RadioGraphics 2012; 32:475-476
Laura K. Nason, MD , Christopher M. Walker, MD , Michael F. McNeeley, MD ,Wanaporn Burivong, MD , Corinne L. Fligner, MD , J. David Godwin, MD
The diaphragm is both the physical barrier that separates the thorax from the abdomen and the primary muscle of ventilation. Its dysfunction is a frequent contributor to dyspnea. Despite its importance, the diaphragm is often underappreciated and incompletely evaluated by clinicians and radiologists. The diaphragm is composed of four components: the transverse septum, pleuro-peritoneal folds, esophageal mesentery, and muscular body wall (Fig 1). An anterior (Morgagni) hernia results from a defect in fusion of the transverse septum to the lateral body wall. A posterior (Bochdalek) hernia likely represents a developmental defect of the pleuroperitoneal folds or failure of fusion of the folds and transverse septum with the intercostal muscles. Innervation for both sensory and motor functions is provided by the paired phrenic nerves, which originate from cervical nerves C3-C5. During inspiration, the diaphragm contracts in concert with the accessory muscles of respiration. This contraction expands the thoracic cavity, decreasing intrathoracic pressure and drawing air into the lungs.