Adrenal gland metastasis is secondary to disseminated or invaded tumor from another primary malignant lesion. On account of the excellent vasculature in the adrenal gland, it is a common site of metastases rendering incidental findings of lesions in this organ very frequent.
Adrenal gland metastases are found in every other suspected mass lesion of the adrenal gland, most of them are incidental during a radiologic examination of the abdominal cavity. In such cases, the adrenal masses are called incidentalomas [1]. Most common primary sites of adrenal gland metastasis are as follows: lung, breast, kidney, gastrointestinal tract, melanoma, and thyroid gland malignant lesions [1] [2]. A thorough evaluation of these sites is significant in identifying the cause of malignancy. Metastases occur bilaterally in a typical case but can also be unilateral with the mass being smaller in size [3].
Patient's symptoms are due to a mass lesion in the abdominal cavity i.e. chronic pain that is dull and aching in character. The pain usually does not radiate to other anatomical structures and is not provoked or alleviated by any factors.
On examination physicians encounter sensitive, palpable masses in the abdominal cavity. Inspection of other organs may be specific to primary lesions. Nonspecific findings are seen if these lesions remain asymptomatic [4]. Furthermore, patients can exhibit signs of adrenal insufficiency, but such cases are rarely documented. Adrenal insufficiency manifests as hyperpigmentation of the skin (due to high adrenocorticotropic hormone (ACTH) levels), a decrease in blood pressure which can cause serious complications i.e. shock, electrolyte disturbances and reduced blood glucose levels [5].
Adrenal gland metastasis can be identified with magnetic resonance imaging (MRI). The tumors are actively enhanced with contrast, appearing hypointense during T1-weighted imaging and hyperintense in T2 weighted imaging. Likewise, delayed washout is a characteristic of malignant lesions [3].
Fine needle aspiration (FNA) of the possible metastasis can be effective in identifying the primary cause of malignancy. FNA also makes it possible to differentiate between different types of primary adrenal tumors, if adrenal carcinoma is suspected. Although, use of this method is not preferred due to its low accuracy [3].
Ultrasonography of the abdominal cavity is highly sensitive in diagnosing the lesion in neonates and very young children. Adult adrenal glands are hard to identify because of the close visual similarity to fatty tissues which is abundant in the retroperitoneum. Hence, ultrasound results are highly dependent on the experience of a physician and technical aspects of the ultrasonography machine [6]. If lesions are found, a further referral to CT, MRI or PET scan is essential to confirm the diagnosis.
Computer tomography (CT) scans provide the same accuracy as MRI imaging. A contrast enhancement is also used with this method. Nevertheless, radiologic imaging has to be interpreted with caution, because washout nature in benign tumors can resemble hypervascular hepatocellular carcinoma or renal cell carcinoma [7].
For greater accuracy in differentiating benign and malignant adrenal lesions, a positron emission tomography (PET) scan is advisable. Its sensitivity score is as high as 97% and specificity is 91% [8]. Fludeoxyglucose (FDG) is a standard radiotracer used with PET method when handling cancer patients. Adrenal metastases are associated with a high uptake much of this tracer, appearing as enhancing lesions [9]. Physical characteristics include size (metastases typically exceed 4-6 cm in diameter), uneven borders, signs of necrosis and invasion into contiguous anatomical structures. Also, a metastatic lesion can be suspected if the patient has a known primary tumor [10].