We report the case of a 40-year-old man remitted to our department with a 
history of lower back pain and sciatica with no history of trauma. The 
laboratory analyses showed normal values whereas plain radiographs showed a 
sacrum rarefaction area. A 99mTc-MDP bone scintigraphy was performed to evaluate 
the lumbosacral area. Planar images did not show any abnormality. SPECT images 
revealed photopenic abnormality in the second sacral vertebral right hemibody, 
with no peripherally increased radiotracer accumulation. Subsequent MRI and CT 
myelography demonstrated the nature of the photopenic area as secondary to 
vertebral erosion by sacral perineurial cyst (Tarlov cyst).