|
Feature |
Adenoma |
Carcinoma (Figure 1) |
Pheochromocytoma |
Metastasisa |
|
Size |
Usually <4 cmb |
Usually >4 cm |
No rule |
No rule (often bilateral) |
|
Shape |
Round/oval |
Irregular |
Typically round/oval |
Irregular or round/oval |
|
Margins |
Well defined |
Poorly defined but may be well defined |
Well defined |
Poorly or well defined |
|
Structure |
Homogenous |
Heterogenous (necrotic foci, hemorrhage, calcifications) |
Heterogenous in large tumors (pseudocysts, necrosis, hematomas, calcifications) |
Homogenous or heterogenous (in large tumors) |
|
Single-phase CTc |
≤10 HUd,e |
>10 HU (usually >20) |
>10 HU |
>10 HU (usually >30) |
|
Contrast-enhanced CT with washout assessmentf |
>40% relative and >60% absolute washout with contrast |
<40% relative and <60% absolute washout with contrast |
Variable contrast media washout |
>40% relative and >60% absolute washout with contrast |
|
Lipid content on MRI |
Present in considerable amountse |
Absent or present in small amounts |
Absent |
Absent |
|
Tumor growth on follow-up imaging |
<0.5 cm/y (stable or slow) |
>1 cm/y (rapid or very rapid) |
0.5-1 cm/y (often slow) |
Usually rapid; no rule |
|
a Often primary kidney and lung cancers. b Adenomas may measure up to 10 cm, while the size of myelolipoma, another benign tumor, may exceed 20 cm. c Plain CT. d Single-phase CT: benign phenotype; an additional test with contrast enhancement is usually not needed. e Adenomas originating in the reticulate zone may be poorer in lipids and have density of 10 to 20 HU. f Tested before and 1 minute after contrast administration (enhancement assessment) and after another 10 minutes (washout assessment). |
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CT, computed tomography; HU, Hounsfield unit; MRI, magnetic resonance imaging. |
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