Elsevier

Clinical Radiology

Volume 67, Issue 10, October 2012, Pages 988-1000
Clinical Radiology

Pictorial Review
Adrenal neoplasms

https://doi.org/10.1016/j.crad.2012.02.005Get rights and content

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.

Introduction

Adrenal neoplasms are commonly encountered in routine clinical practice with incidental adrenal lesions detected in up to 10% of the general population on imaging.1, 2 Accurate radiological evaluation is essential for formulating appropriate diagnoses and for differentiating benign from malignant neoplasms. A variety of imaging methods are available for evaluating adrenal neoplasms including ultrasound, computed tomography (CT), magnetic resonance imaging (MRI) and nuclear medicine techniques such as meta-iodobenzylguanidine (MIBG) scintigraphy and positron-emission tomography (PET). In this review, the imaging appearances of adrenal neoplasms are discussed with emphasis on key findings that facilitate lesion characterization and differentiation.

Section snippets

Adrenal anatomy and physiology

The adrenal glands are suprarenal retroperitoneal organs situated within the perirenal fat and enclosed by Gerota’s fascia. On axial cross-sectional imaging, the right adrenal has an inverted “V”-shaped configuration and the left adrenal an inverted “Y” or “lambda”-shaped configuration. The adrenals are each composed of a body and medial and lateral limbs. Both adrenals are approximately located at the axial level of the T12 vertebral body, with the right adrenal situated the more cephalad of

Adenoma

Adenomas represent 80% of all adrenal neoplasms and are found in 0.2% of 20–29-year-olds and in 7–10% of elderly patients on CT.1, 2 Most adenomas are non-functioning, while functioning adenomas account for approximately 6% (5% cortical-secreting, 1% aldosterone or sex-hormone secreting).1 On imaging, adenomas are typically 1–3 cm, well-circumscribed, ovoid-shaped, homogeneous lesions.1, 3, 4 These benign neoplasms show stable size on interval imaging assessment. Large size, calcifications,

Myelolipoma

Adrenal myelolipomas are benign neoplasms composed of macroscopic fat and haematopoietic tissue. Originally described by Gierke in 1905, these were termed “formations myelolipomatoses” by Oberling in 1929.15, 16 Adrenocortical metaplasia secondary to necrosis, infection, or stress is postulated to be a precipitating factor.17 Myelolipomas are typically asymptomatic and incidentally discovered on post-mortem (0.08–0.2% prevalence) or imaging (representing 5–10% of adrenal incidentalomas).2, 18

Phaeochromocytoma

Originally described by Frankel in 1886, phaeochromocytomas are catecholamine-secreting neuroendocrine tumours of the adrenal medulla.26 A 0.8 per 100,000 annual incidence, a 0.02% post-mortem prevalence, and a 0.6% prevalence in patients with hypertension is reported.26, 27, 28, 29, 30, 31 Phaeochromocytomas account for 5% of all adrenal incidentalomas, being incidentally discovered on imaging in 25% of cases.26, 32, 33 While most phaeochromocytomas are sporadic in origin, recent discoveries

Metastases

Metastases are the most frequently encountered malignant adrenal neoplasms with the adrenals being the fourth most common site of metastases overall.44 Approximately 27% of cancer patients have adrenal metastases at post-mortem.45 Furthermore, an adrenal mass in a cancer patient has a 50–75% probability of being a metastasis.46 Melanoma, breast, lung, colon, and kidney cancers are the most common neoplasms that metastasize to the adrenals. Breast cancer and lung cancer have a 39% and 35%

Adrenocortical carcinoma (ACC)

ACC is the most common primary malignant neoplasm of the adrenal cortex accounting for <5% of all adrenal incidentalomas. It has a one to two cases per million annual incidence and is responsible for 0.2% of all cancer deaths.52, 53 A bimodal distribution in the 4th and 5th decades of life and in children <5 years of age is recognized.53, 54 A female to male ratio of 1.5:1 is reported.52, 53 Sixty percent of ACCs are functional and may secrete cortisol, aldosterone, or sex-hormones. Li–Fraumeni

Neuroblastoma

Neuroblastomas are embryonal malignancies of the sympathetic nervous system and the most common solid extra-cranial neoplasms of childhood representing 8–10% of all paediatric neoplasms and 15% of paediatric cancer mortality.65 Approximately 10.5 per million children younger than 15 years of age are affected.65 The adrenal medulla is the site of origin in 35%. At presentation, 50% of children are under age 2 years, 75% under age 4 years, and 90% under age 10 years.66 A more favourable prognosis

Lymphoma

Secondary adrenal lymphoma is found in 25% of post-mortems and 4% of CT examinations in patients with disseminated non-Hodgkin’s lymphoma.68, 69 In comparison, primary adrenal lymphoma (PAL) accounts for 3% of extra-nodal lymphoma with <100 cases reported.70 PAL has an uncertain aetiology but is postulated to arise from haematopoietic tissue within the adrenal glands.71 Diffuse large B-cell lymphoma subtype accounts for 70%.72 PAL has a mean age at presentation of 65 years, a 2:1 male to female

Algorithm for evaluating patients with adrenal incidentalomas

An adrenal incidentaloma is an adrenal mass (≥1 cm) discovered incidentally on a cross-sectional imaging examination performed for another reason.77 In most cases, this would include solid adrenal lesions detected but not adequately characterized on previous CT studies performed. A proposed diagnostic algorithm for evaluating adrenal lesions is discussed in this section and included in Fig 21. This is based on the authors' own preferences and is adapted from the American College of Radiology’s

Conclusion

Neoplasms of the adrenal glands encompass a heterogeneous group of benign and malignant diseases that may present with variable imaging findings. Advances in imaging have enhanced the ability of radiologists to characterize adrenal lesions and to differentiate benign from malignant neoplasms. Some tumours show characteristic imaging appearances. In others, imaging findings may overlap between different diseases. Knowledge of the imaging findings of adrenal neoplasms is essential for improving

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