Hernias can and do develop in the side of the body, though they are far less common than the inguinal and midline hernias most people picture. The two main types are Spigelian hernias, which push through the lateral abdominal wall, and lumbar or flank hernias, which emerge through weak points in the lower back and side. Both are easy to miss on a physical exam and sometimes take years of vague side pain before anyone orders the right imaging. What makes them worth knowing about is that they carry real risks if ignored, yet they are treatable once correctly identified.
The Two Main Types of Side Hernias
When people say “hernia in the side,” they are usually describing one of two things, and the distinction matters because the anatomy, the causes, and the surgical approach differ.
A Spigelian hernia occurs along the outer edge of the rectus abdominis muscle, roughly where a vertical line running down the side of your abdomen meets the layers of flat muscles that wrap around your flank. The tissue pushes through a gap in the aponeurosis of the transversus abdominis, the deepest of the three flat muscle layers. These hernias make up only about one to two percent of all abdominal wall hernias, and they tend to sit below the navel, often on the lower right or left side.1The American Surgeon™. Spigelian Hernia: Surgical Anatomy, Embryology, and Technique of Repair Because the bulge is often hidden underneath the external oblique muscle rather than visible at the skin surface, a doctor performing a standard physical exam can easily miss it.
Lumbar and flank hernias, by contrast, develop in the back and side of the torso between the lower ribs and the top of the pelvis. There are two classic weak spots here: a small triangle just below the twelfth rib (called the superior lumbar triangle) and a larger one just above the hip bone (the inferior lumbar triangle). Anatomic studies show the upper triangle averages only about five square centimeters in surface area, while the lower one is considerably larger at roughly nineteen square centimeters, leaving more room for tissue to push through.2PubMed. The triangles of Grynfeltt and Petit and the lumbar tunnel: an anatomo-radiologic study A direct tunnel connects the two triangles, which means weakness in one area can predispose the other to trouble as well.
What Causes a Hernia in the Side
Groin hernias often develop from a combination of chronic straining and an inherent anatomic weakness. Side hernias share some of those risk factors but have a few causes that are uniquely their own.
Previous Surgery
The most common route to a flank hernia is a prior surgical incision through the side of the abdomen. Kidney operations are the classic culprit. One study of patients who had open radical nephrectomy found that roughly half developed a persistent flank bulge more than a year after surgery, a rate the authors described as considerably higher than previously assumed.3PubMed. Permanent flank bulge is a consequence of flank incision for radical nephrectomy in one half of patients Not every bulge is a true hernia with a fascial defect; some are caused by nerve damage during surgery that leads to muscle wasting and a floppy, ballooning abdominal wall without an actual hole. But genuine incisional hernias do occur. A review of published data across more than a thousand patients put the overall incidence of incisional flank hernia at around seventeen percent.4PubMed. Incidence, etiology, management, and outcomes of flank hernia: review of published data
Research into what makes one patient develop a flank hernia after surgery and another escape has pointed to a handful of independent risk factors: a higher body mass index, the use of self-retaining retractors that press on nerves during surgery, failure to identify and preserve the neurovascular bundle during the incision, and significant abdominal distension after the operation.5PubMed Central. Risk factors for the development of flank hernias and bulges following surgical flank approaches to the kidney in adults Wound infection and constipation also pushed the rate up in that same cohort. The nerve-damage piece is worth emphasizing: the nerves that control the lateral abdominal wall muscles (primarily branches from T11 and T12) run right through the tissue that surgeons have to cut during flank incisions. Injuring those nerves leads to muscle atrophy and laxity that can look and feel exactly like a hernia, or can weaken the wall enough that a true hernia follows.6Asian Journal of Surgery. Current understanding of abdominal bulge with a novel classification: A retrospective study
Trauma
A direct blow to the side, such as from a car accident, a handlebar impact, or a fall, can tear the abdominal wall muscles without breaking the skin. These traumatic flank hernias are rare, occurring in less than one percent of blunt abdominal traumas.7PubMed Central. The Management of Traumatic Abdominal Wall Flank Hernia Along the Spigelian Aponeurosis Using Component Separation, Synthetic, and Biological Mesh They sometimes do not become apparent until months or even years after the injury, as one case report described a man whose flank hernia showed up three years after severe multiple trauma.8PubMed Central. Repair of traumatic flank hernia with mesh strip suture: a case report Because the original injury may have been treated in an emergency setting focused on life-threatening problems, the hernia sometimes goes unrecognized until the patient notices a growing bulge or nagging side pain.
Congenital Weakness
Some people are born with lumbar hernias. A systematic review of congenital cases found that flank bulging was the main symptom, with a roughly even split between boys and girls. About forty-two percent involved the upper lumbar triangle and about thirty-three percent the lower triangle, while a quarter were classified as diffuse. Around ten percent of these children had hernias on both sides.9PubMed. Congenital lumbar herniae: a systematic review Congenital lumbar hernias are sometimes associated with other developmental anomalies, as in a reported case of a six-year-old with both a congenital lumbar hernia and vertebral abnormalities.10PubMed Central. A Rare Co-occurrence of Lumbo-Costo-Vertebral Syndrome With Congenital Lumbar Hernia in a Six-Year-Old Child
Why Side Hernias Are Hard to Diagnose
If you have a groin hernia, you can often see or feel a lump that pops out when you cough or strain. Side hernias are trickier. Spigelian hernias in particular tend to slide between the muscle layers rather than pushing all the way out to the skin, which is why they earned a reputation as “clinically elusive.” One case involved a woman who experienced five years of intermittent lower abdominal discomfort that worsened with activity before imaging finally revealed a defect in the Spigelian fascia with bowel poking through it.11PubMed Central. Spigelian Hernia Masquerading as Chronic Lower Abdominal Pain: A Case Report
CT scanning is considered the gold standard for pinning down a flank or Spigelian hernia. It shows the exact location and size of the defect, what is herniating through it, and the surrounding anatomy surgeons need to plan their repair. Ultrasound can be a useful screening tool, especially dynamic methods where the patient is asked to strain while being scanned, but there is no standardized ultrasound protocol for lumbar and flank hernias the way there is for groin hernias.12Springer International Publishing. Flank Hernia In practice, if your doctor suspects a side hernia based on symptoms and an equivocal physical exam, a CT scan is the next step.
Adding to the diagnostic challenge is the muscle-denervation bulge mentioned earlier. After flank surgery, nerve damage alone can cause one side of the abdomen to bow outward. On visual inspection this looks identical to a hernia, but on CT there is no fascial defect, just thinned-out, atrophied muscle. The management is completely different: a true hernia with a hole needs surgical repair, while a denervation bulge without a defect may not benefit from an operation. Getting the imaging right matters.
The Role of Obesity and Abdominal Pressure
Higher body weight is a consistent risk factor across studies of flank hernia, Spigelian hernia, and abdominal hernias in general. The mechanism is straightforward: more visceral fat means more pressure pushing outward against the abdominal wall from the inside. Men tend to accumulate more visceral fat than women, and visceral adipose tissue is more metabolically active, producing inflammatory signals that may weaken the connective tissue of the abdominal wall over time.13PubMed Central. Obesity and abdominal hernia in ambulatory patients, 2018–2023 In the flank-surgery population, a BMI of about 26 or higher was independently associated with developing a postoperative hernia or bulge.5PubMed Central. Risk factors for the development of flank hernias and bulges following surgical flank approaches to the kidney in adults Studies of partial nephrectomy patients found a similar pattern, with those who developed hernias averaging a BMI around 30 compared to 26 in those who did not.14PubMed. Occurrence of abdominal bulging and hernia after open partial nephrectomy: a retrospective cohort study
This does not mean thin people are immune. Congenital lumbar hernias occur in children and infants, and traumatic hernias affect people across the weight spectrum. But if you are carrying extra weight around the middle and have had prior flank surgery, or you are noticing a new bulge in your side, the combination raises the index of suspicion.
When a Side Hernia Becomes Dangerous
The word “strangulation” in hernia medicine means that whatever tissue has slipped through the defect, usually a loop of bowel, has had its blood supply pinched off. Without blood flow, the trapped tissue starts to die, and that constitutes a surgical emergency. Spigelian hernias carry a strangulation risk estimated at roughly seventeen to twenty-four percent, which is considerably higher than the average for hernias in general.15PubMed. Spigelian hernia as a cause of small bowel obstruction The sharp, rigid edges of the fascial defect in a Spigelian hernia act almost like a snare, making it easier for trapped bowel to lose circulation.16PubMed Central. Spigelian hernia, a case report
Strangulated side hernias have been reported with small bowel obstruction and, in at least one case, strangulation of both small bowel and the appendix simultaneously.17PubMed. Spigelian hernia associated with strangulation of the small bowel and appendix In a surgical series of Spigelian hernias evaluated by CT, bowel ischemia was found during surgery in four out of ten operated patients.18PubMed. Spigelian hernia: CT findings and clinical relevance Warning signs include sudden severe pain at the hernia site, nausea and vomiting, the inability to push a previously reducible bulge back in, and redness or warmth over the area. Any of those symptoms warrant an emergency room visit, not a wait-and-see approach.
How Side Hernias Are Repaired
Nearly all side hernias that produce symptoms or carry strangulation risk are treated with surgery. Mesh is used in virtually every repair, because the lateral abdominal wall is under constant tension from the oblique and transversus muscles pulling in different directions, and a simple suture closure is unlikely to hold long-term.4PubMed. Incidence, etiology, management, and outcomes of flank hernia: review of published data
One of the things that makes flank hernia repair technically harder than a standard midline incisional hernia repair is the proximity to bone. The iliac crest (the top ridge of your hip bone) and the lower ribs border the area, and surgeons need to anchor the mesh securely to structures that can actually hold it. Some teams have used suture anchors drilled directly into the iliac crest to fix mesh in place, borrowing a technique from orthopedic surgery.19The American Surgeon™. Flank Hernia Repair with Suture Anchor Mesh Fixation to the Iliac Crest This bony anchoring problem is a major reason why flank hernias have historically had higher recurrence rates than hernias in more forgiving locations.
Approaches vary between open surgery, laparoscopic surgery, and hybrid techniques. A series using a combined open-and-laparoscopic method reported a median hospital stay of three days and a recurrence rate of about six percent over a median follow-up of roughly three years.20Hernia. Combined open and laparoscopic approach for repair of flank hernias: technique description and medium-term outcomes of a single surgeon A large single-center series of 142 consecutive open repairs reported a recurrence rate of about three and a half percent over roughly two and a half years of follow-up, with wound infections in about eight percent.21PubMed. Open repair of flank and lumbar hernias: 142 consecutive repairs at a high-volume hernia center For traumatic flank hernias specifically, a systematic review and meta-analysis found an overall recurrence rate of about eight percent at a mean follow-up of fifteen months.22PubMed Central. Management of post-traumatic non-iatrogenic lumbar/flank hernias: diagnosis and treatment options-systematic review, meta-analysis and management algorithm
Those recurrence numbers compare favorably to older data, and they reflect the fact that surgeons have gotten better at these repairs over the past decade. The broader literature review across all flank hernia repairs puts the average recurrence at about seven percent, with a perioperative complication rate of around twenty percent (most of which are wound-related issues like seromas rather than serious events).4PubMed. Incidence, etiology, management, and outcomes of flank hernia: review of published data
Chronic Pain After Repair
An underappreciated aspect of side hernias is the pain burden they leave behind even after a successful operation. The same review that reported a seven percent recurrence rate also found that about eleven percent of patients had chronic post-procedure pain.4PubMed. Incidence, etiology, management, and outcomes of flank hernia: review of published data A prospective international study painted an even more mixed picture: while quality of life improved in up to fifty-seven percent of patients who had preoperative pain, up to thirty percent reported bothersome pain or abnormal sensation at the surgical site a full year after the repair.23Journal of the American College of Surgeons. Long-Term Quality of Life Outcomes in Laparoscopic and Open Repair of the Flank Hernia: A Prospective, International Study In the large open-repair series mentioned earlier, about a fifth of patients reported chronic pain at six months, and two-thirds of those individuals had already been dealing with pain before their surgery.21PubMed. Open repair of flank and lumbar hernias: 142 consecutive repairs at a high-volume hernia center
The nerve-rich landscape of the lateral abdominal wall is partly to blame. The same intercostal nerves (T11 and T12) that can be injured during the surgery that caused the hernia in the first place are at risk again during the repair. Mesh placement near these nerves, scar tissue formation, and the tension of the repair itself all contribute. For patients weighing the decision to operate on a side hernia that is not at immediate risk of strangulation, the possibility of persistent discomfort is a legitimate factor in the conversation. Many surgeons recommend repair for symptomatic Spigelian hernias regardless of size, because the strangulation risk is high enough to outweigh the pain trade-off. For large, slowly enlarging flank hernias in patients who are otherwise coping well, the decision is more nuanced and depends on the specific anatomy, the patient’s activity level, and their pain tolerance.
Side Hernias in Children
Congenital lumbar hernias are unusual but not extraordinarily rare in pediatric surgery. They tend to present as a soft, reducible bulge in the flank that parents notice when their baby cries or strains. The systematic review of these cases found that the average age at presentation was under ten months, suggesting that most are caught early. The upper lumbar triangle was the most common location, followed by the lower triangle. A small but meaningful fraction, roughly ten percent, were bilateral.9PubMed. Congenital lumbar herniae: a systematic review When congenital lumbar hernias appear alongside other anomalies like vertebral or rib defects, the combination is sometimes called lumbocostovertebral syndrome, which warrants a broader workup to check for kidney and spinal abnormalities.10PubMed Central. A Rare Co-occurrence of Lumbo-Costo-Vertebral Syndrome With Congenital Lumbar Hernia in a Six-Year-Old Child All the congenital cases in the systematic review were managed electively rather than as emergencies, which suggests that strangulation in this age group is less common than in the adult Spigelian population.
Parents who notice a lopsided bulge in their child’s flank that comes and goes with crying or straining should mention it to their pediatrician. It may be nothing more than a benign muscular asymmetry, but imaging can rule out a true hernia quickly and without discomfort.
Why Flank Surgery Is Shifting Toward Minimally Invasive Approaches
The high rate of flank bulging and hernia after open kidney surgery has been one of the driving forces behind the adoption of laparoscopic and robotic nephrectomy. The observation that nearly half of patients developed a persistent flank bulge after a traditional open flank incision gave surgeons a strong argument for approaches that use small port-site incisions instead of a long muscle-splitting cut.3PubMed. Permanent flank bulge is a consequence of flank incision for radical nephrectomy in one half of patients Smaller incisions mean less disruption of the intercostal nerves, less division of the oblique muscles, and a lower chance of the abdominal wall failing down the road. The shift has been substantial over the past two decades, and while laparoscopic kidney surgery has its own complication profile, reducing the flank-hernia problem was a meaningful part of the calculus.
For patients now facing kidney or retroperitoneal surgery and weighing their options, the risk of postoperative flank hernia is a legitimate consideration to discuss with their surgeon. Factors like tumor size, location, and the complexity of the planned operation may still favor an open approach in specific cases, but knowing that hernia risk is part of that equation helps patients make more informed decisions.