NORD gratefully acknowledges Shokei Yamada, MD, PhD, FACS, Professor and Former Chairman, Department of Neurosurgery, Loma Linda University, for assistance in the preparation of this report.
Tethered cord syndrome is a stretch-induced functional disorder associated with the fixation (tethering) effect of inelastic tissue on the caudal spinal cord, limiting its movement. This abnormal attachment is associated with progressive stretching and increased tension of the spinal cord as a child ages, potentially resulting in a variety of neurological and other symptoms. Due to the variation of the growth rate of the spinal cord and the spinal column, the progression of neurological signs and symptoms is highly variable. Some individuals present with tethered cord syndrome at birth (so-called congenital), while others develop the symptomatology in infancy or early childhood. Other individuals may not develop any noticeable symptoms until adulthood. Although some authors call these cases acquired, the majority of these cases are mostly developmental, corresponding to the progressive development of excess fibrous connective tissue (fibrosis) in the filum terminale. The filum terminale is a strand of tissue that bridges the spinal cord tip and the tailbone (sacrum). The inelastic structures in children originated from defective closure of the neural tube (the precursor of the spinal cord) during embryonic development, eventually forming a condition known as spina bifida. Because of its functional (physiological) nature, tethered cord syndrome can be reversible if surgically treated in its early stage.
The specific symptoms, severity and progression of tethered cord syndrome vary from one individual to another. In most cases, individuals experience symptoms during childhood. In some cases, symptoms are stabilized in childhood, but become apparent only in adulthood.
A high percentage of pediatric cases, with tethered cord syndrome show cutaneous tufts of hair, skin tags, dimples, benign fatty tumors, skin discoloration or hemangiomas. Additional symptoms include lower back pain that worsens with activity and improves with rest (although rarely complained by young children, because of inability to express pain), leg pain or numbness, difficulty walking (gait disturbances), foot and spinal deformities, such as abnormal side-to-side curvature of the spine (scoliosis) or hollow lowback (exaggerated lordosis), high-arched feet and hammertoes, and less commonly difference in leg strength. Tethered cord syndrome can also cause difficulties with bladder and bowel control. Affected children may experience involuntary urination or defecation (incontinence) and repeated urinary tract infections. Symptoms in children may be slowly progressive.
Adult onset of tethered cord syndrome was considered to be rare for many years, but an increasing number of cases have been reported in recent years. This trend is due to improvement in neurological examinations and in the interpretation of imaging studies. Symptoms common to adult tethered cord syndrome include constant, often severe back and leg pain, which may extend to the rectum and genital area in some cases. Progressive sensory and motor deficits may affect the legs potentially resulting in numbness, weakness or muscle wasting (atrophy) in the affected areas. More than 50 percent of the affected individuals experience bladder and bowel dysfunction, manifested by increased frequency or urgency of urination or constipation. In some cases, a fluid-filled cavity (syrinx) is found, sometimes associated with typical signs and symptoms syringomyelia, such as burning pain in the analgesic (painless on examination) area, decreased motor function and loss of muscle mass, or occasional headaches,
Tethered cord syndrome can be of a congenital (primary) origin or acquired (secondary or developmental).
Various congenital anomalies, particularly spina bifida, are often associated with congenital tethered cord syndrome. Spina bifida is a birth defect due to incomplete closure of the posterior spinal cord and bony vertebral arch (lamina). Many cases with this anomaly leave a portion of the spinal cord protruded through the spinal canal, typically forming a myelomeningocele. Such birth defects, if located in the tail (caudal) end of the spinal cord, can cause tethered cord syndrome. In others, where the anomalous structure is attached to the wide area of the spinal cord, signs and symptoms reflect local effects on the spinal cord, and not stretched-induced dysfunction (tethered cord syndrome).
Types of spina bifida associated with tethered cord syndrome include an abnormal connection of inelastic tissue to the caudal spinal cord, dermal sinus tract, which extends from the intraspinal connective tissue to the skin (dermal sinus tract), a split spinal cord (diastematomyelia), and a benign fatty mass or tumor (lipoma) continuous to the spinal cord. The other fatty anomaly is a lipomyelomeningocele, in which a lipoma extrudes from the spinal canal underneath the lining of the spinal cord (meninges), but covered by normal skin.
In many individuals, tethered cord syndrome is caused mechanically by an inelastic often-thickened filum terminale. This structure, which is composed of glial tissue (the supportive structure of nerve cells) and covered by pia mater, is a delicate strand of fibrous tissue, bridging the spinal cord tip and the sacrum (the tailbone). Due to its high viscoelasticity, the filum allows movement of the spinal cord. If abnormal fibrous tissue grows into the filum and replaces glial tissue, the filum loses its elasticity and abnormally fixes (tethers) the spinal cord, and becomes the mechanical cause of tethered cord syndrome. The inelastic filum is commonly thickened in children, but found less frequently in adolescents and adults.
Genetic factors are involved in development of anomalous caudal spine and spinal cord, e.g. myelomeningocele, and in some cases of lipomyelomeningocele. Since tethered cord syndrome is a physiological disorder and develops only when it is abnormally stretched, it cannot be connected to genetic factors, unless the congenital susceptibility of spinal cord to oxidative metabolic impairment is proven.
Secondary causes of tethered cord syndrome include tumors, infection or the development of scar tissue (fibrosis) connected to the spinal cord. Tethered cord syndrome may develop as a complication of spinal surgery. Trauma to the spine results in a band of scar formation attached to the spinal cord and can cause tethered cord syndrome. However, some researchers believe that trauma alone is not enough to cause the disorder. They propose that tethering and abnormal tension were already present before the trauma, which worsened the condition.
Some researchers have speculated that some cases of tethered cord syndrome that occur due to anomalies that can cause stretching of the spinal cord may have a genetic basis or that some individuals are genetically predisposed to developing the disorder in these specific cases. Although genetic factors are found in patients with myelominingocele, more research is necessary to determine the exact role that genetic factors play in the development of stretch-causing anomalies.
Pathophysiologically, neuronal dysfunction in tethered cord syndrome results partly from inability for the spinal cord neurons to utilize oxygen, that is, the impaired oxidative metabolism, partly due to lack of oxygen supply (ischemic effect), and partly to ion channel dysfunction directly related neuronal membrane stretching. The spinal cord consists of a long bundle of neuronal fibers (axons) and the interneurons that connect sensory and motor fibers within the cord. During gestation, the spinal cord is continuous to the brain and runs in the spinal canal to the tailbone area. In general, the spinal cord is protected from external insult by two mechanisms; 1) encased in the spinal column, that is, a rigid structure, 2) floating free in the spinal fluid space of the spinal canal. In addition, the spinal cord is continuous to the filum terminale, which is extremely extensible because of its high viscoelasticity. If the spinal cord is tethered at its caudal end, and if the spinal cord is unable to grow as fast as the vertebral column in childhood, the spinal cord is stretched beyond its physiological tolerance. In turn, this causes various metabolic abnormalities in the spinal cord and, ultimately, the various neurological symptoms of this disorder.
Normally, the spinal cord ascends in the spinal canal as the spinal column starts to grow faster than the spinal cord at 9th weeks of gestation. Consequently, the spinal cord is pulled upwards due to this growth difference. By three months of age, the tip of the spinal cord reaches the normal level between T12 and L2 vertebrae. An elastic, extremely extensible filum allows for the ascension of the less elastic spinal cord. If the filum becomes inelastic in an embryo, then the spinal cord tip is anchored and ceases to ascend. Compensatory to the stretching force, the lower (lumbosacral) spinal cord naturally grows more than seen in normal subjects, and becomes elongated. Associated with tethered cord syndrome, the elongated cord is often noted in children, but less often in adults.
In most cases, the abnormal tension of the spinal cord increases over time, but disturbing symptoms often develop quickly during a few weeks. Certain activities such as flexing or extending the lower spinal column can put additional tension on the spinal cord and often worsen tethered cord syndrome. Participation in physical activities such as strenuous sports and ballet dancing with high kicks can worsen the signs and symptoms. Special physical features such as abnormal curvature of the spine (scoliosis and exaggerated lordosis) are the potential for symptomatic acceleration. It should be warned that slight flexion of the lower (lumbosacral) spine always aggravates back pain by spinal cord stretching.
Tethered cord syndrome affects males and females in equal numbers. The exact incidence of the disorder in the general population is unknown. In the past, the diagnosis of tethered cord syndrome has been controversial and the disorder often still remains unrecognized and underdiagnosed. After many years of skepticism, tethered cord syndrome is now considered a distinct clinical entity. In order to help clarify the situation, a proposed definition for true tethered cord syndrome limits that this disorder to individuals who exhibit neurological signs and symptoms due to inelastic structures anchoring the caudal end of the spinal cord. There are cases in which individuals have the symptoms and signs similar to true tethered cord syndrome, but have associated defects that cause compression and impaired blood flow of the spinal cord, or congenital neuronal dysgenesis (failure of neuronal development). For example, in myelomeningoceles and lipomyelomeningoceles that are directly connected to the entire dorsal surface of lumbosacral spinal cord, their neurological deficits are unrelated to spinal cord stretching (tethered cord syndrome). Symptomatically, patients with these anomalies present with complete or nearly complete paralsysis of lower limbs and total loss of bladder and rectal control.
The most important signs that can be found in late teenagers and adults are back pain aggravated immediately on flexion of the lumbosacral spine, which elongates the lumbosacral spinal canal, simultaneously stretching the lower spinal cord. The 3-Bs sign is useful for initiating suspicion of tethered cords syndrome. They include 1) bending slightly (over the sink), 2) Buddha sitting with legs crossed (like the Yoga pose) and 3) Baby holding (or equivalent weight) at the waist level.
A diagnosis of tethered cord syndrome is made based upon identification of characteristic signs and symptoms (see the symptom section) that can neurologically locate the lesion to be above the attachment of the anomalies to the spinal cord. For this purpose, a detailed patient history and a thorough clinical evaluation and detailed MRI studies must be carried out. In children, typical imaging features such as a low lying spinal cord and a thickened filum terminale is confirmed by special imaging techniques such as magnetic resonance imaging (MRI) or computed tomography (CT) scan and ultrasound studies.
An MRI uses a magnetic field and radio waves to produce cross-sectional images of particular organs and bodily tissues. In addition, demonstration of spina bifida (bony defect of the lamina) supports a diagnosis of tethered cord syndrome.
In late teenagers and adults, the displacement of the filum located posterior to the cauda equina (a bundle of nerve roots that originate from the lower spinal cord) is a consistent finding. This important feature is proved by the combination of MRI, endoscopy and surgical findings. During CT scanning (a computer tomography) and MRI special techniques are used to create cross-sectional images of vertebrae and nervous system. In some cases, electromyography (EMG) and nerve conduction studies may be used to assess nerve function. EMG is a test that records electrical activity in skeletal (voluntary) muscles at rest and during muscle contractions. The abnormalities in this examination are only shown in patients with an advanced stage of tethered cord syndrome.
In children, surgery to release "untether" the spinal cord is recommended to prevent or reverse progressive neurological symptoms. The type of surgery varies depending on the mechanical causes, such as an inelastic filum, myelomeningocele, lipomyelomeningocele, and dermal sinus. Accordingly, the surgical prognosis varies depending upon the presenting symptoms and tethering-producing anomalies. It has been said that treatment for adult patients with tethered cord syndrome is controversial However, it is clear that in both pediatric and adult patients who have firm evidence of tethered cord syndrome, prompt surgical intervention results in reversal, or at least stabilization, of symptoms in many cases.
Parents should talk to their physician and medical team about their child's specific problems, associated symptoms and deformity of the spine and spinal cord. In an individual with only minimum complaint his/her physician may advise conservative treatment rather than surgery and will monitor the condition to see whether the symptoms progress Many experts of tethered cord syndrome recommend against surgery to individuals who present with the MRI finding of "cord elongation and thickened filum" but have no symptoms. Some neurosurgeons may prefer cutting the thickened filum in these cases for the prophylactic purpose.
The responses to treatment for tethered cord syndrome by repairing myelomeningocele or removal of scarring formation, varies from one person to another. After the repair, the spinal cord may become "retethered" and additional surgery may be recommended.
In individuals with severe arachnoiditis (adhesion of the meninges to the spinal cord) found by MRI or CT scan, careful evaluation of pain and neurological condition is required to find if surgical treatment is warranted. At surgery, release of arachnoid adhesion must be performed with meticulous technique. Or re-adhesion or extensive scar formation might follow the surgery. To circumvent this problem, two special surgical procedures have been advocated: 1) transection of the spinal cord to relieve severe back and leg pain, and 2) shortening of the spinal column by resection of one or two vertebrae to relieve spinal cord tension.
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Contact for additional information about tethered cord syndrome:
Shokei Yamada, MD, PhD, FACS
Professor and Former Chairman
Department of Neurosurgery
Loma Linda University
11234 Anderson. Loma Linda, CA 92354
E-mail: [email protected]
Arrowhead Regional Medical Center
Department of Neurosurgery
400 N. Pepper Avenue, Colton, CA 92342-1819
Kaiser Permanente Medical Center, Fontana
Department of Neurosurgery
99855 Sierra Avenue, Fontana, CA 92335
Contact: Daniel J. Won, MD, Associate of Dr. Yamada
Department of Neurosurgery
University of Mississippi Medical Center
2500 n. State Street
Jackson, MS 31296-4500
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FROM THE INTERNET
National Institute of Neurological Disorders and Stoke. Tethered Spinal Cord Syndrome Information Page. February 7, 2006. Available at: http://www.ninds.nih.gov/disorders/tethered_cord/tethered_cord.htm Accessed: 10/13/10
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