The diaphragm is a large, dome-shaped muscle separating the chest cavity from the abdomen, serving as the body’s primary muscle for breathing. When it contracts, it flattens downward, pulling air into the lungs. Routine chest imaging, such as an X-ray, can sometimes show an abnormal contour or elevation of one side of this muscle, particularly the left, often described as “tenting.” Understanding the causes of this elevation and how it affects lung function is necessary to determine its clinical significance.
Understanding Diaphragm Tenting
The diaphragm is divided into right and left hemidiaphragms, each controlled by its own phrenic nerve. On a chest X-ray, the right hemidiaphragm usually sits slightly higher than the left, primarily because the liver is directly beneath it. The left side is positioned lower, with the stomach and spleen underneath.
“Tenting” refers to a localized, peaked, or non-uniform elevation of the muscle contour, distinct from a smooth, generalized elevation of the entire dome. This localized peaking is sometimes called the juxtaphrenic peak sign in medical imaging. This appearance suggests a portion of the muscle is being pulled upward or is weakened in a specific area.
Tenting often results from localized tethering or retraction, frequently caused by scarring or volume loss in the adjacent lung tissue. For instance, a scar from a past infection or a collapsed lung lobe can pull the diaphragm up, creating the peaked shape. A generalized elevation suggests a problem affecting the entire muscle or a large mass pushing it up from below.
Common Reasons for Left-Sided Elevation
The causes of left hemidiaphragm elevation fall into three main categories: mechanical, neurological, and structural. Mechanical causes involve factors pushing the diaphragm upward from the abdominal cavity, including temporary stomach distension (gastric bubble) or chronic enlargement of the spleen (splenomegaly).
A less common mechanical finding is the Chilaiditi sign, where a loop of the colon becomes trapped between the diaphragm and the liver, creating the illusion of elevation. A subpulmonic effusion (fluid collecting between the lung and the diaphragm) can also mimic an elevated hemidiaphragm. These causes involve displacement, not muscle weakness.
Neurological issues involve the phrenic nerve, the sole motor supply to the diaphragm. Damage to this nerve causes diaphragmatic paralysis or paresis (partial weakness), leading to the entire hemidiaphragm being pulled superiorly by negative chest pressure. Damage can result from trauma, complications following surgeries like coronary artery bypass grafting, or underlying neurological disorders.
Structural or congenital issues include diaphragmatic eventration, which is a thinning of the muscle tissue. Eventration occurs when the diaphragm muscle is poorly developed, resulting in a weak sheet that balloons upward. This weakness causes an abnormal, elevated contour, usually involving the entire hemidiaphragm.
Assessing the Severity of the Finding
The seriousness of left hemidiaphragm tenting or elevation is determined by the underlying cause and the presence of associated symptoms. Most cases of isolated tenting, especially those caused by old lung scarring or minor mechanical displacement, are incidental findings on X-rays. These are typically harmless and require no specific intervention.
Approximately 90% of people with unilateral diaphragm dysfunction remain asymptomatic, compensated by accessory breathing muscles and the healthy hemidiaphragm. The finding becomes significant when associated with respiratory impairment. Symptoms such as dyspnea on exertion (shortness of breath during physical activity) indicate reduced lung capacity.
A more severe symptom is orthopnea, which is difficulty breathing when lying flat. This is a classic sign of diaphragmatic dysfunction, worsened by abdominal contents pushing against the weakened muscle. A physical sign correlating with true severity is paradoxical movement of the diaphragm.
Instead of moving downward during inspiration, the weakened hemidiaphragm moves upward into the chest cavity. This movement is detected during the fluoroscopic sniff test. Paradoxical motion reduces lung volume, increasing the work of breathing and potentially leading to recurrent respiratory infections.
Necessary Follow-Up and Treatment Options
Initial follow-up for an elevated left hemidiaphragm begins with a detailed history and physical examination to assess for symptoms like dyspnea or orthopnea. If symptoms are present or the cause is unclear, further diagnostic imaging is necessary to assess muscle function. The fluoroscopic sniff test is a common method where the patient sniffs sharply while diaphragm movement is monitored under X-ray.
Imaging, such as a computed tomography (CT) scan or ultrasound, helps differentiate between a structural abnormality, a mass pushing the diaphragm up, or true nerve damage. These scans provide clear views of the diaphragm’s structure and surrounding organs. Pulmonary function tests may also quantify the degree of restrictive lung defect caused by reduced volume.
Treatment depends on the cause and symptom severity. For asymptomatic patients, the standard approach is conservative management, involving observation. If the elevation is caused by an underlying condition, such as a subphrenic abscess, treating that primary condition can resolve the elevation.
For severe cases of paralysis or eventration resulting in significant breathing difficulties, diaphragmatic plication may be recommended. This surgical procedure involves flattening and tightening the weakened diaphragm muscle, which effectively lowers the hemidiaphragm and restores lung volume. In select cases of phrenic nerve paralysis, nerve pacing may be an option, using a device to stimulate the diaphragm muscle to contract.