question and answer
The lowdown on elevated hemidiaphragm
September 2006
"What can cause an elevated right hemidiaphragm?" asks SUSAN AU, MD, of Toronto, ON. "I see this occasionally on chest x-ray reports for patients who seem asymptomatic."
Normally, lung volumes can be evaluated by observing how much the lung tissue extends to the periphery and the diaphragm moves to the level of the 9th-11th ribs posteriorly. The left hemidiaphragm is normally located lower than the right because the presence of the liver in the right upper quadrant of the abdomen elevates it slightly. In healthy patients, the lung volumes should be assessed on the posterior-anterior chest x-ray performed at full inspiration. The dome of the right hemidiaphragm is typically situated at the level of the 6th rib anteriorly +/- one rib interspace, although it can be slightly higher in women and in most people over age 40. The right hemidiaphragm usually sits 1-2.5 cm higher than the left. The normal excursion of the hemidiaphragms between full inspiration and full expiration views is 1.5-2.5 cm.

The most common cause of a significant discrepancy between the two sides is focal or diffuse eventration of the higher hemidiaphragm. Eventration occurs when the diaphragm's muscular sheet is replaced by a thin membranous sheet, causing local or broad elevation, or mounding, of the affected hemidiaphragm, due to upward pressure from the subjacent abdominal viscera liver, colon, spleen, stomach, omentum, etc. Typically, one-third to one-half of the hemidiaphragm is affected. The pattern is either a smooth single bulge or multiple wavy contours. Diffuse eventration of the hemidiaphragm, more often on the left side, can simulate true elevation. In such cases, acquired paralysis of the hemidiaphragm should be considered and ruled out. Other pathologic processes simulating hemidiaphragm paralysis can include subphrenic abscess, peritonitis, distended gas-filled stomach or colon, or pulmonary infarct with volume loss.

If elevation of a hemidiaphragm is shown to be a new finding, when comparing previous chest radiographs, true phrenic nerve pathology must be ruled out. The most common cause of unilateral diaphragmatic paralysis is a malignancy invading the mediastinum, affecting the phrenic nerve. Another is nerve root impingement secondary to cervical spine degenerative disease, with lateral foraminal narrowing. Other less likely causes would include blunt or penetrating mediastinal trauma, aortic aneurysm, viral infection and neurologic disease such as polio or herpes zoster. Patients with unilateral hemidiaphragm paralysis without underlying lung disease are often asymptomatic at rest, developing moderate dyspnea with exertion.

Diagnosis of unilateral hemidiaphragm paralysis can be made by a radiographic 'sniff test,' a fluoroscopic real time assessment of diaphragmatic excursion during deep inhalation and exhalation. A paralyzed hemidiaphragm won't move. Ultrasound can also be used to assess diaphragmatic excursion. Perhaps the best diagnostic test, though, is electromyographic stimulation, which can isolate the affected cervical nerve roots, along with other potential causes. MM

References:
Nchimi A et al. AJR Am J Roentgenol 2005;184(1):24-30.
MacIntyre NR et al. Respir Care 2002;47(1):69-90.
Nicolas JM et al. Chest 1998;113(6):1715-7.
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