Signs and Symptoms

Tethered cord syndrome often presents differently in children versus adults. In children, the onset of symptoms is usually gradual over time, whereas in adults the onset may be more precipitous after only minor or no symptoms in childhood. Adult tethered cord syndrome is therefore sometimes divided into two types: one type with onset of symptoms in adulthood and the other type with minor symptoms in childhood but major symptoms in adulthood, possibly triggered by degenerative changes or disc herniation that contribute to stretching of the spinal cord. This latter group also includes patients that may have unrecognized tethered cord until minor trauma such as a blow to the back, the lithotomy position of childbirth, and other instances of sudden trunk flexion or extension causes precipitous neurologic decline.

Adults with underlying tethered cord commonly present with pain (67% to 82%), weakness (37% to 72%), sensory changes (24% to 79%), urinary dysfunction (50% to 69%), and scoliosis (46%). Pain is often localized to the perineal or gluteal region but is more common as a presenting sign in adults than children. In both groups, the sensory loss or pain distribution may be nondermatomal, which can lead to a delay in diagnosis or misdiagnosis. Pain is also often a presenting symptom in children, but it may be more difficult to recognize in very young children. In infants, parents may notice crying or irritability with diapering or other maneuvers that cause truncal flexion. In toddlers, this behavior may present as a perceived need to rest during play. In a 2008 review of pediatric tethered cord syndrome by Bui and colleagues, the reported incidence of pain as a presenting symptom was only 6%. Delay in acquisition of gross motor skills such as cruising or walking can be an early sign of lower extremity weakness in children.

Symptomatic retethering can present in a similar fashion to primary tethering. One may see gait and postural changes, increasing lordosis, or increased stumbling and falling, particularly in toddlers or young children. Non-neurologic signs of tethered cord include urinary incontinence, which may present as regression of toileting skills in a young child previously toilet trained. Bowel involvement typically presents as constipation in the early years.

A patient presenting with symptoms suggestive of tethered cord should receive a careful inspection of the midline skin overlying the entire spinal axis, even in the older patient, because subtle skin findings such as small dimples, hemangiomas, or tracts may have been missed in infancy or their significance gone unrecognized. A cutaneous marker is seen in up to 70% of patients with an underlying spinal dysraphism and is found in only 3% of people who do not have an underlying tethered cord. These cutaneous markers can include a midline skin dimple or sinus tract, hypertrichosis (often seen with split cord malformation), “cigarette burn” (meningocele manqué or aplasia cutis), raised subcutaneous mass (lipoma or cerebrospinal fluid [CSF] containing), dermal appendage, deviated or forked gluteal cleft, or a vascular hemangioma. Even an isolated lumbosacral capillary hemangioma was found to have an incidence of underlying tethered cord of 17.5% by Tubbs and colleagues.

Careful inspection of the natal cleft for dimples and symmetry may reveal a dimple below the top of the gluteal crease in 2% to 4% of normal newborns. Although it has long been recognized that midline uncomplicated dimples located within the gluteal crease (so-called coccygeal pits) are unlikely to be associated with a tethering lesion, Gomi and associates have classified all sacral dimples into three subtypes to further aid in decision making about which low-lying dimples require imaging workup. Type 1 are the aforementioned dimples located within the gluteal crease near the anus and none of these required surgical intervention for tethered cord, although 17% had imaging abnormality of the filum (fibrolipoma, filar cyst, and thickened filum) but all had normal conus location. Another study found that the risk of significant spinal malformations with these simple sacral dimples was only 0.13%. Type 2 dimples were described as those at the upper end of the gluteal crease associated with asymmetry of shape of the gluteal crease itself. About 45% of these patients had imaging abnormalities of the filum and in 6% this was associated with low-lying conus, which led to a recommendation for surgical untethering. Type 3 dimples were defined as those sacral dimples located above the gluteal crease, and of these, 50% had filar abnormality or dorsal lipoma and 37% met criteria for tethered cord. Gomi and associates have therefore advocated imaging evaluation for all patients with type 2 and type 3 dimples.

Patients with tethered cord syndrome may also need evaluation for scoliosis. The incidence varies from 28% in patients with lipomyelomeningocele to 50% to 60% in patients with split cord malformations. In patients with myelomeningocele, as many as 40% will have progressive scoliosis as one of the indications for surgical untethering, and up to 11% may have this condition as the sole indication for surgery for symptomatic retethering, although the long-term results in reversing or even halting the progression with advanced curves > 46 degrees, especially in patients with high level lesions, require further study.

Evaluation

Several imaging modalities are available to evaluate a patient with possible tethered spinal cord. Spinal ultrasound may be useful in infants younger than a few months of age where the cartilaginous spine allows a sonographic window into the thecal sac. It can serve as a cost-effective screening tool for patients with borderline dimples (who are felt to be at intermediate risk for an underlying tethering lesion) and does not require sedation. It can assess the location and pulsatility of the conus and rule out intraspinal tethering lesions such as an intradural lipoma. The modality of choice for most patients remains an magnetic resonance imaging (MRI) but a computed tomography (CT) myelogram may on occasion be used in some select cases of split cord malformation or if an MRI is contraindicated due to the presence of surgical implants. Diffusion weighted sequences are sometimes used to help identify intraspinal dermoid cysts, although the radiographic differentiation from other small intraspinal lesions in a postoperative patient can be challenging in some instances. X-rays are still used for the determination of scoliotic curves, both pre and postoperatively, and at times for intraoperative localization.

Another important part of the evaluation for tethered cord syndrome in most patients is a complete urologic workup, typically including urodynamic studies. Not only does this provide objective data for decision making in borderline cases, but also it allows for better pre and postoperative comparison of function. This has been found to be useful for perioperative guidance, even in young children with limited capacity to cooperate with testing.

Rationale for Treatment

The rationale for treatment of a patient with a progressive neurologic deficit related to an underlying tethered cord is to stabilize or improve the deficit. Particularly when the presenting symptom is pain, especially back pain, results are generally good in alleviating the presenting symptom. The goal of surgery in the patient with a fixed deficit and a congenital closed dysraphic lesion is to stabilize the deficit. The deficit may in part result from the effects of traction on the conus and the resulting tethering, but also from the fixed irreversible myelodysplasia itself.

There continues to be debate about the timing of such intervention, particularly in the more complex dysraphic states where surgical risk has to be taken into account and rates of symptomatic retethering remain relatively high (ranging from 5% with some lipomas to 30% with myelomeningocele). Proponents of prophylactic surgery even for asymptomatic children with congenital tethering lesions point to natural history studies, which suggest that surgery offers greater protection of function than conservative management even for complex lesions. However, there is still a recognized paucity of prospective randomized studies available to help guide management for some of these lesions.

Myelomeningocele

The incidence of myelomeningocele, which has decreased since the 1980s due at least in part to the wide availability of folic acid supplementation, is currently 3.5 per 10,000 live births in the United States, with females having up to a 14% higher prevalence than males. Periconceptual folic acid has been shown to reduce the incidence and recurrence rate of having a child with an open neural tube defect. The most common locations for open neural tube defects are lumbosacral, thoracolumbar, and cervical (in order of decreasing frequency). Almost all patients with an open defect have an associated Chiari II malformation, although this is not exclusive to myelomeningoceles, as it is being increasingly recognized in patients with myelocystoceles.

Prenatal Diagnosis and Repair

Fetal MRI is increasingly being used to confirm a prenatal diagnosis of an open neural tube defect because of the availability of in utero repair of myelomeningocele as an option for some patients. Fetal MRI in these cases is typically obtained after screening tests that may include elevated maternal serum alpha-fetoprotein, the finding of a spinal defect and posterior fossa abnormality on obstetric ultrasound, and amniocentesis that reveals elevated alpha-fetoprotein and positive acetylcholinesterase. Fetal MRI can characterize the anatomy of the developing brain, certain features of the Chiari II malformation, features of the myelomeningocele and spinal cord, as well as associated anomalies of the spine, particularly kyphosis ( Fig. 161-1 ). In addition, fetal MRI is helpful in looking for associated anomalies of other systems because patients with myelomeningocele have a significant incidence of anomalies of genitourinary, gastrointestinal, pulmonary, craniofacial, and cardiovascular systems.

Sagittal True-FISP/FIESTA image from fetal MRI at 22 weeks gestational age demonstrating an open lumbosacral spinal dysraphism (small arrow) and Chiari II malformation with hindbrain herniation (large arrow).

The rationale for offering fetal surgery for myelomeningocele repair is based on the results of the Management of Myelomeningocele Study (MOMS trial) published in 2011 in the New England Journal of Medicine. This prospective randomized trial was conducted at three large centers comparing in utero repair of myelomeningoceles before 26 weeks of gestation to standard postnatal repair. Primary end points were fetal or neonatal death and the need for placement of a CSF shunt by the age of 12 months. The second primary outcome was a composite score of the mental development and motor function at 30 months.

The trial was halted early because results showed clear efficacy of prenatal surgery. Rates of shunting were 40% in the prenatal surgery group, versus 82% of the postnatal surgery group. Traditionally the literature for myelomeningocele repaired after delivery indicates that shunts are required in 85% of patients. In addition, prenatal surgery resulted in improvement in the composite score for mental development and motor function at 30 months of age. There was also an improvement in several secondary outcomes, including the degree of hindbrain herniation (Chiari II malformation) by 12 months. The durability of these results long term is still being studied. Prenatal surgery, however, was associated with an increased risk of preterm delivery and uterine dehiscence at delivery.

Postnatal Management

The myelomeningocele may be surgically repaired within the first 48 to 72 hours of life without a significant increase in neurologic morbidity or infectious complications. The exposed placode is sharply dissected from the surrounding skin, taking care to avoid injury to the exiting nerve roots. Every effort should be made to remove remnants of skin from the edges of the placode to minimize the chance of development of an inclusion cyst. The surrounding dura can then be circumferentially elevated from the underlying fascia and approximated to create a capacious dural sac. Dural grafts are generally not necessary, do not decrease the risk of subsequent tethering, and may potentially increase the risk of CSF leakage. Benefits of closing additional layers (such as the lumbodorsal fascia) between the dura and skin remain unclear.

Hydrocephalus is present or develops in 80% to 90% of children born with myelomeningoceles. Some children present at birth with obvious signs of hydrocephalus, and a CSF diversionary procedure can be performed at the same time as the myelomeningocele closure without increased risk, which may protect against wound CSF leakage. More commonly, hydrocephalus is not clinically obvious at birth and develops days to weeks after initial closure. Hydrocephalus may also worsen or exacerbate signs or symptoms of the Chiari II malformation or cause leaking from the spinal incision even without changes in intracranial ventricle size.

One of the major sources of morbidity and mortality in myelomeningocele patients is symptomatic brain stem dysfunction related to the Chiari II malformation. Although as many as 29% to 76% of children may develop symptoms referable to the Chiari II malformation, only about one third require treatment. Brain stem dysfunction manifesting as stridor, apnea, dysphagia, or bradycardia may become symptomatic due to untreated hydrocephalus or shunt malfunction and often resolves after adequate treatment of hydrocephalus, either with a CSF shunt or endoscopic third ventriculocisternostomy (ETV) using the criteria of the ETV success score as a guide. However, there are patients who continue to neurologically deteriorate despite having adequate CSF diversion. In these cases, many authors advocate early decompression of the Chiari II malformation, although patients who present with bilateral vocal cord paralysis tend to have less chance of recovery even with aggressive surgical management.

Long-Term Follow-Up

Postoperatively, longitudinal multidisciplinary follow-up is needed for these patients to monitor for progressive neurologic, urologic, or orthopedic impairments that may in part reflect symptomatic retethering in patients with myelomeningocele. Several studies have documented improvement or stabilization of neurologic function, urologic disorders, and orthopedic deformities after surgical procedures for untethering. Tethered cord releases were performed in 32% of patients in one large series, showing improvement or stabilization in 97% of patients. Comprehensive care that can be provided in the setting of a multiprovider clinic not only facilitates making this diagnosis but allows it to be done in a cost-effective manner that consolidates visits for the family and the patient.

A spinal cord syrinx may also develop in 50% to 80% of patients with myelomeningocele, but it only becomes symptomatic in ~1.8% to 5%. It may lead to symptoms such as muscle weakness, sensory loss, spasticity, pain, and scoliosis. (Just as with symptomatic Chiari II malformation and retethering, shunt malfunction always needs to be ruled out first if the patient has shunt dependent hydrocephalus and develops new symptomatology.) Treatment of a syrinx depends on the location of the syrinx and type of symptoms the patient develops. La Marca and coworkers outlined an algorithm that can be helpful in deciding whether to address the syrinx directly with shunting, to decompress an associated Chiari II malformation, or to consider a lumbar laminectomy for untethering of the neural placode. This algorithm uses the patient’s symptomatology to determine which of these options is most likely to be beneficial in treating the syrinx.

Long-Term Outcome

Bowman and colleagues reviewed the 25-year outcomes of a cohort of 118 patients treated for myelomeningocele in the modern era. They found that the overall mortality rate was 24%, with early deaths due to the Chiari II malformation and late deaths due to shunt failures. Scoliosis was present in 49% of patients, with 43% eventually requiring a spinal fusion. Seizures occurred in 23% of the cohort. In terms of education, 85% of patients attended or graduated from high school or college. More than 80% achieved social bladder continence. Overall the study points out that these patients with complex medical conditions continue to need our assistance as they get older and face the challenges of adulthood.