Prenatal magnetic resonance imaging diagnosis of molar tooth sign at 17 to 18 weeks of gestation in two fetuses at risk for Joubert syndrome and related cerebellar disorders.

We report on the prenatal MRI diagnosis of Joubert syndrome and related cerebellar disorders (JSRD) in 2 unrelated fetuses at 17-18 weeks of gestation who were referred to us with history of siblings with JSRD and additional renal affection in the second case. Ultrasonography (US) showed non-specific cranial findings in both fetuses such as prominent cisterna magna and ventricular system as well as bilateral renal enlargement in the first case. MRI identified the molar tooth sign (MTS) and suggested a JSRD affection in both fetuses. The final suggested diagnosis for both cases was Joubert syndrome with intrafamilial variability in renal expression. This report describes the earliest prenatal detection of MTS. We include a discussion of the differential diagnosis of renal affection in conjunction with MTS and review the previously reported cases with prenatal MRI detection of MTS. The report emphasizes the role of MRI in the early specific prenatal diagnosis of JSRD through the recognition of MTS.