Prenatal Ultrasonographic Molar Tooth Sign: Case Reports and Review of Literature

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

Publication History

Received: 12 October 2020

Accepted: 14 January 2021

Article published online:
05 May 2023