Imaging in Cushing's syndrome

Abstract

Once the diagnosis of Cushing's syndrome (CS) has been established, the main step is to differentiate between ACTH dependent and independent disease. In adults, 80% of CS is due to ACTH-dependent causes and 20% due to adrenal causes. ACTHsecreting neoplasms cause ACTH-dependent CS. These are usually anterior pituitary microadenomas, which result in the classic Cushing's disease. Non-pituitary ectopic sources of ACTH, such as a small-cell lung carcinoma or carcinoid tumours, are the source of the remainder of ACTH-dependent disease. In the majority of patients presenting with clinical and biochemical evidence of CS, modern non-invasive imaging can accurately and efficiently provide the cause and the nature of the underlying pathology. Imaging is essential for determining the source of ACTH in ectopic ACTH production, locating the pituitary tumours and distinguishing adrenal adenomas, carcinomas and hyperplasias. In our chapter we review the adrenal appearances in ACTH-dependent and ACTH-independent CS. We also include a discussion on the use of MRI and CT for the detection and management of pituitary ACTH secreting adenomas. CT of the chest, abdomen and pelvis with intravenous injection of contrast medium is the most sensitive imaging modality for the identification of the ectopic ACTH source and detecting adrenal pathology. MRI is used for characterising adrenal adenomas, problem solving in difficult cases and for detecting ACTH-secreting pituitary adenomas. RESUMO Imagem em Síndrome de Cushing.Uma vez estabelecido o diagnóstico da síndrome de Cushing (SC), o passo principal é diferenciar entre a doença ACTH-dependente e a independente. Em adultos, 80% da SC é devida a causas ACTH-dependentes e 20% a causas adrenais. Neoplasias secretoras de ACTH causam a SC ACTH-dependente: usualmente são microadenomas da hipófise anterior que resultam na clássica doença de Cushing. Fontes ectópicas (não hipofisárias) de ACTH, como o carcinoma pulmonar de célu-las pequenas e tumores carcinóides, são a origem do restante da doença ACTHdependente. Na maioria dos pacientes que se apresentam com evidências clínicas e bioquímicas da SC, técnicas modernas de imagem não invasivas podem apontar acurada e eficientemente a causa e a natureza da patologia subjacente. A imagem é essencial para a determinação da fonte de ACTH na produção ectópica desse hormônio, na localização de tumores hipofisários e na distinção entre adenomas, carcinomas e hiperplasias adrenais. Nesse artigo revisaremos a imagem adrenal na SC ACTH-dependente e independente. Incluiremos, também, uma discussão sobre o uso da RM e da TC na detecção e manejo dos adenomas hipofisários secretores de ACTH. TC de tórax, abdome e pelve, com a injeção intravenosa de meio de contraste, é a modalidade de imagem mais sensível para a identificação da fonte ectópi-ca de ACTH e na detecção da patologia adrenal. A RM é empregada para a caracterização de adenomas adrenais, para a solução de problemas em casos difíceis e para a detecção de adenomas hipofisários secretores de ACTH.

Cushing’s Syndrome With Uncontrolled Hypertension, Occasional Hypokalemia, and Two Pregnancies

“…Once the diagnosis of ACTH‐independent CS is made, the next step is adrenal imaging. Hyperfunctioning adrenal adenomas, best seen on computed tomography (CT), are usually 2–7 cm, and have low or soft tissue attenuation which usually enhances with contrast 11 . Almost all are lipid rich with noncontrast CT attenuation values ≤10 Hounsfield units 11 .…”

“…Hyperfunctioning adrenal adenomas, best seen on computed tomography (CT), are usually 2–7 cm, and have low or soft tissue attenuation which usually enhances with contrast 11 . Almost all are lipid rich with noncontrast CT attenuation values ≤10 Hounsfield units 11 . MRI characteristics of adrenal adenoma are low homogenous signal on T1 weighted images and a signal intensity greater than or equal to liver on T2‐weighted images.…”

“…Adrenal carcinomas are usually 6 cm or larger with CT and MRI characteristics readily separating them from adenomas. CT characteristics used to characterize the substantial lipid content that distinguishes adrenal adenoma from carcinoma are nonenhanced CT attenuation, delayed‐enhancement CT attenuation, and percentage of contrast enhancement washout attenuation 11 . Generally CT adrenal imaging is preferred over MRI due to greater spatial resolution.…”

“…11 Almost all are lipid rich with noncontrast CT attenuation values 10 Hounsfield units. 11 MRI characteristics of adrenal adenoma are low homogenous signal on T1 weighted images and a signal intensity greater than or equal to liver on T2-weighted images. The contralateral adrenal gland as well as the involved gland external to the hyperfunctioning nodule are either normal in size or atrophic due to the prolonged absence of ACTH.…”

Rapid Recovery of Hypothalamic-Pituitary Axis after Successful Resection of an ACTH-secreting Neuroendocrine Tumor

“…First, it is sometimes difficult to biochemically differentiate ectopic ACTH syndrome from Cushing's disease (3). Second, it may not be easy to find the responsible tumors for ectopic ACTH syndrome (4). Third, the causative tumors cannot be completely removed in some patients and other therapies need to be considered to control Cushing's syndrome (5).…”