Читать книгу Essential Endocrinology and Diabetes - Richard I. G. Holt - Страница 102

Simple X‐rays, CT and MRI depict tissues and organs but provide limited insight into the cells that compose these structures or their function. In later life, many organs develop benign tumours of little or no significance. For instance, incidental adrenal tumours (incidentalomas) can affect ∼5% of the population after ∼40 years. In a person with hypertension, it would be important to distinguish these from a phaeochromocytoma that could be the curable cause of elevated blood pressure (Chapter 6). Uptake markers (or ‘tracers’) specific to a particular cell type can provide valuable clues. For instance, meta‐iodobenzylguanidine (mIBG) acts as an analogue of norepinephrine and is taken up by adrenal medulla cells. When labelled with radioactive iodine‐123 (I¹²³) it can be used to distinguish a phaeochromocytoma from other tumours (Figure 4.9). At higher doses, it can even be used as targeted therapy, when instead of marking cells, it kills them. I¹²³ or technetium‐99m pertechnetate can also be used to delineate different causes of hyperthyroidism (Chapter 8) when taken up by the thyroid gland. In Graves disease, the uptake is homogeneous; with a solitary ‘toxic’ adenoma, the uptake is restricted to the relevant nodule.

Figure 4.6 Ultrasound of a polycystic ovary. The presence of multiple small cysts (one shown by the arrow) is consistent with, but not required for, the diagnosis of polycystic ovarian syndrome (Chapter 7). Ultrasound does help to exclude the single mass of an androgen‐secreting tumour (Chapter 7).

Image kindly provided by Dr Sue Ingamells, University of Southampton.

Figure 4.7 Abdominal computed tomography (CT) with contrast. This patient presented with Cushing syndrome (see Figure 6.9). The right adrenal mass on the CT (arrow) was a cortisol‐secreting adenoma.

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 I¹²³ mIBG 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.