Case Report
Metastatic Adenocarcinoma Within an Adrenal Adenoma: Detection with Chemical Shift Imaging
Roger Y. Shifrin 1, Robert E. Bechtold, Eric S. Scharling
. iscrimination between benign and malignant adrenal mass lesions is a frequent clinical problem. These masses may be detected incidentally or may be found during a dedicated search for meta- static disease. Various techniques have been proposed for differentiating benign adrenal adenomas from other adrenal mass lesions. Recently, chemical shift imaging has emerged as a powerful technique for this evaluation. We present a case of metastatic carcinoma within an adrenal adenoma. The typical fea- tures of adrenal adenomas on chemical shift images are evident. However, a small portion of the adrenal mass displays features that are not characteristic for adenoma. This portion corresponds to a focus of metastatic adenocar- cinoma found by means of pathologic exami- nation following adrenalectomy.
Case Report
A 51-year-old woman came to the emer- gency department with epigastric pain that radiated through to her back. An abdominal sonographic examination was performed and revealed cholelithiasis without evidence of cholecystitis or choledocholithiasis. A 4.2 x
2.8 × 3.6 cm right adrenal mass was also noted on the sonogram. Further evaluation of the mass was performed with MR imaging, including chemical shift imaging. The MR imaging was performed on a high-field- strength (1.5 T) scanner with standard T1- weighted spin-echo sequences (TR/TE, 400/ 10) as well as in-phase (TR/TE, 92.9/4.2; flip angle, 60° ) and opposed-phase (92.9/2.5, 60°) gradient-echo sequences. The adrenal mass was isointense to muscle on the T1-weighted spin-echo sequence and the in-phase gradient- echo sequence (Fig. 1A). A dramatic loss of signal was seen in most of the mass on the opposed-phase gradient-echo sequence (Fig. 1B). However, a small (approximately 5 mm) portion of the mass did not lose signal on the opposed-phase sequence (Fig. IC). A chole- cystectomy was performed, at which time the adrenal mass was also removed. Pathologic examination of the adrenal mass showed a large adrenocortical adenoma. However, con- tained within the adenoma was a 0.6-cm soft- tissue nodule of poorly differentiated meta- static adenocarcinoma (Fig. 1D). Further eval- uation, including chest CT, found a left hilar mass consistent with bronchogenic carcinoma (not shown).
Discussion
Adrenal mass lesions may represent a variety of pathologic entities, including benign and malignant primary tumors of the adrenal cortex or medulla, secondary malignancies of the adre- nal gland (i.e., metastases), and other benign conditions such as hemorrhage, granulomatous inflammation, and simple cyst. Of these possi- bilities, adenomas and metastases make up most of adrenal mass lesions in the adult population. Autopsy studies have shown a prevalence of adrenal adenomas of approximately 2-10% in adults [1, 2]. This high prevalence, coupled with an increasing use of noninvasive imaging stud- ies, results in the detection of many adrenal ade- nomas. However, many other adrenal mass lesions are detected by these studies as well. The characterization of an adrenal mass as an ade- noma may be supported by the presence of a clinical syndrome related to elevated serum lev- els of an adrenal hormone (hyperfunctioning adenoma). However, most adrenal adenomas do not produce elevated serum hormone levels (nonhyperfunctioning adenomas). In this case, the differentiation of adenoma from metastatic disease is more problematic and has obvious implications for treatment alternatives and prog- nosis. A variety of techniques have been used in
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Fig. 1 .- 51-year-old woman with epigastric pain radiating through to her back. A and B, Gradient-echo images through adrenal mass. In-phase image (A) shows mass lesion (arrow, in right ad- renal gland) which is isointense to adjacent liver. Opposed-phase image (B) shows marked loss of signal in ad- renal mass (arrow) reflecting large lipid content of lesion. C and D, Magnified view of opposed-phase image (C) again shows low signal intensity of mass relative to adja- cent liver. However, small portion of mass remains approximately isointense to liver (arrow). Gross specimen (D) of adrenal mass shows fatty tissue characteristic of adrenal adenoma. However, small focus of poorly differen- tiated adenocarcinoma (arrow) is contained within adenoma and corresponds to focus of isointensity evident on opposed-phase image.
D
an attempt to differentiate between adrenal ade- nomas and other adrenal mass lesions. These techniques include analysis of CT attenuation values, adrenal MR tissue relaxation times, adre- nal MR signal intensity, and ratios of adrenal MR signal intensity to the MR signal intensity of other tissues such as the liver, muscle. and spleen [3-5]. The distinction between adenomas and nonadenomas with these techniques is based primarily on the known high lipid content of adrenal adenomas [6-8]. This fact is also the basis for distinction between adenomas and non- adenomas by chemical shift imaging of the adre- nal glands. Because of the different local magnetic environments of water protons and lipid protons, these protons will possess different precessional frequencies when exposed to a magnetic field. As a consequence, these two populations of protons will periodically precess in phase and out of phase with each other. If the timing of the MR image is set so that the center of K-space is acquired when the two populations are out of phase, then the signals from the two populations will cancel, and any voxel that con-
tains tissue having significant amounts of water and lipid will appear dark. This condition is met in most adrenal adenomas. Therefore, if an adre- nal mass is approximately isointense to muscle on in-phase gradient-echo images and becomes dark on opposed-phase gradient-echo images, then the diagnosis of adenoma is likely [7]. However, the case we report shows that the entire mass must lose signal on the opposed- phase image to diagnose adrenal adenoma exclusively. If a portion of the mass does not lose signal. then a metastasis or other nonade- nomatous component (e.g., hemorrhage or malignancy) of the mass cannot be strictly excluded. This realization is important in that up to 10% of people with an underlying malig- nancy may have a coexisting adrenal adenoma. If the possibility of metastasis to the adrenal gland is to be confidently excluded, then all of an adrenal mass should be accurately character- ized as benign.
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