In the course of staging or follow-up of oncologic patients or during scanning of normal patients, incidental findings may often be seen on imaging. Among the more common of these lesions are the solitary lung nodule, subcentimetre liver or renal hypodensities or adrenal mass. This article briefly reviews the imaging management of these lesions.
Although most solitary pulmonary nodules have benign causes, others may represent metastasis or even early stage lung cancer. Distinction between benign and malignant nodules is therefore important. Evaluation of morphologic features may be of some use e.g. the presence of intranodular fat is a reliable indicator of a hamartoma while calcification is often due to a benign cause. Small size (< 1 cm) and smooth, well-defined margins are also usually indicative of a benign aetiology while a lobulated or irregular/spiculated contour is typically due to malignancy.
There is however considerable overlap in the imaging features (e.g. margins, attenuation, cavitation) of benign and malignant lung nodules such that initial evaluation often results in non-specific findings, in which case the nodule is classified as indeterminate and require further evaluation to exclude malignancy. In this regard, follow-up scans to assess growth rate or development of new lesions, positron emission tomography and/or image-guided needle aspiration biopsy may be useful depending on the size and location of the lesion and the level of clinical suspicion.
Liver and renal hypodensities are probably even more commonly encountered than the incidental pulmonary nodule. While ultrasound may sometimes resolve the issue by demonstrating these hypodensities to be due to small cysts rather than metastases particularly in the kidneys, other lesions may not show classic sonographic features of a cyst or may be technically difficult to assess by ultrasound due to their location e.g. lesions near the liver dome. In such instances, MRI can often resolve the issue albeit at a cost. In the case of renal cystic lesions, the use of Bosniak’s classification may also provide a standard framework for their management. This takes into account the enhancement, homogeneity, wall thickening and interface, water content and calcification.
Incidental adrenal masses are not uncommonly encountered in abdominal CT scans with a reported incidence of 0.6 to 1.3 %. While the vast majority of adrenal masses are benign in the general population, they assume an added importance in oncologic patients, as the adrenals are a common site for metastasis. Where functioning adenomas can be excluded by clinical and biochemical grounds, MR imaging may further help identify some non-functioning adenomas by demonstrating fat within the lesion (Fig 1). When these are inconclusive, imaging may aid in guiding biopsy of the adrenal mass or in the follow-up of the lesion to look for interval size change.
Both the clinician and radiologist need to be mindful of the presence of incidentalomas for while it is important to detect metastases, it is equally important not to overcall lesions as this may lead to overstaging and deny patients of more appropriate or aggressive treatment.
Fig.1a
Fig. 1a,b & c. Incidental right adrenal mass (thick black arrow) detected on CT in a patient with carcinoma of the colon (a). In and out of phase coronal MR (b & c) scan show signal loss in the latter. This confirms the presence of fat within the lesion indicating it is an adenoma rather than metastasis.
Dr Quek Swee Tian
Senior Consultant
Oncologic Imaging
National Cancer Centre, Singapore
