Prenatal Diagnosis of Thanatophoric Dysplasia Type I Based on Classical Ultrasound Findings During Anomaly Scan: A Case Report

Thanatophoric dysplasia (TD), the most common lethal skeletal dysplasia, results from FGFR3 mutations causing impaired endochondral ossification. Where molecular testing is unavailable, ultrasound evaluation is the diagnostic cornerstone. We report a 24-year-old primigravida undergoing a routine anomaly scan at 22 weeks. Ultrasonography showed severe micromelia with femoral bowing (telephone-receiver appearance), a markedly narrow thoracic cage (thoracic circumference of 11.79 cm, falling below the fifth percentile), thoracoabdominal dip, and platyspondyly with a shortened trunk. Neurosonography revealed bilateral temporal lobe polymicrogyria, supporting TD type I. No fractures, hypomineralization, cloverleaf skull, or visceral anomalies were seen; amniotic fluid was normal. The parents opted for termination at 23 weeks after counselling. Postnatal confirmation and FGFR3 testing were declined due to personal beliefs and financial constraints. This case highlights a systematic ultrasound approach, including thoracic assessment and neurosonography, for diagnosing TD type I when genetic confirmation is not feasible.