Colorectal Quiz Episode 30: Tethered Cord
With Dr. Christina Ho & Dr. John Maceros · hosted by Dr. Shimon Jacobs · Colorectal Channel
Cued at 7:51 · stops at 8:36 · press play
Educational content from recorded physician discussions — not medical advice. Talk to your (or your child's) care team about your situation.
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What the experts said
After about 3 or 4, maybe 5 months of age, the lamina get broad enough that the ultrasound wave cannot make it through.
If ultrasound shows the conus in a normal position, no further imaging is needed.
If the conus is clearly low on ultrasound, do not do an MRI right then; refer to neurosurgery and image after 3 months of age when MRI resolution is better and of surgical quality.
The conus medullaris is the very end of the spinal cord; just below it the filum terminale takes off with no further neural tissue, which is why it can be cut.
In a normal person, the spinal cord inside the dura is fairly free and as we grow, the spinal cord goes up with us.
A tethered cord is when the cord is low because during development it has become either attached or fixed in position, and all that tension with growth is felt at the bottom of the cord.
The spinal cord is attached to the dura by little dentate ligaments, so all tension from tethering is at the bottom of the cord where nerve roots to lower extremities and bowel/bladder exit.
Tethering causes the cord to become so taut that little micro vessels, particularly arterioles at the end of the cord, get occluded or stenosed, leading to local ischemia; lower sacral nerve roots to bowel and bladder are super sensitive to this ischemia.
When the conus is at the L2-3 disc or upper part of L3 on ultrasound, it is difficult to interpret because the conus does not find its final resting spot until about 4 months of age.
If ultrasound at 1 month shows conus at mid-L3, it may go up to a normal level; repeat ultrasound at 3-4 months rather than rushing to MRI.
If repeat ultrasound still suggests tethering, obtain an MRI; barring symptoms, follow the child, but if symptoms develop, consider untethering.
Urologic manifestations of tethered cord in babies can include recurrent febrile UTIs, bladder stones, and blood in the urine; older children may show inability to potty train or urinary incontinence.
It is very hard, almost impossible, to pick up subtle neurologic issues in a baby; symptoms may not be known until the child gets up on their feet.
Orthopedic manifestations of tethered cord may include one leg shorter than the other, one foot smaller, not moving one leg, or hip dislocation.
In a non-walking infant, tethered cord may present with asymmetric reflexes or asymmetric movement; in a toddler, delayed walking due to asymmetry in lower extremity function is concerning.
Children should not complain of back pain; a 4-year-old with back pain is concerning for tethered cord.
Midline cutaneous abnormalities above the gluteal cleft—such as a small meningocele, midline dimple, residual tail, midline lipoma with appendage, or large hemangioma—are classic signs of tethered cord that do not require MRI for diagnosis, though MRI reveals the anatomy and structure.
Dimples within the gluteal cleft (sacral dimples) seldom indicate tethered cord; most are very low coccygeal dimples with tracts going caudal toward the tip of the coccyx, not rostral toward the cord, and show no cord tethering on imaging.
Urinary retention right after PSARP is always something urologists take note of as a potential sign of neurogenic bladder.
Significant bladder trabeculation on cystoscopy can be a red flag for neurogenic bladder.
A normal spinal cord should end between T12-L1 and L2-L3 disc spaces; a cord ending at L4-L5 disc space is way too low and clearly tethered.
Fat should not be present inside the spinal canal; while not necessarily bad and present in some normal children, children with tethered cords have a higher incidence of fat in the filum.
In some tethered cord cases, the actual problem is that the filum is thick, non-flexible, and noncompliant, preventing it from stretching; the surgery for this is fairly straightforward.
Some children with anorectal malformations and tethered cords have a spinal cord lipoma (lipomyelomeningocele) attached to the dura or extending through the fascia to the skin.
Urodynamics is the gold standard for diagnosing neurogenic bladder, especially when clinical symptoms cannot be relied upon.
Urodynamics measures bladder parameters including storage capacity, compliance, pressures within the bladder, and pelvic floor activity during both filling and voiding phases.
In the case patient, functional bladder capacity was 14cc (expected 60cc for age), with significant detrusor overactivity, detrusor-sphincter dyssynergia, and incomplete emptying—defining a hostile neurogenic bladder.
The tendency is to untether babies with tethered cords upfront because evidence shows somewhere around 80% will eventually become symptomatic, and early surgery helps avoid missed symptoms.
Unless the conus is below the L2-3 disc (mid-L3 or lower), it is not considered radiographically tethered.
If the conus is at L2-3 disc space, untethering will not be performed regardless of clinical concerns; if below the upper end plate of L3 with any concerning findings, the family should be strongly counseled to consider untethering.
It is very hard to parse out whether bladder dysfunction after an operation is due to the tethered cord or to surgical injury, since both can cause the same problem.
In a little baby with urodynamic studies concerning for a real neurogenic problem and a tethered cord, filum sectioning is a 45-minute operation with relative risks close to zero and potential benefits that are huge.
If there is any dysfunction, weakness, numbness, prolonged pain, or bladder dysfunction for a long period of time, you are probably not going to get that back with surgery; you may prevent it from worsening, but you are probably not going to reverse it.
One of the biggest benefits to tethered cord repair, especially in infants, is that it prevents bladder dysfunction from worsening; in older children it may not undo what has been done already, but the goal is to prevent worsening that could lead to renal dysfunction.
Blood and infection in tethered cord operations increase the risk for retethering by causing inflammatory processes that allow nerve roots to clump and the cord to potentially retether.
The incidence of retethering from sectioning a filum is exceedingly low.
The filum sectioning operation can now be done through a small incision without a complete laminectomy, taking a little bit of one lamina and the one below, opening a door about 1 centimeter, and using a microscope for visualization.
With filum sectioning, there are just two raw ends of a very small (3-4 millimeter) filum; the chances those will come back together is essentially zero, and the chances the end attached to the spinal cord will get stuck somewhere are pretty small.
Children with big lipomas on the end of their cords will have some residual lipoma after untethering; taking out the entire lipoma is not necessary nor safe because you would end up in the cord.
Children with lipomas have a much bigger surface area of scar typically on the dorsal aspect of the spine; because children lie on their back and sleep, the cord falls back against the dura and eventually retethers.
If all tethered cord patients with anything more than filum sectioning (and even those) are re-imaged, essentially all look like they are tethered, but not that many are clinically tethered.
For complex tethered cords, the retethering rate is quoted at 40% clinically, probably somewhere between 20-40%; for filum sectioning, retethering is pretty close to zero.
Urodynamics are always repeated about 3 months after a tethered cord release, which is enough time to allow inflammation to settle out and to see the effects on the bladder.
Key urodynamic findings for neurogenic bladder include decreased functional capacity, incomplete bladder emptying, detrusor overactivity, detrusor-sphincter dyssynergia, and impaired compliance with high storage pressures.
Babies with an anorectal malformation have approximately 25% association of a spinal problem.
All babies with anorectal malformation need to be screened in the newborn period with a spinal ultrasound.
Higher types of anorectal malformations are more likely to have associated spinal and sacral problems.
Bladder dysfunction without a spinal problem usually represents an iatrogenic injury to the bladder neck.
A radiographically tethered cord at L3 or below in infants should be strongly considered for release to prevent later issues; in older children without neurological, orthopedic, or urologic dysfunction, conservative observation may be appropriate.
Sectioning a tethered cord in infants can be easier to perform with lower rates of retethering than lipomyelomeningoceles.
After tethered cord release, repeat urodynamics and clinical follow-up is vital to determine need for future urologic and bowel management procedures.