New Intraspinal cause of physiological FDG uptake

Abstract

We present a paediatric case of Papillary Ca thyroid under evaluation for elevated Thyroglobulin (Tg) level with negative (131)I wholebody scintigraphy. Differentiated thyroid cancer (DTC) arises from follicular epithelium and retains basic biological features like expression of sodium iodide symporter (NIS), which is the cellular basis of radio iodine ((131)I) concentration during thyroid ablation. Once dedifferentiation of thyroid cells occurs, cells fail to concentrate (131)I, posing both diagnostic and therapeutic problems in DTC and one may have to resort to other imaging techniques for disease localization. As DTC progression is slow, patients have a relatively good prognosis. However children with thyroid malignancies need aggressive management, as initial presentation itself maybe with nodal metastases. It is well known that FDG PET CT apart from its oncological applications, is also used in the evaluation of vascular inflammation especially Takayasu's arteritis. It is also reported in literature, that (18)F-FDG uptake can be seen relatively frequently in the arterial tree of cancer patients. Dunphy et al reported the association of vascular FDG uptake in inflammation as well as in normal arteries. This study typically describes FDG uptake in a patchwork of normal vessel, focal inflammation and or calcification of vessels. The other plausible reasons for significant vascular (18)F-FDG uptake are drugs such as potent non steroidal anti-inflammatory agents, dexamethasone, prednisone and tacrolimus. Our patient showed false positive (18)F Fluorodeoxyglucose (FDG) uptake in spinal cord at D11/12 and D12/L1 vertebral levels in FDG PET CT imaging performed as part of raised Thyroglobulin workup. This intra spinal FDG uptake is attributed to physiological uptake and inadequate FDG clearance from artery of Adamkiewicz, which can be added as a new physiological cause of FDG uptake unreported in literature as yet.

Keywords: Artery of Adamkiewicz; Dedifferentiated thyroid cancer; FDG PET scan; papillary Ca thyroid; radioiodine I 131 scan; thyroglobulin.

Figure 1

a) Followup Whole body ¹³¹I scan in 2008 (in anterior and posterior projections) 6 months post I 131 therapy showing persistent minimal I 131 uptake in anterior neck; b) Post therapy whole body ¹³¹I scan, 2^nd dose (in anterior and posterior projections) showing focal I 131 uptake in anterior neck as expected in an immediate post therapy setting with no new focal spots elsewhere

Figure 2

Followup Whole body ¹³¹I scan in 2009 (in anterior and posterior projections) showing no abnormal I 131 uptake in anterior neck as well as in rest of whole body survey

Figure 3

a) Sagittal view MR of Lumbosacral spine showing no abnormal signals; b) Sagittal view FDG PET CT showing linear focus of FDG uptake in D11/12 vertebral level

Figure 4

a) Showing pictorial representation of vessels supplying Spinal cord in sagittal and transaxial views. The Adamkiewicz artery is the largest segmental medullary artery typically arises from a left posterior intercostal artery, which branches from aorta and supplies two thirds of the spinal cord via anterior spinal artery. In 75% of people, the artery of Adamkiewicz originates on the left side of the aorta between the D9 and D11 vertebral segments. In approximately 30% of people it arises from the right side. 25% of population can have two large anterior segmental medullary arteries; b) MR Transaxial view showing no altered signals in D11/D12 levels; c) Transaxial view of FDG PET CT depicting abnormal FDG uptake intraspinally at D11/12 vertebral level (SUV Max is 3.95 g/ml). The branching of vessels supplying spinal cord have been highlighted with arrow in all three images