The foramen magnum is the large oval opening at the base of the skull through which the brainstem transitions into the spinal cord. It is an important anatomical landmark in fetal ultrasound because conditions like Chiari malformation involve herniation of brain tissue through this opening. On neonatal cranial ultrasound, the foramen magnum region can be evaluated through the posterior fontanelle to assess the relationship between the cerebellar tonsils and the foramen magnum. In musculoskeletal and interventional ultrasound, the upper cervical spine near the foramen magnum is occasionally evaluated for pathology or as a landmark for procedures.
Sonography Term