Few studies have dealt with incidental findings in abdominal MRI. In a recent retrospective study, Herfarth et al[13
] analyzed extra-intestinal findings in MRI-enteroclysis. In 710 patients with suspected or known inflammatory bowel disease 57% had extra-intestinal lesions and 12% of the observed lesions were of major clinical importance. In 5 patients (0.7%) extra-intestinal findings were suspicious of previously unknown malignant disease. However, findings of major importance were mainly abscesses related to CD, and comparison with the present study is difficult because of different study designs.
Extensive work has been done on extra-intestinal findings in CT-colonography. Results are summarized in a comprehensive review from 2005 including 17 studies. In total 40% of patients were recorded to have extra-colonic abnormalities, 14% had further diagnostic work-up and extra-colonic cancers were detected in 2.7%[16
]. The cancer detection rate was reported in 5 studies and varied from 0.4% to 4.6% with the highest rates in the elderly.
In the present study, MRI-enterography revealed incidental findings located outside the small intestine and not related to CD in 25% of patients resulting in additional examinations in 5%. Additional investigations confirmed abnormal lesions in 1.8%, and one patient had a malignant disease. Two patients benefitted from the additional examinations (aortic aneurysm and prostate cancer), whereas incidental findings led to unnecessary examinations in 9 patients. Detection of extra-intestinal manifestations of CD was rare (1.8%).
Incompletely characterized or clinically important findings were more common in patients with suspected than known CD, suggesting that findings necessitating additional work-up are more frequent in this group of patients. Because of the retrospective nature of this study, and the small number of patients referred for additional examinations, it was not possible to elucidate further on this assumption or whether incidental findings could explain the patients’ symptoms. A prospective study would clarify this issue.
Comparing studies can be troublesome because of differences in population characteristics, classification systems, examination protocols and study designs. In the present study we used an MRI technique with intravenous contrast in a young population with a low risk of malignant disease. Compared to the study by Ajaj et al[14
] we detected fewer extra-intestinal lesions, and the frequency of malignant disease was much higher when performing MRI-colonography. In an overall comparison with CT studies we also found a lower frequency of extra-intestinal findings and a lower rate of additional work-up. These discrepancies probably arise from differences in age, prior morbidity and the risk of malignant disease in the study populations.
MRI-enterography is a relatively new modality for evaluating CD in the small intestine. Ileo-colonoscopy, CT-enterography, capsule endoscopy, abdominal ultrasound and small bowel enteroscopy are alternative examinations. Choosing between modalities relies on several factors. Primarily a modality with a high sensitivity and specificity for luminal abnormalities as well as pathology in the bowel wall and extra-intestinal manifestations of CD is essential. Also other aspects of the investigations should be considered: risk of complications (aspiration, capsule retention, radiation exposure, etc.), patient discomfort, complexity of the examinations, accessibility, costs, and finally the impact of incidental findings. In the present study, the detection rate of clinically significant lesions outside the small intestine was low. In contrast, incidental findings led to unnecessary examinations in a substantial number of patients. Hence, in comparison with other modalities the detection rate of important incidental lesions was too low to be an argument in itself for performing MRI-enterography in patients with suspected or known CD.
Our study was limited by its retrospective design. Radiological reports were not performed with the focus on incidental findings, and underestimation of clinically unimportant findings are likely. The study population contained a preponderance of women (ratio 2:1), which is reflected by the frequency of incidental findings in the female genitalia. The second most common finding was ovarian cysts, and lesions in the female genitals were common in all classification groups. It is well established that CD is more common in females (1.2-1.5:1) and in specialized centers for inflammatory bowel diseases the prevalence of women with irritable bowel syndrome is up to 4 times as high as that of men[17,18
In conclusion, incidental findings were common in patients with known and suspected CD having MRI for evaluation of small intestinal disease. Additional examinations revealed important disease in only a minority of patients. However, a substantial number of patients experienced unnecessary morbidity because of the additional examinations of benign or normal conditions. The detection rate of important incidental lesions not related to CD was too low to be an argument in itself for performing MRI-enterography in this group of patients.