[Normal and pathological ultrasonography of the fetal brain]

Advanced ultrasonic technology enabled the bidimensional imaging of fetal brain throughout pregnancy. The number of visible structures increases with gestational age. In order to certify the described items they were compared to similar anatomical sections available from brain specimens or an atlas of anatomy. Real-time as well as automatic compound scanning machines were used to obtain echographic images of fetal brain anatomy in utero. Many different scans were collected along three orthogonal directions: every 2 mm, with the automated compound scan and as close from each other as possible with the linear array real-time scanner. The material included 59 normal fetuses between the 15th and 40th week of gestation. Eight typical sections are made but the only structures identified are those being visible on every section obtained at the same level. Brain structures such as grey and white matter, nuclei, vessels and ventricles have different sonic properties. They are subsequently distinguishable on the ultrasonic image if the equipment is capable of detecting and showing such differences. Grey matter is more echogenic than white, choroid plexuses are very reflective as are vessel walls which also pulsate. Four horizontal sections are described in detail (Figs. 2-7). The coronal planes are demonstrated at three different levels (Figs. 8-12) and the sagittal plane is represented by Fig. 13. Thirty five structures were identified (Table 2). In the second section some brain and skull anomalies are briefly described. The principal signs of the abnormalities and possible encountered variations are listed such as cranial defects in anencephaly, acrania, encephalocele, iniencephaly; the anomaly of size and shape of head and ventricle, as in hydrocephaly and microcephaly, cystic-like- and solid-tumor lesions and Dandy Walker syndrome and hydranencephaly. Attention is drawn to possible artifacts and pitfalls in the differential diagnosis between similar looking pictures. Examples are given such as noise in the near field, occurring more often in sectorscan machines, inadequate orientation of scan plane producing asymetrical display of the hemisphere and the Sylvian fissure described as if it was the lateral ventricle wall. Anomalies can also be confused such as exencephaly, anencephaly, iniencephaly, encephalocele. An excellent knowledge of normal brain anatomy and pathology, together with excellent equipment and a careful scrutiny of the echograms are required qualities for fetal brain examination.