Is Chest X-ray or High-Resolution Computed Tomography Scan of the Chest Sufficient Investigation to Detect Pulmonary Metastasis in Pediatric Differentiated Thyroid Cancer?

Abstract

We reviewed the clinical characteristics, pattern of disease at presentation, histopathologic subtype, treatment, course, and outcome of differentiated thyroid cancer (DTT) in children and adolescents presenting with pulmonary metastasis and tried to assess the effectiveness of routine chest x-ray and high-resolution computed tomography (CT) scan of the chest vis-à-vis ¹³¹I whole-body scan (WBS) in revealing pulmonary metastasis. In our series of 1754 patients, 122 (7%) were 20 years of age or younger, of whom 28 (23%) had pulmonary metastasis. Mean age was 13.9 ± 4.4 years (F:M ratio = 12:16). All but 2 patients had undergone near-total thyroidectomy with some form of neck dissection. Histopathologic examination was papillary in 89% and follicular in 11% cases, with confirmed nodal metastasis in all. Twenty-one (75%) patients had normal chest x-ray. However, WBS revealed pulmonary metastasis in all cases. In 15 (54%) children pulmonary metastasis was detected by first postsurgery 2-3 mCi ¹³¹I WBS and in 4 (14%) patients by postablation ¹³¹I WBS. Seven cases (25%) and 2 cases were detected by first and second posttherapy ¹³¹I WBS, respectively. No statistically significant difference was observed in any of the demographic or clinical parameters in patients in whom pulmonary metastasis was detected by first postsurgical low-dose WBS versus those in whom metastasis was discovered at a later stage. When chest x-ray-positive children were compared to x-ray-negative children, a statistically significant difference was observed only for mean first dose, cumulative dose, and total number of doses of ¹³¹I, which were significantly higher in x-ray-positive children. Eighteen of 21 children who had normal chest x-ray also underwent CT scan of the chest. CT could detect micronodular pulmonary shadows in 5 (28%) children only. Complete radioiodine treatment and outcome information was available in 20 patients. Mean first dose and cumulative doses of administered ¹³¹I were 75.4 ± 39.5 mCi and 352 ± 263 mCi, respectively. After an average number of 3.3 doses of ¹³¹I and mean duration of 33.2 ± 28.5 months, pulmonary lesions disappeared in 14 (70%) patients and thyroglobulin (Tg) becoming undetectable. In 4 children, however, there was no radiologic or scintigraphical evidence of pulmonary metastasis, Tg was high and in 2 patients, disease was persisting clinically. To conclude, a large majority of pediatric patients with DTC have x-ray- and even high-resolution-negative pulmonary metastasis. However, these metastases are ¹³¹I avid, and thus are amenable to detection and treatment with radioiodine. Therefore, postsurgical evaluation with ¹³¹I is recommended in all children and adolescents.