Adrenal neoplasms

Abstract

Adenoma, myelolipoma, phaeochromocytoma, metastases, adrenocortical carcinoma, neuroblastoma, and lymphoma account for the majority of adrenal neoplasms that are encountered in clinical practice. A variety of imaging methods are available for evaluating adrenal lesions including ultrasound, computed tomography (CT), magnetic resonance imaging (MRI), and nuclear medicine techniques such as meta-iodobenzylguanidine (MIBG) scintigraphy and positron-emission tomography (PET). Lipid-sensitive imaging techniques such as unenhanced CT and chemical shift MRI enable detection and characterization of lipid-rich adenomas based on an unenhanced CT attenuation of ≤ 10 HU and signal loss on opposed-phase compared to in-phase T1-weighted images, respectively. In indeterminate cases, an adrenal CT washout study may differentiate adenomas (both lipid-rich and lipid-poor) from other adrenal neoplasms based on an absolute percentage washout of >60% and/or a relative percentage washout of >40%. This is based on the principle that adenomas show rapid contrast washout while most other adrenal neoplasms including malignant tumours show slow contrast washout instead. ¹⁸F-2-fluoro-2-deoxy-d-glucose-PET (¹⁸FDG-PET) imaging may differentiate benign from malignant adrenal neoplasms by demonstrating high tracer uptake in malignant neoplasms based on the increased glucose utilization and metabolic activity found in most of these malignancies. In this review, the multi-modality imaging appearances of adrenal neoplasms are discussed and illustrated. Key imaging findings that facilitate lesion characterization and differentiation are emphasized. Awareness of these imaging findings is essential for improving diagnostic confidence and for reducing misinterpretation errors.

Adrenal lesions encountered in current medical practice − a review of their radiological imaging

“…Primary tumours that commonly metastasise to the adrenal gland include bronchogenic, breast, thyroid and colon carcinomas and melanoma. [14] Half of adrenal metastases are bilateral. When small, adrenal metastases have no specific features.…”

“…[2] Most ACCs demonstrate aggressive features with vascular invasion, local infiltration, distant metastases and retroperitoneal lymphadenopathy. [14] ACCs have irregular margins and can display necrosis, intratumoral haemorrhage and calcification. The tumours enhance avidly, and characteristically have a rim of peripheral nodular enhancement.…”

“…Smaller lesions are homogenous and display a density of 40 -50 HU. [14] Larger lesions have a heterogeneous appearance with areas of cystic necrosis, Historically, the use of intravenous ionic contrast in patients with phaeochromocytomas was guarded, as it could potentially precipitate an adrenal crisis. However, recent experience shows no adverse events with non-ionic contrast, eliminating the need for premedication.…”

“…Ten to 20 per cent of adenomas are bilateral. [14] Adenomas measure 1 -3 cm in size. Most are round/ oval in shape, well-defined, smooth-margined, homogenous and stable/slow-growing.…”

“…The classic 'light bulb' T2 hyperintensity that was thought to be a characteristic feature, is only present in 34% of phaeochromocytomas. [14] Imaging plays a vital role in demonstrating local invasion and metastatic spread, being the only reliable criteria that help to establish a diagnosis of malignant phaeochromocytoma (Figs 9A -C).…”