Endoscopic Ultrasound Imaging of the Adrenals

Introduction

Endoscopic ultrasound (EUS) imaging of the adrenal glands and the systematic use of EUS imaging in the diagnosis of adrenal diseases have been frequently described since the initial report in 1996 [1] [2] [3] [4] [5] [6] [7] [8] [9]. The present article aims to provide an overview of the technique and procedure of endoscopic ultrasound imaging of the adrenals, illustrating typical findings and discussing the clinical indications for adrenal EUS.

EUS imaging of the adrenals is carried out using an endosonoscope with a longitudinal transducer. Imaging of the left adrenal gland (with the patient lying supine and at a setting of 7.5 MHz) is carried out from the proximal stomach. The anatomic landmarks are the cranial pole of the left kidney, the distal tail of the pancreas, and the splenic vessels (Figure [1], [2]). For imaging of the right adrenal (with the patient lying on the right side and at a setting of 5 MHz), the transducer has to be placed in the antrum just in front of the pylorus, and is completely flexed toward the right. The anatomic landmarks are the cranial pole of the right kidney, the inferior vena cava, the caudal parts of the liver, and the portal vein (Figure [3], [4]). The resolution makes it possible to distinguish the echoes generated by the adrenal medulla and the cortex (Figure [5]).

Figure 1 Endoscopic ultrasound imaging of the left adrenal gland. The patient is lying supine, the transducer is positioned in a craniocaudal direction, and the sound is directed dorsally.

Figure 2 A normal left adrenal gland. The landmarks in this image are the tail of the pancreas and the splenic vein.

Figure 3 Endosonographic imaging of the right adrenal gland. The patient is lying on the right side, the transducer is positioned in the prepyloric region in a right cranial direction, the sound is directed dorsally.

Figure 4 A normal right adrenal gland. The landmarks in this image are the most caudal parts of the liver and the inferior vena cava.

Figure 5 Distinguishing between the echoes generated by the medulla and the cortex in a normal left adrenal gland (normal findings).

EUS of the adrenal glands can contribute to the diagnostic work-up in the sets of conditions and circumstances described below.

Detection of small adrenal tumors. EUS of the adrenal glands now makes it possible to detect morphological abnormalities such as nodular formations in the adrenal glands down to a diameter of about 3 mm. Characterization of adrenal tumors. Nodular hyperplasia of the adrenal glands can be differentiated from solitary adenoma on the basis of its morphology (round or oval shape) and detection of a capsular border to the normal adrenal tissue. This may be an important piece of information in the differential diagnosis of primary hyperaldosteronism and adrenocorticotropic hormone-independent Cushing syndrome. If the adrenals are enlarged, it is also possible to identify lipid-containing tumors such as myelolipoma, due to their strong echogenicity. Criteria for assessing malignancy in adrenal tumors. Preoperative detection of signs suggesting malignancy in adrenal masses may be relevant when planning the surgical strategy. Adrenocortical carcinomas are generally heterogeneous, with a complex echo structure, but malignant and benign pheochromocytomas can also have similar characteristics. Heterogeneity in an adrenal tumor is thus not a clear criterion for malignancy. EUS can demonstrate or exclude infiltration of neighboring organs as a valid criterion for malignancy. In addition, the detection of effusions, local or regional lymph-node metastases, and vascular invasion is suggestive of malignancy. Early detection of recurrences of malignant adrenal tumors. In the postoperative care of patients with adrenocortical carcinomas and pheochromocytomas, EUS may make it possible to detect small recurrences in the tumor area and in neighboring regions earlier than with other techniques. Preoperative identification of morphologically normal parts of the adrenals. Bilateral adrenal masses may be detected in patients with genetically caused diseases such as the multiple endocrine neoplasias. These patients are often young. If there is hormonal activity, it is very important to know preoperatively whether there are any parts of an adrenal gland that are morphologically completely normal and can be left in situ in order to avoid lifelong substitution treatment with adrenal steroid hormones in these patients. Detection of extra-adrenal/ectopic masses (pheochromocytoma). Pheochromocytomas may be ectopic and can be found either in a para-adrenal location or in other regions of the body. EUS may make it possible to locate the lesions in these circumstances. Differentiation between different entities causing adrenal insufficiency. Different diseases causing adrenocortical insufficiency have typical morphologies, which can be detected by EUS. EUS-guided fine-needle aspiration biopsy. EUS makes it possible to take ultrasound-guided fine-needle aspiration biopsies of the adrenal glands 10 11 12. Biopsy of an adrenal mass makes it possible to distinguish between adrenal tissue and nonadrenal tissue - i. e., in particular, to detect metastases or lymphomas, or both. However, it is not possible to distinguish between adrenocortical adenoma and adrenocortical carcinoma using fine-needle aspiration biopsy, and this is therefore not an indication for biopsy. Due to complications reported in the literature caused by mechanical manipulations of pheochromocytomas, fine-needle aspiration biopsy of adrenal masses should not be carried out unless pheochromocytoma has been excluded 13.

EUS imaging of the adrenal glands has developed from an experimental approach into an established diagnostic procedure and provides a level of resolution that cannot be obtained with any other diagnostic procedure that can be used in vivo. When EUS is conducted by an experienced investigator after the patient has received appropriate premedication, it is a low risk procedure for the patient [14] [15] and may reveal important information that can influence the further diagnostic and therapeutic strategy. However, as in all other invasive diagnostic procedures, EUS imaging of the adrenal glands requires clear indications and should be restricted to patients in whom the procedure is considered likely to have an impact on the further diagnostic and therapeutic strategy. Prospective clinical studies on this topic are clearly needed.

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