An 18-year-old male patient was thrown from a horse and suffered extensive damage to the back and pelvic region. After 2 weeks of recovery, it is noted that the patient has a spastic neurogenic urinary bladder. Although the patient is unable to initiate micturition, the bladder periodically empties itself. Where is the lesion affecting control of the bladder in this patient located?
- cauda equine
- spinal cord, above the level of S2
- spinal cord, at the level of S2
- spinal cord, at the level of S3
- spinal cord, at the level of S4
Answer(s): B
Explanation:
Since the patient presents with a spastic neurogenic bladder, the lesion is in the spinal cord above the level of S2. The micturition reflex works as follows: when the bladder becomes distended, sensory impulses travel back from the bladder to synapse onto preganglionic parasympathetic neurons located at the levels of S2-S4. These neurons, in turn, excite postganglionic parasympathetic neurons which innervate and cause contraction of the detrusor muscle of the urinary bladder, thus emptying the bladder. This primitive reflex loop comes under supraspinal influence in early childhood when the child learns control of the micturition reflex. When the supraspinal influence is removed, as happens with spinal lesions above the level of S2, the primitive reflex loop remains and the neurogenic spastic bladder empties itself reflexively whenever it becomes full. Lesions in the cauda equina (choice A), or in the spinal cord at the level of S2 (choice B), S3 (choice D), or S4 (choice E) will result in a flaccid bladder because of loss of innervation to the detrusor muscle. In this case, the bladder does not contract by itself and the patient will have to be catherized to prevent cystitis.