Dual Role for l-[Methyl-¹¹C]-Methionine PET in Acromegaly: Confirming Remission and Detecting Recurrence

Molecular imaging using the amino acid PET tracer l-[methyl-¹¹C]-methionine (¹¹C-Met PET) is emerging as an important addition to the armamentarium of clinicians treating pituitary disease. In acromegaly cases, ¹¹C-Met PET can accurately localize sites of residual tumors to guide (further) surgery or radiotherapy (1,2). However, ¹¹C-Met PET can also help confirm remission. Here, we illustrate both roles in a single patient.

A 31-y-old woman with recently diagnosed acromegaly (insulin-like growth factor 1, 103.0 nmol/L; upper limit of normal, 45.0) underwent endoscopic transsphenoidal surgery for a macroadenoma (21 mm). Gross total resection was achieved, with complete biochemical remission (insulin-like growth factor 1, 21.3 nmol/L; nadir growth hormone, 0.33 μg/L). Although postoperative MRI suggested a possible right-sided tumor remnant, ¹¹C-Met PET demonstrated only physiologic uptake in the remaining normal gland (Fig. 1A).

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FIGURE 1.

MRI, ¹¹C-Met PET, and coregistered images during initial remission (A), at recurrence (B), and after successful repeat surgery (C). Normal pituitary gland (demonstrating typical variability in uptake between scans) is indicated by white arrows; recurrence (visually appreciated on second scan only) is indicated by yellow arrows. (A) MRI showing indeterminate appearance in right sella but with ¹¹C-methionine uptake confined to residual normal gland in left side of sella. (B) MRI unchanged despite disease relapse; ¹¹C-Met PET reveals discrete, new focus of ¹¹C-methionine uptake in right sella. (C) Normalization of insulin-like growth factor 1 after repeat surgery correlates with absence of right-sided tracer uptake. Coronal MRI of T1-weighted fast-spoiled gradient echo images: repetition time, 11.5 ms; echo time, 4.2 ms; isotropic voxel spacing of 1 mm × 1 mm (256 × 256 matrix size) × 1 mm (slice thickness). ¹¹C-Met PET static images acquired on GE Discovery-690 20–40 min after administration of ¹¹C-Met. Ordered-subset expectation maximization reconstruction: attenuation correction, time-of-flight, point-spread function, 3 iterations, 24 subsets, and gaussian postprocessing filter (3.2 mm in 2011, 2 mm in 2020–2021). coreg = coregistered.

Nine years later, the patient experienced clinical and biochemical recurrence (insulin-like growth factor 1, 44.9 nmol/L; upper limit of normal, 35.5; nadir growth hormone, 1.75 μg/L). However, the contemporaneous MRI was unchanged. Therefore, a second ¹¹C-Met PET study was performed, which revealed a new focus of radiotracer uptake in the right sella adjacent to, but distinct from, the normal gland (Fig. 1B). The patient underwent repeat surgery, and the tumor was resected from the site identified on the ¹¹C-Met PET scan. The patient reentered remission (insulin-like growth factor 1, 15.6 nmol/L; upper limit of normal, 28.0; nadir growth hormone, <0.05 μg/L), with repeat ¹¹C-Met PET demonstrating uptake only in the residual normal gland (Fig. 1C), consistent with otherwise preserved pituitary function. This report therefore illustrates the dual role of ¹¹C-Met PET in acromegaly, confirming remission and detecting recurrence (1).

• © 2024 by the Society of Nuclear Medicine and Molecular Imaging.

• Received for publication August 1, 2023.
• Revision received September 12, 2023.