MR of an adrenal pseudocyst

MR imaging of the adrenal glands

MR imaging is used commonly for imaging the adrenal glands. Its high-contrast resolution and multiplanar imaging capability enables the detection and characterization of many adrenal masses. The advent of chemical-shift imaging revolutionized the role of MR imaging in characterizing adrenal masses. In this article, the authors discuss the range of MR appearances of common and uncommon adrenal masses, focusing on the nonfunctioning incidentally discovered mass and its characterization methods. MR imaging is continuously improving. The increasing use of higher strength magnets and the introduction of newer coils, sequences, and techniques will help detect and characterize very small adrenal masses, quantify their fat content, and provide exquisite morphologic images of the gland and its vascular supply.

Imaging of adrenal masses

Adrenal pathology may be discussed based on hormonal functionality of the adrenals, appearances on imaging modality, or pathological determination. There are three main categories of adrenal function. Hyperfunctional states include Conn's or Cushing's syndrome. Lesions with normal function may be detected incidentally. Hypofunctional states may occur from idiopathic Addison's disease or some bilateral adrenal pathology. The most common modalities for characterization of adrenal pathology are non-enhanced CT, often followed by contrast CT or chemical shift MRI. The common appearance on non-enhanced CT is a well-defined homogeneous lesion with low-density due to the microscopic fat present and adrenal adenomas. When density criteria are not met, many of these may be characterized as adenomas by washed out of contrast or signal decrease using in phase and out-of-phase MRI sequences. Other non-invasive modalities may incidentally discover adrenal lesions, but are not typically used in the work-up. NP-59 is an uncommonly used nuclear medicine technique which is very specific for adenoma when correlated with pathology on other imaging studies. In the rare cases where non-invasive imaging is non-specific, fine needle aspiration or core biopsies may be necessary. However, biopsies have associated risks including infection and hemorrhage. The imaging appearance of an adrenal lesion is often specific such that further imaging is not necessary. These lesions include adrenal adenoma, pheochromocytoma, myelolipoma, adrenal cyst, and some large adrenocortical carcinomas. However, the findings in lesions such as metastasis, smaller primary adrenal carcinomas, lymphoma, granulomatous disease, and many adenomas are not as specific. In the proper clinical situation, follow-up imaging may be necessary, or biopsy may be warranted.

Management of Adrenal Cysts

Adrenal cysts have been traditionally managed by excision to rule out malignancy. We reviewed the 613 cases of adrenal cysts (including 6 new cases of our own) to evaluate whether this is still appropriate. Descriptive statistics and distribution of each pathologic type have been updated, based on 515 cases, and have changed from statistics compiled on 155 cases by G. A. Absehouse et al. Only seven per cent of all adrenal cysts are malignant or potentially malignant. There is only one reported case of a malignancy found in a nonfunctioning adrenal cyst that was initially thought to be benign. In this case, no CT or aspiration was performed. There have been 19 cases of adrenal cysts managed with aspiration. All were nonfunctioning and benign. One had a bloody aspirate. Reaccumulation occurred in 32 per cent of the cases (six cases); six per cent were symptomatic, four per cent were excised. Follow up was available in 15 cases from 4 months to 3.5 years. Management of the patient with a suspected adrenal cyst should include a careful history and physical and biochemical screening to rule out a functioning lesion. A CT scan, and aspiration of the cyst with a cystogram should be performed to confirm a simple cyst of the adrenal. If the suspicion of malignancy is low, and the lesion is nonfunctional, the adrenal cyst may be managed by aspiration alone. If the cyst recurs and is asymptomatic, it may be observed. If a symptomatic cyst recurs, it may be reaspirated or excised.

MR imaging of the adrenal glands and kidneys

MR imaging of the adrenal glands and kidneys can completely and accurately assess these organs for a variety of abnormalities. One of the major strengths of MR imaging of the adrenal glands is the ability of chemical shift imaging to determine the presence of intracellular lipid, thus enabling distinction of benign adrenal adenomas from other adrenal masses. The multiplanar imaging capability of MR can assist in determining the origin of large retroperitoneal masses. MR imaging of the kidneys has many applications, including staging of renal cell carcinomas and evaluating the renal vasculature. Gadolinium is a safe and non-nephrotoxic contrast agent that can be used to evaluate the kidneys in patients with renal compromise. The many advances and current research being performed in the rapidly expanding field of abdominal MR make performing these cases both exciting and challenging.