A 62-year-old man is admitted to the emergency department due to increasing difficulty in urinating over a period of several months. Physical examination reveals prostatic hypertrophy. After several unsuccessful attempts to catheterize the penile urethra, the urologist orders drainage of the urinary bladder by the least invasive procedure, avoiding entry into the peritoneal cavity or the injury of any major vessels or organs. Which of the following spaces needs to be traversed by the needle to reach the bladder?

The retropubic space (of Retzius) is the extraperitoneal space between the pubic symphysis and the bladder. A needle placed over the pubic bone, through the body wall, and into the space of Retzius will enter the full bladder but avoids entry into the peritoneum and there is little risk of damaging major organs or vessels. Entry through the ischioanal fossa would not provide a direct route to the bladder. With entry through the superficial perineal cleft, perineal body, and deep perineal pouch there is a high risk of damaging important structures.