53-year-old male, who started with pain and impotence in both lower limbs, numbness in the legs with paraesthesia and, in recent weeks, difficulty in walking. The symptoms were partially relieved when lying down and did not worsen when sitting. The predominant symptomatology was sensory, with severe pain in the lower limbs.
The pain increased with Valsalva manoeuvres and suffered cyclical worsening.
The whole picture began in September 2002, one year before being seen in the neurosurgery department.
The patient's only antecedents were back pain and a bilateral inguinal hernia operation years before, under general anaesthesia.
Magnetic resonance imaging showed an extradural, intrathecal, polylobulated, intrathecal collection compressing 90% of the dural sac. It was reported by the radiologist as an L2-L3 synovial cyst.

Spinal angiography was not performed, although neither the MRI images nor the surgical procedure revealed any type of vascular malformation.
Intervention
A laminectomy was performed from L4 to L2. At L3 and L2, fragments of bone and cartilaginous tissue began to be obtained, infiltrated by a dark liquid which, in addition, spilled into the operative field with an appearance similar to fuel oil. The tissue is removed from the area, decompressing the dural sac, and the incision is closed.
Pathological anatomy
The pathology report describes the extemporaneous and postoperative specimens as osteocartilaginous tissue, muscle and fibrous tissue, with areas of haemorrhage and macrophages in the periphery laden with haemosideric pigment.

No other lesions or malignant or atypical cells were observed.
Postoperative outcome
Postoperative recovery was excellent with no complications and total improvement of symptoms.
After one year of follow-up the patient remains totally asymptomatic.

