(Radiographics. 1999;19:235-239.)
© RSNA, 1999
Residents' Teaching Files
Adrenal Adenoma and Hematoma Mimicking a Collision Tumor at MR Imaging
Nadia J. Khati, MD1,
Marcia C. Javitt, MD1 and
Arnold M. Schwartz, MD2
1 Departments of Radiology (N.J.K., M.C.J.)
2 Pathology (A.M.S.), The George Washington University Medical Center, 901 23rd St, NW, Washington, DC 20037.
Index Terms: Adrenal gland, CT, 862.1211 • Adrenal gland, hemorrhage, 862.546 • Adrenal gland, MR, 862.12141 • Adrenal gland, neoplasms, 862.317, 862.5411
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INTRODUCTION
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The incidental discovery of an adrenal mass is becoming commonplace in patients undergoing abdominal imaging. Differentiation between a benign mass and a malignant mass is critical for appropriate therapy, especially in patients with a known primary malignancy. Collision tumors (ie, the coexistence of two contiguous but histologically different tumors within the same organ) are uncommon (1). In this article, we describe an unusual case in which adrenal adenoma and coexistent adrenal hematoma mimic a collision tumor at magnetic resonance (MR) imaging.
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CASE PRESENTATION
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A 43-year-old man who had experienced one previous episode of diverticulitis 8 years earlier presented to the emergency department with sudden onset of left-sided abdominal pain and low-grade fever and an elevated white blood cell count. Contrast material–enhanced computed tomography (CT) of the abdomen and pelvis was performed to evaluate for a sigmoid colon lesion and revealed mild mural thickening of a segment of the distal left side of the colon with surrounding inflammatory stranding. A round, 3.5-cm mass was discovered incidentally in the left adrenal gland (Fig 1). Diagnostic considerations included sigmoid colon malignancy, diverticulitis, or inflammatory bowel disease with an incidental left adrenal mass. There was no evidence of lymphadenopathy within the abdomen or pelvis. Statistically, the mass was most likely to represent an incidental adenoma; however, it remained indeterminate on the basis of CT findings alone because no unenhanced or delayed enhanced CT scans were obtained at that time to assess the degree of enhancement, and an adrenal metastasis from a possible primary neoplasm of the colon could not be excluded with certainty. Consequently, MR imaging was performed to further characterize the mass.
The adrenal glands were evaluated with axial, sagittal, and coronal T1- and T2-weighted multi-echo MR imaging followed by axial T1-weighted in-phase and opposed-phase gradient-echo MR imaging. Imaging findings revealed a 3.4-cm left adrenal mass that had low signal intensity on T1-weighted images (Fig 2a), was isointense relative to the liver (low signal intensity) on T2-weighted images (Fig 2b), and was isointense relative to the spleen on in-phase images (Fig 3a). Opposed-phase images showed only partial signal dropout peripherally with an eccentric area of higher signal intensity, implying the presence of two different components (Fig 3b) and suggesting the presence of a collision tumor within the left adrenal gland.
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Figure 2a. (a) Axial T1-weighted fast spin-echo (repetition time msec/echo time msec = 749/12) MR image of the abdomen obtained at the level of the adrenal glands shows a heterogeneously hypointense left adrenal mass. Note the area of intermediate signal intensity (from subacute blood) within the mass (arrowhead). (b) Axial T2-weighted fast spin-echo (3,150/102) MR image shows the left adrenal mass (arrow) as slightly heterogeneous and nearly isointense relative to the liver.
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Figure 2b. (a) Axial T1-weighted fast spin-echo (repetition time msec/echo time msec = 749/12) MR image of the abdomen obtained at the level of the adrenal glands shows a heterogeneously hypointense left adrenal mass. Note the area of intermediate signal intensity (from subacute blood) within the mass (arrowhead). (b) Axial T2-weighted fast spin-echo (3,150/102) MR image shows the left adrenal mass (arrow) as slightly heterogeneous and nearly isointense relative to the liver.
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Figure 3a. (a) Axial in-phase gradient-echo (36.5/4.2) MR image shows the left adrenal mass with homogeneous low signal intensity (isointense relative to the spleen). (b) Axial opposed-phase gradient-echo (32.1/2.5) MR image obtained at the level of the left adrenal mass shows signal dropout peripherally with an eccentric area of higher signal intensity (arrow). This high-signal-intensity area corresponds to the coexistent hematoma.
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Figure 3b. (a) Axial in-phase gradient-echo (36.5/4.2) MR image shows the left adrenal mass with homogeneous low signal intensity (isointense relative to the spleen). (b) Axial opposed-phase gradient-echo (32.1/2.5) MR image obtained at the level of the left adrenal mass shows signal dropout peripherally with an eccentric area of higher signal intensity (arrow). This high-signal-intensity area corresponds to the coexistent hematoma.
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The patient underwent left hemicolectomy with colorectal anastomosis and left adrenalectomy. Pathologic examination revealed diverticulitis of the left side of the colon with no malignancy. The adrenal gland contained a 2.5-cm hemorrhagic cyst with a surrounding adrenal adenoma.
At gross examination, two tumorous processes were seen to replace the adrenal gland. Histologic analysis revealed a cystic hemorrhagic mass representing cystic degeneration with recent hemorrhage rather than an independent tumor (Fig 4a). An adjacent yellow-orange benign cortical adenoma with marked vascularity and a diameter of approximately 2.5 cm was seen to deform the normal adrenal gland architecture (Fig 4b).
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Figure 4a. (a) Low-power photomicrograph (original magnification, x20; hematoxylin-eosin stain) demonstrates a cystic hemorrhagic area (arrows). (b) High-power photomicrograph (original magnification, x100; hematoxylin-eosin stain) shows a highly vascular clear cell cortical adenoma (arrows) adjacent to the cystic hemorrhagic area deforming the normal architecture of the adrenal gland.
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Figure 4b. (a) Low-power photomicrograph (original magnification, x20; hematoxylin-eosin stain) demonstrates a cystic hemorrhagic area (arrows). (b) High-power photomicrograph (original magnification, x100; hematoxylin-eosin stain) shows a highly vascular clear cell cortical adenoma (arrows) adjacent to the cystic hemorrhagic area deforming the normal architecture of the adrenal gland.
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DISCUSSION
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Adrenal masses have been studied extensively with cross-sectional imaging in an attempt to develop an imaging algorithm to differentiate benign from malignant lesions. Sonography is reserved for infants and children due to small body habitus and undesirable ionizing radiation from CT. Abdominal CT is often the first examination performed in the evaluation of an adrenal mass. CT criteria such as mass size, interval change in size on serial examinations, contour and margins, and presence or absence of calcifications or gross fat (myelolipoma) have been proposed to differentiate between benign adrenal adenomas, adrenal carcinomas, and metastatic lesions (2).
At CT, benign adrenal adenomas typically manifest as masses less than 5 cm in diameter with sharp margins and smooth contours and do not demonstrate growth on serial examinations. Adenomas have been discovered at autopsy in up to 10% of cases (3).
Attenuation measurements on unenhanced and delayed CT scans appear to be more accurate in evaluating the benign or malignant nature of adrenal masses. Different threshold values have been proposed for the diagnosis of adenomas with unenhanced CT. Boland et al (4) reported a specificity and sensitivity of 100% at a threshold of 13 HU for differentiation of benign from malignant lesions. However, the authors also pointed out the possibility of necrotic metastatic lesions having attenuation values of less than 10 HU. Other investigators have reported a specificity and sensitivity of 100% and 87% respectively at a threshold of 10 HU (5), and of 92% and 93% respectively at a threshold of 18 HU (6).
Attenuation values also differ on contrast-enhanced CT scans obtained after a 15-minute delay. Adenomas can be diagnosed on delayed CT scans with a specificity and sensitivity of 96% at thresholds of 24 HU (4) and 37 HU (5). Attenuation measurements obtained on initial dynamic contrast-enhanced CT scans cannot be used to differentiate reliably between adenomas and nonadenomas due to the considerable overlap of values (4,6). Many imaging centers do not perform unenhanced or early delayed contrast-enhanced CT of the abdomen unless specifically indicated. As a result, many adrenal masses remain indeterminate, warranting further investigation with MR imaging, repeat tailored CT, or adrenal scintigraphy.
At conventional MR imaging, adrenal adenomas are typically hypointense relative to the liver with T1-weighted sequences and hypointense to isointense relative to the liver with T2-weighted sequences (7), whereas metastases have a high signal intensity relative to the liver with T2-weighted sequences (7,8). Attempts to calculate signal intensity ratios between adrenal masses and adjacent liver or fat with T2-weighted sequences have resulted in a 20%–30% overlap between adenomas and nonadenomas (2,7). On fat-saturated spin-echo MR images, adenomas appear to have a hyperintense rim that is thought to represent either a surrounding capsule or normal adrenal tissue that is compressed at the edge of the mass (7). On dynamic contrast-enhanced MR images, adenomas show moderate enhancement with rapid washout of contrast material, whereas metastases show early and intense enhancement with delayed washout (4,7–9). However, there are no accurate threshold values available to help assess the degree of enhancement on contrast-enhanced MR images, with 24% of cases remaining indeterminate (9). Several recent studies have reported on the efficacy of chemical-shift MR imaging in the diagnosis of adrenal adenomas made on the basis of their intracytoplasmic lipid content (2,3,9,10).
In-phase and opposed-phase gradient-echo MR imaging appear to be the most useful techniques for evaluating indeterminate adrenal masses seen at CT or conventional MR imaging. Adenomas typically demonstrate signal dropout on opposed-phase images relative to in-phase images (7,9), reflecting the presence of intracellular lipid. The use of an adrenal lesion-to-spleen ratio (ie, the signal intensity ratio between the adrenal lesion and the spleen on opposed-phase and in-phase images) (10) allows identification of all adenomas with a ratio of less than 70. Visual inspection for decreased signal intensity is adequate to make the diagnosis in the vast majority of cases (2,5). In our case, the adrenal mass was isointense relative to the spleen on in-phase images, whereas opposed-phase images showed partial signal dropout medially with a focus of higher signal intensity laterally, suggesting the presence of a collision tumor.
With collision tumors, there may be admixture of the two different cell types at the tumor junction (11). Both tumors may be malignant, or one may be benign and the other malignant (1). Adrenal collision tumors are extremely rare, and their prevalence is unknown. However, many cases may go undiagnosed because of sampling error at fine-needle biopsy or a significant difference in the size of the two components, making it more likely that only the larger component will be examined at pathologic analysis (1). Collision tumors should be suspected on chemical-shift MR images when there is only focal decrease in the signal intensity of the mass on opposed-phase images. In our case, the hypervascular adenoma is thought to have undergone acute spontaneous hemorrhage that, together with the adenoma, formed the hemorrhagic cyst.
Adrenocortical scintigraphy with NP-59 (131I-6b-iodomethylnorcholesterol) is highly accurate in differentiating adenomas from nonadenomas (2,12). When the uptake of NP-59 is more prominent on the side corresponding to the known adrenal mass at CT (concordance), a diagnosis of adenoma can be made with confidence. The effectiveness of NP-59 is limited in masses less than 2 cm in diameter with indeterminate uptake (12).
In addition to adenomas and metastases, the differential diagnosis of an adrenal mass includes cysts, myelolipomas, hemangiomas, and adrenocortical carcinomas, all of which have characteristic imaging features.
True cysts are extremely rare, occurring in .064%–.180% of the population (13). They are usually solitary and can measure up to 20 cm in diameter (13). True cysts appear as well-defined, homogeneous masses with water attenuation on unenhanced CT scans and remain unenhanced after administration of contrast material (13).
Myelolipomas are uncommon benign lesions composed of mature adipose and hematopoietic tissue. Although most patients are asymptomatic, some may present with pain (7). The finding of a fatty mass at unenhanced CT is virtually diagnostic. Acquisition of thin sections through the mass may be warranted in doubtful cases such as those involving intratumoral hemorrhage or infarction (9). Fat-saturated MR imaging can help confirm the diagnosis by demonstrating signal dropout within the mass (7).
Hemangiomas of the adrenal gland are rare. They vary from 2 to 22 cm in size and are usually clinically silent (8). CT findings include a mass with thick, irregular walls containing central areas of low attenuation that may represent necrosis or fibrosis (7). Calcifications are seen in 28%–87% of cases (7). Gadolinium-enhanced T1-weighted MR images show a characteristic pattern of peripheral enhancement that persists on delayed images (7).
Adrenocortical carcinomas are extremely rare, occurring in one of every 1 million individuals (8). Patients may complain of abdominal pain or present with a large, palpable mass (9). Approximately 50% of these tumors are hyperfunctioning, and Cushing syndrome may be evident at presentation (2). CT findings include a large (usually 
5 cm) mass with central areas of necrosis and hemorrhage and containing calcifications in 30% of cases (9). Liver metastases, lymphadenopathy, and venous invasion are usually present at the time of diagnosis.
This case is interesting and unusual in that two benign entities—an adrenal adenoma and a concomitant hemorrhagic cyst—mimic a collision tumor of the adrenal gland at MR imaging (14).
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Footnotes
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Address reprint requests to N.J.K.
Received for publication August 17, 1998.
Revision received August 26, 1998. October 2, 1998.
Accepted for publication October 2, 1998.
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References
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Schwartz LH, Macari M, Huvos AG, Panicek DM. Collision tumors of the adrenal gland: demonstration and characterization at MR imaging. Radiology 1996; 201:757-760.[Abstract/Free Full Text]
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Korobkin M, Francis IR. Imaging of adrenal masses. Urol Clin North Am 1997; 24:603-622.[Medline]
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Boraschi P, Braccini G, Grassi L, et al. Incidentally discovered adrenal masses: evaluation with gadolinium enhancement and fat-suppressed MR imaging at 0.5 T. Eur J Radiol 1997; 24:245-252.[Medline]
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Boland GW, Hahn PF, Pena C, Mueller PR. Adrenal masses: characterization with delayed contrast-enhanced CT. Radiology 1997; 202:693-696.[Abstract/Free Full Text]
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Korobkin M, Brodeur FJ, Francis IR, Quint LE, Dunnick NR, Londy F. CT time-attenuation washout curves of adrenal adenomas and nonadenomas. AJR 1998; 170:747-752.[Abstract/Free Full Text]
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Szolar DH, Kammerhuber F. Quantitative CT evaluation of adrenal gland masses: a step forward in the differentiation between adenomas and nonadenomas. Radiology 1997; 202:517-521.[Abstract/Free Full Text]
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Francis IR, Korobkin M. Incidentally discovered adrenal masses. Magn Reson Imaging Clin N Am 1997; 5:147-164.[Medline]
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McNicholas MMJ, Lee MJ, Mayo-Smith WW, Hahn PF, Boland GW, Mueller PR. An imaging algorithm for the differential diagnosis of adrenal adenomas and metastases. AJR 1995; 165:1453- 1459.[Abstract/Free Full Text]
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Banik S, Hasleton PS, Lyon RL. An unusual variant of multiple endocrine neoplasia syndrome: a case report. Histopathology 1984; 8:135-144.[Medline]
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Francis IR, Smid A, Gross MD, Shapiro B, Naylor B, Glazer GM. Adrenal masses in oncology patients: functional and morphologic evaluation. Radiology 1988; 166:353-356.[Abstract/Free Full Text]
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Rozenblit A, Morehouse HT, Amis ES, Jr. Cystic adrenal lesions: CT features. Radiology 1996; 201:541-548.[Abstract/Free Full Text]
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Shifrin RY, Bechtold RE, Scharling ES. Metastatic adenocarcinoma within an adrenal adenoma: detection with chemical shift imaging. AJR 1996; 167:891-892.[Free Full Text]
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INTRODUCTION
CASE PRESENTATION
