Abstract Introduction Follicular tumors of uncertain malignant potential (FT-UMP) are rare histological entities with borderline features between benign follicular adenomas and carcinomas. Granulomatous thyroiditis due to systemic sarcoidosis is also uncommon. Their coexistence in the same thyroid lobe, particularly in a background of Hashimoto thyroiditis and repeated atypia of undetermined significance (AUS), is exceedingly rare. Clinical Case A 60-year-old woman with known Hashimoto thyroiditis, chronic kidney disease, hypertension, and biopsy-proven pulmonary sarcoidosis was followed for multinodular goiter and hypothyroidism. Between 2020 and 2024, four consecutive fine-needle aspirations (FNAs) from a 2 cm anterior mid-right lobe thyroid nodule were reported as AUS. She declined surgery in 2020 but re-presented in August 2024 with increasing nodule size and persistent cytological atypia. Neck ultrasound revealed heterogeneous thyroid parenchyma and suspicious nodules; PET-CT demonstrated FDG uptake in thyroid and mediastinal lymph nodes (SUVmax: 8.4), consistent with sarcoid activity. The patient underwent a right lobectomy and an isthmectomy in June 2025. Final histopathology revealed FT-UMP (2 x 1.5 cm) in the right lobe, Hashimoto thyroiditis with widespread oncocytic metaplasia, non-caseating epithelioid granulomas with sarcoid-like architecture, and one reactive lymph node. The postoperative course was uneventful, and no radioiodine therapy was planned. Systemic sarcoidosis remained in remission with normalized ACE levels and stable imaging findings. Conclusion This case represents a unique coexistence of FT-UMP and granulomatous thyroiditis secondary to sarcoidosis, both developing within a background of Hashimoto thyroiditis. The patient’s long history of AUS findings and delayed surgery emphasize the importance of repeated evaluation and histopathological confirmation in indeterminate thyroid nodules. Clinicians should consider granulomatous infiltration in the differential diagnosis of thyroid nodules in patients with sarcoidosis, particularly when PET-CT shows intense uptake.Figure 1:PET-CT showing a right thyroid nodule with diffuse FDG uptake suggestive of thyroiditisPET-CT image showing a hypodense nodule measuring approximately 17 mm in the anterior mid-portion of the right thyroid lobe. Diffuse heterogeneous F-18 FDG uptake is observed in both lobes of the thyroid gland (SUVmax: 4.87), suggestive of underlying thyroiditis. Table 1:Laboratory Findings
Baykal et al. (Thu,) studied this question.