Background: Midline cerebral structures are essential for the normal morphogenesis and function of the fetal brain. However, the diagnosis of congenital anomalies of midline cerebral structures. 
The Aim of The Work: This study aimed to evaluate the role of 2D versus 4D ultrasound in the diagnosis of midline structures of the fetal brain at the second trimester of pregnancy.
Patients and Methods: 200 pregnant women at the second trimester [18-22 weeks] were selected. They were clinically evaluated to check the female and fetal wellbeing. Then a screening of fetal brain midline strictures had been performed by two- and four-dimensional ultrasound, aiming to discover any anomalies of the fetal brain midline structure. Both scans were compared with the postnatal transcranial ultrasound.
Results: The 2D ultrasound detected no abnormality in 194 out of 200 fetuses [97.0%], and 4 cases [2.0%] had mega-cisterna magna, and 2 cases [1.0%] had encephalomylocele, which were detected by the 4 D and confirmed by postnatal transcranial ultrasound. The 4 D US discovered 2 cases [1.0%] of Dandywalker malformation, which was confirmed by postnatal transcranial US. There was a complete agreement between prenatal 4D ultrasound and postnatal transcranial ultrasound. The prenatal 2D ultrasound had a sensitivity of 75.0%, specificity of 100.0%, PPV of 100.0%, NPV of 98.7% and overall accuracy of 99.0%. Otherwise, the prenatal 4D ultrasound was 100.0% sensitive and specific.  
Conclusion: 4D ultrasound showed superiority in the diagnosis and confirmation of the fetal brain midline structure's abnormalities. Also, the prenatal 4D ultrasound was 100.0% sensitive as postnatal transcranial US.