Key Points

• The substantial variability in the normal position of the diaphragm, related in part to age, weight, and anteroposterior thoracic dimension, should be kept in mind when assessing whether the diaphragm is depressed or elevated.
• Advancements in understanding the embryology of the diaphragm enable us to explain various diaphragmatic derangements.
• Although fluoroscopy and radiographs are the primary modality of choice of diagnosing diaphragmatic abnormalities, multidetector computed tomography (CT) and multiplanar magnetic resonance imaging (MRI) are the primary imaging modalities for confirming and determining the contents of diaphragmatic hernias.
• Traumatic rupture of the diaphragm usually occurs in the setting of multiple traumatic injuries, and herniation may not be present initially, so diagnosis often requires a high index of suspicion and close radiographic surveillance.

The human diaphragm is a unique skeletal muscle separating the thoracic and abdominal cavities with a primary function of enabling respiration. The diaphragm is steadfast in this duty and typically goes unremarked upon in imaging reports. However, when abnormal, whether by congenital or acquired means, the consequences for patients can be severe. Abnormalities that affect the diaphragm are often first detected on chest radiographs as an alteration in position or shape. Cross-sectional imaging studies, primarily computed tomography (CT) and occasionally magnetic resonance imaging (MRI), can depict structural defects and intrinsic and adjacent pathology in greater detail. Fluoroscopy is the primary radiologic means of evaluating diaphragmatic motion, though MRI and ultrasound also are capable of this function. This chapter begins with discussing normal diaphragmatic appearance followed by updates in the embryogenesis of the diaphragm and concludes with the role of imaging in specific conditions, including congenital and acquired diaphragmatic derangements.