Chapter One

Khaled M. Elsayes, Isaac R. Francis, Melvyn Korobkin and Gerard M. Doherty

1.1 Introduction

Most adrenal adenomas are initially detected incidentally by computed tomography (CT), in patients who undergo the examination for other indications. But CT and magnetic resonance imaging (MRI) are also used in the investigation of adrenal hyperfunction.

Adrenal adenoma is the most common adrenal mass that is seen on cross-sectional imaging, usually CT and MRI. The majority of these lesions contain abundant lipid and can be seen on unenhanced CT as low density masses measuring less than 10 Hounsfield units [HU], and exhibit loss of signal intensity on out-of-phase (opposed phase) gradient-echo MR images. Adenomas also exhibit rapid intravenous iodinated contrast enhancement washout and therefore can be distinguished from malignant lesions which do not exhibit this feature.

CT and MRI can be used to stage adrenal cortical carcinomas and detect pheochromocytomas. FDG PET scans can help differentiate adrenal metastases from adenomas by their strong avidity for FDG, but some adenomas show mild tracer uptake.

There are several masses such as uncomplicated adrenal cysts, adrenal myelolipomas and acute adrenal hemorrhage which can be readily characterized on CT and MRI.

Utility of various imaging modalities in diagnosis of adrenal gland masses:

Ultrasound: Ultrasound is sensitive but not specific for diagnosis adrenal masses

Computed Tomography (CT):

* Most commonly used modality for detection and characterization of adrenal masses

* Measuring the unenha