The spine is composed of small bones called vertebrae that surround the spinal cord. Between each vertebra is a cushion called a disc. With time or trauma, the jelly-like center of the disc may shift and leak out through a crack in the tougher, outer covering. This is called a disc herniation or "slipped disc." The lower, or lumbar, regions of the spine are a common area for disc herniation. Although pain is the most common symptom of lumbar disc herniation, complications involving the bladder and the bowel may occur in rare cases.
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An L1/L2 herniation is an especially common type of disc herniation. It occurs at the disc between the first and second lumbar vertabrae. An L2/L3 herniation occurs between the second and third lumbar vertebrae. Herniations involving L2 may result in different but related syndromes. Conus medullaris syndrome is the name given to the collection of symptoms that occur when the nerve fibers at the end of the spinal cord -- the conus medullaris -- are damaged. Cauda equina syndrome occurs when the nerve fibers that hang below the spinal cord -- the cauda equina -- are damaged.
A possible complication of both of these syndromes is urinary retention, in which the bladder becomes paralyzed and cannot empty normally. Severe lower abdominal or pelvic discomfort and difficulty initiating urination are potential symptoms of urinary retention.
A lumbar disc herniation resulting in conus medullaris or cauda equina syndrome may also lead to urinary incontinence. This occurs because the bladder becomes overfilled with urine, but the muscles within the bladder are paralyzed and cannot contract to propel the urine out. The patient is not able to voluntarily empty the bladder but urine leaks out involuntarily.
A sphincter is simply a medical term for a ring of muscles that controls the opening and closing of body passages. The anal sphincter, for instance, controls the exit of stool from the end of the bowel. The urethral sphincter controls the exit of urine from the bladder. When a lumbar disc herniates and causes conus medullaris or cauda equina damage, these sphincters may not function properly.
If the anal sphincter is not working, fecal incontinence may occur. This means the patient loses the ability to control the passage of stool from the bowels. If the urethral sphincter is not working properly, urine leaks from the bladder. Thus, two factors can cause urinary incontinence with a lumbar disc herniation.