Evaluation and Management of Adrenal Masses

Sergio Gugisch Moreira, Jr, MD, and Julio M. Pow-Sang, MD

Disclosures

Cancer Control. 2002;9(4) 

In This Article

Imaging of the Adrenal

CT is the most effective technique for examining the adrenal glands. Perinephric fat allows the gland to be displayed clearly, and tumors as small as 10 mm in diameter are routinely identified with a sensitivity of up to 100%. The adrenal gland is be examined using contiguous 5-mm collimated slices; even narrower collimation may be used to clarify equivocal findings. CT has become the imaging procedure of choice for most patients with known or suspected adrenal lesions. CT can demonstrate the adrenal glands in virtually all patients and can usually identify the size, location, appearance, and presence of local or vascular invasion, lymph node involvement, and presence of distant metastases. In patients with adrenal lesions, the contralateral adrenal gland must be carefully evaluated to determine whether the disease is unilateral or bilateral. Intravenous contrast is generally not required for evaluation of the presence of an adrenal mass, although it is mandatory in defining vascular involvement, including the vena cava.

An adrenal adenoma usually appears as a small, well-defined, homogeneous, round mass, with low enhancement with contrast medium. Calcification, hemorrhage, and necrosis are uncommon. Due to the high cytoplasmic lipid content, the density is low and varies from 0 to 30 HU. Unenhanced images of less than 18 HU have been reported to diagnose an adenoma with 100% specificity and 85% sensitivity, whereas a more conservative cutoff of 10 resulted in a specificity of 96% to 100% and sensitivity of 68% to 79%. Delayed scans taken 15 minutes after injection of contrast show that lesions less than 37 HU are adenomas. However, it is necessary to ensure that the lesions are homogeneous and devoid of thickened walls.[31] CT of adrenocortical carcinoma reveals a large mass with central areas of low attenuation due to tumor necrosis with calcifications in 30% of cases. Evidence of metastatic spread to regional lymph nodes and the liver or direct invasion of adjacent structures, such as the kidney and inferior vena cava, suggests a malignant process. Adrenal metastases are solid masses of variable size with central necrosis or areas of hemorrhage and may be bilateral. Pheochromocytomas of the adrenal gland are usually 2 to 5 cm in diameter, vascular, and rich in intracellular water. On CT they are rounded or oval masses of soft-tissue density, frequently with central necrosis and marked enhancement after intravenous contrast material. Glucagon should not be used as an antiperistaltic agent because it may induce a hypertensive crisis and, similarly, injection of ionic contrast medium can precipitate such a crisis in some patients who have not received -adrenergic blockade.

MRI of adrenal masses by several pulse sequences provides not only anatomical details, but also tissue characterization and extension into adjacent structures, and it defines the relationship between adrenal tumors and major vessels. Chemical shift MRI has become a popular technique for diagnosing adrenal adenomas with 96% to 100% accuracy.[31] Benign adrenal adenomas, which typically are composed of approximately 16% lipid based on in vitro studies, can demonstrate measurable differences in signal intensity when their appearance on in-phase gradient-echo images is compared with that on out-of-phase counterparts (Fig 3). Compared with benign lesions, metastases usually show higher signal intensity on T2-weighted images, although there is a substantial overlap in signal intensities between them. However, metastases from hepatocellular carcinomas, renal cell carcinomas, liposarcomas and, rarely, adrenocortical carcinomas can contain fat, thus resulting in false-negative images. In contrast, some functioning adenomas (aldosteronomas) may contain insufficient lipid to result in signal loss (Fig 4). Although experience with MRI in the evaluation of adrenocortical carcinomas is limited, tumors are usually heterogeneously hyperintense on T1- and T2-weighted sequences due to frequent hemorrhage and necrosis. Postcontrast studies often demonstrate peripheral nodular enhancement and central hypoperfusion. MRI is particularly useful in patients with suspected pheochromocytomas and is the imaging procedure of choice when a patient presents biochemical data suggesting catecholamine excess. Pheochromocytomas tend to be hypointense on T1-weighted images and characteristically hyperintense on T2-weighted images. Tumors often have a heterogeneous appearance on the latter image due to the presence of cystic regions, necrosis, and fibrosis. MR angiography using gadolinium may be useful to delineate the anatomic relationships between adrenal tumors and vascular structures. This technique has been refined to the point where it is unusual to require invasive angiographic procedures, even in the setting of large invasive tumors.

Benign adrenal adenomas on in-phase gradient-echo MRI images compared with out-of-phase counterparts (arrows). (A) In-phase gradient of left adrenal mass. (B) Out-of-phase gradient in the same patient demonstrating a decrease in signal intensity.

Benign adrenal adenomas on in-phase gradient-echo MRI images compared with out-of-phase counterparts (arrows). (A) In-phase gradient of left adrenal mass. (B) Out-of-phase gradient in the same patient demonstrating a decrease in signal intensity.

(A) MRI of small left adrenal mass on T1. (B) The same lesion on T2. The pathologic diagnosis was an aldosteronoma.

(A) MRI of small left adrenal mass on T1. (B) The same lesion on T2. The pathologic diagnosis was an aldosteronoma.

Adrenal Scintigraphy. The widespread application of adrenal scintigraphy is limited by the lack of experienced nuclear medicine centers. In addition to anatomical localization, adrenocortical scintigraphy provides a functional characterization of the adrenals based on the uptake and accumulation in functioning adrenocortical tissues of radiotracers, such as iodocholesterol-labeled analogs (131 I-6- -iodomethyl-19-norcholesterol [NP-59] and 75 Se-6- -selenomethyl cholesterol). Hypersecreting tumors (eg, cortisol, aldosterone, and androgen secreting adenomas) and nonhypersecreting adenomas show radiocholesterol uptake, whereas primary and secondary adrenal malignancies appear as "cold" nodules. Incidentalomas may show different radiocholesterol uptake patterns related to their nature and functional status.

Adrenal medullary scintigraphy requires radioiodinated guanethidine analogs, 131I-MIBG and 123I-MIGB, which are specifically concentrated in the sympathomedullary system by the active high-affinity type 1 transport mechanism. 123I-MIGB scintigraphy localizes pheochromocytoma as focal increased adrenal uptake with 86% sensitivity and 99% specificity. Masses less than 1.5 to 2 cm in diameter and large tumors with extensive tumoral necrosis and/or hemorrhage may not show sufficient MIBG uptake for visualization. False-negative results also may be due to drugs that interfere with uptake.

Positron Emission Tomography (PET). PET is a promising imaging modality in oncology to measure noninvasively biochemical and/or physiological processes in vivo. In a study performed to differentiate adrenal masses of unknown nature in patients with cancer, 2-[18 F]-fluoro-2-deoxy-D-glucose PET correctly distinguished benign adrenal lesions that showed no uptake and adrenal metastases characterized by high uptake with 100% sensitivity and specificity.[32] A feature unique to PET is the use of intravenous radiopharmaceuticals that closely mimic endogenous compounds. Specific inhibitors of adrenal steroidogenesis, etomidate and metomidate, have recently been used to develop suitable PET tracer. These molecules seem to be suitable as in vivo tracers for specific visualization of the normal adrenal cortex and positive identification of adrenocortical tumors.

Angiography. Arteriography and venography were once commonly used in the preoperative evaluation of large adrenal lesions. However, due to the unique sensitivity of spiral CT and MRI scans, these invasive techniques have become obsolete. The exception is in the patient with a small aldosteronoma in whom venous samples may be required for localization. An experienced interventional radiologist is required because the right adrenal vein can be difficult to catheterize.

Fine-Needle Aspiration Biopsy (FNAB). Percutaneous biopsy using either CT or ultrasound guidance can be performed to evaluate adrenal lesions. Adrenal FNAB cannot differentiate between an adrenal cortical carcinoma and an adrenal adenoma. FNAB of adrenal masses is invasive and produces significant morbidity. Complications such as pneumothorax, septicemia, and hemorrhage have been reported in 8% to 13% of cases. Although Favia et al[28] recently showed a 100% sensitivity and a 100% accuracy with FNAB for any incidental adrenal mass, most would agree that FNAB should be reserved only for suspected metastases (sensitivity 80% to 100%). Also, FNAB should not be performed in patients with occult adrenal lesions who have not undergone a biochemical evaluation to rule out pheochromocytoma.

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