Is there a future for adrenal scintigraphy?

Nuclear medicine imaging in the evaluation of endocrine hypertension

Endocrine hypertension forms a small (< 5%) but curable subset of patients with hypertension. Common endocrine causes of hypertension include pheochromocytoma, Cushing's syndrome, primary hyperaldosteronism, and thyroid disorders. Nuclear medicine imaging plays an important role in evaluation of patients with endocrine hypertension. It has established role in patients of pheochromocytoma/paraganglioma, Cushing's syndrome, aldosteronism, and thyroid disorders. We present a brief overview of role of nuclear medicine imaging in endocrine hypertension. Development of newer radiotracers might further broaden the role of nuclear medicine in these patients.

6-Deoxy-6-[131I]iodo-L-ascorbic acid for the in vivo study of ascorbate: autoradiography, biodistribution in normal and hypolipidemic rats, and in tumor-bearing nude mice

Normal female rat distribution studies showed high and specific uptake of 6-deoxy-6-[(131)I]iodo-L-ascorbic acid (6-(131)IAsA) into the adrenal glands, known to highly express the ascorbate sodium-dependent vitamin C transporter-2 (SVCT-2), and the adrenal gland was clearly visualized by whole-body autoradiography. Preinjection of sulfinpyrazone, a known blocker of ascorbate transport, with 6-(131)IAsA resulted in decreased uptake of radioactivity in rat adrenal glands compared to the control group, seemingly illustrating the participation of the SVCT transporter (probably the SVCT-2 subtype) in the uptake process in vivo. 4-Aminopyrazolo[3,4-d]pyrimidine-induced hypolipidemic rats showed a 1.7-fold increase in adrenal uptake of radioactivity at 30 min postinjection of 6-(131)IAsA, compared to the control, with increased adrenal-to-liver and adrenal-to-kidney ratios. To further characterize 6-(131)IAsA for its tumor uptake properties, biodistribution studies were also performed using male nude mice implanted with either Y-1 adrenocortical tumor cells or adrenal medulla-derived PC12 cells. None of these tumors exhibited relevant uptake of 6-(131)IAsA while normal adrenal glands showed high uptake of radioactivity, suggesting that these tumors in this model have only a poor transport capacity for this agent. The present study demonstrates that the use of radioiodinated 6-IAsA may help to obtain information about functional alterations in diseased adrenal glands, but it does not exhibit desirable properties as a tumor-seeking agent for ascorbic acid bioactivity.

Contemporary adrenal scintigraphy

INTRODUCTION

High-resolution computed tomography (CT) and magnetic resonance (MR) imaging have replaced scintigraphy as primary imaging modalities for the evaluation of adrenal diseases.

DISCUSSION

Thin-slice CT, CT contrast washout studies and MR pulse sequences specifically designed to identify adrenal lipid content have radically changed the approach to anatomic imaging and provide unique insight into the physical characteristics of the adrenals. With a confirmed biochemical diagnosis, further evaluation is often unnecessary, especially in diagnostic localization of diseases of the adrenal cortex. However, despite the exquisite detail afforded by anatomy-based imaging, there are not infrequently clinical situations in which the functional insight provided by scintigraphy is crucial to identify adrenal dysfunction and to assist in localization of adrenocortical and adrenomedullary disease. The introduction of hybrid PET/CT and SPECT/CT, modalities that directly integrate anatomic and functional information, redefine the radiotracer principle in the larger context of high-resolution anatomic imaging. Instead of becoming obsolete, scintigraphy is an element of a device that combines it with CT or MR to allow a direct correlation between function and anatomy, whereby the combination creates a more powerful diagnostic tool than the separate component modalities.

Adrenal Gland Scintigraphy

There is no question that high-resolution imaging techniques have revolutionized the approach to diagnostic imaging. Computed tomography (CT) and magnetic resonance imaging provide exquisite images of the adrenal glands and offer the best initial imaging approach in the evaluation of patients with suspected adrenal disease. However, an assessment of anatomy is only a portion of the diagnostic effort, which begins with a biochemical evaluation to establish the presence of adrenal gland dysfunction. With a confirmed biochemical diagnosis in hand, a logical and stepwise diagnostic approach can be tailored to a particular patient. Where scintigraphy fits in the evaluation of diseases of the adrenal cortex and medulla in the context of high-resolution imaging and which radiopharmaceuticals should be deployed has changed substantially during the last 2 decades. Adrenal functional imaging has evolved from classic planar scintigraphy to single-photon emission computed tomography (SPECT) and positron emission tomography (PET) using tracers that, by targeting specific metabolic or synthetic processes within the gland, have depicted adrenal pathophysiology. New PET/CT and SPECT/CT technologies integrate anatomic and functional information and redefine the radiotracer principle in the larger context of high resolution anatomic imaging.

A comprehensive approach to adrenal incidentalomas

Improvements in abdominal imaging techniques have increased the detection of clinically inapparent adrenal masses, or incidentalomas (AI), the appropriate diagnosis and management of which have become a common clinical problem for health care professionals. Once an adrenal mass has been detected, the clinician needs to address two questions: 1) is the tumor hormonally active? and 2) is there any chance of the mass being malignant? The majority of AI is non-hypersecretory cortical adenomas, but an endocrine evaluation can lead to the identification of subtle hormone excess. An overnight low-dose dexamethasone suppression test, fractionated urinary or plasma metanephrine assay and, in hypertensive patients, establishing the upright plasma aldosterone/plasma renin activity ratio are recommended as preliminary screening steps. Masses greater than 4cm are at greater risk of malignancy. Morphological imaging features may be helpful in the distinction between benign and malignant forms. Fine-needle aspiration biopsy is an important tool in the evaluation of oncological patients to establish any metastatic disease. Adrenalectomy is indicated by evidence of a functional adrenal mass, or a suspected malignant form. We advocate adrenalectomy of subtle hypercortisolism, especially in the presence of hypertension, obesity, diabetes or osteoporosis potentially aggravated by glucocorticoid excess. A close follow-up is needed, particularly in the first year after diagnosis.

[Contribution of the scintigraphy with iodocholesterol (I-COL) to the diagnosis and characterization of silent adrenal masses]

OBJECTIVE

To assess the role of the adrenal cortical scintigraphy with 131-I Norcholesterol (I-COL) in the diagnosis and characterization of silent adrenal masses.

METHODS

We selected 57 patients who underwent an adrenal scintigraphy with I-COL, 36 women and 21 men (mean aged: 62.5 years), and who were classified into two groups: Group I or Incidentalomas, 39 patients without signs or symptoms of adrenal disease in whom an adrenal mass is incidentally discovered during a CT or ultrasound scan; and a second group or Group II, 18 patients with history of cancer in whom an adrenal mass is discovered. We defined the following Scintigraphic patterns in relationship with the CT: Normal, concordant unilateral (CU) or exclusive; discordant unilateral (DU); concordant asymmetrical (CA) or prevalent; discordant asymmetrical (DA) and nonvisualization (NV). The final diagnosis was obtained with clinical, analytical, and radiological evaluation and in some cases surgery.

RESULTS

In Group I, the diagnoses were: 17 adrenal masses without criteria of malignancy or hormonal overproduction (the Scintigraphic patterns were 10 CA, 5 normal and 2 CU), 9 Subclinical Cushing's syndrome (4 CU, 4 CA and 1 normal), 5 adenomas (all CU), 3 adrenal primary carcinomas, with no uptake in the scintigraphy, and 5 were other diagnoses. In group II, 14 patients had benign masses (all patterns were normal or concordant) and 4 patients metastases (3 discordant and 1 NV patterns). The follow-up time was at least one year.

CONCLUSIONS

The adrenal cortical scintigraphy with I-COL provides us information on the functional status of silent adrenal masses and it is an useful tool to distinguish benign from malignant lesions; for this reason we considered that it must be integrated in the diagnostic algorithm as a complement to other techniques.

The clinically inapparent adrenal mass: update in diagnosis and management

Clinically inapparent adrenal masses are incidentally detected after imaging studies conducted for reasons other than the evaluation of the adrenal glands. They have frequently been referred to as adrenal incidentalomas. In preparation for a National Institutes of Health State-of-the-Science Conference on this topic, extensive literature research, including Medline, BIOSIS, and Embase between 1966 and July 2002, as well as references of published metaanalyses and selected review articles identified more than 5400 citations. Based on 699 articles that were retrieved for further examination, we provide a comprehensive update of the diagnostic and therapeutic approaches focusing on endocrine and radiological features as well as surgical options. In addition, we present recent developments in the discovery of tumor markers, endocrine testing for subclinical disease including autonomous glucocorticoid hypersecretion and silent pheochromocytoma, novel imaging techniques, and minimally invasive surgery. Based on the statements of the conference, the available literature, and ongoing studies, our aim is to provide practical recommendations for the management of this common entity and to highlight areas for future studies and research.