In positron emission tomography (PET) with F-18-fluorodeoxyglucose (FDG), non-tumorous focal uptake is often observed around the lumbar spinous processes (LSPs). Close approximation of LSPs with sclerosis is often seen, which is called Baastrup disease. The aim of this study was to characterize this finding in terms of location and subjects' age and investigate the relation between PET and CT findings.
The PET/CT scans of 40 patients each in the fifth, sixth, seventh, eighth, and ninth decades were screened for FDG uptake around the LSPs from L1-2 through L5-S1. Patients with metastasis to the lumbar spine or recent chemotherapy or rheumatoid arthritis-related disease were excluded. Focal uptake greater than blood pool activity was considered positive. Positive uptake was compared among the ages and locations. We also evaluated the relationship between FDG uptake and CT morphology.
Overall, focal uptake was observed in 122 LSPs in 71 patients. At least one positive uptake was seen in 9, 21, 15, 12, and 14 of 40 patients (16, 30, 30, 20, and 26 of 200 regions) in each age group of 40s through 80s, respectively (p = 0.12). As for the location, uptake around L1-2, L2-3, L3-4, L4-5, and L5-S1 was observed in 19, 22, 39, 35, and 7 regions, respectively (p < 0.01). There was no statistically significant difference in PET positivity among the five age groups, but positive uptake was predominantly seen in L3-4. Degeneration on CT was apparent in 58, 74, 108, 123, and 144 regions in each age group, respectively (p < 0.01), and in 38, 79, 131, 151, and 108 regions in each location, respectively (p < 0.01). The PET positive ratio was higher in CT positive group than in CT negative group (14 vs. 10 %, p < 0.05), but there was no significant difference of quantitative values (p = 0.10). Of 42 regions in 27 patients who had serial PET/CT scans that were initially PET-positive, 35 regions (83 %) turned negative on a later PET-scan.
Focal uptake around the LSPs was commonly seen in the mid-lumbar vertebrae, independent of age, and was not always correlated with morphological changes. This uptake should not be assumed to represent osseous metastasis.