Abnormal reduction in ossification of the calvaria (roof of the skull consisting of the frontal bone, parietal bones, temporal bones, and occipital bone).
Comment:
A hypomineralised skull castes little or no acoustic shadow on prenatal ultrasound. This makes visualisation of the intracranial anatomy clearer than normal. In conditions associated with profound hypomineralisation, the skull shape can be distorted by pressure from the ultrasound transducer later in pregnancy.