Adrenal Carcinoma Imaging 

Adrenocortical carcinoma (ACC) is a rare malignancy with a poor prognosis. (See the images below.)

The reported incidence of adrenal carcinoma is 2 cases per million persons. When identified, tumors frequently are large, measuring 4-10 cm in cross-sectional diameter. Adrenal carcinomas arise from the adrenal cortex and are bilateral in up to 10% of patients. Approximately 50-80% are functional tumors, with most causing Cushing syndrome.

In one large patient-population study in the United States, 3982 patients diagnosed with ACC from 1985 to 2005 were identified from the National Cancer Data Base (NCDB), and tumor, treatment, and hospital factors associated with survival after resection were examined. Of the patients with nodes examined, 26.5% had nodal metastases, and distant metastases were found in 21.6% of patients. Overall 5-year survival for all patients who underwent resection was 38.6% (median survival, 31.9 months). A higher risk of death was associated with increasing age, poorly differentiated tumors, involved margins, and nodal or distant metastases.^[1]

Preferred examination

Computed tomography (CT) scanning is the study of choice in the evaluation of an abdominal mass or, more precisely, to differentiate a benign adrenal mass from a malignant lesion.^{[2, 3, 4, 5]}

Limitations of techniques

Although CT is used most widely for evaluating abdominal masses, the origin of the mass often is difficult to discern. In addition, the presence or absence of invasion of adjacent structures is difficult to determine in some patients.

Because adrenal carcinomas are often large at presentation, radiographs of the abdomen may demonstrate mass effect from the tumor. The calcifications observed in more than 30% of patients are often more difficult to detect with abdominal radiographs than with CT scanning.

On excretory urography, adrenal carcinoma often causes mass effect on the ipsilateral superior pole of the kidney, usually displacing the upper pole of the kidney laterally and, when large enough, inferiorly.

With the advent of cross-sectional imaging, the evaluation, staging, and treatment of adrenocortical carcinoma have vastly improved. CT should be the first imaging of choice to define an adrenal mass such as adrenocortical carcinoma.

On CT scans, adrenocortical carcinoma appears as a large mass, often with central necrosis. Calcification, seen in the images below, is observed in as many as 30% of patients.

On unenhanced images, heterogeneity is often found with larger masses. On enhanced images, the tumor enhances heterogeneously, with the greatest enhancement often at the periphery and often irregular.

CT findings that increase the index of suspicion for adrenocortical carcinoma include the following:

• Large mass (>4 cm)
• Central necrosis or hemorrhage
• Heterogeneous enhancement
• Invasion into adjacent structures
• Venous extension into the renal vein or inferior vena cava

Degree of confidence

Occasionally, differentiating an adrenal carcinoma from other pathology in the upper abdomen may be difficult because the mass is large and the fat planes are indistinct. In these patients, multiplanar magnetic resonance imaging (MRI) is the better imaging test. In particular, the imaging findings of large pheochromocytomas and metastasis may be identical. Therefore, it may be prudent to obtain spot vanillylmandelic acid (VMA) or metanephrines prior to resection to prevent a hyperintensive crisis as not all pheochromocytomas are clinically overt.

False positives/negatives

False-positive lesions could include exophytic renal masses and exophytic pancreatic tail masses.

MRI often demonstrates a large mass with lower signal intensity than the liver on T1-weighted images and higher signal intensity than the liver on T2-weighted images. Often, the tumor demonstrates heterogeneously hyperintensity on T1- and T2-weighted images, due to the central necrosis and hemorrhage. Because the mass usually does not contain any significant intracellular lipid, it will not lose signal on out-of-phase imaging. (See the image below.)

Coronal and sagittal images may be helpful in determining adrenal origin of the mass, thus differentiating it from renal cell carcinoma or hepatocellular carcinoma, especially if CT is equivocal.

Degree of confidence

MRI is advantageous for evaluating tumors, since its depiction of vascular invasion and extension into surrounding structures often is superior to that of CT. Additionally, the most cephalad extension of the tumor must be evaluated so that the surgeon can obtain vascular control of the tumor. This can be achieved with CT but often is easier with MRI.

False positives/negatives

Larger adrenal adenomas are radiologically similar to adrenal cortical carcinomas. The pathologic distinction between adrenal adenoma and adrenal carcinoma is largely based on size, with the cutoff in the range of 4-5 cm.

Adrenocortical carcinoma demonstrates a homogeneous echo texture when small, but the echo pattern becomes heterogeneous with cystic areas when the tumor grows as a result of hemorrhage and necrosis. (See the image below.)

Because different planes are obtainable on ultrasonography, it is helpful in some patients to determine the organ of origin of the mass.

Nuclear scintigraphy does not play much of a role in the evaluation of adrenal carcinoma, except to exclude other lesions such as pheochromocytomas or aldosteronomas. Iodine-121 metaiodobenzylguanidine (MIBG) and indium-111 octreotide can be used to visualize pheochromocytomas, while iodine-131 6-beta-iodomethyl-19-norcholesterol (NP-59) can be used to detect aldosteronomas or other hyperfunctioning cortical tumors. Positron emission tomography imaging performed with fluorine-18 fluorodeoxyglucose (FDG) has shown some promise in differentiating benign adrenal lesions from malignant lesions.^[6]

Prior to cross-sectional imaging, arteriography was the preferred modality for evaluating abdominal masses. On angiograms, adrenal carcinomas are usually hypovascular masses, which helps distinguish them from hypernephromas. Little vascular shunting, puddling, or venous laking is found with adrenal carcinoma compared with renal cell carcinoma. Usually, faint tumor vascularity is seen on abdominal aortograms, and it is not until selective adrenal arteriography is performed that tumor vessels are identified. The predominant arterial supply to the adrenal gland and to adrenal carcinoma is the superior adrenal artery off the inferior phrenic artery.