Modern scanners see almost everything. A CT done after a minor accident, an ultrasound for back pain, a whole-body MRI bought as a birthday present — any of them can return a sentence nobody asked for: “a 2 cm lesion in the liver”, “a cyst in the left kidney”, “a nodule in the right adrenal gland”. Radiologists call these incidentalomas: findings discovered by chance in organs nobody was worried about. Most are harmless. The skill lies in recognising the few that are not — without turning everyone else into a patient.
How common are they?
Very. As our article on whole-body MRI describes, a systematic review found that about one in three healthy people had at least one relevant incidental finding on such a scan. Looking at single organs, the American College of Radiology (ACR) Incidental Findings Committee estimates that adrenal masses occur in about 3–7% of adults, and that kidney cysts can be seen in as many as 40% of patients on CT, becoming more frequent with age. Liver haemangiomas — small tangles of blood vessels — are present in an estimated 5% of people on imaging and in up to 20% in autopsy series, according to the European Association for the Study of the Liver (EASL).
The liver: mostly benign, often no follow-up
The three most frequent liver findings in healthy people are usually harmless:
- Haemangioma. EASL states that, because of its benign course, a typical haemangioma does not need imaging follow-up, and that a conservative approach is appropriate for most patients. Specialist review is reserved for large, symptomatic or growing lesions.
- Focal nodular hyperplasia (FNH), a benign overgrowth of normal liver cells. For a lesion with typical features, EASL says follow-up is not necessary (unless there is underlying vascular liver disease) and treatment is not recommended.
- Simple liver cysts are the most common cystic liver lesion and mostly cause no symptoms. Under the EASL 2022 guideline on cystic liver disease, follow-up is indicated only if there are complications or symptoms.
The exception worth knowing is hepatocellular adenoma, a rarer benign liver tumour. EASL recommends considering removal of adenomas that stay larger than 5 cm or keep growing, because of the risk of bleeding.
The kidney: the Bosniak classification
Kidney cysts are sorted by the Bosniak classification, updated in 2019 to include MRI and more precise definitions. Categories I (simple cysts) and II (cysts with a few thin septa or fine calcification) are considered reliably benign — the risk of cancer is below 1% — and need no follow-up. Category IIF (“F” for follow-up) is probably benign and is monitored with imaging. Category III is genuinely indeterminate: about half turn out to be malignant. Category IV, with enhancing solid nodules, is malignant in about 90% of cases.
The 2019 authors were frank about why the update was needed: cystic kidney cancer is likely overdiagnosed and overtreated, and many benign or indolent masses have been removed without clear benefit. The revision deliberately moves more lesions into lower-risk classes.
The adrenal gland: two questions
For an adrenal incidentaloma, the 2023 guideline of the European Society of Endocrinology (ESE) asks two separate questions: is it malignant, and does it produce hormones?
Malignant? The key is an unenhanced CT. A uniform mass with a density of 10 Hounsfield units (HU) or less is a benign, fat-rich adenoma and needs no further imaging, whatever its size. A uniform mass of 11–20 HU and smaller than 4 cm can be further characterised immediately or rescanned once after about 12 months. Masses of 4 cm or more that are heterogeneous or above 20 HU belong in a multidisciplinary team discussion; surgery is usually advised.
Hormonally active? ESE recommends a 1 mg overnight dexamethasone suppression test for everyone with an adrenal incidentaloma to look for excess cortisol (it may be omitted in frail people with limited life expectancy). Metanephrines, to exclude a phaeochromocytoma, are measured when the mass does not look like a typical benign adenoma. The aldosterone/renin ratio is checked in people with high blood pressure or unexplained low potassium. If initial tests are normal, ESE advises against repeating them unless new signs appear.
Why “just to be safe” is not free
Every additional scan, biopsy or operation has its own risks, costs and waiting time — and can produce new incidental findings. In a US national survey of internists, 99.4% had seen such cascades of care, and 86.7% reported cascades that caused patients harm, most often psychological distress (68.4%), treatment burden (65.4%) and financial burden (57.5%); physical harm was reported by 15.6%. A third of physicians said the test that started their most recent cascade may not have been clinically appropriate. The best way to avoid a cascade is often not to start one: follow the guideline category, and stop where it says stop. What should happen when a finding is serious is covered in our article on next steps after a screening finding.
Questions to ask your doctor
- What exactly is the finding, and which guideline category does it fall into (for example Bosniak class or HU value)?
- Does the guideline recommend follow-up for this category — or none at all?
- For an adrenal finding: has the hormonal work-up been done?
- If further tests are suggested, what would they change, and what are their own risks?
- Who will coordinate the next steps, and when can I stop worrying about this?
Bottom line
Most incidental findings in the liver, kidneys and adrenal glands are benign. Typical haemangiomas, FNH, simple cysts and Bosniak I–II kidney cysts need no follow-up; adrenal masses need one careful imaging assessment and a hormonal work-up. Investigate according to guideline categories — not out of vague unease. Evidence: ★★ Moderate (consensus guidelines based largely on observational data).
References
- Fassnacht M, Tsagarakis S, Terzolo M, Tabarin A, Sahdev A, Newell-Price J, et al. European Society of Endocrinology clinical practice guidelines on the management of adrenal incidentalomas, in collaboration with the European Network for the Study of Adrenal Tumors. Eur J Endocrinol. 2023;189(1):G1–G42. doi:10.1093/ejendo/lvad066
- Mayo-Smith WW, Song JH, Boland GL, Francis IR, Israel GM, Mazzaglia PJ, et al. Management of incidental adrenal masses: a white paper of the ACR Incidental Findings Committee. J Am Coll Radiol. 2017. doi:10.1016/j.jacr.2017.05.001
- Herts BR, Silverman SG, Hindman NM, Uzzo RG, Hartman RP, Israel GM, et al. Management of the incidental renal mass on CT: a white paper of the ACR Incidental Findings Committee. J Am Coll Radiol. 2017. doi:10.1016/j.jacr.2017.04.028
- Silverman SG, Pedrosa I, Ellis JH, Hindman NM, Schieda N, Smith AD, et al. Bosniak classification of cystic renal masses, version 2019: an update proposal and needs assessment. Radiology. 2019;292(2):475–488. doi:10.1148/radiol.2019182646
- European Association for the Study of the Liver (EASL). EASL Clinical Practice Guidelines on the management of benign liver tumours. J Hepatol. 2016;65:386–398.
- Lowry S, Karnsakul W. Cystic liver lesions: from diagnosis to recognition of complications and when to treat. Hepatobiliary Surg Nutr. 2022;11(6):909–912. doi:10.21037/hbsn-22-533 (commenting on EASL Clinical Practice Guidelines on the management of cystic liver diseases. J Hepatol. 2022;77(4):1083–1108)
- Ganguli I, Simpkin AL, Lupo C, et al. Cascades of care after incidental findings in a US national survey of physicians. JAMA Netw Open. 2019;2(10):e1913325. doi:10.1001/jamanetworkopen.2019.13325
This article is general information and not individual medical advice. Decisions about tests and treatment belong in a conversation with your own physician.