Which of the following statements about diaphragmatic anatomy is true?

A.  The azygos vein passes through the aortic hiatus.

B.  The foramen of Morgagni is a posterior diaphragmatic defect.

C.  Innervation is by the phrenic nerves which arise from the lower trunk of the cervical plexus.

D.  The thoracic duct passes through the esophageal hiatus.

Answer A

The diaphragm is a large musculotendinous sheet composed of a large central tendon and a muscle mass that arises from the lower margin of the thorax (the costal muscle) and the upper lumbar vertebrae (the crural muscle).  The diaphragm has three major openings: the vena caval foramen, which is the most anterior of the three and involves the tendinous portion; the esophageal hiatus; and the aortic hiatus which is the most posterior and through which passes the aorta, thoracic duct and azygos vein.  The diaphragm is innervated by the phrenic nerves which arise from the C3, 4 and 5 nerve roots.  There are two congenital diaphragmatic hernias: the posterolateral Bochdalek hernia which is associated with neonatal respiratory failure and the retrosternal (or anterior) Morgagni hernia through which there is herniation between the xiphoid process and the costochondral attachments of the diaphragm.