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Incidental findings are results discovered during research that fall outside the study’s aims but may matter for a participant’s health or reproductive choices. A researcher who reads this page should be able to define the term for an IRB, estimate how often brain-imaging studies turn them up, and write the consent and methods wording that goes with them.
What are incidental findings in research?
An incidental finding is “a finding concerning an individual research participant that has potential health or reproductive significance” and that is discovered in the course of research but is beyond the aims of the study (the definition adopted by Parker 2008, following Wolf and colleagues). The standard examples come from imaging: a brain MRI run to measure cortical thickness in a psychology study shows a mass that nobody was looking for.
Two features carry the definition. First, the finding concerns an individual participant, not the group. Second, it is defined by the study’s aims, not by whether it surprised anyone. Parker argues that defining incidental findings by “unexpectedness” makes advance planning impossible, because a finding that recurs in a given method is by definition expected; defining by aims lets the team anticipate recurring findings and plan for them before enrolment.
Types of incidental findings
Parker distinguishes three types, which is a more useful working taxonomy than a single undifferentiated category.
| Type | What it is | Example given in the source | Planning implication |
|---|---|---|---|
| Routine | Findings that arise from procedures that are not responsive to the study aims, such as eligibility checks | Blood pressure taken at screening | Decide in advance what is recorded and what is communicated |
| Predictable | Findings tied to the method itself | Misattributed parentage in genetic work | Anticipate them and plan a response before enrolment |
| Unpredictable | Findings no one could foresee | An unusual result outside any expected pattern | Tell participants only that such findings are possible; return them only under stringent criteria, such as clear clinical utility |
Incidental findings vs secondary findings
A secondary finding is sought on purpose, so it is part of the plan rather than outside it. An incidental finding is by definition outside the study’s aims. The distinction matters for consent: a deliberately sought finding belongs in the description of study procedures and results returned, while an incidental finding belongs in a statement of what the team will do if one arises. Where a method reliably produces a certain kind of result (Parker’s “predictable” category), the practical handling resembles planned disclosure even though the finding was never a study aim.
How common are incidental findings on brain MRI?
The most-cited prevalence evidence for neuroimaging is Morris and colleagues’ systematic review and meta-analysis of brain MRI (BMJ 2009). Its pooled results are below; the crude proportions and Wilson intervals are calculated here from the reported counts.
| Category | Studies | People | Cases | Pooled prevalence (95% CI), as published | Crude proportion |
|---|---|---|---|---|---|
| Neoplastic | 16 | 19,559 | 135 | 0.70% (0.47-0.98) | 135 / 19,559 = 0.69% |
| Non-neoplastic* | 15 | 15,559 | 375 | 2.0% (1.1-3.1) | 375 / 15,559 = 2.41% |
*Excluding white matter hyperintensities, silent infarcts and microbleeds.
The pooled and crude figures differ because the published estimate comes from the meta-analytic model rather than from adding counts; quote the published pooled value and its interval in a consent estimate, and use the crude figure only to show the arithmetic. As a rough reading, 0.70% is about 1 in 143 people (1 / 0.007 = 142.9) with a neoplastic finding.
Scan resolution changes the answer. The same review reports that incidental brain findings overall were more common with high-resolution sequences (4.3%) than with standard-resolution sequences (1.7%), P<0.001. If your protocol uses a high-resolution sequence, the standard-resolution figure may understate the likely rate of incidental findings.
Interpreting the numbers
| If you see | Read it as |
|---|---|
| A pooled prevalence with a 95% CI | The plausible range for the average rate across the studies pooled; individual scanners and populations will differ |
| A crude proportion (cases / people) | A simple count-based rate that ignores differences between studies; useful for showing the arithmetic |
| Higher overall incidental-finding rate at high resolution | Scanning protocol affects how many findings are detectable, so match the estimate to your own sequence |
| A low neoplastic rate (under 1%) | Rare but not negligible across a large sample; the authors state these findings deserve mention in informed consent but do not on their own justify screening asymptomatic people |
Planning a management pathway
Parker’s preventive-ethics approach is to anticipate the findings a method will recurrently generate and decide in advance what happens to them. A pathway worth writing down before the first participant is scanned:
- Who looks. State whether scans are read by a qualified reviewer, or whether researchers only view images for research purposes. There is no field-wide consensus that every research scan must be read clinically, so the protocol should say which model applies.
- What counts. Define the findings that trigger action, by reference to health or reproductive significance and clinical utility.
- What happens next. Specify who contacts the participant, how, and what referral or information is offered.
- Privacy. Say how findings are recorded, stored and kept out of, or placed in, medical records.
- Non-disclosure. Describe when a finding will not be returned and why.
Parker also argues that incidental findings should not be counted as benefits in the risk-benefit assessment of a study, at most as indirect benefits. See also psychology research ethics for how review boards frame risk and benefit.
What to put in consent and the IRB protocol
Under Parker’s account, participants should be told that incidental findings may be generated, and told their likelihood and nature as far as that can be known, together with the plans for recording, disclosing or not disclosing them, and protecting privacy. Morris and colleagues likewise write that brain MRI incidental findings “deserve to be mentioned when obtaining informed consent”.
A checklist for adapting to your own study:
- A plain statement that scans are for research and are not a clinical diagnostic examination, if that is the model you use.
- The estimated frequency, taken from a published source and matched to your scan resolution.
- Who reviews images, and whether participants can choose whether to be told.
- What will be done with a finding and who will contact the participant.
- The possibility that a finding may lead to follow-up, stated without minimising it.
The protocol submitted to the institutional review board should contain the same pathway so the board can review the consent language against it. For the wider consent framework, see informed consent in research and the informed consent definition; for how a full submission is laid out, see the IRB protocol worked example.
Assumptions and common mistakes
- Treating “unexpected” as the definition. Anything the method routinely produces is anticipatable and needs a plan.
- Quoting one prevalence without its scan context. The rate depends on sequence resolution and population.
- Presenting findings as a participant benefit. They are not counted as benefits in the risk-benefit assessment.
- Promising a clinical read you do not provide. Consent wording must match the real review process.
- Using a pooled estimate for a different population. The Morris data concern brain MRI and do not transfer to other modalities.
How to report incidental findings (APA-style methods wording)
State the pathway in the procedure section and report any findings in the results or participants section. The wording below is a template to adapt, not a quotation from any style manual:
Participants were informed during consent that research MRI scans are not clinical examinations and that an incidental finding of potential health significance could be identified. Scans were reviewed by [a qualified reviewer / were not reviewed clinically]. Under the approved protocol, [n] participants (x%, 95% CI [lower, upper]) had an incidental finding that was referred for clinical follow-up; these participants were [included / excluded] from analyses.
Report counts and the proportion with an interval so readers can judge precision; see confidence interval for a proportion for the Wilson method used below.
Calculate a prevalence and interval
Excel: enter =135/19559 for the crude proportion (0.0069).
R (Wilson interval, no continuity correction):
prop.test(135, 19559, correct = FALSE)$conf.intPython:
from math import sqrt x, n, z = 135, 19559, 1.96 p = x / n d = 1 + z**2 / n c = (p + z**2 / (2 * n)) / d h = z * sqrt(p * (1 - p) / n + z**2 / (4 * n**2)) / d print(p, c - h, c + h) # 0.0069, 0.0058, 0.0082This gives 0.69% (95% Wilson CI 0.58% to 0.82%) for the crude neoplastic proportion. It is not the same as the published pooled estimate (0.70%, 0.47 to 0.98), which comes from the meta-analytic model.
FAQ
What is an incidental finding in research?
A finding about an individual participant, with potential health or reproductive significance, discovered during research but outside the study’s aims.
What is the difference between incidental and secondary findings?
A secondary finding is looked for deliberately as part of the plan. An incidental finding is outside the study’s aims.
How common are incidental findings on research brain MRI?
In Morris et al. (2009), about 0.70% of people had a neoplastic finding and about 2.0% a non-neoplastic one, and incidental findings overall were more common with high-resolution sequences (4.3%) than standard-resolution sequences (1.7%), P<0.001.
Do participants have to be told about incidental findings?
Participants should be told in consent that such findings may arise and how they will be handled. Whether a specific finding is returned follows the protocol and the board’s requirements.
Should incidental findings count as a benefit of participating?
No. Parker argues they should not be counted as benefits in the risk-benefit assessment, at most as indirect benefits.
Sources
- Parker LS. The Future of Incidental Findings: Should They be Viewed as Benefits? J Law Med Ethics 2008;36(2). pmc.ncbi.nlm.nih.gov/articles/PMC2586168 (read 8 November 2026).
- Morris Z, et al. Incidental findings on brain magnetic resonance imaging: systematic review and meta-analysis. BMJ 2009. pmc.ncbi.nlm.nih.gov/articles/PMC2728201 (abstract read 8 November 2026).
