Cauda Equina Syndrome
The spinal cord transmits the signal to and from the body to the brain as it travels down the vertebral column. Enclosed in the vertebral canal, the spinal cord is protected by the vertebral column. The spinal cord gives numerous branches known as nerve roots that unite to form spinal nerves.
The spinal cord ends at the lower level of T12 or L1 vertebrae. At its termination, the spinal cord forms a collection of spinal nerves L1-S5 that continues down the vertebral canal and exiting at various neural foramina. This collection of spinal nerves is known as Cauda Equina (horse’s tail).
The nerves in Cauda Equina control the movement of the lower limbs and maintain the bladder bowel control. The nerves also transmit the sensory signals from the lower extremities and the saddle area to the brain. The nerves in Cauda Equina are more sensitive to any compression compared to other nerves in the body.
Causes & Pathology
Intervertebral disc herniation is the most common cause of cauda equina syndrome. The herniated disc may compress the thecal sac leading to compression of the spinal nerves. Spinal canal stenosis may also lead to compression of the cauda equina.
Trauma due to falling from a height or motor vehicle accident may cause dislocation, collapse, or retropulsion of fracture fragments in the canal. The subsequent compression leads to cauda equina syndrome. Misplaced vertebrae, known as spondylolisthesis, may lead to narrowing of the vertebral canal.
Other causes of cauda equina syndrome include spine tumors, epidural hematoma (blood collection in the outer layer of the dural sac), or inadvertent injury during spinal surgery.
The mechanical pressure on the nerve roots leads to the decreased blood supply to the nerves. The resulting ischemia leads to damage to the nerve fibers, leading to loss of the neural signal transmission.
The most common initial complaint is back pain, usually followed by leg pain in one or both legs. The patients may complain of numbness in the perianal/saddle area. The patients often complain of not being able to feel the toilet paper. Patients may also complain of sexual dysfunction.
There may be a weakness in one or both of the legs. The patients may also complain of numbness and tingling sensation in the legs. In advanced cases, there may be loss of bladder control. The patients may feel a sense of incomplete evacuation or involuntary evacuation of the bladder. In rare cases, the patients may experience loss of bowel control as well.
The physician makes the diagnosis of cauda equina syndrome after a detailed history and physical examination. The physician may perform a thorough neurological analysis to ascertain the motor and sensory functions of the limbs and the peri-anal area.
An MRI is the imaging study of choice for evaluating neurological compression. An X-ray is usually done in traumatic injury cases and to assess the bony structures along with MRI. A CT myelography may be done in patients who are unable to do an MRI evaluation.
Blood investigations may be done if an infection is the suspected cause of cauda equina syndrome. Bladder investigations such as urodynamic studies may be done to assess the filling volumes of the bladder before and after voiding.
Cauda Equina syndrome is a surgical emergency, and the standard management is decompression surgery. The decompression surgery may involve discectomy, discectomy with laminectomy, or discectomy with laminectomy and fusion. The surgical technique involved in the management depends on the patient’s anatomy and the compressing structures.
In discectomy surgery, the herniated intervertebral disc is removed to alleviate the pressure on the spinal nerves. The discectomy is usually performed after creating a hole in the lamina (laminotomy). In cases of spinal stenosis, discectomy is often done along with lumbar laminectomy surgery. The surgeon may also add implants along with lumbar fusion surgery if instability is suspected.
Complications occur in untreated cauda equina syndrome cases or in cases where the surgery was delayed for more than 48 hours. The symptoms of cauda equina syndrome may persist or may recover very slowly over the years. Bladder dysfunction may require a permanent catheterization of the bladder. Sexual dysfunction, chronic pain, and weakness of the lower extremities may persist for years.
As with any surgery, there may be potential complications associated with decompression surgery, such as nerve root injury, bleeding, infection, blood clots, dural tear, epidural fibrosis, etc.