The indeterminate adrenal lesion

Abstract

With the increasing use of abdominal cross-sectional imaging, incidental adrenal masses are being detected more often. The important clinical question is whether these lesions are benign adenomas or malignant primary or secondary masses. Benign adrenal masses such as lipid-rich adenomas, myelolipomas, adrenal cysts and adrenal haemorrhage have pathognomonic cross-sectional imaging appearances. However, there remains a significant overlap between imaging features of some lipid-poor adenomas and malignant lesions. The nature of incidentally detected adrenal masses can be determined with a high degree of accuracy using computed tomography (CT) and magnetic resonance imaging (MRI) alone. Positron emission tomography (PET) is also increasingly used in clinical practice in characterizing incidentally detected lesions. We review the performance of the established and new techniques in CT, MRI and PET that can be used to distinguish benign adenomas and malignant lesions of the adrenal gland.

Figure 1

Non-contrast-enhanced CT. There are 2 left adrenal masses (arrows) with attenuation values of 0 HU and −6 HU in keeping with benign adrenal adenomas. The patient has remained under CT surveillance and the adenomas remain unchanged after 2 years.

Figure 2

Coronal T1-weighted image demonstrating a large left adrenal mass. There are small pockets of high T1 signal intensity in the mass in keeping with fat (arrows). The adrenal mass was resected and the pathological specimen confirmed a myelolipoma with scant amounts of macroscopic fat.

Figure 3

(A) Non-contrast-enhanced CT in a 35-year-old woman who developed unexplained hypotension following minor abdominal surgery. The CT scan shows bilateral adrenal enlargement with surrounding peri-adrenal diffuse soft tissue (arrows). The pre-procedural CT (not illustrated) showed normal adrenal glands. (B) Contrast-enhanced CT obtained 60 s following administration of intravenous contrast. Both adrenal glands show no focal mass or enhancement and the appearances in the clinical context are consistent with bilateral adrenal haemorrhage.

Figure 4

(A) Non-contrast-enhanced CT demonstrating a left adrenal mass (arrow) with an attenuation value of 15 HU. (B) Axial in-phase image obtained as part of chemical shift imaging demonstrating the left adrenal mass with intermediate signal intensity (arrow). (C) Axial out-of-phase image obtained as part of chemical shift imaging shows marked loss of signal intensity, making the adrenal mass a benign adrenal adenoma.

Figure 5

(A) Non-contrast-enhanced CT in a 45-year-old man with refractile hypertension. The CT shows a large heterogeneous right adrenal mass with an attenuation value of 15 HU. (B) Contrast-enhanced CT obtained 60 s following administration of intravenous contrast. The right adrenal mass demonstrates heterogeneous enhancement with central necrosis and histological confirmation of a phaeochromocytoma was obtained.

Figure 6

Contrast-enhanced CT obtained 60 s following administration of intravenous contrast in a patient with small cell carcinoma of the lung. There are bilateral heterogeneous adrenal metastases (arrows) confirmed on PET-CT.

Figure 7

Non-contrast-enhanced CT of a lipid-poor adenoma with a mean CT attenuation value of 25 HU. The overlaid histogram shows the adenoma with the range of pixels within the mass ranging from −9 to 51 HU. Five percent of pixels have a negative pixel value in keeping with an adenoma.

Figure 8

Coronal PET-scintigraphy MIP image in a patient with a right renal cell carcinoma (arrow) and a left adrenal metastasis (block arrow).

Figure 9

(A) Non-contrast-enhanced CT in a patient undergoing a restaging CT for follicular lymphoma. A right adrenal mass is seen (arrow) with an attenuation value of in keeping with a lipid-rich adenoma. (B) Fused axial PET-CT image demonstrating [F]FDG uptake in the adrenal adenoma equivalent to some portions of the liver (arrow).

Figure 10

(A) Non-contrast-enhanced CT acquired as part of an [F]FDG-PET/CT study in a patient undergoing staging for non-Hodgkin lymphoma. A left adrenal mass is present with an attenuation value of −4 HU in keeping with a benign lipid-rich adrenal adenoma (arrow). (B) Fused axial PET/CT image demonstrating significantly higher [F]FDG uptake in the adrenal adenoma compared with the liver (arrow). The absolute SUV of the adrenal adenoma was 6.

Figure 11

(A) Non-contrast-enhanced CT acquired as part of an [F]FDG-PET/CT study in a patient undergoing staging for colorectal carcinoma. A small right adrenal mass is seen with an attenuation value of 7 HU in keeping with a lipid-rich adrenal adenoma (arrow). (B) Fused axial PET/CT image demonstrating significantly higher [F]FDG uptake in the right adrenal adenoma compared with the liver (arrow). The absolute SUV of the adrenal adenoma was 8.