[Perineural cysts causing severe back pain and pathological fracture of the massa lateralis of the sacrum].

We report on the case of an 81-year-old woman who was hospitalised because of severe pain at the sacro-iliacal joint radiating into the left leg without any accompanying neurological defect. X-rays demonstrated a step in the left massa lateralis of the sacrum, thus CT scans and MRI were performed, and multiple perineural cysts (Tarlov's cysts) were found. The patient underwent microsurgical treatment by fenestration of the cyst wall and evacuation of the fluid content in order to avoid further expansion of the cysts. Under consequent treatment with pain killers, complete mobilisation of the patient could be achieved. Ambulant follow-up by clinical controls and X-rays demonstrated a substantial resolution of the patient's preoperative symptoms. Symptomatic perineural cysts should be included into differential diagnosis of severe low back pain, thus CT or MRI scans should be performed in case of long-lasting or intrackable pain.