Visualization of Distal Spinal Cord on F-18 FDG PET/CT

Abstract

The purpose of this study was to evaluate frequency, intensity, and associations of distal spinal cord F-18 FDG uptake visible on PET/CT. Normal cervical, but not distal cord uptake, has been reported previously. This is a retrospective review of consecutive oncologic whole body PET/CTs from 14 June, 2006 to 9 August, 2006 in 108 patients (49 male, 59 female; mean age, 61.9 years; range, 26-91 years) on Siemens Biograph 6 at 60 minutes post IV F-18 FDG (median dose 577.2 MBq). Distal spinal cord visual intensity was graded on a 3-point scale. Age, gender, race, weight, diabetes, glucose level, F-18 FDG dose, scan delay, and standard uptake value (SUV) of distal cord, vertebra, blood pool, and liver were recorded. The electronic medical record was reviewed more than 2 years later for history of radiation therapy (RT) or evidence of distal spinal cord malignancy, which might cause uptake. There was visible distal spinal cord uptake in 55% of patients, mild in 39% and moderate in 16%, seen as a narrow band of activity up to 2 segments in length at T11-L1. None showed history of regional RT or spinal cord malignancy on medical record review. Statistically significant associations were found between distal cord visual intensity and younger age, lower blood glucose, female gender, and white race (P < 0.05, χ(2) test). In multiple predictor fitted regression, age and glucose were statistically significant (P < 0.05); gender and race were not. Higher visual intensity was associated with higher distal cord SUV (highest maximal SUV, 3.7) and higher SUV ratios to vertebra, blood pool, and liver, but with much overlap. There was no significant association with other variables. Mild to moderate distal spinal cord F-18 FDG uptake on PET/CT is a common normal variant, more common in younger age and in patients with lower glucose levels. It likely represents metabolic activity of lumbosacral plexus nerve cell bodies.