Adrenal imaging
At this time, most of the adrenal incidentalomas are detected by ultrasound, which reflects the widespread use of this technique (17). Additional imaging by CT is usually performed, as detailed characterization of an adrenal mass by ultrasound alone cannot be obtained. An exception is the highly echogenic adrenal myelolipoma, which does not need further imaging investigation. On CT, adrenal adenomas typically appear homogeneous and exhibit a density lower than water (< 15 HU) and well defined margins (20, 74, 75). A cut-off of < 2 HU was recommended to avoid overlooking a "malignoma", but this low threshold leads to many nondefinite adrenal tumors (76). Therefore, a cut-off of 10 HU (23) and 24 HU with a 14 min delay on contrast enhanced CT scan seems to be practicable to distinguish between adenomas and metastases (40). Adrenal cortical carcinomas are generally larger, inhomogeneous and show soft tissue density. Irregular margins and central necrosis or haemorrhage increase the probability of malignancy. However, benign pheochromocytoma may also present as a large inhomogeneous tumor with haemorrhage (77).
Although chemical shift MRI is commonly performed, it probably does not provide additional information beyond that which is already available on unenhanced CT. In difficult cases, MRI may be helpful to further differentiate benign from malignant adrenal tumors, although again a clear discrimination cannot be achieved (78-81). Adenomas exhibit a decreased intensity on T2-weighted MRI compared to non-adenoma. Gadolinium-enhanced dynamic studies have found strong enhancement and slow wash-out in malignant neoplasms, while adenomas showed rapid wash-out (82, 83). However, there are contrary results in the differentiation of benign and malignant lesions (84). The recently developed chemical shift MRI (CSI) is the recommended method of choice today. Benign tumors like adrenal adenomas with high lipid content demonstrate a typical signal intensity loss on chemical shift imaging relative to the liver (85). Recently a sensitivity of 91 % and specificity of 94 % was reported using CSI in comparison to histopathology (78).
Additionally, 131I-methylnorcholesterol scan was recommended as a valuable screening tool for subclinical Cushing╢s syndrome, as evidence was provided that unilateral uptake is related to functioning adenomas (86). Adrenocortical scintigraphy with NP-59 and 75Se-methylnorcholesterol has been advocated for analysis of adrenal incidentalomas (20). In malignant neoplasms the uptake of the radiotracer is decreased or missing at the tumor bearing side leading to a "discordant" pattern. Otherwise, benign adrenal adenomas typically exhibit a "concordant" pattern. In a recently published study it was concluded that morphology-functional examination of incidentaloma > 2 cm by 75Se-methylnorcholesterol seems to provide useful data about the likelihood of malignancy (87). However, some adrenal cortical carcinomas may mimic benign lesions with a "concordant" uptake. Therefore, we recommend a restriction of adrenal scintigraphy to larger (> 3 cm) nonfunctioning lesions if the HU-values in CT are above those expected for adrenal adenomas (20).
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В общем, настолько редко, что в нашем госпитале не делали такого исследования 7 лет точно. Я в нем 7 лет работаю.
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