A 43-year-old man presented with a 2-year history of low back pain and he had undergone conservative medical treatment with a diagnosis of L5 spondylolysis. He consulted us with a complaint of left severe sciatica causing difficulty in walking for 3 weeks. He had no obvious history of trauma. Neurological examination revealed normal deep tendon reflexes in the lower legs bilaterally (patellar tendon reflex and Achilles tendon reflex) and a negative result upon performing the straight leg raising test. There were no sensory disturbances, motor weakness or urinary incontinence. Plain lumbar spine radiographs showed spondylolysis and anterolisthesis of L5. Magnetic resonance imaging (MRI) demonstrated an extradural mass on the left side at L4. This mass lesion showed mixed high and iso-intensity on T1-weighted imaging, and mixed high and low intensity on T2-weighted imaging (Fig. ). The mass also exhibited clear rim enhancement upon T1-weighted imaging with Gadolinium (Gd) (Fig. ). The mass compressed the dural tube and was continuous with the left L4-5 facet joint. A myelogram of the lumbar spine showed a large defect of contrast medium extending from the level of the L4 pedicle to the L4-5 facet joint on the left side; in addition, the left L4 and L5 roots were not described. A computed tomography (CT) myelogram revealed an extradural defect of contrast medium at the L4 level and an erosion of the L4 lamina (Fig. ).
The patient was taken to the operating room for spinal decompression, resection of the mass and histological diagnosis. He was placed in the prone position and a 7-cm-long midline skin incision was made, so as to expose the L4 lamina on only the left side. The paraspinal muscle on the right side was not divided. A unilateral osteoplastic laminectomy was performed for the left L4 lamina. The left lamina was cut at a slanting angle at the level of the pedicle, while exercising care to protect the L4 root. The spinous process was split in half using a micro-bone saw and chisel. The left lamina was temporarily removed en bloc after the articular capsule of the left L4-5 facet joint was incised. The softly elastic and dark reddish-brown mass lesion originating from the left L4-5 facet joint was observed at the dorsum of the ligamentum flavum. The mass adhered to the L4 and L5 roots on the left side, and was approximately 25 mm in diameter. The mass was totally resected along with the capsule of facet joint (Fig. ). Finally, the previously resected lamina was replaced en bloc and was firmly fixed using a 30 mm cancellous screw, 4.5 mm in diameter (SYNTHES, Davos, Switzerland) as a lag screw.
Pathologically, the mass was composed of mononuclear cells and showed varying degrees of cellularity. There was marked synovial invasion by masses of polygonal and round cells with round nuclei. Scattered osteoclast-like giant cells and hemosiderin-laden macrophages were also present (Fig. ). CD68 staining was positive for macrophages [
8]. The histological findings were consistent with a diagnosis of PVNS.
Postoperatively, the patient recovered with a complete relief of his symptoms. Three years after surgery he still had no pain and his neurological examination was normal. Plain lumbar spine radiographs and a CT scan showed the union of L4 laminae in the original position (Fig. ). An MRI at that time demonstrated no recurrence of PVNS (Fig. ).
1 Yugo Yoshida,1 Hiroyuki Ohnari,1 Hirokazu Iida,1 Noriko Sakaida,2 and Yoshiko Uemura2
