ADRENAL GLANDS PATHOLOGY SCANNING

THE ADRENAL GLANDS
Normal appearances
The normal adrenal glands can be seen on ultrasound in the vast majority of patients, if you know where and how to look. Each adrenal gland is constructed with a central fold or ridge, which points anteromedially, from which extend two thin ‘wings’ of tissue—a medial and a lateral wing. The ultrasound appearances are therefore of a < shape in LS, or a thin, linear structure as the transducer is moved medially towards the central ridge. The wings of the gland appear hypoechoic and are no more than 2 mm in thickness.

Ultrasound technique
For the right adrenal, use the liver as an acoustic window. Scan the upper pole of the kidney intercostally through the liver, and angle slightly medially to the kidney, where the gland can be located between the liver and the diaphragmatic crus. Continue angling slightly medially towards the IVC and the central ridge of the gland is seen behind the IVC. For the left gland the spleen must be used as a window. To avoid overlying bowel this is best achieved with the patient supine, using a coronal section. When the upper pole of the left kidney is located through the spleen, the left adrenal can be seen in the small triangular area between the spleen, kidney and diaphragmatic crus.

Pathology of the adrenal glands
Adenoma
Small (less than 3 cm) solid adrenal nodules are a common, incidental finding in non-symptomatic patients. Benign, non-hyperfunctioning adenomas account for the majority of adrenal nodules, and are of no clinical significance. Their incidence increases with age and they are present in around 2% of adult autopsies. Small nodules in asymptomatic patients generally require no further action, but endocrine function may be evaluated to rule out a functioning mass. A hyperfunctioning adenoma (a determination made by evaluation of the endocrine function), although an essentially benign mass, usually requires surgical resection. As a solitary abdominal finding in a patient with no relevant clinical history, it is generally safe to assume a small adrenal nodule requires no further action. However, because it is not possible to distinguish benign, incidental nodules from other forms of more serious pathology, incidental nodules of greater than 4 cm should be investigated further to confirm their benign nature. Non-functioning adenomas will remain stable in size on ultrasound follow-up.

Metastasis
The adrenal glands are a common site for metastases, particularly from lung, breast and bowel cancer. Although frequently accompanied by liver metastases, they may be present in the absence of any other obvious abdominal deposits, and therefore the adrenal glands should routinely be examined when staging malignant disease. The adrenal glands are also commonly involved in non-Hodgkin’s lymphoma. Like adenomas, they are often small, welldefined and hypoechoic on ultrasound. It is not possible to differentiate between benign adenoma and metastasis on the ultrasound appearances alone, but a small adrenal mass in the absence of a known primary carcinoma is likely to be benign, and will remain stable on follow-up. A solitary adrenal mass in the presence of known carcinoma requires biopsy for diagnosis.

Adrenal cysts
Simple cysts are uncommon in the adrenal gland, but are easily differentiated from solid lesions with ultrasound. Some cysts may be the sequelae of previous haemorrhage, but most are simple, epithelial cysts.

Myelolipoma
The adrenal myelolipoma is found, uncommonly, as an incidental mass. It is highly echogenic and well-defined, due to its fatty content. These are relatively rare, require no further management, and are endocrinologically nonfunctioning.

Phaeochromocytoma
The phaeochromocytoma is uncommon, but may be found in up to 1% of patients with hypertension. It is a tumour arising in the chromaffin cells of the adrenal medulla (most commonly) or in autonomic nervous tissue. It may be bilateral and appears solid on ultrasound, although larger masses may have areas of necrosis within them. Most are benign, but 5–10% are malignant. It presents on a background of episodic, severe hypertension and the urine contains catecholamines. (Although this is also a feature of adrenal neuroblastoma, the latter is predominantly a childhood tumour.) These lesions should be treated with great care—vigorous palpation may precipitate a severe hypertensive episode and biopsy should therefore be avoided. Although most phaeochromocytomas arise in the adrenal glands, and are therefore demonstrable on ultrasound, those arising in the sympathetic chain may be obscured by bowel gas and are not possible to exclude on ultrasound. If there remains biochemical evidence of phaeochromocytoma in the presence of normal adrenal glands, a Meta-Iodobenzylguanidine isotope scan will demonstrate increased activity in a phaeochromocytoma and CT scan can then be targeted to the appropriate area. Phaeochromocytomas are also associated with von Hippel–Lindau syndrome.

Adrenal carcinoma
Primary adrenal carcinomas are rare in the adult. They are commonly endocrinologically inactive in adults, and therefore tend to present late when they are quite large. They may invade the IVC and metastasize to the liver. Surgical removal of tumours in the absence of liver metastases has a good prognosis and, in patients with metastases, radiofrequency ablation of the adrenal mass may have some benefit in prolonging survival.