Visualization of Macroprolactinoma by 18F-Fluorocholine PET/CT in a Patient With Multiple Endocrine Neoplasia Type 1.

The diagnostic performance of 18F-fluorocholine (FCH) positron emission tomography (PET)/CT for the detection of hyperfunctioning parathyroid glands in the setting of primary hyperparathyroidism (HPT1) seems promising [1, 2]. Its interest in the surgical management of these diseases has also been reported [3].

A 32-year-old man was diagnosed with a multiple endocrine neoplasia type 1 (MEN1) syndrome as part of a family screening. A diagnosis of HPT1 was made with an elevated ionized calcium level of 1.39 mM (normal range 1.17 to 1.3 mM) and inappropriate serum parathyroid hormone level of 3.59 pM (normal range 0.48 to 4.2 pM). Further hormonal testing revealed a hyperprolactinemia of 3292 mUI/L (normal range 86 to 324 mUI/L). There was no evidence of a pancreatic neuroendocrine tumor. Parathyroid scintigraphy with metoxyisobutylisonitil labeled with technetium-99m (MIBI), including a single photon emission CT/CT acquisition, showed an abnormal focus of uptake in the upper-right quadrant of the neck (Fig. 1A). Parathyroid sonography identified a concordant-enlarged, 16-mm parathyroid gland in the same region and a second 5-mm lesion in the upper-left quadrant. To address these discordant findings, we performed a FCH-PET/CT. An increased focus of uptake was observed in two parathyroid glands, as a result of a maximum intensity projection view (Fig. 1B, blue arrows), whereas it was observed in all four parathyroid glands on a FCH-PET/CT fused view (maximum standardized uptake value at 5 and 13.1 for inferior and superior right and 2.9 and 6.8 for inferior and superior left; Fig. 1C, arrow: inferior left parathyroid). Interestingly, on a highest-intensity projection view, an increased focus of uptake was also visualized in the pituitary gland (maximum standardized uptake value at 8.7; Fig. 1B, red arrow). Gadolinium T1-weighted pituitary MRI showed a macroadenoma of 11 × 10.5 × 13 mm, compatible with diagnosis of macroprolactinoma (Fig. 1D, left). FCH-PET/MRI-fused view showed the increased focus of uptake in macroprolactinoma (Fig. 1D, right). Pathological findings after parathyroid surgery revealed adenomas in two parathyroid glands and hyperplasia in another one. The remaining one, measured at 6 mm on FCH-PET/CT, was left in place. After surgery, the patient had hypoparathyroidism with a calcium level of 2.11 mM (normal range 2.25 to 2.6 mM) and serum parathyroid hormone level of 0.56 pM (normal range 0.48 to 4.2 pM). Cabergoline was initiated to treat prolactinoma.

Figure 1.

Macroprolactinoma visualized by 18F-Fluorocholine PET/CT. (A) Parathyroid scintigraphy with metoxyisobutylisonitil labeled with technetium-99m (MIBI) with focus of uptake in the right upper parathyroid gland. (B) Maximum intensity projection of FCH-PET visualized two parathyroid glands (blue arrows) and also a macroadenoma (red arrow). (C) FCH-PET/CT fused view showed an increase of uptake in all four parathyroid glands. Arrow shows inferior left parathyroid. (D) On the left, gadolinium T1-weighted pituitary MRI showed a macroadenoma of 11 × 10.5 × 13 mm and on the right FCH-PET/MRI fused view showed the increased focus of uptake in macroprolactinoma.

In MEN1 patients, the estimated penetrances of HPT1 and prolactinoma by the age of 40 are, respectively, ~90% and ~20% [4]. Incidental detection of pituitary adenoma by FCH-PET/CT was recently reported but not in a MEN1 patient or for prolactinoma [5-7]. In our case, the prolactinoma presented an intense FCH focus of uptake compared with what is usually reported as physiologic [8], but MIBI scintigraphy did not reveal anything. Proton magnetic resonance spectroscopy studies have found that the concentration of choline-containing compounds was significantly higher in pituitary adenomas [9, 10]. MIBI avidity by tissues is related to the number of mitochondria per cell [11]. Presumably, this would explain why in our case, the prolactinonoma was positive on FCH PET/CT and negative on MIBI scintigraphy. Pituitary adenomas with an increased focus of uptake of fluorodeoxyglucose [7] or tetraazacyclododecanetetraacetic acid-Tyr3-octreotide [12] on PET/CTs have already been reported, but these radiotracers are not relevant to explore parathyroid glands.

FCH-PET/CT needs to be evaluated in a larger number of patients with MEN1. Indeed, it could help to detect more hyperfunctioning parathyroid glands than other imaging modalities and identify other potential endocrine tumors as well.