CT of Adrenal Tumors: Frequency and Clinical Significance of Low-Attenuation Lesions
Hidetoshi Miyake1 Hirofumi Maeda1 Makoto Tashiro1 Koji Suzuki1
Hidehiro Nagatomo1 Hisayuki Aikawa2 Akira Ashizawa1 Seiji lechika3 Akira Moriuchi4
The CT values of adrenal tumors were evaluated in 36 patients to determine the frequency and significance of negative CT values. Twenty-seven patients had adreno- cortical adenomas (13 had primary aldosteronism, 12 had Cushing syndrome, and two had nonhyperfunctioning adenoma), one had adrenocortical carcinoma, and eight had pheochromocytomas. The CT values in primary aldosteronism (mean, 1.8 ± 9.9 H) were lower than those in Cushing syndrome (27.6 ± 12.0 H) and pheochromocytoma (35.9 ± 9.8 H). Six adrenocortical adenomas had homogeneous, low CT attenuation, with CT values ranging from -20 to -0.4 H. Four of these had primary aldosteronism, one had Cushing syndrome, and one had nonhyperfunctioning adenoma.
Our results suggest that adrenal tumors with homogeneous, slightly negative CT attenuation are likely to be adrenocortical adenomas, mainly primary aldosteronism and nonhyperfunctioning adenomas. This finding may be especially useful in diagnosing nonhyperfunctioning adenoma.
CT is an established procedure for detecting and evaluating adrenal lesions [1]. Several authors have reported examples of adrenal tumors with low attenuation on CT [2, 3]. We studied the CT scans of 36 pathologically proved adrenal tumors to determine the frequency and significance of negative CT values.
Patients and Methods
Thirty-six patients with pathologically proved adrenal tumors (10 men and 26 women, age 18-74 years) had CT scans done at the Medical College of Oita and the Nagasaki University School of Medicine. Thirteen had primary aldosteronism caused by an adrenal adenoma (ranging from 1.0 to 4.0 cm). Twelve had Cushing syndrome caused by an adrenal adenoma (2.5-4.0 cm in size), two had nonhyperfunctioning adenoma (3.4 and 4.0 cm), and one had adrenocortical carcinoma (14 cm). Eight had pheochromocytoma (5.0-9.0 cm). Cases of adrenal myelolipoma were excluded from the study.
CT scans were performed at 5- or 10-mm intervals using cuts of 5- or 10-mm thickness. A GE CT/T 9800 (General Electric, Milwaukee, WI) was used at Medical College of Oita (16 cases) and a GE CT/T 8800 was used at Nagasaki University School of Medicine (20 cases). In 30 patients, the CT scans were performed before and after IV infusion of contrast material (65% Angiografin, 100 ml, Nihon Schering, Osaka, Japan). In the remaining six patients, only noncontrast CT scans were done.
Results
The CT values of the 27 adrenocortical adenomas and the eight pheochromo- cytomas on pre- and/or postcontrast CT scans are shown in Figure 1. The adrenocortical carcinoma showed attenuation values of 42 H on precontrast CT scans and 55 H on postcontrast scans. The CT values in the primary aldosteronism on noncontrast CT scans ranged from -18 to 13 H (mean, 1.8 ± 9.9 H). In cases with Cushing syndrome, the range was -0.4 to 46 H (mean, 27.6 ± 12.0 H). In
Received October 3, 1988; accepted after revi- sion January 19, 1989.
1 Department of Radiology, Medical College of Oita, 1-1506, Idaigaoka, Hazama-machi, Oita-gun, Oita 879-56, Japan. Address reprint requests to H. Miyake.
2 Department of Radiology, Nagasaki University School of Medicine, 7-1 Sakamoto-machi, Naga- saki, 852, Japan.
3 Department of Urology, Medical College of Oita, 1-1506, Idaigaoka, Hazama-machi, Oita-gun, Oita 879-56, Japan.
4 Department of Pathology, Medical College of Oita, 1-1506, Idaigaoka, Hazama-machi, Oita-gun, Oita 879-56, Japan.
AJR 152:1005-1007, May 1989 0361-803X/89/1525-1005
American Roentgen Ray Society
cases of pheochromocytoma, the range was 21 to 50 H (mean, 35.9 ± 9.8 H).
Six of 36 patients had adrenal tumors with negative CT values (-20 to -0.4 H) on noncontrast CT scans. All of the tumors showed a homogeneous interior before and/or after IV administration of contrast material (Fig. 2A). On these six patients, four had primary aldosteronism (-18 to -5 H), one had Cushing syndrome (-0.4 H), and one had a nonhyper- functioning adenoma (-20 H).
Histologically, the adenomas of four patients with primary aldosteronism and one patient with nonhyperfunctioning ad- enoma were composed of vacuolated, large clear cells (Fig. 2B). Large amounts of cytoplasmic lipid were confirmed with oil red O stain in one patient (Fig. 2C). Unlike the other patients with Cushing syndrome, the adenoma in one patient with Cushing syndrome comprised more clear cells than compact cells.
100
CT Value (H)
80
60
40
20
0
-20
Nonhyper - functioning adenoma
Primary aldosteronism
Cushing syndrome
Pheochromocytoma
Discussion
Adrenocortical tumors are classified as those associated with Cushing syndrome, primary aldosteronism, adrenogeni- tal syndrome, and nonhyperfunctioning tumor on the basis of clinical and biochemical evidence of hormonal hypersecretion. However, the adenomas in Cushing syndrome generally are composed of enlarged, lipid-laden clear cells scattered among more common compact cells. The cells in primary aldoster- onism are mostly large, lipid-laden clear cells similar to those seen in the zona fasciculata [4]. Therefore, cytoplasmic lipid is apt to occur more commonly in primary aldosteronism than in Cushing syndrome.
The CT values of tumors in our cases of primary aldoster- onism were lower than those in the patients with Cushing syndrome and pheochromocytoma. Thirty-one percent (4/13) of tumors associated with primary aldosteronism had slightly negative CT values on noncontrast CT scans. In Cushing syndrome, adenomas with more clear cells than compact cells may show slightly negative CT values. The vacuolated, large clear cells of the adenomas are presumed to cause the negative CT values in these cases [5].
It may be that nonhyperfunctioning adenoma cells are unable to use the lipid, resulting in the accumulation of drop- lets within the cells [6]. There was one nonhyperfunctioning adenoma with negative CT values on precontrast CT scans in our series. Liessi and Spigariol [3] have reported five nonhyperfunctioning adenomas with negative CT values (-20 to -10 H), but there have also been a few reports in which the mean attenuation values varied from -2 to 38 H [7, 8].
In our series, we found homogeneous, slightly negative attenuation on CT scans of adrenocortical adenomas, mainly in cases of primary aldosteronism and nonhyperfunctioning adenoma, not in adrenocortical carcinoma and pheochromo- cytoma. This finding is not rare in primary aldosteronism, but, to our knowledge, it has not been described. Homogeneous, slightly negative CT attenuation may be especially useful in
A
B
C
distinguishing nonhyperfunctioning adenoma from primary al- dosteronism diagnosed by clinical and biochemical evidence of hormonal hypersecretion. Metastatic adrenal tumors con- taining fat and adrenal myelolipomas may be included in the differential diagnosis of adrenal masses with negative CT values. Metastatic adrenal tumors containing fat are ex- tremely rare [9]. The CT numbers in myelolipomas depend on the relative contents of fat, bone-marrow elements, and other tissue. Myelolipomas usually have an inhomogeneous interior with fat on CT and have no clinical and biochemical evidence of hormonal hypersecretion [10, 11].
In conclusion, homogeneous, slightly negative CT atten- uation on noncontrast CT scans is not rare in adrenocortical adenoma, especially in cases of primary aldosteronism and nonhyperfunctioning adenoma. This finding may be especially useful in differentiating nonhyperfunctioning adenoma from other adrenal tumors that do not show clinical and biochemical evidence of hormonal hypersecretion.
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