The diaphragm is a musculotendinous sheet. It is located at the inferior-most aspect of the ribcage and acts as the floor of the thoracic cavity and the roof of the abdominal cavity.
It has three muscular parts: sternal, costal, and lumbar. It is subdivided into two hemidiaphragms, each one innervated by the ipsilateral phrenic nerve (C3-C5 roots).
The left hemidiaphragm lies above the stomach and spleen. The liver is under the right hemidiaphragm. The heart is located above the diaphragm and fixed to it with its pericardial sheet. Lungs are also positioned above the diaphragm and have broad concave bases (facies diaphragmatica). They are surrounded by pulmonary pleurae, which consists of two layers: visceral and parietal.
The costodiaphragmatic recess (also known as the costophrenic recess or phrenicocostal sinus) is a space in the pleural cavity that is located at the lower border of the chest wall at the junction of the costal and diaphragmatic pleura. There are two lung wings in the human body. Consequently, we can find the left and right recess. Each recess extends from the 7th costal cartilage anteriorly to the neck of the 12th rib posteriorly. Its course is obliquely downward and backward. The recess is deepest after forced expiration and shallowest after forced inspiration. Pleural effusion collects in the recess when the person is standing. The curtain sign is useful in detecting early pulmonary pathological processes that occur at the costodiaphragmatic recesses and the lateral lung bases. The sign occurs when the aerated lung moves over an effusion with respiration.
The diaphragm has three openings called hiatuses. The following structures pass through them:
- caval hiatus (Foramen v. cavae): inferior vena cava, terminal branches of phrenic nerves
- esophageal hiatus (Hiatus oesophageus): esophagus, left and right vagus nerve, esophageal branches of left gastric artery/vein
- aortic hiatus (Hiatus aorticus): aorta, thoracic duct, azygos vein