Clinical History: A 64 year-old male complains of back pain extending into the left leg. (1a) A left lateral T2-weighted sagittal and (1b) and T1-weighted axial image at the level of the L4-5 disc are provided. What are the findings? What is the diagnosis?
Incidental finding of extensive retroperitoneal lymphadenopathy. A subsequent biopsy indicated metastatic colon carcinoma.
An incidental finding, often referred to as an “incidentaloma” both in the literature and in the daily lexicon of radiologists, is a finding found by coincidence while examining a patient for another clinical symptom or suspicion1. A more magnetic resonance imaging (MR) specific definition defines an incidentaloma as a disease or physical condition found as a secondary by-product of capturing the necessary volume of tissue within the field of view of the MR examination.
The nature of incidental imaging findings varies greatly in terms of size, location and clinical import on the patient. An incidental finding may have no clinical impact on the patient whatsoever, or as in the current case, may be life-threatening. These findings, such as an incidental adrenal mass on a lumbar MRI (4a,5a), may need further work up if size or other criteria are met2. Other medically significant findings may need to be documented by the radiologist, but immediate action may not be taken, such as is the case with incidental identification of asymptomatic gallstones on a lumbar spine MRI (6a,7a).
Incidentalomas may be seen on virtually any type of orthopaedic or spine MR examination and may involve any osseous or soft-tissue structure within the field of view. They can be quite subtle or extremely large. When at the periphery of the field of view, or when isointense to normal structures, they can be extremely challenging to identify, particularly in a high volume practice. The following cases are presented to demonstrate incidental findings that have been seen in our busy, MR focused practice.
The frequency, site and multiplicity of incidentalomas have been studied in many settings, with one of the most extensive studies performed at the University of California San Diego on 1192 consecutive patients who underwent whole body electron beam computed tomography (CT) screening3. Spinal lesions, followed by vascular, lung, kidney and hepatic incidental findings were most common, and 86% of patients had at least one abnormality on their whole body CT. In musculoskeletal MR imaging, the majority of incidental finding are related to the osseous structures, both spinal and peripheral, as hemangiomata of the vertebral bodies, enostoses (bone islands) and cysts dominate the landscape. The preponderance of spine and sacrum, pelvic and hip exams, however, allow inclusion of a large volume of urologic (kidney, adrenal, bladder, prostate) and female gynecologic (uterus, cervix, vulvar, adnexal) tissues in the field of view, so abnormalities in these regions are commonly encountered as well.
Incidentalomas may be encountered in the form of a developmental variation, such as in the case of the horseshoe kidney (10a,11a) , where a perturbation of fetal development lends itself to variant anatomy. An incidentally recognized finding may not be part of the main study, but rather seen only on a rudimentary scout examination (4a), used for slice selection and centering of the body part to examined, and typically not well optimized for either spatial or contrast resolution. Incidental findings can be obscured by motion, pulsation and magnetic susceptibility artifact, and image distortion can occur in relation to technical factors, such as magnetic field strength and field of view constraints, which may be particularly severe at the periphery of a given image.
Rarely, an incidental finding may harbor its own incidental finding (17a,18a), as in the following case of patient with an unsuspected pregnancy found to be in breach and harboring a nuchal cord. This finding was important to verify and record, as fetuses in breech position and with a nuchal cord are more likely to be delivered via caesarean section4.
Incidental findings are an important subset of abnormalities that may be found on any MR imaging study, be they central and obvious, or tiny and peripheral. Proper knowledge of this issue sets the tone for a careful search pattern. Though some findings are of minor significance, others have great medical import, and recognition of the abnormality in such cases can have a dramatic impact on patient care.
1 Westbrook JI, Braithwaite J, McIntosh JH. The outcomes for patients with incidental lesions: serendipitous or iatrogenic? AJR 1998; 171:1193-1196.
2 Mitchell IC, Nwariaku FE. The Oncologist 2007; Vol. 12, No. 2: 168-174.
3 Furtado CD, Aguirre DA, Sirlin CB, et al. Whole-body CT screening: spectrum of findings and recommendations in 1192 patients. Radiology 2005 ; 237 (2): 385-94.
4 Ogueh O, Al-Tarkait A, Vallerand D, Rouah F, Morin L, Benjamin A, Usher R. Obstetrical factors related to nuchal cord. Acta Obstetricia et Gynecologica Scandinavica 2006; Volume 85, Number 7: 810-814.