What Causes Bochdalek Hernia in Adults?

A Bochdalek hernia in adults traces back to a congenital defect: incomplete closure of a passage in the diaphragm that should have sealed during fetal development. Most people born with this small gap go their entire lives without knowing it exists. What makes it appear in adulthood is usually not a new injury to the diaphragm but a set of circumstances that finally push abdominal contents through a weak spot that has been there since before birth. Pregnancy, chronic coughing, aging-related tissue weakening, and even sustained heavy lifting can tip a silent defect into a symptomatic one.

The Embryological Defect Behind It

During early fetal development, the diaphragm forms as several tissue components fuse together to create a complete muscular sheet separating the chest from the abdomen. One of the last areas to close is a pair of openings at the back and sides of the diaphragm called the pleuroperitoneal canals. If one or both of these canals fail to close fully, a gap persists. That gap is the Bochdalek defect, first described in the mid-nineteenth century.¹

In newborns, a large Bochdalek hernia can be a surgical emergency because abdominal organs migrate into the chest and compress developing lungs. Adults with the same type of defect almost always have a much smaller opening, one that allowed the lungs to develop normally and never caused symptoms during childhood. The defect is still congenital in origin, but its clinical story in adults is entirely different from the dramatic neonatal presentation.

Genetic research has shown that the broader category of congenital diaphragmatic hernia can involve chromosomal abnormalities, copy-number variants, and single-gene mutations.² Most of those severe genetic forms present in infancy, though. When a Bochdalek hernia first surfaces in an otherwise healthy adult, the underlying genetics are usually less dramatic: a mildly incomplete fusion of the pleuroperitoneal membrane that produced a small, clinically insignificant gap.

How Common Is It in Adults?

The answer depends heavily on how carefully you look. Older studies that relied on chest X-rays estimated adult Bochdalek hernias were extremely rare. Modern CT scanning tells a different story. One review of over 13,000 abdominal CT scans found incidental Bochdalek hernias in about 0.17% of patients, with an average age of roughly 67 and none of them symptomatic.³ That number sounds small, but an earlier CT-based study of 900 adults reported a far higher figure of 6%, calling it over a hundred times more frequent than previously thought.⁴

The wide gap between those estimates likely reflects differences in how the researchers defined a hernia versus a simple thinning of the diaphragm. A study using multidetector CT found posterior diaphragmatic hernias in about 12.7% of adults scanned, with the prevalence climbing from roughly 10% in people in their fifties to about 20% in those in their seventies.⁵ The takeaway is that tiny, silent Bochdalek defects are far more common than the condition’s reputation suggests. The vast majority never cause trouble.

Why a Lifelong Defect Suddenly Becomes Symptomatic

If the defect has been present since birth, the natural question is what changes. The short answer is pressure. The abdomen and chest sit on opposite sides of the diaphragm with a constant pressure difference between them. Anything that raises abdominal pressure or weakens the diaphragm’s tissue can widen a small congenital gap just enough for fat, omentum, or abdominal organs to push through.

A systematic review of adult Bochdalek hernias found that roughly a quarter of cases had an identifiable precipitating factor. The most common trigger was pregnancy, which accounted for about a third of those cases with a clear precipitating event.⁶ That makes intuitive sense: the growing uterus pushes abdominal contents upward while simultaneously increasing intra-abdominal pressure. Data from another review found that about 5% of precipitating factors involved pregnancy specifically.⁷ The discrepancy between these figures likely reflects different case collections and definitions, but both confirm pregnancy as a recognized trigger.

Other documented precipitating factors include chronic constipation, severe or prolonged coughing, binge eating, and even unusual physical activities like hanging upside down or diving.⁶ All of these share the common thread of temporarily or chronically raising pressure inside the abdomen. In the remaining three-quarters of adult cases with no identifiable trigger, gradual age-related weakening of the diaphragm and surrounding connective tissue is the most likely explanation. The steep rise in prevalence from the fifties to the seventies supports the idea that tissue deterioration compounds the original congenital weakness over decades.⁵

Left Side, Right Side, and the Role of the Liver

In newborns, Bochdalek hernias are overwhelmingly left-sided, and the traditional explanation is straightforward: the liver sits beneath the right side of the diaphragm and acts as a physical plug, blocking abdominal organs from migrating upward on that side. In adults, the picture shifts. One large CT study found that 68% of incidentally discovered adult Bochdalek hernias were actually on the right, 18% on the left, and 14% bilateral.³

This apparent reversal likely reflects how the hernias are detected rather than a true difference in biology. Small right-sided defects that contain only a sliver of fat are harmless and easy to spot on CT but rarely cause symptoms, so they show up in incidental imaging studies. Left-sided hernias, when they occur, have more room for mobile organs like the stomach, spleen, or colon to herniate through, so they are more likely to become symptomatic and present clinically. The classic teaching that Bochdalek hernias favor the left side remains accurate for the symptomatic cases that bring people to emergency rooms. The modern CT data just reveals that the right side has plenty of small, silent defects that older imaging never picked up.

How Symptoms Present in Adults

When a Bochdalek hernia does cause problems, the symptoms can be confusingly varied. Because the defect sits at the boundary between the abdomen and chest, it can mimic conditions in either compartment. Respiratory symptoms often include chest pain and shortness of breath. Gastrointestinal complaints can include intermittent abdominal pain, vomiting, and difficulty swallowing.⁸ The overlap with heart disease, lung disease, acid reflux, and gallbladder problems means that adult Bochdalek hernias frequently get misdiagnosed on initial presentation.

The most dangerous scenario is strangulation: when a loop of bowel or another organ herniates through the defect and its blood supply gets pinched off. This can lead to intestinal obstruction, tissue death, and perforation, all of which are surgical emergencies.⁹ Strangulation is uncommon in incidentally discovered hernias that contain only fat, but the risk rises when solid organs or bowel loops have migrated into the chest. One study of incidental cases found that about 73% contained only fat or omentum, while 27% involved solid or enteric organs such as the spleen, small intestine, or large intestine.³ That latter group carries a meaningfully higher risk of complications if the hernia enlarges.

How Doctors Find It

A plain chest X-ray can raise suspicion if it shows an unusual shadow or what looks like bowel gas above the diaphragm, but it misses many cases, especially right-sided ones or small hernias containing only fat. CT scanning, particularly multidetector CT, is the definitive imaging tool. It shows the focal defect in the diaphragm, identifies exactly what has herniated through, and reveals the hernia’s characteristic posterolateral position.¹⁰ The typical appearance on CT is a bulge of fat or soft tissue sitting on top of the diaphragm at the back of the chest.

Because most adult Bochdalek hernias are found by accident during scans ordered for something else, the diagnosis often triggers a decision about whether to operate or simply monitor. Small, fat-only hernias in patients with no symptoms usually warrant watchful waiting. Hernias containing organs, growing in size, or producing symptoms generally warrant repair.

Surgical Repair

When repair is needed, the surgery involves pushing the herniated contents back into the abdomen and closing the diaphragmatic defect. Traditionally this was done through an open incision in the chest or abdomen, but laparoscopic and thoracoscopic approaches are now widely used. The choice of approach depends on the surgeon’s experience and the size of the defect.¹¹ Small defects can often be closed with sutures alone. Larger ones may need a mesh patch to reinforce the repair.

Outcomes for elective repair in adults tend to be good. One reported case involved an 86-year-old woman with shortness of breath and difficulty swallowing caused by her stomach and omentum herniating through a left-sided Bochdalek defect. She underwent a laparoscopic mesh repair and went home on the sixth day after surgery.¹² Emergency repairs for strangulation carry higher complication rates, which is one argument for repairing symptomatic hernias before they become emergencies.

Pregnancy as a Special Case

Pregnancy deserves its own mention because it creates a perfect storm of triggers. The enlarging uterus displaces abdominal organs upward, intra-abdominal pressure rises progressively, and labor itself generates sudden, intense pressure spikes. Data from a systematic review of pregnancy-associated Bochdalek hernias showed that these occur regardless of whether the woman is in her first pregnancy or has had several previous pregnancies. About 65% of cases presented during pregnancy itself, with the majority appearing in the second or third trimester, while about 35% presented after delivery.⁶

The challenge during pregnancy is that symptoms like chest pain, shortness of breath, and nausea are easily attributed to normal pregnancy-related changes. A high index of suspicion and willingness to image with CT or MRI when symptoms are disproportionate to what is expected can prevent delayed diagnosis. When strangulation occurs during pregnancy, both the mother and fetus are at risk, so early recognition matters enormously.

Iatrogenic Diaphragmatic Hernias in Adults

Not every diaphragmatic hernia found in an adult is a Bochdalek hernia. Surgery on the chest or upper abdomen can injure the diaphragm and create a new hole, producing what is called an iatrogenic diaphragmatic hernia. These are rare but have been reported after thoracoscopic lung surgery and after endoscopic removal of tumors near the top of the stomach.¹³¹⁴

What makes iatrogenic hernias tricky is that they can present months or even years after the original operation. The persistent pressure difference between the chest and abdomen gradually widens a small surgical injury into a full hernia over time.¹⁴ One reported case appeared twelve years after an endoscopic procedure. Because these hernias are acquired rather than congenital, they are mechanistically distinct from Bochdalek hernias, but they can look similar on imaging and cause the same kind of symptoms. Any adult who develops unexplained chest or upper abdominal symptoms after prior thoracic or upper abdominal surgery should have diaphragmatic hernia on the differential diagnosis. Lipoma resection on the diaphragm itself has also been implicated.¹⁵

The Condition in Animals

Bochdalek-type diaphragmatic hernias are not unique to humans. They have been documented in dogs, with Cavalier King Charles Spaniels appearing to have a breed predisposition. In these dogs, defects of the left diaphragmatic crus can allow the stomach to herniate into the chest cavity, sometimes causing a life-threatening condition called tension gastrothorax.¹⁶ The parallel is interesting because it confirms that the embryological error in diaphragm closure is not a uniquely human problem but a shared vulnerability in mammalian development.

Cats, by contrast, appear to be an exception. All reported true diaphragmatic hernias in cats have been located on the ventral (front) part of the diaphragm rather than the posterolateral position characteristic of a Bochdalek hernia. There are currently no published reports of a posterolateral hernia in cats matching the human Bochdalek pattern.¹⁷ Whether this reflects genuinely different diaphragmatic anatomy or simply an underreporting gap remains unclear, but the species difference reinforces that the posterolateral location of a Bochdalek defect depends on specific developmental anatomy that varies across mammals.

1
PubMed Central. An unusual case of dyspnoea in an elderly man
2
PubMed Central. Genetic causes of congenital diaphragmatic hernia
3
PubMed. Prevalence of incidental Bochdalek’s hernia in a large adult population
4
PubMed. Bochdalek hernia: prevalence and CT characteristics
5
Journal of Thoracic Imaging. Late-presenting Posterior Transdiaphragmatic (Bochdalek) Hernia in Adults: Prevalence and MDCT Characteristics
6
PubMed Central. Maternal Bochdalek Hernia during Pregnancy: A Systematic Review of Case Reports
7
PubMed Central. Laparoscopic Repair of Bochdalek Diaphragmatic Hernia in Adults
8
The Annals of Thoracic Surgery. Symptomatic Bochdalek hernia in an octogenarian
9
PubMed Central. Strangulated Bochdalek Hernia in Adults: Timely Recognition and Surgical Intervention Can Prevent a Lethal Outcome
10
Frontiers in Medical Case Reports. Left Sided Boshdalek Hernia in Adult: A Case Report
11
PubMed Central. Laparoscopic repair of a Bochdalek hernia in an adult woman
12
PubMed. Laparoscopic dual mesh repair of a diaphragmatic hernia of Bochdalek in a symptomatic elderly patient
13
PubMed Central. Delayed iatrogenic diaphragmatic hernia after thoracoscopic lobectomy
14
PubMed Central. Iatrogenic diaphragmatic hernia – a serious delayed complication: Three cases report and literature review
15
PubMed Central. Delayed iatrogenic diaphragmatic hernia after thoracoscopic resection of diaphragm lipoma
16
PubMed. Congenital pleuroperitoneal hernia presenting as gastrothorax in five cavalier King Charles spaniel dogs
17
Research Square. Congenital diaphragmatic hernia with multiple malformations in a fetal pig