Visualization of distal spinal cord on 18FDG PET/CT

Objectives To evaluate frequency, intensity and associations of distal spinal cord F-18 FDG uptake on PET/CT. Normal cervical but not distal cord uptake has been reported.

Methods This is a retrospective review of consecutive oncologic whole body PET/CTs from 6/14 to 8/9/06 in 108 patients (49 male, 59 female, mean age 61.9, range 26-91 years) on Siemens Biograph 6 at 60 minutes post IV F-18 FDG (median dose 15.6 mCi). Distal spinal cord visual intensity was graded on a 3-point scale. Age, gender, race, weight, diabetes, glucose level, FDG dose, scan delay, and SUV of distal cord, vertebra, blood pool and liver were recorded. The electronic medical record was reviewed > 2 years later for history of RT or evidence of distal spinal cord malignancy which might cause uptake.

Results 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 found between distal cord visual intensity and younger age, lower blood glucose, female gender, and white race, (p<0.05, chi square test.) In multiple predictor fitted regression, age, glucose and race were statistically significant (p<0.05); gender was 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.

Conclusions Mild to moderate distal spinal cord FDG uptake on PET/CT is a common normal variant, more common in younger age, white race, and lower glucose levels. It likely represents metabolic activity of lumbosacral plexus nerve cell bodies.