The spectrum of 124I uptake in the lacrimal gland and nasolacrimal sac/duct on PET/CT imaging

Introduction This study characterizes the spectrum of physiologic I-124 uptake of the lacrimal system in patients with a history of differentiated thyroid cancer (DTC) who underwent multi-timepoint I-124 PET/CT imaging. Methods I-124 PET/CT in 31 DTC patients was performed at 2, 24, 48, 72, and 96 h after oral administration of 31.5 or 62.9 MBq (0.85 or 1.7 mCi) of I-124 after either recombinant human thyroid-stimulating hormone injections or thyroid hormone withdrawal. All but two patients had a history of prior I-131 therapy. Patterns of I-124 uptake in the lacrimal glands and nasolacrimal sac/ducts (NLD) were assessed. Results A total of 173 individual I-124 PET/CT scans (forming 35 sets of scans) were reviewed for 31 patients. Lacrimal glands were visualized bilaterally in only 4 patients. The focal mild uptake (grade 2), best seen on the 2-h images, was crescent-shaped and located in the lateral upper quadrant of the orbit. In contrast, the NLDs were identified in all patients (bilateral in 29 of 31 patients) with high focal uptake (grade 4) peaking on the 2- and 24-h timepoints; however, the overall pattern of uptake was variable. Of the 29 patients with prior I-131 therapy, three patients had a relatively fixed and unchanging pattern of uptake on at least one side of the NLDs. Conclusions In patients with DTC, I-124 activity in the NLDs is more frequently visualized, more intense, more prolonged, and more variable than in the lacrimal glands. The lack of clearance may suggest possible obstruction or stasis of an NLD.