US assessment of the fetal head and neck: A state-of-the-art pictorial review

When attention is paid to the details of normal and abnormal fetal head and neck anatomy, abnormalities that normally would be missed at prenatal ultr asonography can routinely be diagnosed. Five basic views are used to assess the fetal head and neck: a transverse view of the head in the plane of the cavum septum pellucidum and cerebellum, a sagittal and a coronal view of t he face to visualize the nose and lips, a sagittal view of the cervical spi ne, and a transverse view of the orbits to measure the biorbital and intero rbital distances. Thickened nuchal fold, a common sign of Down syndrome, ca n be assessed with transverse images of the head. Transverse views are also useful to demonstrate cystic hygroma, occipital meningocele, and encephalo cele, all of which can be associated with other severe anomalies. Micrognat hia, cleft lip and palate, and macroglossia, which are best depicted with s agittal and coronal views of the face, are also associated with other fetal abnormalities. Visualization of these entities should prompt further searc h and amniocentesis. Lymphangioma of the tongue appears similar to macroglo ssia but is an isolated anomaly. Transverse views through the orbits are he lpful for demonstrating orbital teratoma, orbital encephalocele, and hypo- and hypertelorism (the latter two being associated with other abnormalities ). Sagittal views of the neck can demonstrate cystic hygroma, teratoma, and an enlarged thyroid.