Study evaluating possible causes of the normal variant 18F-FDG uptake in the thoracic spinal cord in patients without CNS malignancy.

Abstract

e21144 Background: Focal increased lower thoracic spinal cord 18F-FDG uptake is not infrequently observed and may be confused for spinal cord metastases. The cause of this physiological uptake is indeterminate though various theories have been postulated. We hypothesized that there may be a correlation between the thoracic (T11-T12) spinal uptake and lower limb movements or to bowel FDG activity. In the absence of paired FDG PET studies in same patients with and without leg movements we correlated the FDG uptake of the lower thoracic cord in ambulatory to that in bedridden patients. Methods: Sixty-three consecutive patients (12 bedridden) with 18F- FDG PET-CT with no known evidence of spinal cord or bony spine metastases were included. The SUV max/avg values of the liver, Thoracic: T11-T12 and Cervical: C3-C5 spinal cord segments and the bowel FDG activities of the ambulatory and bedridden patients were determined and compared. Statistical analysis was performed to evaluate various factors predictive of increased spinal cord FDG uptake. Results: Median age was 54 years (18- 93). Primary tumor histology was lung (21.8%), breast (9.3%), melanoma (15.6 %) and lymphomas (21.8%). The mean SUV max/avg values were liver (2.89/2.43); Thoracic cord (2.46/1.89); Cervical cord (2.25/1.82) and Bowel (4.4/2.9). Visible 18F-FDG thoracic spinal uptake was seen in 28%. Our analysis showed no significant correlation between the ambulatory status (p=0.219) or bowel FDG activity (p=0.210) and T11-T12 cord uptake. Conclusions: Although of no significance in this study, there might be a correlation between limb movements (amongst other factors) and physiological FDG uptake in the lower T-spine which warrants further dual studies in the same patient with and without leg motion. This may also help in differentiating normal variant spinal cord uptake from spinal cord metastatic lesions. [Table: see text]