An incidental finding is something a doctor discovers on a medical test that has nothing to do with the reason the test was ordered. You go in for a CT scan after a car accident, and the radiologist spots a small nodule on your lung. You get an MRI for back pain, and it reveals a cyst on your kidney. These unexpected discoveries are incidental findings, and they’re remarkably common: roughly 20 to 40% of CT scans contain at least one.
Most incidental findings turn out to be harmless. But because they weren’t expected, they often trigger a chain of follow-up tests, monitoring, and sometimes real anxiety. Understanding what they are, how common they are, and what typically happens next can help you make sense of an unexpected line in your radiology report.
Why Incidental Findings Are So Common
Modern imaging technology is incredibly detailed. A CT scanner looking at your abdomen after an injury captures everything in its field of view, not just the organ your doctor is asking about. The radiologist reading those images is trained to report anything abnormal they see, whether or not it’s related to your symptoms. That thoroughness is a feature, not a flaw, but it means findings pile up quickly.
Across all types of diagnostic imaging, approximately 15 to 30% of scans contain at least one incidental finding. For CT scans specifically, that number climbs to 20 to 40%. As people age, the odds increase further. The body accumulates benign growths, cysts, and other changes over decades, and high-resolution imaging picks all of them up. A scan of a 75-year-old will almost always reveal something that wasn’t there on a scan at 40, even if the person feels perfectly healthy.
The Most Common Types
Incidental findings span a wide range, from tiny cysts that will never cause problems to masses that need immediate attention. The most frequently discovered types include:
- Lung nodules: Small spots on the lungs, often found on chest CTs ordered for something else entirely. The vast majority are benign, especially when they’re small.
- Adrenal masses: Growths on the adrenal glands (small organs that sit on top of each kidney) show up in 1 to 4% of the general population and in more than 10% of people over 70. About 80% of these are non-functioning benign adenomas, meaning they don’t produce excess hormones and don’t become cancerous.
- Thyroid nodules: Commonly spotted on neck or chest imaging. Most are benign, but some require a biopsy to rule out thyroid cancer.
- Kidney cysts: Fluid-filled sacs on the kidneys that are extremely common with age and almost always harmless.
- Vascular aneurysms: Bulges in blood vessel walls, particularly in the aorta. These are less common but more clinically significant, since large aneurysms carry a risk of rupture.
Doctors sometimes call these discoveries “incidentalomas” when they involve a mass or growth. The term captures the peculiar nature of the situation: a tumor-like finding that nobody was looking for and that may not need any treatment at all.
Incidental Findings Beyond Imaging
While imaging scans account for the majority of incidental findings, they also arise in other contexts. Genetic testing is a growing source. When a person undergoes whole-genome or whole-exome sequencing for one condition, the lab may identify gene variants linked to entirely different diseases, such as inherited heart conditions or cancer syndromes like familial adenomatous polyposis. The American College of Medical Genetics and Genomics maintains a list of genes that labs are recommended to report when found, even if they weren’t the reason for the test.
Blood work can also produce incidental findings. A routine blood panel might reveal an unexpectedly high calcium level or an abnormal liver enzyme, prompting further investigation into conditions the patient had no symptoms of.
What Happens After a Finding
The next steps depend entirely on what was found and how suspicious it looks. For many findings, the answer is simply “watch and wait.” A small lung nodule under a certain size, for instance, may only need a follow-up scan in 6 to 12 months to check whether it’s grown. If it hasn’t changed, monitoring may continue at longer intervals or stop altogether.
For findings that look more concerning, your doctor may order additional imaging with a different technique (an MRI after a CT, or an ultrasound for a closer look), blood tests to check for related hormone or marker levels, or in some cases a biopsy. The American College of Radiology has published management guidelines for many types of incidental findings, giving radiologists and referring doctors a standardized framework for deciding which findings genuinely need follow-up and which can safely be left alone.
One real challenge is that incidental findings sometimes fall through the cracks. The radiologist notes the finding in the report, but the ordering physician, focused on the original clinical question, may not act on it. Some hospitals have developed dedicated tracking programs to make sure incidental findings that need follow-up actually get it.
The Emotional Side of Unexpected Results
Learning that a scan revealed something unexpected can be deeply unsettling, even when your doctor reassures you it’s probably nothing. Patients frequently describe a spike of anxiety that starts the moment they read the report or hear the news, and that anxiety can persist through weeks or months of monitoring.
Neurologists interviewed about incidental findings on brain scans described patients who had “convinced themselves they have MS” by the time they arrived for a follow-up appointment, requiring long consultations just to address the fear before any medical discussion could begin. The more anxious a patient feels, the more likely they are to push for additional procedures, even invasive ones, despite the associated risks.
Beyond the emotional toll, incidental findings can create practical problems. Some patients report difficulty obtaining health or life insurance after an incidentaloma appears in their medical record, even if it was confirmed to be benign. The label of “finding” can linger in a chart long after the clinical concern has resolved.
The Risk of Doing Too Much
Not every incidental finding benefits from aggressive investigation, and pursuing one too far can cause real harm. This is the problem of overdiagnosis: detecting something that meets the technical definition of a disease but would never have caused symptoms or shortened the person’s life.
Thyroid nodules are a well-documented example. Biopsies of incidentally discovered thyroid nodules sometimes reveal cancer cells, leading to surgery. But thyroid surgery carries its own risks, including permanent hoarseness from nerve damage and the lifelong need for hormone replacement if the gland is removed. For slow-growing thyroid cancers that might never have caused problems, the treatment can end up being worse than the disease itself.
Prostate findings follow a similar pattern in older men. When imaging reveals a suspicious area and a biopsy confirms cancer, treatment options like surgery and radiation carry risks of incontinence and impotence. For men over 70 with slow-growing tumors, these harms frequently outweigh the benefits. A healthy person, in effect, gets turned into a patient burdened by the physical, psychological, and financial costs of a disease that may have never affected them.
How Doctors Decide What to Tell You
There’s an active ethical discussion in medicine about how to handle incidental findings, particularly when the significance of a finding is unclear. The guiding principles are straightforward: weigh the potential benefit of telling you against the potential harm, including unnecessary anxiety and unneeded procedures.
U.S. bioethics guidelines recommend that doctors ideally discuss the possibility of incidental findings before ordering a test, especially for imaging or genetic testing where unexpected discoveries are likely. The idea is to give you a chance to understand what might come up and to express your preferences about what you’d want to know. In practice, this conversation doesn’t always happen, particularly for routine scans ordered in urgent or fast-paced settings.
When a finding does appear and the evidence clearly suggests it’s harmless, your doctor may simply note it and explain why no action is needed. When the evidence is less clear, the decision about how to proceed should involve your own values and preferences. Some people want to investigate every finding aggressively for peace of mind. Others, understanding the risks of overdiagnosis, prefer a more conservative approach. Neither instinct is wrong, but the choice is easier to make when you understand what an incidental finding actually is and what the realistic range of outcomes looks like.