Pediatric thyroid cancer is rare. Risk factors include a family history and previous radiation exposure [4
]. The patient presented, however, had no identifiable risk factors. Sporadic papillary thyroid cancer represented only 1.4% of newly diagnosed childhood carcinomas in the USA from 1975–1995 according to the SEER database [5
]. Interestingly, the incidence among gender lines changes according to age group with males having a 6:1 increased incidence at ages 5–9, a similar incidence among males and females from ages 10–14 and a ratio more consistent with adult patients with 5:2 female to male ratio after age 14 [5
Palpable thyroid abnormalities are rare in childhood and should be approached with suspicion and an aggressive evaluation. The incidence of thyroid nodules in children before the onset of puberty is less than two percent in iodine sufficient areas and the aggregate risk of thyroid cancer in a pediatric thyroid nodule can surpass 25% [6
]. Our patient had an abnormal thyroid exam for as long as four years prior to being seen in our clinic. The family was unsure of any discrete nodule noted in the past. In this case, the thyroid cancer was diffusely spread through the patient's gland as described and therefore no discrete nodule was present at our initial exam.
The gold standard diagnostic test to define thyroid lesions is fine needle aspiration (FNA) biopsy. Cytological analysis has been evaluated in the pediatric population though the data is somewhat limited by the far less frequent occurrence of pediatric thyroid nodules and FNA biopsies. In a series of 101 specimens from 82 pediatric patients, the diagnostic sensitivity and specificity of detecting carcinoma were 87% and 92% respectively [6
]. The initial biopsy in this case was read as benign. Based on the concerning clinical features, we simply did not believe that the FNA material was representative of the disease state. It is likely that since there was no discrete nodule the needle simply was not targeted to a malignant portion of the gland. Although an ultrasound guided FNA of an abnormal lymph node would have been an appropriate next step, scheduling difficulties made a second palpation guided FNA after evaluation of the US a better option. Again, the vigilance that is appropriate for pediatric thyroid abnormalities pushed us to continue the pursuit of a clinically suspicious diagnosis. The second FNA confirmed papillary thyroid cancer.
Thyroid ultrasound now plays a prominent and expanding role in the evaluation of thyroid nodules. In a study of patients all under the age of 18 years, thyroid nodule ultrasound features including irregular borders and increased vascular flow assessed by power doppler had positive predictive value for thyroid cancer nodules under 15 mm [8
]. The importance of thyroid ultrasound experience cannot be stressed enough in the evaluation of a thyroid gland that is clinically suspicious for a nodule or malignant process. The initial US in this case occurred in a children's hospital where these studies are not routinely performed. Our expert thyroid ultrasound radiologist immediately noted the concerning features for malignancy of echogenic foci (microcalcifications) in the thyroid as well as the same features in enlarged lateral neck lymph nodes [9
Extensive lymph node disease at the time of diagnosis of pediatric papillary thyroid cancer is not a surprising finding. For adults diagnosed between the ages of 30–60, regional cervical and upper mediastinum lymph node metastases occur in 38–43% of patients [10
]. In pediatric patients (age < 21 years old), however, regional nodal metastases occur in 60–80% of cases [3
]. We chose to evaluate for distant metastases in this patient's course to help prepare a post-surgical treatment plan. Distant metastases in adult well differentiated papillary thyroid cancer are rare, occurring in only 2–4% of patients at the time of diagnosis [10
]. The pediatric population however has distant parenchymal metastases (most often lung) in 10–20% of cases at diagnosis [3
The assessment of pulmonary metastases prior to radioactive iodine therapy has important implications for choosing a treatment dose and avoiding toxicity, especially pulmonary fibrosis. In children, dosimetry is preferred to assess a safe maximum dose to ideally keep the blood dose of 131
I < 200–300 cGy and the pulmonary dose to < 80 mCi to avoid pulmonary fibrosis [4
]. Our institution does not routinely utilize dosimetry for choosing an adult dose of 131
I for well differentiated thyroid cancer and we considered giving an empiric dose of 200 mCi to this child. However, dosimetry was appropriately pursued by our nuclear medicine physicians and a dose of 150 mCi was felt to be the safe tolerable dose from a pulmonary safety standpoint.
With such aggressive presentations of pediatric papillary thyroid cancer, one may think that there is excessive mortality. This is not the case. In a retrospective analysis of 14 patients under the age of 17 years diagnosed with sporadic papillary thyroid cancer, all of whom had pulmonary metastases at the time of diagnosis or within 6 months of diagnosis, there was 100% survival over a mean 19 year follow up [2
]. Although there is not a high mortality rate, these patients do suffer significant morbidity with a high recurrence rate of their thyroid cancer that requires either multiple surgeries and/or doses of radioactive iodine, as well as long term thyroid hormone suppressive therapy [4