Clinical significance of the large adrenal mass
Current clinical teaching indicates that large ( > .
5 cm in diameter) adrenal masses are often malignant. In a retrospective analysis of patients studied between 1977 and 1988 with computed tomography (CT), adrenal scintigraphy, and when available, magnetic resonance imaging ( M R I ) 4.5 were found to have adrenal masses greater than 5 cm (range 5-19 cm) in diameter. Thirty were benign (16 phaeochromocytomas, six adrenocortical adenomas, four adrenal cysts, two rnyelolipomas, an adrenal hematoma and a ganglioneuroma). Of 1.5 malignant masses, there were seven adrenocortical carcinomas, jive adrenal metastases and three adrenal lymphomas. With the exception of the adrenal myelolipomas, cysts, and the ganglioneuroma neither CT nor M R I demonstrated sufficient diagnostic specificity to distinguish benign from malignant lesions. Functional scintigraphy with '1-6-8- iodomethyl-I9-norcholesterol for suspected adrenocortical lesions and ' I-metaiodobenzylguanidine f o r suspected phaeochromocytomas frequently provided useful information.
The differential diagnosis and optimal management of coincidentally discovered adrenal masses remains a matter of controversy which has been heightened by the availability of high-resolution computed tomography (CT). Abnormalities of adrenal morphologymasses larger than 1 cm in diameterare found incidentally in approximately 1 per cent of all patients undergoing abdominal CT'-3 and up to 26 per cent of patients with primary extra-adrenal malignancies have adrenal metastases at autopsy4. Adrenal cortical tumours producing syndromes of steroid hormone excess have an estimated incidence of approximately 4 per million per year and are equally divided between adenomas and carcinomas5. Phaeochrornocytomas occur with an estimated incidence of 1.5 million per year with only 10 per cent being malignant6. Reviews of functioning5.' and 'incidental'8 adrenal masses have emphasized the positive correlation between size of the mass and the likelihood of malignancy. Recommended thresholds for surgical exploration have included diameters of 3-35 cm (References I , 2 and 9), 5 cm (Reference 10) and 6 cm (Reference 8). Among 'non-hyperfunctioning', incidental, unilateral adrenal masses size was found to be a poor discriminator of malignancy, with benign masses ranging between 1 cm and 7 cm in diameter and malignant masses between 1.5 cm and 10 cm (Reference 11). In a subgroup of 28 patients with known extra-adrenal malignancies only ten such masses proved to be adrenal metastases' '. The clinical, radiologic, scintigraphic and pathological characteristics of large adrenal masses ( 5 cm or greater in diameter), both hyperfunctioning and nonhyperfunctioning, referred to Ann Arbor between 1977 and 1988 have been studied.