Conditions: phrenic nerve and elevated hemidiaphragm
What is the diaphragm and how does it work?
The diaphragm is a thin muscle that separates the chest from the abdomen. The diaphragm is the main muscle used in breathing. It is shaped like a dome, especially at the end of an expiration, when the lungs are not full. When the muscle contracts, its shape transforms from a high dome to more like a trampoline. By doing so, the volume within the chest is made larger, and this draws in air from the upper airway.
The course of the left and right phrenic nerves, shown in red.
The left and right phrenic nerves pass from the neck through the chest to its side of the diaphragm. Click to enlarge.
What is the phrenic nerve?
One left and one right phrenic nerve arises in the neck and travels through the chest to its target, the diaphragm. The left and right phrenic nerves send the signal for the diaphragm to contract, each nerve activating one side of the diaphragm, or hemi-diaphragm.
What causes phrenic nerve weakness?
Weakness of one or both phrenic nerves, also known as phrenic palsy, may occur as a result of many different potential causes. These include trauma, tumor, infection, neurologic disease including Guillain–Barré, among others. Trauma may include that associated with a surgical procedure. Phrenic nerve dysfunction may range in severity from slight to total, and it may be one-sided or involve both left and right sides.
Why is the phrenic nerve affected by surgery?
Several surgical operations require dissection in proximity to the phrenic nerve. In the neck, removal of lymph nodes and/or tumor near or on the phrenic nerve is one such example. Despite best efforts, injury to the phrenic nerve during surgery in the proximity to this nerve risks its injury.
What are the symptoms of phrenic palsy?
Fortunately, if one but not both of the phrenic nerves is weak or paralyzed, the individual usually does not experience any symptoms. Patients with one weak phrenic nerve are typically without symptoms due to the compensation and recruitment of other inspiratory muscles, and often the healthy hemidiaphragm compensates. In some cases, especially when one or both phrenic nerves is very significantly impaired, an affected individual may experience shortness of breath, especially with exercise or disturbance with breathing during sleep. In some severe cases, the weakness affects blood return to the heart, which may impair circulation. Symptoms tend to be more severe in patients who are obese or have associated heart or lung conditions.
Frequently, diagnosis of a dysfunctional phrenic nerve is observed incidentally on a chest x-ray that was performed for another reason. While an x-ray does not show the nerve itself, the position of the diaphragm may hint at possible phrenic nerve weakness.
How is phrenic nerve neuropathy identified?
As noted above, the left and the right phrenic nerves cause that side of the diaphragm muscle to contract from a high dome to more of a flat trampoline. When either the left or the right half of the diaphragm (hemidiaphragm) stays in a high dome position, even at the end of a full inspiration, it suggests something is wrong with either the muscle or the phrenic nerve.
Under normal conditions, the right hemidiaphragm is slightly higher than the left because the liver on the right pushes that side of the diaphragm up.
When a static image, such as a chest x-ray or a CT scan suggests an elevated hemidiaphragm, additional dynamic imaging tests (like ultrasound or fluoroscopy) and pulmonary function tests may be undertaken in an effort to better assess movement of the diaphragm. Less commonly, testing of the phrenic nerve with electrical tests might be undertaken.
HOw is phrenic nerve injury during surgery prevented?
While tumors may attach to or invade a phrenic nerve, potentially making nerve weakness impossible to prevent, a surgeon’s knowledge of the anatomy and careful dissection technique minimizes risk of injury during surgery. Nevertheless, despite every effort to avoid injury to this nerve or any other anatomic structure, sometimes unintended injury from a procedure is unavoidable.
Does phrenic palsy improve over time?
The treatment of diaphragmatic paralysis depends mainly on its cause and the symptoms experienced by the patient.
In general, patients without symptoms and one normally functioning hemidiaphragm do not require treatment. Among those with symptoms, all associated factors are be treated, including obesity, respiratory or chronic heart diseases, which could worsen the symptoms of paralysis. Phrenic nerve weakness can improve spontaneously over time in some situations, including traumatic injury, which may inform a decision to observe for healing in some situations. During a period of observation, respiratory rehabilitation and inspiratory muscle training may be of benefit.
What treatements are available if observation fails?
Treatment options depend on the symptoms and causes of the problem. If breathing is acceptable while awake but insufficient during sleep, CPAP (continuous positive airway pressure) may be helpful. Procedures for the management of severe phrenic nerve weakness may include surgery on the diaphragm itself (i.e., plication of the diaphragm) or placement of a diaphragmatic pacemaker. Mechanical ventilation is an option for patients with paralysis of both sides of the diaphragm.