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Journal of Endocrinology & Metabolism

Case Report

Volume 4, Number 5-6, December 2014, pages 148-150

Myelolipomatous Adrenal Adenoma and Adrenal Scintigraphy: A Case Presentation and Review of Literature

Adrenal scintigraphy (with ¹³¹I-6beta-iodomethyl-19-norcholesterol) is seldom used in clinical practice in the US. However, there are certain circumstances where it might be helpful especially when there is a suspicion for subclinical Cushing’s. We present a case and review of literature about the use of adrenal scintigraphy.

A 66-year-old woman presented with an adrenal incidentaloma found during a regular abdominal ultrasound. Her medical history included severe obesity (BMI 38.6), type 2 diabetes treated with insulin, resistant arterial hypertension, coronary artery disease (history of placement of coronary stents) and chronic congestive heart failure. Complete hormonal workup found subclinical (ACTH independent) Cushing’s syndrome: labs showed an elevated 24 h urine free cortisol (85 nmol/24 h), suppressed ACTH (< 1 pmol/L) with an absence of cortisol suppression (113 nmol/L, N < 50) after 2 mg dexamethasone suppression test with DHEA of 0.2 µmol/L (normal range 0.26 - 6.68).

Abdominal CT and MRI scan showed a 6.5 cm right adrenal mass containing soft tissue, calcifications and macroscopic fat with no loss of signal intensity in the out-of-phase image(s) in the MRI (Fig. 1). A diagnosis of myelolipoma was made by radiology. This could not explain the source of elevated serum cortisol since myelolipoma is seldom hormonally active.

Figure 1. (A) Heterogenous signal on MRI. Fatty content areas with high T2 signal (upper left) and low T2 fat sat signal (upper right). (B) Absence of loss of signal intensity on out-of-phase T1 images (right image) compared to in-phase T1 images (left image), suggesting that there was no intracellular fat. (C) Unilateral uptake visible on 131I-19-iodocholesterol (planar static image, posterior view, SPECT and CT fusion image: small image) which was consistent with a cortisol-secreting adrenocortical tumor. (D) Islands of adrenal tumoral cells admixed with fatty and fibrous territories as well as hemorrhagic areas. Higher magnification showing details of the myeloid tissue with characteristic megakaryocytes (hematoxylin-eosin stain × 400).

Adrenal cortex scintigraphy with ¹³¹I-6beta-iodomethyl-19-norcholesterol (NP-59) without dexamethasone premedication showed a unilateral tracer uptake (Fig. 1).

A laparoscopic adrenalectomy was performed. Histological examination confirmed the diagnosis of myelolipomatous adrenocortical adenoma, a rare but not uncommon condition (Fig. 1). The patient had significant clinical improvement post-adrenalectomy.

Some of the common adrenal neoplasm(s) encountered in clinical practice include benign adrenal adenoma, pheochromocytoma, myelolipoma, adrenal lymphomas and metastasis to adrenal glands from primary malignancies [1]. The imaging of the adrenal glands usually relies on lipid-sensitive techniques. An unenhanced CT of lipid rich tumors (which are mostly benign and non-functional) usually show a Hounsfield units (HFU) less than or equal to 10 while MRI shows signal loss on opposed-phase compared to in-phase T1-weighted images [1]. Positron emission tomography (PET) with fluorine-18 deoxyglucose (FDG) may sometimes be used to distinguish between benign (low PET uptake) from malignant adrenal mass (high PET uptake) [2].

Adrenal myelolipomas are usually benign and non-functioning masses that have adipose tissue and hematopoietic elements [3]. However, they may be indistinguishable from an adrenocortical adenoma with widespread myelolipomatous metaplasia through conventional imaging techniques like CT and MRI, and these tumors may be responsible for Cushing’s syndrome [3]. In our case, adrenal scintigraphy was used to demonstrate an increased uptake in an otherwise benign looking adrenal myelolipoma on CT and MRI that turned out to be a functioning adrenal myelolipomatous adenoma.

There have been other reports in the literature describing the histopathology of the myelolipomatous adenomas: these lesions have sheets of adrenocortical cells with large areas of mature adipose tissue and infiltrating band of stromal small cells [4]. Rarely, extensive lipomatous metaplasia with myxoid change may be seen in an adrenocortical carcinoma [5].

On the other hand, rarely adreno myelolipoma may also cause increased uptake in FDG-PET suggesting some form of malignancy [6].

Adrenal scintigraphy with NP-59 (with concomitant SPECT/CT) is an imaging technique that can help in distinguishing between aldosterone-producing adenoma (APA) and idiopathic adrenal hyperplasia (IAH) [7]. The technique is particularly suited if adrenal vein sampling (AVS) is inconclusive [7].

In a most recent retrospective chart review done at a single center, it was seen that adrenal cortical scintigraphy positivity was highly predictive in determining the outcome of subclinical Cushing’s [8]. Adrenal scintigraphy had an accuracy of 93.7% for predicting post-operative hypoadrenalism in persons who had surgical resection [8]. In medically treated persons, a positive test was associated with worsening hyperglycemia and diastolic blood pressure [8].

Myelolipomatous adrenal adenoma (that may mimic adrenal myelolipoma on conventional imaging) may be a rare cause of subclinical Cushing’s, and adrenal scintigraphy may be a useful imaging technique that may help in localizing the lesion, that can then be treated surgically.

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Journal of Endocrinology and Metabolism is published by Elmer Press Inc.