A 73-year-old man with hypothyroidism has been in hospitalized with a spinal cord injury is evaluated at the bedside. He is unable to have bowel movements; he has only passed a stool 2 times within the past 10 days. He states that he has had involuntary passage of small loose or liquid stools during this time; it has been associated with abdominopelvic discomfort. His dietary history is remarkable for a low-fiber diet that lacks raw fruits and vegetables. Of note, he takes oxycodone for chronic back pain. He denies any abdominal or pelvic pain, weight loss, hematochezia, melena, fever, chills, or urinary complaints. His rectal exam reveals good sphincter tone, but a firm, immovable mass is detected. Bedside pelvic radiograph displays the following image.

What is the most likely diagnosis?

A) Rectal cancer
B) Prostatitis
C) Acute colitis
D) Rectal abscess
E) Fecal impaction