Case Report: A case of Joubert syndrome in twin pregnancy: MRI manifestations and literature review.

Introduction: Joubert syndrome (JS) is a rare autosomal recessive disorder belonging to the ciliopathies and can cause a series of neurological symptoms after birth. Prenatal diagnosis of this disease is rare, as the results from prenatal ultrasonography for JSRD are relatively nonspecific. Prenatal MRI is usually the preferred diagnostic method. On fetal MRI, it presents as a typical midbrain-hindbrain malformation characterized by the molar tooth sign (MTS). Currently, reports of prenatal MRI diagnosis for JS are rare, with no documented twin gestations. Herein, we report a case of JSRD in a twin pregnancy detected at the 25th gestational week through prenatal MRI, with a review of the etiology, imaging features, and differential diagnosis of JS. Patient presentation: A 31-year-old woman was pregnant at the 25th gestational week with fetal cerebellar vermis hypoplasia suspected from prenatal US. Fetal MRI demonstrated the characteristic MTS, which is the hallmark of JS, and strongly supported the diagnosis at our hospital. The amniotic fluid prenatal diagnosis revealed that the twins had compound heterozygous TMEM67 variants classified as Variants of Uncertain Significance (VUS). The couple finally opted to terminate the pregnancy. Conclusions: Currently, the diagnosis of JS is typically made postnatally. MRI is extremely advantageous for evaluating posterior fossa structural anomalies prenatally. In combination with genetic testing, it can provide guidance for early diagnosis and prenatal counseling.