tailieunhanh - Handbook of Diagnostic Endocrinology - part 4

Do kích thước hiện lâm sàng, hầu hết các khối u trong tuyến thượng thận có thể dễ dàng chụp CT hoặc MRI. Các tác nhân tương phản là không cần thiết để hình dung những khối u này do kích thước của chúng | 98 Lawrence and Dluhy Fig. 2. See Table 1. Ộ Recumbent levels. See Text for details. From Endocrine Hypertension Harwood Specialist in Medicine Endocrinology in Clinical Practice P. Harris Ed. Harwood Academic Publishers Reading United Kingdom with permission. pericardium or bladder. These tumors may be localized by conventional imaging magnetic resonance imaging MRI CT or by scintigraphic techniques iodine-labeled meta-iodobenzyl guanidine MIBG or octreotide scintigra Chapter 5 Endocrine Hypertension 99 phy . Due to the size at clinical presentation most intra-adrenal tumors are easily imaged by CT or MRI. Contrast agents are unnecessary to visualize these tumors due to their size and in fact should be avoided since they may precipitate a hypertensive crisis. MRI is particularly useful for identifying paragangliomas especially outside of the abdomen such as intracardiac tumors. On T2-weighted imaging the tumor is usually 3x as intense as liver and on T1-weighted images the tumor is usually iso-intense with the liver. With in-and-out of phasing MRI techniques for determination of fat content pheochromocytomas can usually be distinguished from lipid-laden cortical adenomas so-called incidentilomas . However these radiographic characteristics are not always met and the pheochromocytomas may appear indistinguishable from other adrenal tumors. MIBG has chemical similarities to norepinephrine and therefore concentrates within intracellular storage granules of catecholamine-secreting tissues 37 . Imaging with MIBG is especially useful for localization of extra-adrenal pheochromocytoma and for diagnosing metastatic lesions. Its sensitivity is reported to be greater than 90 with a specificity of 100 38 39 . MIBG labeled with 123I is the preferred isotope since it is considered to provide greater sensitivity. Thyroid uptake should be blocked with iodine prior to administration of the iodine-labeled MIBG. Medicines that might interfere with catecholamine processing should be