Q. A 56-year-old male was admitted yesterday with a history of chronic leg pain, difficulty walking, and recent episodes of incontinence. The patient describes difficulty initiating urination, and a weak urinary stream. He reports the symptoms have progressively worsened over the past few years. He has a history of untreated syphilis, which was diagnosed 10 years ago. He also reports that he has been experiencing sharp, shooting pains in his legs, particularly at night, for the past several months. He has been using over-the-counter pain medication to manage the pain but has found it to be ineffective. Today, the patient appears to be in moderate distress, with obvious pain and discomfort in his legs. On physical examination, the patient is noted to have bilateral Argyll Robertson pupils. His neuromuscular assessment demonstrates a positive Romberg test, decreased deep tendon reflexes particularly in his Achilles tendons and knee reflexes, positive loss of position sense in his lower extremities, and a positive loss of vibration sense. Warmth, erythema, and mild edema is noted over the dorsum of his feet bilaterally. Bilateral Babinski's reflexes are also observed. You order a bladder ultrasound to assess the patient’s complaints of incontinence (see image). Based on the information you have at this point in time, which of the following is the most likely cause of his incontinence?