Purely Giant Extradural Lumbar Spinal Schwannoma Residing Completely Outside the Neural Foramina

A 50-year-old man arrived with prolonged and progressive low back pain accompanied by weakness in his left leg. Magnetic resonance imaging of the lumbar spine demonstrated a purely extradural, well-encapsulated mass measuring 6 × 5 × 4 cm originating from the third lumbar spinal root. The lesion exhibited the characteristic T2 “target sign,” suggesting a spinal nerve schwannoma residing completely outside the neural foramina, which was confirmed with histopathology. Although rare, lumbar schwannoma should be included in the differential diagnosis of radicular low back pain; the T2 “target sign” and well-encapsulated morphology are key diagnostic clues.