What Happens If Something Is Left Inside You After Surgery?

When a surgical instrument, sponge, or needle is accidentally left inside a patient’s body, the consequences range from no symptoms at all to life-threatening infection, bowel obstruction, or organ damage. The body treats the forgotten object as an invader and mounts an immune response around it, and the nature of that response determines whether the item causes trouble in days or hides silently for years. Roughly 1 in 7,500 operations results in a retained surgical item, and while the rate has been declining, the problem has not been eliminated.

How Common Is This, Really?

A retained surgical item sounds like something from a horror story, but it happens more often than most people expect. An analysis of over 26 million surgical hospitalizations in the United States between 2018 and 2022 found that about 4,570 carried a diagnosis for a retained foreign body, which works out to roughly 1 in every 5,400 to 6,000 cases depending on the year.¹ A separate study tracking U.S. data from 2016 to 2023 reported an overall rate of about 1.3 per 10,000 surgeries, with the rate dropping from roughly 1.6 per 10,000 in 2016 to about 1.1 per 10,000 by 2023.² The decline is real, but even the lower figure means hundreds of cases every year across the country.

What Gets Left Behind

Sponges are by far the most commonly retained items. In a landmark study from the New England Journal of Medicine, sponges accounted for about 69% of retained foreign bodies, with surgical instruments making up the remaining 31%.³ The reason sponges lead the list is straightforward: they are soft, absorbent, and once soaked in blood they blend in with surrounding tissue. A clamp or retractor is rigid and distinctive, and while those do get left behind, they are easier to spot during wound closure.

Surgical needles are another category. A survey of over 300 minimally invasive surgeons found that 64% had experienced a lost needle during a procedure, with at least 112 needles reported lost in a single year across the respondents alone.⁴ Needles are tiny and can disappear into tissue folds or port sites during laparoscopic surgery. While a small needle might never cause symptoms, reported complications include chronic pain, ongoing irritation, and injury to surrounding organs.

How Your Body Responds to a Foreign Object

The body does not simply ignore a piece of cotton gauze or a metal clamp sitting in the abdomen. It launches an immune response, and that response follows one of two general paths.

The first is an inflammatory reaction. The immune system recognizes the object as foreign and tries to destroy or isolate it by flooding the area with white blood cells. If bacteria are present on the object, this can escalate into an abscess, a walled-off pocket of pus and infected tissue. This tends to produce symptoms relatively quickly, usually within days to weeks, because the infection drives fever, pain, and elevated inflammatory markers.⁵

The second path is quieter and more insidious. Instead of an acute infection, the body walls off the foreign material with layers of fibrous tissue and granulation tissue, forming what is essentially a scar capsule around the object. This is called an aseptic or granulomatous reaction. Because there is no active infection, the patient can go months or years without any obvious symptoms. The encapsulated mass just sits there, slowly growing as the body adds more scar tissue, sometimes mimicking a tumor on imaging.⁵ About 27% of cases present this way, as a soft tissue mass discovered incidentally or during investigation of vague complaints.⁶

Symptoms People Actually Experience

The symptoms of a retained surgical item are frustratingly nonspecific, which is a big part of why these cases are so often missed or misdiagnosed. The most common complaints include abdominal pain, fever, nausea, vomiting, and weight loss.⁷ None of these point clearly toward a forgotten sponge. They could just as easily suggest a postoperative infection, a bowel problem, or dozens of other conditions.

When the granulomatous (silent encapsulation) type is at play, the main finding is often a palpable mass. A patient or a doctor feels something firm through the abdominal wall that was not there before, and it gets investigated as a possible tumor. When the inflammatory type dominates, intermittent fevers are more prominent and blood work shows elevated markers of infection.⁷

In some cases, presentation is more dramatic. A retained sponge can cause pressure on the bowel wall, leading to tissue death at the contact point. The sponge then gradually migrates through the wall and into the bowel lumen itself. This can trigger bowel obstruction, bleeding, or malabsorption.⁸ The perforation the sponge creates in the bowel wall can actually seal itself after the object passes through, which means the evidence of migration partly disappears.⁹ Other reported complications include fistula formation, where abnormal tunnels develop between organs or between an organ and the skin, and in rare cases, retained sponges in the upper abdomen have led to fistulas connecting the stomach to the lung, causing coughing up of blood and foul-smelling breath.¹⁰

Items Can Hide for Years or Decades

One of the more unsettling aspects of retained surgical items is how long they can remain undetected. When the body walls off the object with scar tissue and no infection develops, there may be no strong signal that something is wrong. Case reports document asymptomatic periods of extraordinary length. One widely cited case series found a median interval of five years between the original surgery and the discovery of a retained gauze, while another series reported intervals ranging from seven days to 21 years.¹¹

That patient from the breast surgery gossypiboma case is illustrative: the sponge created an aseptic reaction, became encapsulated with adhesions and granuloma tissue, and remained silent for a long period before eventually causing septic shock, a sudden and life-threatening deterioration.¹² The shift from silent to dangerous can happen unpredictably when the fibrous capsule breaks down, bacteria get in, or the object migrates into a new anatomical area.

Why These Cases Get Misdiagnosed

Even when a retained item starts causing symptoms and imaging is performed, the correct diagnosis is not always obvious. A sponge encased in scar tissue and granulation can look remarkably like a solid tumor on CT scans. In one reported case, a retained abdominal sponge produced a mass with a distinct feeding artery on high-resolution CT, making it look like a gastrointestinal stromal tumor (a type of gut wall cancer). The patient went through preoperative workup for cancer before the true cause was found during surgery.¹³

This kind of diagnostic confusion happens because the body’s immune response to the foreign material can generate new blood vessels and dense tissue that look, on imaging, exactly like the kind of abnormal growth that accompanies malignancy. The longer the item has been in place, the more developed this tissue becomes, and the harder it is to distinguish from a real tumor without surgery or biopsy.

Who Is Most at Risk

Retained surgical items are not random bad luck distributed evenly across all operations. Certain conditions make them far more likely. The New England Journal of Medicine study that established the key risk factors found three standout predictors. Emergency surgery raised the risk nearly ninefold compared to planned procedures. An unplanned change in the operation during surgery, such as discovering unexpected bleeding or pathology that forces the team to pivot, roughly quadrupled the risk. And higher body mass index was associated with a small but statistically significant increase for each additional unit of BMI.³

The reasons make intuitive sense. In an emergency, the team is working fast, the patient may be unstable, and the focus is on saving a life rather than meticulously counting every sponge. When an operation changes course midway through, additional instruments and sponges get introduced that were not part of the original count. And in patients with higher body weight, there is simply more tissue volume in which a small item can hide. In that same study, patients with retained items were also less likely to have had proper sponge and instrument counts performed at all.³

About 69% of the patients with retained foreign bodies in that study required reoperation to retrieve the item, and one patient died.¹⁴

Getting a Retained Item Out

Once a retained item is identified, removal is almost always necessary, though the approach depends on where the object ended up and how much damage it has caused. Traditional open surgery has been the standard, particularly when the item has caused bowel obstruction, fistulas, or significant adhesions that need to be dealt with at the same time. But minimally invasive approaches have gained ground. In cases where the anatomy is favorable and the item has not caused extensive complications, laparoscopic or even endoscopic retrieval can offer a shorter hospital stay and fewer complications.¹⁵

When a sponge has migrated into the bowel lumen, it can sometimes be retrieved endoscopically through the natural openings without any incision at all. But when the object has eroded into multiple organs or created complex fistula tracts, open surgery with resection of the damaged tissue may be unavoidable.

How Hospitals Try to Prevent This

The primary defense against retained surgical items has long been manual counting. Before surgery begins, the scrub nurse counts every sponge, needle, and instrument. At the end, they count again, and the numbers must match. If they do not, an intraoperative X-ray is taken to look for any item left behind. This system sounds foolproof, but it relies entirely on humans working under time pressure, fatigue, and the stress of a complex procedure. Data have shown that manual counting and radiographs alone are not sufficient to prevent every case.¹⁶

Modern sponges are manufactured with a radiopaque marker, typically a strip of polypropylene or barium sulfate woven into the fabric, so they show up on X-rays if a miscount is suspected.¹⁷ Newer research is exploring better radiopaque agents like bismuth oxychloride, which provides better visibility on imaging at lower concentrations than traditional barium sulfate and integrates more stably into the sponge material.¹⁸

Technology-assisted systems represent the next layer of defense. Radio frequency identification (RFID) tags can be embedded in sponges, and a wand passed over the patient at the end of surgery can detect whether any tagged sponge remains inside. Early experiments demonstrated that RFID-tagged sponges are at least partially readable inside the body cavity and fully readable once removed.¹⁹ A prospective evaluation of a radio frequency detection system in emergency surgeries found it was effective at preventing retained sponges in precisely the setting where the risk is highest.²⁰

Bar-coding systems offer another approach: each sponge gets a unique bar code scanned in and out of the surgical field. A cost-effectiveness analysis estimated that bar-coding prevents at least 97.5% of retained sponge cases.²¹ The WHO Surgical Safety Checklist, which includes instrument and sponge count verification, has also contributed to the broader decline in surgical complications. A systematic review found that the vast majority of studies examining checklist implementation reported decreases in complication and mortality rates.²²

The Psychological and Legal Aftermath

The physical consequences of a retained item are only part of the story. The psychological impact on patients who discover a foreign object was left inside them can be severe and lasting. A review of Australian case law involving retained surgical items documented patients who suffered years of unexplained pain and illness, underwent multiple additional surgeries, and then experienced significant psychological distress upon learning the true cause. In one case, a patient who had a surgical pack removed from her abdomen 15 years after the original operation became preoccupied with the belief that the pack had damaged her health throughout that period, leading to lasting psychological problems that compounded the physical harm.²³

The sense of betrayal can be profound. These patients trusted a surgical team with their body, and the discovery that something was left behind undermines that trust in a way that is hard to repair. Many go on to develop anxiety about future medical procedures or distrust of healthcare providers generally.

Legally, retained surgical items are treated seriously. An analysis of litigation and compensation related to retained foreign bodies found a mean compensation of about €20,700 per case, and criminal lawsuits were filed in 12% of cases involving non-fatal outcomes, compared to 6% in a control group of other surgical malpractice claims within the same compensation range.²⁴ In many jurisdictions, a retained surgical item is considered a “never event,” something that should never happen under any circumstances, which simplifies the legal question of fault and makes these cases easier for patients to win than other types of malpractice claims.

What Patients Can Do

You have limited control over what happens while you are under anesthesia, but you are not entirely powerless. If you are having elective surgery, you can ask your surgical team whether they use technology-assisted counting systems like RFID or bar-coded sponges. Hospitals that have adopted these systems have demonstrably lower rates of retained items. You can also ask whether a postoperative X-ray or scan is part of the standard protocol for your procedure, particularly if the surgery involves the abdomen or pelvis where items are most commonly retained.

After surgery, be attentive to symptoms that do not resolve as expected. Persistent pain that your surgeon cannot explain, recurring fevers that do not respond to antibiotics, an unexplained lump or mass near a surgical site, or chronic digestive problems that started after an operation all warrant further investigation. If you bring up the possibility of a retained item and your doctor dismisses it, it is reasonable to push for imaging. These cases get diagnosed because someone thinks to look for them, and the earlier the discovery, the simpler the retrieval tends to be.

It is also worth noting that retained items are not always the result of negligence in the conventional sense. The highest-risk scenarios, like emergency surgery or an operation that takes an unexpected turn, involve teams working to save a life under extreme pressure. That context does not undo the harm to the patient, but it explains why even excellent surgical teams at top hospitals occasionally have these events. The most meaningful progress has come not from blaming individuals but from building systems, like RFID sponges and standardized checklists, that catch errors before the patient is closed up.