Diagnostic value of 11C-metomidate Positron Emission Tomography/Computerized Tomography (PET/CT) for the evaluation of primary aldosteronism: a pilot study

Primary aldosteronism (PA) is a relatively common secondary cause of
hypertension. PA is usually due to either bilateral adrenal hyperplasia (BAH)
or an aldosterone producing adrenal adenoma (APA) or primary unilateral adrenal
hyperplasia (PAH). The recommended treatment for BAH is antihypertensive
medication, whereas APA and PAH can be cured in many cases by unilateral
adrenalectomy. Thus, it is of clinical importance to differentiate correctly
between BAH and APA/PAH. Current guidelines recommend adrenal venous sampling
(AVS) as the gold standard for the differentiation between BAH and APA/PAH in
every patient with PA who is a candidate for surgery. However, AVS is an
invasive diagnostic test and is therefore not without risks. Moreover, AVS
requires an experienced radiologist, and is time-consuming and expensive.
Therefore, there is an urgent need for a safer, faster and less expensive
diagnostic test which can correctly distinguish between the two main subtypes
of PA. PET/CT with 11C-metomidate has successfully been used as a functional
imaging technique for several adrenal gland diseases. Until now, its value in
the differential diagnosis in PA has not been well investigated. Our hypothesis
is that 11C-metomidate is selectively taken up by aldosterone producing adrenal
cortical tissue, resulting in a symmetrical tracer uptake during PET/CT in case
of BAH and in a unilateral tracer uptake in a patient with an APA/PAH.

The objective of the study is to determine whether 11C-metomidate PET can
differentiate between BAH and APA./PAH

The present pilot study is a comparative diagnostic trial, in which a new
method of functional imaging with 11C-metomidate PET/CT is compared with the
current reference method of AVS in the evaluation of patients with PA. Both the
patient and the nuclear medicine physician are blinded for the results of the
previous AVS. Interpretation of the 11C-metomidate PET/CT is performed
independently by two nuclear medicine physicians. After completion of
11C-metomidate PET/CT, each patient will receive standard treatment guided by
the final diagnosis based on the AVS results (either medication or surgery).

Burden and risks:
- extra visit to the hospital (department of nuclear medicine)
- pretreatment with dexamethasone 1,5 mg b.i.d. during 5 days prior to
11C-metomidaat PET/CT
- time burden investigation (1.5 hour)
- 4 hours fasting prior to PET/CT. In case of concurrent diabetes mellitus,
adjustment of hypoglycemic medication (oral agents and/or insulin) is indicated
on the day of PET/CT
- risk of pain and/or hematoma due to venipuncture.
- radiation dose of a single 11C-metomidate PET/CT scan is equivalent to 3.2
mSv (11C-metomidate: 1.7 mSv, CT-scan: 1.5 mSv). According to the International
Commission on Radiological Protection (ICRP 62), this radioation dose falls
into category IIB ( 1-10 mSv; small to moderate risk level). The radiation risk
is small compared to other nuclear and radiologic investigations, and is in the
range of the annual background radiation from natural sources received by Dutch
people (2 mSv/year).