Cauda Equina L5-S1 Disc

A 34-year-old male construction worker presents to the emergency department with 12 hours of progressive severe low back pain radiating bilaterally, inability to void, perineal numbness, and bilateral ankle weakness (grade 3/5). Examination reveals saddle anaesthesia (S2–S4), absent anal wink and bulbocavernosus reflex, post-void residual of 720 mL, and absent bilateral ankle jerks. Urgent MRI of the lumbosacral spine shows the structure marked **A** measuring 14 × 12 mm with severe compression of the thecal sac (residual AP diameter <4 mm) and displacement of cauda equina roots. Which of the following is the most appropriate immediate management?