Prolactinomas, the most common type of pituitary adenoma, often present diagnostic and localization challenges, particularly in cases of recurrence or post-treatment residual lesions. Conventional Magnetic Resonance Imaging (MRI) is the primary imaging modality, but its limitations in visualizing subtle lesions or differentiating active tumor tissue from post-surgical changes necessitate the exploration of advanced imaging techniques. This study investigates the clinical value of [18F]fluoroethyl-L-tyrosine Positron Emission Tomography co-registered with MRI ([18F]FET-PET/MRICR), a sophisticated Pet Co-registration technique, in patients with prolactinoma where localization is challenging, aiming to refine diagnostic accuracy and guide clinical decision-making, including surgical planning.
This retrospective study included 17 consecutive patients with prolactinoma who underwent [18F]FET-PET/MRICR between October 2020 and September 2022. The indications for pet co-registration imaging were twofold: (1) to gain further insights into potential tumor remnants in patients with unclear MRI findings after prior transsphenoidal surgery (TSS) or pharmacological treatment, and (2) to establish a radiological diagnosis in cases where conventional MRI did not reveal a definitive adenoma. The patient cohort represented a spectrum of clinical scenarios where standard imaging was insufficient for confident localization and management planning.
The findings demonstrated that [18F]FET-PET/MRICR successfully identified lesions in a significant majority, 14 out of 17 patients. Notably, in two patients with negative conventional MRI but persistently elevated prolactin levels (greater than 7.5 times the upper limit of normal), [18F]FET-PET/MRICR did not detect active lesions, highlighting a potential limitation in cases with very subtle or diffuse disease. In one patient, the pet co-registration results were inconclusive due to diffuse tracer uptake observed 10 weeks following surgery, suggesting post-operative changes may interfere with interpretation in the early post-surgical period. In terms of concordance with conventional MRI, [18F]FET-PET/MRICR showed complete agreement in 10 out of 17 patients and partial agreement in 3 patients, indicating a substantial level of consistency between the two modalities. Importantly, [18F]FET-PET/MRICR identified new lesion foci in 4 out of 17 patients, providing additional diagnostic information not apparent on conventional imaging alone.
The clinical impact of [18F]FET-PET/MRICR was substantial, influencing clinical shared decision-making in 15 out of the 17 patients. As a direct consequence of the pet co-registration findings, 7 patients proceeded with TSS, while 8 patients opted to continue or adjust pharmacological management, demonstrating the technique’s role in tailoring treatment strategies. Interestingly, one patient underwent TSS despite a negative [18F]FET-PET/MRICR result, and another patient pursued additional imaging modalities, indicating that pet co-registration is used within a broader clinical context. Intraoperative findings were consistent with [18F]FET-PET/MRICR in 5 out of 8 surgical cases, and immunohistochemistry confirmed the presence of prolactinoma in 5 out of 8 cases, supporting the accuracy of the pet co-registration technique. The treatment goal was achieved in 7 out of 8 patients who underwent surgery, and remission was attained in 5 out of 7 patients where total resection was deemed achievable, suggesting a positive impact of [18F]FET-PET/MRICR on surgical outcomes.
In conclusion, [18F]FET-PET/MRICR emerges as a valuable adjunct to conventional MRI in the preoperative and treatment planning process for carefully selected patients with prolactinoma, particularly those with challenging localization scenarios or when conventional MRI findings are ambiguous. The ability of pet co-registration to refine lesion detection and inform clinical decision-making underscores its potential to improve patient management and outcomes in this specific clinical context. Further research with larger cohorts is warranted to validate these findings and to explore the optimal integration of [18F]FET-PET/MRICR into the diagnostic and therapeutic algorithm for prolactinoma.
