Richard I. G. Holt - Essential Endocrinology and Diabetes

Figure 4.8 Magnetic resonance imaging of a pituitary tumour. (a) T1‐weighted sagittal image. (b) T2‐weighted sagittal image (cerebrospinal fluid appears white). (c) T1‐weighted frontal image. A large irregularly shaped pituitary tumour (*) has compressed the pituitary stalk (not visible) and raised and tilted the optic chiasm (large arrow) such that it appears draped on top of the tumour sloping down to the right. The tumour has also extended bilaterally into the cavernous sinus to encase partially the internal carotid arteries (small arrow marks the right internal carotid artery).

Figure 4.9 mIBG uptake by a phaeochromocytoma. A whole‐body I 123mIBG scan with imaging from the front and back shows a right phaeochromocytoma with pulmonary and bony metastases. This imaging is helpful to investigate potential metastatic disease prior to adrenalectomy.

Image kindly provided by Dr Val Lewington, Royal Marsden Hospital.

Positron emission tomography (PET) is a form of functional imaging which is widely used to assess metabolism in neoplasia and allows the identification of tumours that may be overlooked by conventional imaging. Cancer cells often have accelerated glucose metabolism and more readily take up glucose than surrounding healthy cells. This process can be visualized by using the radiotracer is 2‐[18F] fluoro‐2‐deoxyglucose [( 18F)‐FDG] which crosses the cell membrane and is phosphorylated to become FDG‐6‐phosphate. This is resistant to further metabolic processes and can be imaged. When the kinetic energy of [( 18F)‐FDG] is dispersed as a positron, this particle travels a short distance and interacts with an electron to release two photons which can be detected by a pair of detectors located on opposite sides of the patient. PET images are obtained simultaneously with CT images to match metabolic changes to specific anatomy.

A number of hormone precursors and amino acids are labelled with 11C and used successfully in the management of parathyroid, adrenal and pituitary tumours but the short‐life of these tracers have limited the clinical application. Newer tracers with longer half‐lives, such as Gallium‐68, are now being applied to neuroendocrine tumours, including phaeochromocytoma.

Diagnosing or excluding endocrine disorders relies on measuring the concentration of hormones and metabolites

Immunoassays provide accurate, reliable laboratory measurement of many hormones and metabolites

Techniques involving mass spectrometry are increasingly being used to measure hormones and metabolites

Cellular and molecular biology can increasingly provide patient‐specific diagnoses of congenital disorders or endocrine neoplasia syndromes; this information can predict and influence patient outcome and management

Imaging investigations localize endocrine disorders and assist surgical intervention

‘Incidentalomas’ are common and conscientious effort is needed to correlate a biochemical endocrine abnormality to a tumour identified on imaging

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