Introduction to Tethered Cord Syndrome

1 Introduction to Tethered Cord Syndrome

Shokei Yamada

The word tether means to restrain, an example of which is an animal held to the maximal range of motion by a rope. This definition leads to the connotation “the harder the pull on the rope, the tenser the rope.” Applying the word tethered to the lumbosacral spinal cord, one visualizes an unnatural, unmitigated, abnormal constraint that aptly applies to the medical condition called tethered cord syndrome (TCS). However, there has been much uncertainty about this syndrome and its diagnosis and treatment because clinicians and scientists did not agree with the usage of this term and because perceptions were based on visual rather than on scientific evidence (F. Anderson, personal communication, 1984). Interestingly, there is no word that has the same definition and connotation as English tether in any other language. The delay in recognizing this syndrome may be due in part to this linguistic difference.

There is now agreement that TCS is a functional disorder caused by stretching of the spinal cord with its caudal end fastened by an inelastic structure.1 The disorder is made worse as spinal cord tension increases with such influences as rapid growth in children, or forceful spinal flexion and extension.

Historical Background of Tethered Cord Syndrome

The concept of TCS evolved slowly but with increasing interest among clinicians and pathologists. A suggestion that stretching of the spinal cord could induce a disorder came from a case with myelomeningocele in 1910.² Other articles followed on disorders such as a sacral lipoma,^3,4 and occult spinal dysraphism⁵; however, the expression tethered cord was avoided in such writings, which appeared to have linked the characteristic neurological deficits to “lipoma infiltration or congenital neuronal dysgenesis.” Although Garceau and others attributed the neurological deficits to the traction effect that a tight filum^6,7 or myelomeningocele (MMC)⁸ exerted on the spinal cord, none of these articles were published in neurosurgical journals.

In 1940, Lichtenstein, an authoritative neuropathologist, was first to propose that tethering of the spinal cord may cause paraplegia and herniation of the brain stem and cerebellum through the foramen magnum.⁹ However, his hypothesis was not accepted, particularly for the development of Chiari malformation.^10–12 Although surgeons noticed neurological improvements in their patients after what is currently called untethering of the spinal cord, two questions remained unanswered. First, if tethering-induced symptoms exist, what part of the nervous system is affected? And second, what is the pathophysiological basis for any reversible lesion?

In 1976 Hoffman et al adopted the term tethered spinal cord in a report on 31 patients presenting with incontinence and motor and sensory deficits in the lower limbs. These symptoms subsided after sectioning of a thickened filum terminale,¹³ which indicated that the neurological lesion was in the lumbosacral cord. In 1981, Yamada et al demonstrated impairments of oxidative metabolism in the lumbosacral cord before surgery and recovery from the impairments after surgery in patients who had the same clinical presentations as those described by Hoffman et al.13 Simultaneously, electrophysiological impairments and recoveries were recorded before and after cord untethering, respectively.^1,14

McLone [moderator] and a panel reviewed such pathophysiological and clinical information during a debate titled “Is the TCS Fact or Fiction?” One conclusion was that tethered spinal cord is a clinical entity based on scientific evidence.¹⁵ Since then, the term TCS has increasingly appeared in the neurosurgical literature.^16–20

Current Understanding of Tethered Cord Syndrome

Expanding the stretch-induced disorder from tethered spinal cord to TCS, Yamada et al included patients with neural spinal dysraphism located in the caudal end of the spinal cord, such as MMCs and lipomyelomeningoceles (LMMCs).¹ This definition engendered misinterpretations and questions despite the fact that these patients presented with the same symptomatology and oxidative metabolic impairment and postoperative metabolic and neurological improvement as those of tethered spinal cord of Hoffman et al.¹³

Two questions evolved: (1) How could the theory of TCS pathophysiology explain the downhill course in some MMC patients after repeated surgical repairs?²¹ and (2) Why are surgical results of TCS patients so variable?²²

Answers to these questions may be derived from a better definition of the differences between TCS and the expressions cord tethering or tethered cord and from studies of TCS pathophysiology. Analyzing these questions, it became apparent that they are missing the fact that TCS is the manifestation of a stretch-induced lesion above the inelastic structure that exerts traction force to the spinal cord. In contrast, MMCs and LMMCs that are located dorsal to the spinal cord can cause neurological deficits by local compression or ischemia, or as a part of neuronal dysgenesis. It is clear that the lumbosacral neurological symptomatology in these patients is not caused by caudal traction effects and is not considered TCS.²³

At the request of Professor Sergio DiRocco to clarify the diagnosis of TCS (DiRocco S, personal communication, 2006), the editor felt it necessary to categorize such expressions as cord tethering and tethered cord, which are derived only from visuals. Based on the pathophysiological analysis on caudal spinal cord anomalies, Yamada and Won divided these into three categories based on experience with individual clinical cases.²⁴

Category 1 represents patients with true TCS who exhibited neurological signs and symptoms due to anchoring structures restricting the spinal cord movement at its caudal end. They include an inelastic filum terminale, caudal lipoma or LMMC, or sacral MMC.²⁵

Category 2 includes patients whose signs and symptoms resemble those of true TCS; however, signs and symptoms are associated with large MMCs, extensive dorsal or transitional LMMCs (see Chapter 11), and postoperative MMCs with extensive fibrous adhesions (category 2A). These structures cause local compression or ischemia to the spinal cord resulting in neurological deficits. In some cases the deficits are related to neuronal dysgenesis. These patients do not belong to true TCS. Only when a part of the signs and symptoms is indicative of a lesion above the anomalies is partial TCS an appropriate diagnosis (category 2B).

Category 3 patients typically present with thoracolumbar MMC and exhibit total paraplegia and urinary and bowel incontinence due to the lack of functional neurons in the lumbosacral region of the cord.

Surgical results differ depending on the patient’s category. After surgical untethering, category 1 patients can expect excellent outcome with pain relief and neurological improvement. Category 2B patients also have good outcome with similar symptomatic improvement. Category 2A patients have good pain relief with deficits stabilized but no neurological improvement. Category 3 patients have no predictable neurological improvement. No surgical treatment is indicated for category 3 patients. There is no hope for reversing incontinence in patients who have been performing intermittent catheterization for more than a few years.

There are special case reports other than the ordinary untethering surgery. One is a report of relief of severe back and leg pain after cord transection was performed on patients with severe adhesive arachnoiditis around the caudal spinal cord and cauda equina.26 When the neurological signs indicate a neurological lesion above the transection, the diagnosis of TCS can be appropriate. Another report indicated reversal of TCS symptomatology by lumbar corpectomy in patients with magnetic resonance imaging (MRI) evidence of severe arachnoiditis. This method relieved spinal cord tension by shortening the length of the vertebral column.²⁷ These atypical treatments will further stimulate the advancement of TCS studies.

Other chapters included in this book cover the pathophysiology of TCS (Chapter 3), embry-ological analysis of TCS (Chapter 2), neurological examination (Chapter 4), imaging studies of TCS (Chapters 5 and 6), pediatric tethered spinal cord (Chapter 9), adult TCS (Chapters 15 and 16), cervical tethered spinal cord (Chapter 10), TCS associated with MMCs and LMMCs (Chapter 11), folate studies in families of neural spinal dysraphism (Chapter 12), in utero repair of myelomeningocele (Chapter 13), TCS associated with dermoid (Chapter 14), urological aspects of TCS (Chapters 7 and 8), intraoperative stimulation studies on sacral cord and roots (Chapter 19), anomaly of the lumbosacral cord (Chapter 17), spinal cord length and filum thickness (Chapter 18), electrophysiology with somatosensory evoked potentials (SSEPs) for TCS evaluation (Chapter 20), and conservative and operative treatment (Chapter 21). Each chapter follows the principle of TCS with expertise and endeavors by proper diagnosis and treatment to improve the care of TCS patients to help them achieve their full potential capacities.

Topics regarding TCS discussed in this book include the following:

Correlation of pathophysiology to clinical manifestation of TCS
Signs and symptoms of TCS to the spinal cord level of neurological lesions
Distal motor and sensory lesions in lower limbs
Patchy motor and sensory lesions in TCS patients
Incontinence becoming irreversible earlier than motor and sensory dysfunction
Hypoactive deep tendon reflex (DTR) seen in TCS patients
Mechanism of later development of TCS in adult and late teenagers
Difference in neurological improvement after what appeared to be complete untethering procedures
Surgical indications and surgical techniques for TCS patients
Essential parts of surgical procedures for untethering
Complications to be anticipated
Rationale for surgical treatment and alternative treatment

The editor recommends that neurosurgeons identify the three categories in patients who present with so-called cord tethering: the true TCS (category 1), relative TCS (category 2B), and non-TCS patients with symptoms similar to TCS. By following the categorization of cord tethering, neurosurgeons can correctly envisage the surgical outcome for the patients in each group. They will be able to convince referring physicians as well as patients and families of their ability to properly diagnose and treat adult TCS patients and to handle those who show similar symptomatology but belong to categories 2A and 3.