Elevated Hemidiaphragm

Excerpt

The diaphragm is a thin, dome-shaped muscular structure that functions as a respiratory pump and is the primary muscle for inspiration. Elevated hemidiaphragm occurs when one side of the diaphragm becomes weak from muscular disease or loss of innervation due to phrenic nerve injury. Patients may present with difficulty breathing, but more commonly elevated hemidiaphragm is found on imaging as an incidental finding, and patients are asymptomatic.

The phrenic nerve runs in the fascia over the anterior scalene muscle. An anesthesiologist commonly performs interscalene blocks for shoulder surgery, such as a rotator cuff repair, humeral fracture, total shoulder replacement, and other arm surgery. phrenic nerve paralysis is a known complication from the interscalene block. It has been observed in many case reports and series in both anesthesia and neurosurgical literature, but only a single case report in the emergency medicine literature.

The diaphragm is the primary muscle for inspiration along with secondary muscles such as the sternocleidomastoid, external intercostals, and scalene muscles. During inspiration, the diaphragm flattens pulling air into the lungs, whereas during expiration, the diaphragm relaxes, allowing air to flow out of the lungs passively. As the diaphragm flattens during inspiration subatmospheric, negative pressure is created within the thoracic cavity that overcomes atmospheric pressure. This forms a vacuum that facilitates the movement of air into the lungs. Also, as the diaphragm contracts, the floor of the thoracic cavity moves downward, and the walls move outward. This causes inflation of the lungs and allows for gas exchange to occur. As the diaphragm relaxes, the tension on the chest wall muscles decreases, causing the muscles to recoil and passively push the air out during expiration.

The diaphragm has three points of origin, creating a C shape that culminates in a stable, dense fibrous center tendon. The sternal group of muscle fibers is attached to the posterior aspect of the xiphoid process. The costal group of muscle fibers originates from the inner surface of seven to twelfth ribs. The lumbar group of muscular fibers arises from the medial and lateral arcuate ligaments and anterior longitudinal ligament, and lumbar vertebral bodies of L2-L3. There are three openings in the diaphragm, allowing structures to pass between the thoracic and abdominal cavity. The esophageal hiatus through which the esophagus and vagus nerve pass, the aortic hiatus through which the aorta, azygos vein and thoracic duct pass, and the caval hiatus through which the inferior vena cava passes.

The diaphragm anatomically separates the thoracic cavity from the abdominal cavity, making the diaphragm the base of the thoracic cavity and the apex of the abdominal cavity. The diaphragm is separated into the right and left half. Each side has it's own blood supply from the inferior and superior phrenic arteries arising directly from the aorta, subcostal and intercostal arteries. Phrenic veins drain blood from the diaphragm directly into the inferior vena cava.

The diaphragm is innervated by the ipsilateral phrenic nerve that arises from the cervical nerve roots of C3-C5. The phrenic nerve emerges through the anterior scalene muscle on either side of the neck and courses posteriorly to the subclavian vein. Both phrenic nerves enter into the thoracic cavity through the thoracic aperture. In the thoracic cavity, the right and left phrenic nerves follow different paths. The right phrenic nerve descends anteriorly over the right atrium of the heart and exits through the inferior vena cava opening to innervate the inferior surface of the hemidiaphragm. The left phrenic nerve crosses the aortic arch and pericardium overlying the left ventricle until it pierces through the diaphragm to innervate the inferior surface of the left hemidiaphragm. Sensory innervation of the diaphragm is from the intercostal nerves 6-11.

Elevated Hemidiaphragm is a condition where one portion of the diaphragm is higher than the other. Often elevated hemidiaphragm is asymptomatic and visualized as an incidental finding on radiologic studies like chest X-ray or chest CT (computed tomography). Patients are typically asymptomatic due to the compensation and recruitment of other inspiratory muscles, and often the healthy hemidiaphragm compensates to maintain the pressure gradient required for adequate gas exchange. However, evidence suggests that the function of the contralateral, healthy hemidiaphragm may be impacted by lower abdominal pressure.

In severe cases of unilateral hemidiaphragm paralysis, patients may lose their inspiratory capacity, which can impair the ability of the heart to pump efficiently. Under normal circumstances, the intrathoracic pressure and contraction of the diaphragm overcome the force of gravity and propel blood into the right atrium from the inferior vena cava (IVC). When the pressure gradient cannot be maintained, the right atrium will collapse, and the patient may present as though they have cardiac tamponade. Accurate diagnosis, treatment, and management of elevated hemidiaphragm are essential in patients presenting with dyspnea and multi-organ involvement.