General Frequency of Incidental Findings in Imaging Research
1376 research participants underwent 1426 research imaging studies. These imaging studies came from 91 different IRB-approved research protocols. Subjects’ mean age was 58 years (range 3–97 yrs). Of the 1426 exams, 690 (48.4%) were on males and 736 (51.6%) were on females.
Out of the 1426 research imaging studies, 567 subjects had at least one IF reported (40.0%). Of the research subjects with IFs, the mean age was 63 (3–97 years), with 251 (44%) being male and 316 (56%) being female. The 567 subjects with IFs had a total of 1055 IFs (284 exams with multiple findings), with a subsequent IF-to-exam ratio of 1.86 (0.74 was the ratio for all 1426 exams).
Frequency and Risk of Incidental Findings by Imaging Modality and Age
The frequency of IFs reported varied widely depending upon body region imaged and the type of imaging modality that was employed (). CT scans of the abdomen/pelvis and thorax produced the highest percentages of imaging exams with an IF (61% and 55%, respectively), providing an average of 1.29 and 1.16 IFs per research imaging exam. Ultrasound and nuclear medicine scans infrequently produced an IF (9% and 4%, respectively).
Multiple variable logistic regression was used to assess associations between factors of interest and the odds for an IF, where factors of interest included age (considered as linear), gender, and type of imaging study. Type of imaging study was significantly associated with IF, p<0.001. Considering ultrasound as the reference imaging study, each of the other exams, with the exception of nuclear medicine exams, was associated with a significantly higher odds of an IF (). The largest ORs were for CT abdomen/pelvis [OR=18.9] and CT thorax [OR=11.9]. reports the OR and 95% confidence interval for an IF for each pair of the 8 imaging studies of interest.
Multiple Variable Logistic Regression, Associations with Incidental Finding Reported at Imaging Study.
Odds Ratio for Having an IF, for Imaging Modality Pairs (row vs. column)†
Older age was also significantly associated with increased odds for IF, OR=1.5 per 10-year increase in age [95% CI; 1.4–1.7]. This increased risk translates into a 4.2% increase in the odds of having an IF per year of age (1.9% per year of age for MR brain alone). There was a non-significant increased odds in males (relative to females), OR=1.04 [0.8, 1.3].
A second multiple variable model was also considered that included categorized age (<40, 40–64, and ≥65 years). Results again were that higher age was significantly associated with a greater odds for IF, age 40–64 (relative to <40) had OR=4.1 [2.5, 6.8] and age ≥65 (relative to <40) had OR=9.7 [5.8, 16.3].
Incidental Findings Producing Clinical Action
Out of the 1426 research imaging studies examined, 35 (2.5%) research participants (8 males, 27 females; mean age 57, range 31–87) received further clinical action based on an IF ().
Brief Description of IFs Investigated Clinically, Final Diagnosis (if known), Description of Clinical Action Taken and Expert Panel Assignment of Medical Benefit/Burden and Gravity of Disease.
Of these 35 subjects, 32 received follow-up imaging and 27 were referred by their primary care physician for subspecialty consultation. Five research subjects underwent non-invasive diagnostic medical tests (serial CA-125 levels, dexamethasone and catecholamine levels, pulmonary function tests, fungal serologies, coagulation tests) while 6 underwent invasive diagnostic procedures (2 bronchoscopies, 2 biopsies, 1 FNA, 1 flexible nasopharyngoscopy). Eight research subjects underwent surgery for an IF, 2 underwent radiofrequency ablation (renal cell carcinoma, carcinoid liver metastasis), and 2 received medical treatment (1 anti-fungals, 1 anti-tussives).
While many imaging modalities and body regions were found to generate large numbers of IFs, only CT chest, CT abdomen/pelvis, CT all other, and MRI head yielded IFs that received further investigation. Clinical investigation did not result from IFs found on non-head MR exams, ultrasound, plain film x-ray or nuclear medicine. CT abdomen/pelvis had the most IFs receiving action, with 19 acted upon out of 207 exams (9.2%) (). The most frequent IFs receiving further action were ovarian/adnexal masses (n=9) in the abdomen/pelvis and indeterminate lung nodules (n=5) in the chest.
Expert Panel Evaluation of Medical Benefit/Burden
Medical burden/benefit and gravity of disease for each IF generating subsequent action is reported in . Six cases were found to be examples of clear medical benefit (rib osteomyelitis, renal cell carcinoma (), small bowel carcinoid, sphenoid sinus aspergillus colonization, ovarian mucinous cystadenoma, grade-2 ependymoma ()), with a mean gravity of disease score of 4.0. Twenty-four cases received an evaluation of unclear medical benefit/burden, while only two cases received the designation of potential medical burden. Three cases were found to represent clear medical burden to the patient, with a mean gravity score of 2.3. These included suspicious mesenteric nodules that were found to be benign reactive lymph nodes at laparoscopy (), an ovarian mass found to be a physiologic cyst at laparoscopy, and an adrenal mass found at surgery to be an adrenal cortical adenoma. No deaths or post-surgical complications occurred.
Figure 2 From an 85-year-old female participating in a research study investigating osteoporosis in post-menopausal women. Transverse image of a CT of the abdomen/pelvis without contrast incidentally reveals a heterogenous lesion arising from the posterior aspect (more ...)
Figure 3 From a 31-year-old female participating in a research study investigating cognitive behavioral therapy in patients with obsessive-compulsive disorder. Sagittal T1 weighted image incidentally demonstrates a partially cystic, partially enhancing mass situated (more ...)
Figure 4 From a 56-year-old female participating in a research study investigating the use of CT in the detection of high grade esophageal/gastric varices in patients with portal hypertension. Transverse image of a contrast enhanced CT of the abdomen/pelvis incidentally (more ...)