La découverte fortuite d’hypermétabolisme pituitaire sur un examen PET/CT 18F-FDG mérite plus d’investigations pour discriminer entre une captation pathologique vs. physiologique. Cependant, une étude récente suggère que l’hypermétabolisme pituitaire est fréquent chez les patient·e·s atteint·e·s de carcinome différencié de la thyroïde (CDT) dans un contexte de sevrage hormonal thyroïdien (thyroid hormone withdrawal, THW).
L’objectif de la présente étude rétrospective était de comparer le métabolisme pituitaire chez les patient·e·s atteints de CDT ayant eu un PET/CT 18F-FDG sous THW versus sous stimulation par l’hormone thyroïdienne recombinante humaine (recombinant human thyroid-stimulating hormone, rhTSH). Les résultats montrent que la prévalence d’hypermétabolisme pituitaire est plus élevée dans le groupe THW par rapport au groupe rhTSH. La valeur de fixation normalisée (standardized uptake value, SUV) pituitaire s’est révélée également plus élevée dans le groupe THW comparé au groupe rhTSH. Finalement, une corrélation positive entre les taux sériques de TSH et le SUV pituitaire a été observée uniquement dans le groupe THW.
Les résultats de cette étude appuient l'hypothèse selon laquelle l'hypermétabolisme pituitaire sur un PET/CT 18F-FDG chez un·e patient·e·s atteint.e de DTC en période de sevrage de l'hormone thyroïdienne est une réponse physiologique à l'hypothyroïdie. La prise de conscience de cet hypermétabolisme pituitaire physiologique est importante pour éviter les pièges potentiels dans l'interprétation des images qui pourraient déclencher des investigations superflues.
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The incidental pituitary hypermetabolism on 18F-FDG PET/CT should be further evaluated for discriminating between pathologic and physiologic uptake, but a recent study suggests that pituitary hypermetabolism is common in patients with differentiated thyroid carcinoma (DTC) undergoing thyroid hormone withdrawal (THW). The aim of this retrospective study was to compare pituitary metabolism in patients with DTC undergoing 18F-FDG PET/CT under THW versus recombinant human thyroid-stimulating hormone (rhTSH) stimulation. We confirmed a higher pituitary SUVmax and SUVratio with a higher prevalence of pituitary hypermetabolism in the THW group compared to the rhTSH group. A positive correlation between serum TSH levels and pituitary SUVmax was observed only in the THW group. The present findings support the hypothesis that pituitary hypermetabolism on 18F-FDG PET/CT in patients with DTC undergoing THW is a common physiological response to hypothyroidism. Awareness of this physiological hypermetabolism is important to avoid potential pitfalls in image interpretation that could trigger unnecessary investigations.
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Background: 18F-FDG PET/CT is performed for the assessment of radioactive iodine non-avid disease in patients with DTC. In patients prepared by THW, increased pituitary uptake of 18F-FDG in the absence of pituitary disease may reflect the physiological activation of pituitary thyrotroph cells by hypothyroidism.
This study aimed to compare pituitary 18F-FDG uptake in patients with DTC under THW vs. rhTSH stimulation. Methods: A total of 57 patients with DTC undergoing 18F-FDG PET/CT (40 under THW and 17 under rhTSH stimulation) were retrospectively analyzed. Pituitary metabolism was expressed as maximum standardized uptake value (SUVmax) and as SUVratio using the right cerebellum as reference. Results: Pituitary hypermetabolism (SUVmax ≥ 4.1) was present in more patients in the THW group compared to the rhTSH group (62.5% vs. 23.5%; p = 0.01). Pituitary metabolism was significantly higher in the THW group compared to the rhTSH group, as assessed by either SUVmax (mean ±SD: 4.61 ± 1.22, 95%CI: 4.22–5.00 vs. 3.34 ± 0.86, 95%CI: 2.9–3.8; p < 0.001) or SUVratio (0.52 ± 0.11, 95%CI: 0.49–0.56 vs. 0.42 ± 0.07, 95%CI: 0.38–0.46; p < 0.001). Serum TSH levels correlated positively with SUVmax (r = 0.41, p < 0.01) and SUVratio (r = 0.44, p < 0.01) in the THW group only. Conclusions: The present findings support the hypothesis that pituitary hypermetabolism on 18F-FDG PET/CT in patients with DTC undergoing THW is a common physiological response to hypothyroidism. Awareness of this physiological hypermetabolism is important to avoid potential pitfalls in image interpretation.