Rare sonographic finding of osteogenesis imperfecta type 2: fluid retention in the subarachnoid space.

Osteogenesis imperfecta (OI) type 2 is the most severe form of this osteogenetic disorder. A 26-year-old woman was referred to our hospital for suspected fetal hydrocephalus at 26 weeks' gestation. Detailed ultrasonographic examination revealed fluid retention in the subarachnoid space. The fetal head was expanded, and the skull bone was easily deformed by the pressure of the ultrasound probe. Pleural effusion and ascites were noted, and the upper and lower extremities were extremely shortened and deformed. On helical 3D-CT, the skull bones could not be imaged, and multiple rib fractures and deformed long bones were suspected. Based on these findings, the fetus was diagnosed with OI type 2, and it was explained to the patient and her family that this disease was fatal. Due to non-reassuring fetal status at 28 weeks, induced breech delivery resulted in a stillborn infant. The head of the infant was soft, and the upper and lower extremities were extremely shortened. Post-mortem radiography confirmed the presence of deformed long bones and ribs with multiple fractures, while the skull bones could not be imaged. Detailed ultrasound observation may detect cerebrospinal fluid retention in the subarachnoid space, a finding that may be associated with the membranous skull bones of this osteogenetic disorder.