What Is Eventration of the Right Hemidiaphragm?

Eventration of the right hemidiaphragm is a condition in which the right half of the diaphragm rides abnormally high in the chest because its normal muscle has been partly or entirely replaced by thin, weak fibrous tissue. The diaphragm itself remains intact, with no hole or gap, but it can no longer contract properly, so the abdominal organs below it push it upward. Complete eventration on the right side is relatively rare compared with left-sided cases, and most people who have it never know because it produces no symptoms at all. When it does cause problems, they tend to show up as shortness of breath, digestive complaints, or both.

What Goes Wrong Inside the Diaphragm

A healthy diaphragm is a dome-shaped sheet of muscle and tendon that separates the chest from the abdomen. When you breathe in, the muscle fibers contract and pull the dome downward, creating the negative pressure that draws air into your lungs. In eventration, all or part of that muscular layer is missing or severely thinned. What remains is largely connective tissue with few or no functioning muscle fibers.¹ Because this tissue cannot contract, the affected portion balloons upward under the constant push of the abdominal organs below it. The result on a chest X-ray is a diaphragm that looks like it has been inflated on one side.

The congenital form, present from birth, appears to stem from a problem early in fetal development. The membrane that eventually becomes the diaphragm forms correctly, but the muscle cells that are supposed to migrate into it and give it strength fail to arrive in adequate numbers. The leading explanation among researchers is that myoblasts, the precursor cells that build muscle, do not travel properly into the developing septum transversum and pleuroperitoneal membrane.² You end up with a diaphragm that looks structurally complete from the outside but lacks the muscular engine it needs to work.

Congenital and Acquired Causes

When eventration is congenital, the problem is simply that the diaphragm never muscularized properly during fetal life, as described above. But eventration can also be acquired at any age. The most common acquired cause is damage to the phrenic nerve, the nerve that tells each half of the diaphragm to contract. Once the phrenic nerve is injured, the affected side becomes paralyzed, and over time the diaphragm thins and elevates.³

In children, phrenic nerve injuries most often happen during heart surgery, birth trauma, or central venous catheter placement. Studies report that phrenic nerve damage during pediatric cardiac operations occurs at a rate anywhere from about 0.3% to nearly 13%, a wide range that reflects differences in surgical technique and how carefully clinicians look for it afterward.⁴ In adults, phrenic nerve injury can follow thoracic or cardiac surgery, but it can also result from infections, tumors compressing the nerve, or, less commonly, something as seemingly routine as a chest drain insertion.⁵ Occasionally the cause is a febrile illness that inflames the nerve, and no clear culprit is ever identified.

Why the Right Side Gets Special Attention

Eventration is more commonly reported on the left side. Complete eventration affecting the entire right hemidiaphragm in an adult is considered relatively rare.¹ One reason the right side behaves differently is anatomy: the liver sits directly beneath the right hemidiaphragm and acts as a kind of buttress. Its bulk helps support the diaphragm from below, which can both mask the elevation on imaging and limit how far the diaphragm can rise compared with the left side, where only the stomach and spleen sit beneath it.

Because right-sided cases are less expected, they are more likely to be initially misread on imaging as something else, such as a mass in the lung base, fluid collection, or a liver that simply appears enlarged. Clinicians who see an elevated right hemidiaphragm on a chest X-ray often have a broader list of possibilities to rule out before landing on eventration.

Symptoms and When Eventration Causes Trouble

Most people with diaphragmatic eventration are asymptomatic. One estimate puts the overall prevalence of the condition at roughly 0.05% of patients, and the majority of those are incidental findings on imaging done for unrelated reasons.⁶ An elevated diaphragm that causes no breathlessness and no digestive issues can simply be monitored over time.

Symptoms tend to appear when the elevated diaphragm compresses enough lung tissue to reduce breathing capacity, or when abdominal organs shift upward into the space the diaphragm can no longer guard. Breathlessness on exertion is the hallmark complaint, and it can worsen when lying flat because gravity allows the abdominal contents to push the weakened diaphragm even higher. Gastrointestinal symptoms are also well documented: heartburn, bloating, a vague aching in the upper abdomen, constipation, and unexplained weight loss can all occur if organs migrate far enough into the chest.⁷

Coexisting conditions tip the balance. Obesity increases intra-abdominal pressure, pushing the weakened diaphragm higher. Heart failure or chronic lung disease eats into whatever respiratory reserve a person has left, so even a modest loss of diaphragm function becomes symptomatic.⁶ A thin, otherwise healthy adult with mild eventration might go decades without a single symptom, while someone with moderate obesity and early emphysema could notice significant shortness of breath from the same degree of elevation.

How Eventration Is Diagnosed

The first clue is almost always a chest X-ray that shows one side of the diaphragm sitting higher than it should. The right hemidiaphragm is normally slightly higher than the left because of the liver beneath it, so the radiologist has to judge whether the elevation exceeds the expected asymmetry. A plain chest film can identify the elevation but cannot explain why it is there.⁸

To figure out whether the diaphragm is simply elevated but still moving (partial eventration) or completely paralyzed, doctors typically turn to a fluoroscopic sniff test. You stand in front of a real-time X-ray screen and take a quick, sharp sniff through your nose. In a normal person, both halves of the diaphragm descend simultaneously. If one side is paralyzed or severely weakened, it moves paradoxically, floating upward when the healthy side drops. The sniff test has a sensitivity of about 90% for detecting one-sided diaphragm paralysis, though its specificity is less impressive because some healthy people have mildly asymmetric diaphragm motion.⁹

Ultrasound and CT scanning add layers of detail. Ultrasound can show whether the diaphragm has a visible muscle layer beneath its surface or is just thin, echogenic tissue. CT provides a comprehensive look at both the diaphragm and the organs above and below it, which matters for surgical planning. One study found that the shape of the diaphragm on a lateral chest film, specifically its radius of curvature, was the most useful factor for distinguishing eventration from true paralysis.¹⁰ An eventrated diaphragm tends to have a smoother, broader dome because it has always lacked muscle, while a paralyzed diaphragm may flatten or deform differently depending on how recently the nerve damage occurred.

Telling Eventration Apart From a Diaphragmatic Hernia

This distinction matters clinically because a hernia involves an actual hole in the diaphragm through which abdominal organs protrude into the chest, while eventration keeps the diaphragm continuous. A hernia typically causes more severe lung compression and can shift the central structures of the chest, something eventration rarely does.¹¹ Treatment strategies differ as well: a hernia usually demands repair to close the defect, whereas eventration is managed with plication, a technique that tightens the existing tissue without patching a hole.

On ultrasound, specific features help. A study examining right-sided cases in children found that a combination of a folded free muscle edge with a narrow-angle “waist” at the diaphragm boundary had perfect specificity for hernia, while a broad-angle waist covered by a thin strip of visible muscle was perfectly specific for eventration.¹² In practice, no single imaging test is always definitive, and clinicians often combine chest X-ray, ultrasound, and CT to build a confident diagnosis, particularly before surgery.¹¹

Surgical Treatment and Technique

Not everyone with eventration needs an operation. If you have no symptoms and your lung function is adequate, observation with periodic imaging is often the best approach. Surgery enters the picture when breathlessness limits daily life, when lung function testing reveals significant impairment, or when digestive symptoms become persistent.

The standard surgical procedure is called diaphragmatic plication. The surgeon gathers the floppy, redundant tissue and folds or pleats it to flatten the diaphragm back into a lower, tighter position. This restores the normal separation between chest and abdomen and gives the lungs room to expand. Plication does not restore muscle function to the diaphragm; it simply removes the mechanical disadvantage created by the ballooned-out tissue.

Traditionally, plication was performed through a full thoracotomy, which means opening the chest with a large incision between the ribs. Over the past two decades, video-assisted thoracoscopic surgery (VATS) has become increasingly common for this procedure. In a comparison of 46 patients who underwent open thoracotomy and 88 who had VATS plication, the minimally invasive group had shorter surgical times, needed less pain medication, stayed in the hospital roughly 4.5 days compared to 7 days, and developed chronic pain symptoms at a rate of just 2% versus 13% in the open group.¹³ Both approaches successfully lowered the diaphragm, and no deaths occurred in either group. The evidence has gotten strong enough that some surgeons argue VATS should be the default approach, noting that its results are at least equivalent and likely better than open thoracotomy in terms of lung function recovery.¹⁴

What Happens After Plication

In the short term, plication tends to work well. A retrospective study of 36 patients found that about 86% reported improvement in their symptoms after surgery, and patients who had preoperative digestive problems improved the most. Lung function tests showed that forced vital capacity and the volume of air exhaled in one second both improved by roughly a quarter at six months.¹⁵ Those are meaningful gains that translate to noticeably easier breathing during exercise and daily tasks.

The longer-term picture is more complicated. In the same study, lung function began to decline gradually after about 18 months, and by the fourth year it had returned roughly to preoperative levels.¹⁵ This does not necessarily mean the surgery was a failure. Symptoms may remain improved even as measured lung function drifts back, possibly because the repositioned diaphragm still provides better mechanical conditions than before. Quality-of-life questionnaires have shown continued symptom improvement out to six months, with breathlessness scores dropping significantly from preoperative levels.¹⁶ Longer quality-of-life follow-up data remain scarce, and that gap makes it hard to give patients confident predictions about how they will feel five or ten years out.

The tension between improving objective numbers in the first year and their gradual decline afterward is something surgeons now discuss openly with patients before operating. For someone whose breathing is barely adequate, even a few years of meaningful relief can be worth the surgery. For someone whose impairment is mild, the calculus is less clear.

Eventration in Newborns and Infants

Congenital diaphragmatic eventration can occasionally be severe enough to cause respiratory distress in newborns. When a baby is born with a markedly elevated hemidiaphragm, the compressed lung on that side may not expand adequately, leading to rapid breathing, low oxygen levels, and feeding difficulties. In the neonatal period, eventration can mimic a congenital diaphragmatic hernia on imaging, which creates urgency because hernias often require emergency surgery. Distinguishing the two preoperatively sometimes proves impossible, and the correct diagnosis is only confirmed once the surgeon sees the intact, thin diaphragm rather than a defect.² In infants, plication is generally well tolerated and can allow the compressed lung to expand over subsequent months as the child grows.

Eventration Diagnosed in Animals

Diaphragmatic eventration is not unique to humans. Veterinary case reports describe the condition in cats and dogs, where it creates similar diagnostic confusion. In one reported case, a two-year-old cat presented with a chronic cough that had been present since infancy. Imaging initially suggested a hernia connecting the abdomen and the sac around the heart, but when the surgeon opened the abdomen, no diaphragmatic defect was found. Instead, the diaphragm was simply lax and displaced. A plication was performed through the abdomen, and the cat’s cough and imaging findings improved afterward.¹⁷ The parallel is worth noting: in both humans and other mammals, the condition fools clinicians into expecting a structural hole that turns out not to be there, and the fix is the same straightforward tightening of tissue that already exists.