Class IIF cysts may have multiple hairline-thin septa with unmeasurable enhancement or minimal smooth thickening or irregular/nodular calcifications of wall or septa without enhancing soft tissue components. Hyperattenuating cystic lesions >3 cm and intrarenal “noncortical” cysts are included in this category. Class IIF cysts require follow-up at 6 months with CT or MRI, then annually for at least 5 years.8
Obviously complicated cysts. Bosniak class III is indeterminate—neither benign nor clearly malignant. Class III cysts may have thickened borders or septa with measurable enhancement, or they may be multilocular, hemorrhagic, or infected. In 5 case series, 29 of 57 class III lesions proved to be malignant.5 MRI may characterize these lesions more definitively than CT prior to urologic referral.
Malignant cysts. Bosniak class IV renal lesions are clearly malignant, with large heterogeneous cysts or necrotic components, shaggy thickened walls, or enhancing soft tissue components separate from the wall or septa. Their unequivocal appearance results from solid tumor necrosis and liquefaction. Diagnosis is straightforward, and excision is indicated.2
A closer look at solid renal masses
Solid renal masses usually consist of enhancing tissue with little or no fluid. The goal of evaluation is to exclude malignancies, such as renal cell cancer, lymphomas, sarcomas, or metastasis. Benign solid masses include renal adenomas, angiomyolipomas, and oncocytomas, among others.
Several lesions can be diagnosed by appearance or symptoms:
Angiomyolipomas are recognized by their fat content within a noncalcified mass. Unenhanced CT usually is sufficient for diagnosis, unless the mass is very small or has atypical features.9
Vascular lesions can be identified because they enhance to the same degree as the vasculature. With the exception of inflammatory or vascular abnormalities, all enhancing lesions that do not contain fat should be presumed to be malignant.
In patients with a known extrarenal primary malignancy, 50% to 85% of incidental solid renal masses will represent metastatic disease.10 Percutaneous biopsy may be warranted to differentiate metastatic lesions from a secondary, primary (ie, renal cell carcinoma), or benign process.11
A study of 2770 solid renal mass excisions revealed that 12.8% were benign, with a direct relationship between malignancy and size. Masses <1 cm were benign 44% of the time.12 Early identification of small renal carcinomas may improve survival rates. Although renal cell carcinomas <3 cm in diameter have low metastatic potential, a solid, nonfat-containing mass should be evaluated for aggressive nephron-sparing surgery.6,13
Incidental adrenal masses occur infrequently
Adrenal incidentalomas are defined as radiographically identified masses >1 cm in diameter.14 They are much less common than their renal counterparts, with a reported prevalence of 0.35% to 5% on CT.15 Because the adrenal glands are hormonally active and receive substantial blood flow, metastatic, hormonally active, and nonfunctional causes for adrenal masses need to be considered.16
Adrenal pathology
Adrenal masses may be characterized by increased or normal adrenal function. Hyperfunctioning syndromes include hypercortisolism, hyperaldosteronism, adrenogenital hypersecretion of adrenocortical origin, and pheochromocytomas of the medulla. Symptom evaluation of these syndromes is important, but not sufficient to rule out a hyperfunctioning syndrome.
In a retrospective review of inapparent adrenal masses, ≤13% of pheochromocytomas were clinically silent.17 Therefore, laboratory testing is necessary for an incidental adrenal mass.
Nonfunctional lesions include adenomas, metastases, cysts, myelolipomas, hemorrhage, and adrenal carcinomas. These masses require evaluation for the possibility of cancer, the most common of which is metastasis. In patients with an extra-adrenal malignancy, the likelihood of malignancy in an incidental adrenal mass is at least 50%.18 An adrenal mass representing metastasis of a previously unrecognized cancer is exceedingly rare.19
Primary adrenal carcinoma is also rare, with an estimated incidence of 2 cases per one million in the general population. For patients with adrenal masses, the prevalence of carcinoma increases with lesion size (2% for tumors <4 cm, 6% for tumors 4-6 cm, and 25% for tumors >6 cm in diameter). 17 For this reason, tumors >4 cm in diameter are usually surgically resected in patients with no previous cancer history, unless radiologic criteria demonstrate clearly benign characteristics.
Although adrenal carcinomas are considered nonfunctioning, some evidence suggests they produce low levels of cortisol that may be associated with clinical features of metabolic syndrome.20
CT is first choice for adrenal mass evaluation
Dedicated adrenal CT with both unenhanced and delayed contrast-enhanced images is the most reliable study to evaluate an adrenal mass, according to the American College of Radiology. Consider another study only in patients with contrast allergy, renal compromise, or cancer history.21
Unenhanced CT can diagnose the approximately 70% of adenomas that are small, well-defined round masses with homogenous low-density lipid deposition.22 Delayed contrast enhancement can characterize most of the remaining 30%.23 Unenhanced CT with attenuation values of <10 Hounsfield units (HU) can diagnose adenomas with 71% specificity and 98% sensitivity,24 and can often diagnose simple cysts and myelolipomas, as well.