A 45-year-old man presents with acute onset severe low back pain radiating bilaterally down the posterior thighs and calves. He reports saddle paresthesias involving the perineum and inner thighs, urinary retention with overflow incontinence, fecal incontinence, and erectile dysfunction following heavy lifting 12 hours ago. On examination, he has bilateral lower extremity weakness affecting dorsiflexion and plantarflexion, diminished ankle jerks, absent anal wink reflex, and post-void residual volume of 600 mL. MRI lumbar spine sagittal T2 demonstrates a large central disc herniation at L4-L5 with inferior migration compressing the cauda equina and obliteration of the CSF space, as marked **A** in the diagram. What is the most appropriate immediate management for this patient?