The patient came to the clinic 31-May-2010 complaining of LBP for three months with left sciatica down to the lateral malleolus. MRI performed 28-February-2010 showing bulge L3-4 and severe lumbar canal stenosis L4-5 and left lateral recess syndrome.

The patient is unable to walk more than 100 meters. On examination: there is exaggerated scoliotic stance with drop left foot 0/5 and weak dorsiflexion right foot and planterflexion left foot -4/5. There is hypalgesia left L5 and S1 roots.

MRI of the lumbar spine performed 01-June-2010 confirming the previous data.

Decompressive laminectomy of L4 and partial of L5 and flavotomy of L3-4 was achieved. Extended foraminotomy of left L5 root was done. After decompressing the root a cystic dural structure appeared lateral to the root. It was inspected and studied so as not to miss and extruded disc or ganglion from the facet. It became clear that it was a Tarlov cyst, which shrunk and disappeared after bipolar coagulation. Inspection of the annulus fibrosis was negative for disc extrusion. Check for instability at the start and the end of the operation was also negative.

Routine closure of the wound and smooth postoperative recovery with dramatic improvement of the power of both feet.

Tarlov cysts are usually below the dorsal root ganglion and they are frequently seen in MR myelography.

This Tarlov type lesion was the lateral side of the axilla of left L5 root, mimicking ruptured ganglion or extruded disc material. The surgeon must be careful in evaluating these findings and Tarlov cyst must be considered in the differential diagnosis as in this case. This finding is extremely rare, but must be kept in mind.