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Enlarged intracranial translucency and molar tooth sign in the first trimester as features of Joubert syndrome and related disorders

A 35-year-old woman, gravida 3 para 0, with a history of termination of pregnancy for vermian dysplasia and hyperechoic kidneys as features of Joubert syndrome and related disorders (JSRD) and an early miscarriage was counseled about her current pregnancy. In a previous pregnancy, the fetus had exhibited double heterozygous mutations (p.Ser872/p.Arg1272) of parental origin. On first-trimester ultrasound examination of the current pregnancy, nuchal translucency thickness was 1.47 mm and crown–rump length was 64.7 mm. Analysis of the posterior fossa showed an increased intracranial translucency and a horizontalized brainstem on sagittal (Figure 1) and coronal (Figure 2) views, and a widened future fourth ventricle and a molar tooth appearance of the cerebellar peduncles in the axial view (Figure 3). The kidneys were apparently normal at this early stage, however, the examination was carried out by transabdominal ultrasound and it is likely that a transvaginal approach would have shown more detail. Chorionic villus sampling was performed and recurrent JSRD with fetal mutations of parental origin was identified, leading to a decision to terminate the pregnancy. Our case adds to the growing list of posterior fossa abnormalities identified by assessment of intracranial translucency (encephalocele, Dandy–Walker malformation, cerebellar vermis anomaly in the context of chromosomal abnormalities, Blake’s pouch cyst) during first-trimester ultrasound examination1,2. Since the initial observation of Chaoui et al.3 of decreased or absent intracranial translucency in some cases of open spina bifida, early analysis of the posterior fossa now includes many subjective and objective sonographic markers for detection of multiple pathologies. Early diagnosis of JSRD has been described previously for which the diagnosis was suspected only from an abnormal fetal posterior fossa in pregnancies at high risk of JSRD recurrence4. In such cases, the abnormality of the posterior fossa was described as cystic, without detailed