Which ultrasound finding is characteristic of Thanatophoric dysplasia type 1?

The characteristic ultrasound finding associated with Thanatophoric dysplasia type 1 is the "telephone receiver femur." This term describes the appearance of the femur, which is typically short and curved, resembling a telephone receiver. Thanatophoric dysplasia is a severe skeletal dysplasia, and the abnormalities in bone structure, particularly the femur, are a key diagnostic feature.

In this condition, the femoral curvature is pronounced, leading to a distinctive diagnostic imaging appearance. The shortening of the long bones, particularly seen in the femur, is one of the primary indicators that clinicians look for when investigating skeletal dysplasias. This imaging feature, along with other clinical findings, helps confirm the diagnosis of Thanatophoric dysplasia type 1.

The other options refer to conditions or findings not primarily associated with Thanatophoric dysplasia. For instance, the molar tooth sign is linked with Joubert syndrome, rhabdomyoma is a cardiac tumor seen in conditions like tuberous sclerosis, and interrupted aortic arch is a congenital heart defect. Each of these has its own specific characteristics and associated conditions, making them unrelated to Thanatophoric dysplasia type 1.