Abstract
131I whole body scan (WBS) is a sensitive procedure for detecting metastases in differentiated thyroid carcinomas (DTCs). Metastatic foci of differentiated thyroid cancer are able to take up radioiodine and usually produce thyroglobulin (Tg), thus supporting a need to administer therapeutic doses of 131I. Unfortunately, a wide spectrum of false positive readings have been reported for WBS (1) and, recently, complementary instrumental procedures aimed at improving WBS diagnostic sensitivity have been proposed (2). To avoid inappropriate administration of therapeutic doses of radioiodine, a proper understanding of the different causes of ectopic radioiodine uptake is crucial. This is even more true in the light of the need to limit as much as possible the cumulative dose of 131I in patients with thyroid cancer with metastatic disease, as this might increase the incidence of second malignancies (3). Here, we describe, perhaps for the first time, a case of 131I accumulation in a meningocele due to a closed spina bifida (CSB).
A 69-year-old woman presented with a large multi-nodular goiter in December 2007. Near-total thyroidectomy was performed in July 2008, and histopathology revealed a 3 cm (maximum diameter) large papillary thyroid carcinoma of the follicular variant. Levo-thyroxine (LT4) suppressive therapy was then started, and a WBS was done in November 2008, which was followed by 5 weeks of LT4 treatment withdrawal and oral administration of 3,7 GBq of 131I (100 mCi). The scan revealed residual thyroid tissue in the thyroid bed with a 24-hour neck uptake of 11% of the administered dose. A focal ectopic radioiodine concentration mimicking vertebral metastasis was also detected at the level of L5 (see Supplementary Fig. S1; Supplementary Data are available online at
At the time that WBS was performed, serum thyrotropin (TSH) and Tg were 54.2 UI/mL and 10.6 ng/mL, respectively. In the absence of anti-Tg antibodies, Tg levels were consistent with the persistence of only thyroid remnants. To understand the discrepancy between the WBS that appeared to be suspicious for vertebral metastasis and the low levels of Tg, we performed a magnetic resonance imaging (MRI). This revealed a “pouch-like” image at the level of the L5-S1 vertebrae corresponding to a meningocele caused by a CSB (see Supplementary Fig. S2). Our patient was unaware of this malformation, which, at clinical examination, appeared to be as a small and soft mass covered by skin. Further follow-up on LT4, over the last 3 years, revealed undetectable Tg values in the presence of suppressed TSH levels. In January 2011, serum Tg assay (Tg testing) carried out over 5 days after the administration of two doses of 0.9 mg of recombinant human TSH (rhTSH) revealed persistently undetectable serum Tg levels.
Ectopic radioiodine accumulations not corresponding to DTC metastases (false positive) have been reported in several organs and associated with different pathological conditions (1,2). Nair et al. have reviewed the potential causes for this (4). The major categories are 131I ectopic uptake due to the presence of sodium-iodide symporter and passive nonspecific accumulation possibly due to local conditions of either increased vascularity or capillary permeability. The present patient probably belongs to the second category, but no definite information is available. To the best of our knowledge, this is the first report of radioiodine accumulation in a meningocele due to CSB.
CSB is a developmental anomaly resulting in defects of the spine that are limited to a failure of bony growth and fusion of the vertebral arch. Clinically, CSB appears as a soft mass corresponding to a meningo/myelomeningocele covered by skin. At MRI, CSB usually appears as a cleft or gap between the vertebral spinous process and laminae. The high frequency of this malformation (often clinically silent and misdiagnosed in the general population all over the world) should be taken into account in patients with DTC with lumbosacral 131I accumulation and inconsistent Tg values to exclude the possibility that the uptake is due to the presence of CSB.