Imaging of adrenal incidentalomas with PET using (11)C-metomidate and (18)F-FDG.
Our aim was to evaluate the use of PET with (11)C-metomidate and (18)F-FDG for the diagnosis of adrenal incidentalomas.


METHODS
Twenty-one patients underwent hormonal screening before dynamic imaging of the upper abdomen with (11)C-metomidate, and for 19 of these 21 patients, static (18)F-FDG imaging followed. Uptake of (11)C-metomidate and (18)F-FDG in incidentalomas was quantified and correlated with the hormonal work-up and the mass size on CT (median, 2.5 cm; range, 2-10 cm).


RESULTS
The final diagnoses were hormonally active adenoma (n = 7), nonsecretory adenoma (n = 5), adrenocortical carcinoma (n = 1), pheochromocytoma (n = 2), benign noncortical tumor (n = 2), normal adrenal (n = 1), and malignant noncortical tumor (n = 3). Diagnosis was established at surgery (n = 9), percutaneous biopsy (n = 4), or follow-up (n = 8). The highest uptake of (11)C-metomidate, expressed as standardized uptake value (SUV), was found in adrenocortical carcinoma (SUV = 28.0), followed by active adenomas (median SUV = 12.7), nonsecretory adenomas (median SUV = 12.2), and noncortical tumors (median SUV = 5.7). Patients with adenomas had significantly higher tumor-to-normal-adrenal (11)C-metomidate SUV ratios than did patients with noncortical tumors. (18)F-FDG detected 2 of 3 noncortical malignancies but failed to detect adrenal metastases from renal cell carcinoma. All inactive and most active adenomas were difficult to detect with (18)F-FDG against background activity, whereas both pheochromocytomas and adrenocortical carcinoma showed slightly increased uptake of (18)F-FDG. There was no correlation between uptake of (11)C-metomidate or (18)F-FDG and mass size.


CONCLUSIONS
(11)C-Metomidate is a promising PET tracer to identify incidentalomas of adrenocortical origin. (18)F-FDG should be reserved for patients with a moderate to high likelihood of neoplastic disease.
Minn
Heikki
H
Turku PET Centre, University of Turku, Turku, Finland. heikki.minn@utu.fi
Salonen
Anna
A
Friberg
Johan
J
Roivainen
Anne
A
Viljanen
Tapio
T
Långsjö
Jaakko
J
Salmi
Jorma
J
Välimäki
Matti
M
Någren
Kjell
K
Nuutila
Pirjo
P
D000310:Adrenal Gland Neoplasms / Q000097:blood / Q000175:diagnosis / Q000000981:diagnostic imaging* / Q000378:metabolism*; D000328:Adult; D000368:Aged; D002250:Carbon Radioisotopes / Q000097:blood; D005045:Etomidate / Q000031:analogs & derivatives* / Q000097:blood / Q000493:pharmacokinetics*; D005260:Female; D019788:Fluorodeoxyglucose F18 / Q000097:blood / Q000493:pharmacokinetics*; D006801:Humans; D033162:Incidental Findings; D008297:Male; D008657:Metabolic Clearance Rate; D008875:Middle Aged; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014055:Tomography, Emission-Computed / Q000379:methods*
D002250:Carbon Radioisotopes; D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18; C084586:metomidate; D005045:Etomidate