diagnosed in the late first trimester (median 12 weeks, range 11–۱۶ weeks) and were always referred from screening facilities with a presumptive diagnosis of alobar HPE. The findings were very homogeneous: in all cases, a standard axial view of the head the midline revealed an absence of the midline echo and one single undivided choroid plexus, in association with severe cranio-facial anomalies or a very flat fetal profile (Figure 1) The median week for a referral at our center was 12 weeks (11–۱۶). Nine patients underwent termination of pregnancy with dilatation and curatteage; one patient with discordant twins decided to continue the gestation. The karyotype was obtained in 8/10 cases, and was normal in 2 cases without detectable microarray anomalies; there were 5 cases of trisomy 13, and 1 case of 68, XX. Associated extracerebral anomalies were present in 9 fetuses (Table 1).