BACKGROUND: Acute low back pain is a very common symptom and reason for many 
medical consultations. In some unusual circumstances it could be linked to a 
rare aetiology.
CASE PRESENTATION: We report a 70-year-old man with an 8-month history of left 
posterior thigh and leg pain who had sudden confusion after a fall from 
standing. It was due to cerebral fat embolism suspected by computed tomography 
scan, later confirmed by brain magnetic resonance imaging (MRI). A spinal MRI 
scan was then performed and revealed a sacral fracture which drained into an 
unknown perineurial cyst (Tarlov cyst). Under medical observation the patient 
fully recovered within three weeks.
CONCLUSIONS: Sacral perineurial cysts are rare, however they remain a potential 
cause of lumbosacral radiculopathy.