A Risk-Adapted Approach Using US Features and FNA Results in the Management of Thyroid Incidentalomas Identified by ¹⁸F-FDG PET

Abstract

Purpose: To assess the risk of malignancy of thyroid incidentalomas found on ¹⁸F-FDG PET/CT by US features and cytologic results, and to evaluate the clinical usage of a combination of US features and cytology for post-FNA management of thyroid incidentalomas on ¹⁸F-FDG PET/CT.

Materials and Methods: From September 2006 to December 2008, 132 patients with 134 thyroid incidentalomas detected on ¹⁸F-FDG PET/CT who had undergone US and US-FNA were included in this study. We evaluated the malignancy rate of thyroid incidentalomas in different subgroups subdivided by US features and US-FNA cytology results. Several variables were compared between the benign and malignant group.

Results: The risk of malignancy was 58.2 % (78/132) in thyroid incidentalomas on ¹⁸F-FDG PET/CT. Age, gender, and tumor size were not significantly different between the malignant and benign group. Malignancy rate of thyroid incidentalomas was significantly higher in the suspicious malignant (88.9 %) than in the probably benign group (11.3 %) on US (p < 0.001). Malignancy rates were high in thyroid nodules with “malignancy”, “suspicious for malignancy”, or “follicular neoplasm” on cytologic results, regardless of US features. However, malignancy rates of thyroid incidentalomas with “unsatisfactory” or “benign” results on cytology were higher in the suspicious malignant (75 %, 12.5 %, respectively) than in the probably benign (0 %) group on US. 

Conclusions: This study demonstrated that the risk of malignancy was high in thyroid incidentalomas on ¹⁸F-FDG PET/CT even without suspicious US features. However, there was no malignancy in nodules with no suspicious US features and benign cytology. Based on these results, we concluded that US may not replace FNA in the diagnosis of PET incidentalomas, and that a follow-up may be considered of thyroid incidentalomas with benign cytology and no suspicious US features.

Zusammenfassung

Ziel: Die Bestimmung des Malignitätsrisikos von Inzidentalomen der Schilddrüse, die im ¹⁸F-FDG PET/CT entdeckt wurden, mittels US-Merkmalen und den zytologischen Ergebnissen sowie die Bewertung des klinischen Nutzens der Kombination von US-Markern und Zytologie für die Behandlung von Inzidentalomen der Schilddrüse nach FNB im ¹⁸F-FDG PET/CT.

Material und Methoden: Von September 2006 bis Dezember 2008 wurden in diese Studie 132 Patienten mit 134 durch ¹⁸F-FDG PET/CT erkannte Inzidentalome der Schilddrüse aufgenommen, bei denen US und eine US-FNB durchgeführt wurden. Wir bewerteten die Malignitätsrate der Inzidentalome in verschiedenen Untergruppen, die wiederum nach US-Merkmalen und den zytologischen Befunden der US-FNB aufgeteilt wurden. Verschiedene Variablen wurden zwischen der gutartigen und der malignen Gruppe verglichen.

Ergebnisse: Das Malignitätsrisiko für Inzidentalome der Schilddrüse im ¹⁸F-FDG PET/CT betrug 58,2 % (78/132). Es gab keinen signifikanten Unterschied bezüglich des Alters, Geschlechts und der Tumorgröße zwischen der gutartigen und malignen Gruppe. Im US war die Malignitätsrate der Inzidentalome in der Gruppe mit Malignitätsverdacht (88,9 %) signifikant höher (p < 0,001) als in der wahrscheinlich-gutartigen Gruppe (11,3 %). In Schilddrüsenknoten mit den zytologischen Ergebnissen „Malignität“, „Malignitätsverdacht“ oder „follikulären Neoplasmen“ waren die Malignitätsraten hoch, unabhängig von den US-Merkmalen. Allerdings waren die Malignitätsraten von Inzidentalomen mit „unbefriedigenden“ und „gutartigen“ Ergebnissen in der Zytologie mit 75 % (unbefriedigend) und 12,5 % (gutartig) höher, als in der wahrscheinlich-gutartigen Gruppe im US (0 %).

Schlussfolgerung: Diese Studie zeigte, dass das Malignitätsrisiko bei Inzidentalomen der Schilddrüse im ¹⁸F-FDG PET/CT hoch ist, selbst ohne verdächtige US-Charakteristika. Es gab jedoch auch nicht-maligne Knoten mit unverdächtigen US-Merkmalen und gutartiger Zytologie. Aufgrund dieser Ergebnisse schlossen wir, dass der US die FNB bei der Diagnose von PET-Inzidentalomen nicht ersetzen dürfte, und dass bei Inzidentalomen der Schilddrüse mit gutartiger Zytologie und unauffälligen US-Markern eine Nachuntersuchung in Erwägung gezogen werden sollte.

Key words

thyroid incidentaloma - ultrasound - PET-CT - PET - fine-needle aspiration

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