Nasolacrimal Duct Obstruction on ¹³¹I SPECT/CT: Atypical False-positive Paranasal Radioiodine Uptake as a Complication of Single-dose RAI Treatment

Abstract

Nasolacrimal duct obstruction (NLDO) is a rare complication after radioiodine therapy and may cause false positive ¹³¹I uptake at the point of obstruction in ¹³¹I whole body scan. Here, we report a 59-year-old female patient with papillary thyroid cancer treated with total thyroidectomy followed by ¹³¹I therapy. ¹³¹I whole body scan revealed focal uptake in the head. Single photon emission computed tomography/computed tomography (CT) showed focal uptake at the right proximal nasolacrimal duct. The ophthalmologic examination and the diagnostic maxillofacial CT confirmed the diagnosis of NLDO.

Figure 1.

¹³¹I whole body scan was performed on a 59-year-old female patient with papillary thyroid cancer (T3N1bM0), who was treated 5 years ago with total thyroidectomy followed by a single dose 150 mCi ¹³¹I therapy. A planar ¹³¹I whole body scan with single photon emission computed tomography/computed tomography (SPECT/CT) and spot neck pinhole images were obtained at the 48^th hour after 5 mCi ¹³¹I oral administration. At the time of imaging, stimulated thyroid-stimulating hormone level was 280 IU/mL, thyroglobulin (Tg) level was 0.20 ng/mL and anti-Tg antibody level was <0.9 IU/mL. The patient had no symptoms at the time of imaging. Planar ¹³¹I whole body scan showed no significant radioactivity uptake that may be compatible with residual thyroid tissue or recurrent thyroid cancer, on the other hand a suspicious focus of intense increased uptake was noted at the right paranasal region, which mimics a metastatic lesion (arrow in planar images). SPECT/CT images revealed 7x4 mm sized soft tissue density lesion-demonstrating ¹³¹I uptake, in the right infraorbital region next to the lateral wall of ethmoid sinus (arrows in fused SPECT/CT images) suggesting nasolacrimal duct obstruction (NLDO). Subsequently, an ophthalmologic examination and a diagnostic maxillofacial CT were performed to confirm the diagnosis. ¹³¹I has been used for many years as a valuable treatment in thyroid diseases such as hyperthyroidism and differentiated thyroid carcinomas (1,2,3). NLDO is an uncommon complication of ¹³¹I therapy, especially rarely occurs after a single dose of radioiodine treatment. Morgenstern et al. (4) reported that the cells of the lacrimal drainage system have the same Na/I symporters expressed by the cells of the thyroid gland and eventually the accumulation of ¹³¹I in these cells results in radiation induced damage. Fibrosis and obstruction of lacrimal drainage system will cause ¹³¹I uptake at the point of obstruction in whole body ¹³¹I scan and that may be misinterpreted as a metastasis (5,6). SPECT/CT can be useful to discriminate these false positive findings of planar ¹³¹I whole-body imaging, as in this study (7). Beside that early identification of these lesions may hasten the subsequent appropriate treatment of the patients and improve quality of life (8).