In medicine, an incidentaloma is a tumor (-oma) found by coincidence (incidentally) without clinical symptoms or suspicion. Like other types of incidental findings, it is found during the course of examination and imaging for other reasons. It is a common occurrence: up to 7% of all patients over 60 may harbor a benign growth, often of the adrenal gland, which is detected when diagnostic imaging is used for the analysis of unrelated symptoms. With the increase of "whole-body CT scanning" as part of health screening programs, the chance of finding incidentalomas is expected to increase. 37% of patients receiving whole-body CT scans may have abnormal findings that need further evaluation. Since many incidentally found lesions may never cause disease, there is a risk of overdiagnosis.
When faced with an unexpected finding on diagnostic imaging, the clinician faces the challenge to prove that the lesion is indeed harmless. Often, some other tests are required to determine the exact nature of an incidentaloma.
Incidental adrenal masses on imaging are common (0.6 to 1.3% of all abdominal CT). Differential diagnosis include adenoma, myelolipoma, cyst, lipoma, pheochromocytoma, adrenal cancer, metastatic cancer, hyperplasia, and tuberculosis. Some of these lesions are easily identified by radiographic appearance; however, it is often adenoma vs. cancer/metastasis that is most difficult to distinguish. Thus, clinical guidelines have been developed to aid in diagnosis and decision-making.
The first considerations are size and radiographic appearance of the mass. Suspicious adrenal masses or those ≥4 cm are recommended for complete removal by adrenalectomy. Masses <4 cm may also be recommended for removal if they are found to be hormonally active, but are otherwise recommended for observation. All adrenal masses should receive hormonal evaluation. Hormonal evaluation includes:
- 1-mg overnight dexamethasone suppression test
- 24-hour urinary specimen for measurement of fractionated metanephrines and catecholamines
- Blood plasma aldosterone concentration and plasma renin activity, if hypertension is present
On CT scan, benign adenomas typically are of low radiographic density (due to fat content) and show rapid washout of contrast medium (50% or more of the contrast medium washes out at 10 minutes). If the hormonal evaluation is negative and imaging suggests benign lesion, follow up should be considered. Imaging at 6, 12, and 24 months and repeat hormonal evaluation yearly for 4 years is often recommended, but there exists controversy about harm/benefit of such screening as there is a high subsequent false-positive rate (about 50:1) and overall low incidence of adrenal carcinoma.
Autopsy series have suggested that pituitary incidentalomas may be quite common. It has been estimated that perhaps 10% of the adult population may harbor such endocrinologically inert lesions. When encountering such a lesion, long term surveillance has been recommended. Also, a baseline pituitary hormonal function test should be done, including measurements of serum levels of TSH, prolactin, IGF-1 (as a test of growth hormone activity), adrenal function (i.e. 24 hour urine cortisol, dexamethasone suppression test), testosterone in men, and estradiol in amenorrheic women.
Some experts recommend that nodules > 1 cm (unless the TSH is suppressed) or those with ultrasonographic features of malignancy should be biopsied by fine needle aspiration. Computed tomography is inferior to ultrasound for evaluating thyroid nodules. Ultrasonographic markers of malignancy are:
- solid hypoechoic appearance
- irregular or blurred margins
- intranodular vascular spots or pattern
Studies of whole body screening computed tomography find abnormalities in the lungs of 14% of patients. Clinical practice guidelines by the American College of Chest Physicians advise on the evaluation of the solitary pulmonary nodule.
The increasing use of MRI, often during diagnostic work-up for back or lower extremity pain, has led to a significant increase in the number of incidental findings that are most often clinically inconsequential. The most common include:
Sometimes normally asymptomatic findings can present with symptoms and these cases when identified cannot then be considered as incidentalomas.
The concept of the incidentaloma has been criticized, as such lesions do not have much in common other than the history of an incidental identification and the assumption that they are clinically inert. It has been proposed just to say that such lesions have been "incidentally found." The underlying pathology shows no unifying histological concept.
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