Abstract
Joubert Syndrome and Related Disorders (JSRD) refers to all disorders presenting as
“molar tooth sign” (MTS) on brain imaging. Fetuses with JSRD present with relatively
nonspecific signs on prenatal ultrasound varying from increased nuchal translucency,
enlarged cisterna magna, cerebellar vermian agenesis, occipital encephalocele, ventriculomegaly,
renal disease and polydactyly. However, the hallmark sign in the diagnosis is MTS
and MRI is the imaging modality of choice. We report two cases in which MTS was identified
on prenatal ultrasound at 22 and 21 weeks (wk) of gestational age respectively. The
other prenatal findings on ultrasound included polydactyly and anteroposteriorly enlarged
4th ventricle and vermian hypoplasia in both, and, aortic stenosis evolving to hypoplastic
left heart in the former. Prenatal MRI was not done. Amniocentesis was done in the
one with associated cardiac anomaly which was reported as normal. In both cases, the
couple opted for termination of pregnancy and declined fetal autopsy and further mutation
analysis. Only a few cases of JSRD diagnosed on prenatal ultrasound, have been reported.
Due to the autosomal recessive inheritance (with 25% recurrence) JSRD has to be differentiated
from Dandy-Walker malformation and cranio-cerebello-cardiac syndrome. As definitive
prenatal genetic testing may not be conclusive in Joubert syndrome (JBTS) due to the
large number of pathogenic variants and genetic heterogenicity, the ability to identify
the MTS sonographically early provides a valuable adjunct to prenatal diagnosis.
Keywords
Prenatal diagnosis - Molar tooth sign - Fetal ultrasound - Joubert syndrome - JSRD
