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 ultrasonography 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 the face to visualize the nose and lips, a sagittal view of the cervical spine, and a transverse view of the orbits to measure the biorbital and interorbital distances. Thickened nuchal fold, a common sign of Down syndrome, can be assessed with transverse images of the head. Transverse views are also useful to demonstrate cystic hygroma, occipital meningocele, and encephalocele, all of which can be associated with other severe anomalies. Micrognathia, cleft lip and palate, and macroglossia, which are best depicted with sagittal and coronal views of the face, are also associated with other fetal abnormalities. Visualization of these entities should prompt further search and amniocentesis. Lymphangioma of the tongue appears similar to macroglossia but is an isolated anomaly. Transverse views through the orbits are helpful 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.