| Tight Filum Terminale | Diastematomyelia |
| Dermal Sinus Tracts | Lipomyelomeningocele |
Tethered cord syndrome
This term describes a range of signs and symptoms consequent to the tethering of a spinal cord at any level. It is often associated with spina bifida occulta and spinal dysraphism. It is diagnosed after an investigation of the embryology, pathophysiology and clinical symptoms using diagnostic neuro-imaging, and examination and observation of the patient. It is "classically defined as having the tip of the [spinal] cord below the L2 vertebra instead of at the L1-L2 disc space level" [Selcuki and Coskun, 1998]. Tethered spinal cords are non-life-threatening congenital conditions, but the consequences of not recognising, not monitoring, and in most cases not correcting, them can be deformed feet and legs, progressive neurological impairment, and, at worst, paralysis and incontinence, depending on the severity and type of cord tethering.
Normal spinal cord
The normal spinal cord begins at the junction of the skull with the cervical (neck) spine, and the cord continues down the spinal column until the mid-back region, the lumbar area. Beyond this point nerves continue down the spinal canal (as the cauda equina) and the spinal cord ends with the non-functioning tissue known as the filum terminale, which usually has the elasticity similar to a rubber band. The cord and the spinal bones (vertebrae) initially start out the same length but as the foetus and child grows, the vertebrae grow faster than the cord and therefore the cord effectively "ascends" within the spinal column. In people with no tethered cord the spinal cord ends up hanging freely within the vertebrae, protected by cerebrospinal fluid and, as there is no obstruction to its movement, it is able to flex and move freely with everyday activities.
I had reservations about including all the following details in this section,
but it may help to explain the embryology and creation of tethered cords.
(Source of information: http://www.yoursurgery.com/).
A tethered spinal cord is characterised by an abnormal attachment of the distal spinal cord to the surrounding tissues. The lower end of a normal spinal cord is found in the upper lumbar spinal canal. The attachment to the spinal canal or bones usually causes the spinal cord to end lower in the lumbar or sacral spinal canal. In the majority of cases, it is congenital (the patient is born with it).
Developmental Anatomy
Pathology
Tethered spinal cord
The embryonic spinal bones fuse together at different rates in a zip-like fashion proceeding in both directions. However, the bones at the caudal (tail) end form by coalescing in a disorganised way, and if the spinal cord becomes trapped in this area of rapidly amassing material, it becomes "tethered". Due to tethering, as the child grows there is no free movement of the cord and it is not able to ascend the spinal column. The lower part of the cord is therefore stretched and progressive neurological damage occurs as more tension is placed on the nerves emanating from the end of the cord. Blood circulation to the cord and the lower extremities may be reduced and in most cases the nerve impulses may be weak, distorted or absent.
Schneider et al (in Tethered Cord Syndrome, edited by Shokei Yamada, published by the American Association of Neurosurgeons Publications Committee, 1996) showed that blood flow was lowered during tethering but was significantly increased after detethering.
Neuronal (nerve) dysfunction due to tethering is subsequent to, firstly, metabolic derangement or hypoxia (the reduction of oxygen supply to tissues below physiological levels, despite adequate passage of blood through the tissue), and, secondly, the electrophysiology of the cord is impaired due to the distortion of neuronal membranes. Effectively, hypoxia means that the cord is deprived of oxygen and therefore electrical impulses are depressed. Physically this causes the nerves to reduce or stop sending impulses, both for sensory and motor functions, thereby creating and exacerbating progressive neurological deterioration.
At birth, there may be few external signs that the cord is tethered and as the spinal cord and its tissues are generally not fully exposed, there is rarely cause to operate immediately, except perhaps in the case of connecting dermal sinus tracts (skin-to-cord). A lipomyelomeningocele is most obviously visible as a skin-covered fatty mass in the lumbosacral region.
It used to be thought that most of the nerve stretching occurs at a time of rapid growth at puberty, but foot deformities and scoliosis can be apparent by the age of two as the cord stretching has effectively been going on since ~ 6 weeks post-conception. Once damaged, neurological function may not necessarily be recovered or improved. As indicated in the sections on spinal dysraphism, both children and adults can experience worsening symptoms of tethered spinal cords. In children the deterioration is caused by stretching of the cord with natural childhood growth. However in adults "without appropriate intervention most deteriorations in tethered cords are gradual, insidious over years. Rarely it can be very sudden, as can occur if one is put in the lithotomy position. Irreversability also occurs slowly and insidiously". [Ian Pople, 2002]. Also see this article by Shokei Yamada, which is very informative: "Pathophysiology of Tethered Cord Syndrome: Correlation with Symptomatology", Neurosurgical Focus, 16(2), 2004, Article 6
Adults with prior stable symptoms of a tethered cord can experience worsening of their symptoms due to general physical wear and tear on the cord and spinal nerves, and subsequent hypoxia and ischaemia of the spinal cord. These symptoms may be increased pain, decreased function, mobility and sensation, and further deformation of already poor feet. They may be fully accustomed to their condition, but any new symptoms that are out of the ordinary should be investigated by neurosurgical consultants who have a special interest in the area of spina bifida and spinal cord tethering. Surgery may be recommended in order to arrest further neurological damage and the deterioration of the function and sensation of the limbs, bladder and bowel.
In Journal of Neurosurgery, April 2001, 94(2 Suppl), the authors R. van Leeuwen, N.C. Notermans and W.P. Vandertop addressed the issue of "Surgery in Adults with Tethered Cord Syndrome: An Outcome Study with Independent Clinical Review". The abstract is below:
"Object: The authors conducted a study to evaluate the risks and short-term benefits of surgical treatment for tethered cord syndrome (TCS) in patients older than 18 years of age.
Methods: The authors studied a series of 57 consecutive adult patients with TCS of varying origins. Patients were examined by the same neurologist in a standard fashion before and after surgery, and most were followed for at least 2 years post-operatively. The patients' ages ranged from 19 to 75 years. The mean age at onset of symptoms and diagnosis was 30 years and 37 years respectively. Muscle strength improved (15 cases) or showed no change post-operatively (38 cases) in a large majority of patients (93%). In four patients a minor decrease in muscle strength was demonstrated, and there was a significant deterioration in two (3.5%). In the two latter patients a rapid decline in motor function was present pre-operatively. Subjective assessment of pain, gait, sensory function, and bladder/bowel function at 4 weeks, 6 months and 2 years post-surgery revealed improvement in a substantial percentage of patients. No major surgery-related complications occurred.
Conclusions: This is the largest series to date in which adult patients with TCS comprise the report. Untethering procedures in these patients were safe and effective, at least in the short term. Patients with rapid loss of motor function, lipomyelomeningocele, or split cord malformation seem to be at a higher risk of post-surgery deterioration. A follow-up period of many more years will be necessary to determine whether aggressive surgery is beneficial in the long term."
Click here for a very informative medical site on tethered cords. It includes images (not too gory!) and text describing symptoms and causes of tethered cords, and is easy to read and understand.
There are four main forms of tethered spinal cord in the spina bifida occulta range.
Tight
filum terminale
Dermal Sinus Tracts
Diastematomyelia
Lipomyelomeningocele
Tight filum terminale (also known as fatty filum or thickened filum)
The following definition of the filum terminale is a wonderfully clear one, provided by a friend of mine, Nancy Van Luven, a member of http://www.tetheredcord.com:
"The filum terminale is like a thin elastic band, about 8 inches long. At the top, it is formed from one of the layers of tissue surrounding your spinal cord, and extends from the bottom of your spinal cord to the tip of your tail bone. The outside of the "elastic band" has a few nerve fibres sticking to it.
The filum terminale works as an anchor for the spinal cord. For people with normal anatomy, the filum stretches when they bend over to allow the spinal cord to move up in the spinal column and then goes back to normal length when the person straightens up and gently pulls the spinal cord back to its normal position.
When the filum is fat-filled, fibrous and tight, it will not allow the spinal cord to move up and down within the spinal column, and so the spinal cord and the nerves end up being stretched instead of the filum. In most people this causes nerve damage".
Everybody has a filum terminale; it is a threadlike piece of tissue that connects the end of the spinal cord to the sacral end of the spinal canal in the pelvic area. In patients with a thickened filum (defined as more than 2 mm in diameter) [Yundt, 1997], the filum is shorter or lower-lying than normal and is thickened with fatty or fibrous tissue. This abnormality causes the filum to become relatively inelastic (a bit like a rope or cord, rather than an elastic band) and the spinal cord becomes tethered at an abnormally low level, thereby giving rise to the recognised signs and symptoms of a tethered spinal cord.
The usual cutaneous marker in 50% of patients is a deep, skin-covered dimple (closed dermal sinus tract) in the spinal midline, very low down on the back around the coccyx area. However thickened filums "may not always be attached to a sinus" [Ian Pople, 2002] and therefore any changes in the development of an apparently normal child's feet, legs, back, bladder and bowel control should be investigated for an underlying thickened filum. The earlier a diagnosis is made may possibly prevent further irreversible neurological damage. "However, it is inevitable that in most children some deformity occurs even after an early detethering, except in those cases with purely a thickened filum presenting with pain, where the neurological outcome is generally better [Ian Pople, 2004].
A diagnosis of a deterioration in the condition of a spinal cord due to a thickened filum terminale is usually made after an MRI (3D scan) as well as taking account of painful physical symptoms. The symptoms of deterioration can include any of the following:
The operation to release the thickened filum is the simplest and least risky of untethering procedures as the filum has no neurological function and the surgery hold a 1-2% risk of causing neurological deterioration or damage. It involves a laminectomy at one or two levels in the lumbar or sacral spine to expose the site of the tether, and a division of the tight filum is made. The patient usually has to lie flat in hospital for about five days to prevent CSF leakage or damage to the incision site. S/he can take graduated gentle exercise as the wound heals and physical strength returns. The sciatica-like leg pain and severe spinal pain, characteristic of this type of tethered cord, usually reduces or disappears in most patients. Some of the post-operative pain can be attributed to being "a feature of released sensory tissue beginning to work after many years of being shut off by the tethering" [Ian Pople, 2002], and some patients continue to suffer chronic pain, varying in types and levels of intensity.
The success of the surgery can be measured when the cord can move in a normal manner, as the tension on it will have been released. A successful detethering will also halt further deterioration of the nerves affecting the lower extremities and of the bladder and bowel. Prior to surgery, the nerves of the cauda equina are stretched vertically like an elastic band. After a successful detethering these nerves are relaxed and lie, as they should do, at right angles to the filum and spinal cord.
I had this type of tethered cord, and I have undergone detethering surgery. Please go to my home page to follow my experiences and progress
Retethering
"A patient with a simple tight terminal filum usually experiences an uneventful postoperative course, and there is little chance of retethering" (M.R. Proctor and R.M. Scott, "Long Term Outcome for Patients with Split Cord Malformation", Neurosurgery Focus, 10(1), Article 5, 2000. Two other articles were particularly informative about retethering of spinal cords post-surgery.
Souweidane, M.M. and J.M. Drake, "Retethering of Sectioned Fibrolipomatous Filum Terminales: Report of Two Cases", Neurosurgery, 42(6) (June 1998): 1390[-]93.
"Objective and Importance: The release of a tethered spinal cord by sectioning a thickened filum terminale is a straightforward surgical procedure that can prevent, arrest, or ameliorate neurological deficits. We recently recognized progressive neurological deterioration cause by filum retethering in two patients years after this procedure was performed. This sequela of a recurrent tethered cord after the sectioning of a filum terminale has not previously been described.
Clinical Presentation: Two female patients, each 13 years of age at presentation, had been previously operated on for tethered spinal cords secondary to fibrolipomatous (fatty) fila terminale. Both presented with bladder dysfunction and one with progressive paraparesis. MRIs revealed a low-lying conus medullaris and a sectioned filum with the proximal stump adherent to the posterior dura.
Intervention: Each patient underwent neurosurgical exploration of the previous site of sectioning, with the recognition of the retethered proximal stump of the filum terminale. After re-release of the fatty filum, the patient with only bladder dysfunction stabilized and a motor examination revealed normal results for the patient with progressive paraparesis.
Conclusion: Retethering of the spinal cord is a rare sequela (consequence of) [after] the sectioning of a tight filum terminale. The clinical presentation is typical for recurrent cord tethering and the radiographic findings are subtle. Careful surgical exploration should be offered for spinal cord untethering. Awareness of this rare and hitherto undescribed sequela is necessary for appropriate long-term management of tethered spinal cords cause by fatty filum terminale."
Phuong, L.K., K.A. Schoeberl, and C. Raffel, "Natural History of Tethered Cord in Patients with Meningomyelocele", Neurosurgery, 50 (2002): 989[-]995
"Objective: The purpose of this study was to describe the natural history of tethered cord in patients who have undergone meningomyelocele repair.
Methods: We performed a retrospective review of 45 patients with a history of neonatal meningomyelocele repair who consequently developed symptoms of tethered cord. Symptoms of tethered cord in this cohort consisted of the development of bladder spasticity or orthopedic foot deformity. None of these patients were treated with cord untethering; instead they were treated symptomatically.
Results: On follow-up, 40 (88.9%) of these patients subsequently required additional orthopedic or urological procedures because of further symptoms of tethered cord. The incidence of progression of tethered cord syndrome is 27.5, 40, and 60% at 1, 2, and 5 years respectively.
Conclusion: Although this study does not address the question whether cord untethering will prevent further symptom development, these results do provide a strong rationale for consideration of an untethering procedure in patients with repaired meningomyelocele at the time of the onset of symptoms of tethered cord."
In another study, it was noted that "~10-16% of children with spina bifida are at risk of a secondary tethering where 87% of these are diagnosed by neuro-urological surveillance, and a further 4 out of 191 children were diagnosed with a secondary rethering because they developed a peripheral neurological deterioration in the lower extremities as detected by routine neurological examination" (Ilker, Y. et al) (see Information Pages)
At present there appears to be no guaranteed way to prevent retethering, although various methods are being used. Aliredjo et al [1999] support the use of a Gore-Tex membrane to prevent adhesions after cord detethering but other surgeons are experimenting with an anti-adhesion gel .
The risk of retethering can vary according to the patient's age, the type, and the severity of the entire condition. In children the risk of cord retethering is approximately 20% "because the spinal canal in the baby is shallow and therefore postoperatively the neural contents are in direct contact with the posterior dura (back covering of the spinal cord) [Zide et al., 1995]. In adults who have been detethered, there may be a ~5-10% risk of the cord retethering.
Journal and research paper extracts
Below are some extracts of research papers from journals, relating to thickened filum terminale.
"The best results [of a cord detethering surgery] were obtained in patients in whom the cord tethering resulted from an anomalous filum terminale. Results were significantly worse in patients suffering long standing symptomology and showing surgically mixed mechanisms of cord tethering" [Guyotat et al., 1998].
"The most common tethering lesions [in adults exhibiting symptoms of a tethered cord] were intradural lipoma and a short thickened filum terminale ... the surgical outcome was gratifying in relation to pain and sensory-motor deficits but disappointing in the resolution of sphincter disorders" [Caruso et al, 1996].
In studies of patients with "tight filum terminale, split cord malformation and lipomyelomeningocele ... long term surgical improvement was reported ... 79% called the operation a long-term success; 75% believed they had significant postoperative improvement (and not just stabilization) in pain and/or neurological function" [Iskandar et al., 1998].
"The patients presenting with low back pain and sciatica responded to surgery better than those with sphincter problems" [Akay et al., 2000].
Urological aspects of tethered cords
"Adults with the tethered cord syndrome are less likely to have urodynamic or bladder function improvement after cord release and most often present with irreversible findings which rarely become worse after surgery. These patients need to have careful and continuous follow-up, including urodynamic studies, due to possible re-tethering with time" [Giddens et al., 1999].
In a group of patients with primary cord tethering "the most common preoperative urodynamic finding was hyperreflexia, which improved or resolved after untethering in 62.5% of the patients. Four adults also reported improved bladder sensation or decreased urgency". In a second group of patients who had undergone a second detethering surgery "only 14% had improved symptoms of urinary control but 28% had improved lower extremity function". The conclusion was that "urological symptoms and urodynamic patterns may be improved by early surgical intervention in patients with occult spinal dysraphism. However, untethering did not consistently benefit patients with secondary spinal cord tethering" [Fone et al., 1997].
In children with lower urinary tract dysfunctions "significant improvements can be achieved with a judiciously timed division of the tethered spinal cord" [Balkan et al., 2001].
"Changes in bladder-sphincter function after untethering are usually transient and often the result of partial denervation [mostly in patients with myelomeningocele and lipomyelomeningocele] ... however the individual outcome cannot be predicted [Boemers et al., 1995].
This condition manifests itself as a small skin-lined tube (a fistula) found along the midline of the back, usually in the lumbar or sacral part of the spine, which extends through two (possibly damaged) laminae, through spinal cord coverings, and deep into the end of the spinal canal. The dermal sinus is usually attached to the spinal cord, thus causing tethering of the cord. It is caused when the neural tube fails to separate fully from the overlying ectoderm during weeks 3-5 of pregnancy. See Yamada (pp. 6-20) for detailed explanations of these processes.
Cutaneous markers may be any of the following:
Surgery to correct this condition is generally required, due to the risk of spinal cord abscesses, the entry of bacteria through the tract with the increased risk of meningitis and the potential damage due to the tethering of the spinal cord. The surgery generally involves removing any portions of the sinus tract that connect with the spinal cord and covering the tract to reduce infection.
Diastematomyelia (also called split cord malformation).
This type of tethered cord occurs when the spinal cord is split in two longitudinally by a spur of bone or cartilage and is formed at approximately days 16/17 post-conception. Each half usually possesses its own dorsal and ventral nerve roots and is enclosed within its own dural sheath (cord covering). The two cords may reunite above and below the dividing structure. Diastematomyelia may be associated with bone abnormalities such as split or fused vertebrae, may also be seen with a short filum terminale, a tumour, or the tethering of nerve roots around the diastematomyelia. It is commonly located at the lower thoracic or upper lumbar areas of the back. It acts as a tethering process as it slows the normal growth of the spinal cord by preventing the upward migration of the cord.
Cutaneous features may include any of the following, depending on the level of tethering and the inclusion of other tethering factors:
Some cases of diastematomyelia are initially asymptomatic and require careful monitoring. However, in many cases neurological deterioration occurs and therefore surgery is indicated. The standard surgery, which is described by Proctor and Scott is "the removal of the fibrous or bone septum, resection of any other local spinal cord attachments causing tethering, and exploration for associated tethering-related anomalies such as dorsal tethering bands or thick filum, which can be seen in the majority of SCM patients. Following the detethering procedure, the dura was closed posteriorly with or without placement of a patch graft ... the patients were kept flat postoperatively for an average period of 72 hours, and were then allowed to progressively advance to full activity levels". This releases the tethering of the cord and modest neurological improvement is reported.
This is the most severe form of tethered cord that is covered by skin, and accounts for 84% of occult spinal cord malformations. Adipose tissue collects in a defect of the spinal column, and the spinal cord, functioning nerve roots, conus and filum terminale become embedded in this pad of fat thereby tethering the spinal cord. This situation can compress the cord leading to possibly irreversible neurological damage and deterioration.
The cutaneous marker is obvious upon examination in the form of a non-symptomatic lump under the unbroken skin. The placement of this lipoma is usually in the lumbosacral region of the back.
Clinical features secondary to the lipoma may include
These symptoms can cause progressive problems in adulthood after a possibly relatively symptom-free childhood, and surgery is usually required to prevent further neurological deterioration.
The operation to correct this condition consists of removing the fatty lipoma and thus detethering the spinal cord and its nerves. Some literature (found at http://nyneurosurgery.org) indicates that surgeons detether this type of cord by using a laser to vaporise the water content in the fat, thus "melting" the lipoma and enabling its removal without injury to the neural structures around it.
One journal paper was very informative - "Recurrent Tethering: A Common Long-Term Problem after Lipomyelomeningocele Repair", by A. Colak, I.F. Pollack, and A.L. Albright, Pediatric Neurosurgery, 29(4): October 1998.
They wanted to "determine the incidence and time course of symptomatic retethering in a control group of 94 patients ... 20% of patients (19 people) reviewed required 28 subsequent operations for retethering. The median time between the initial procedure and reoperation for retethering was 52 months. The primary complaint of 12 patients was intractable low-back or leg pain, ... progressive bowel and/or bladder dysfunction, deterioration of motor function and foot deformities ... people with lipomas had a higher frequency of retethering rather than those with dorsal lesions ... none of a variety of types of dural graft materials appeared to entirely prevent retethering. Following reoperation pain complaints resolved and many of the other symptoms improved partially or resolved completely".
The researchers concluded that "symptomatic retethering is a common problem in children with lipomyelomeningoceles even after an adequate initial operation. To date, no type of graft material has been shown to entirely prevent this problem".
Before surgical techniques were developed to detether lipomyelomeningoceles safely and effectively, patients with the condition often experienced considerable difficulties as both children and older adults. The following story illustrates how the condition can progress without childhood surgery. It also shows that lipomyelomeningocele can be improved by surgery, but that there is a greater risk that detethering surgery may have to be experienced more than once.
"In 1945 when I was born, little was known about spina bifida and tethered cord had never been heard of. There were also no shunts to prevent hydrocephalus. Surgeons simply closed the back and hoped for the best. My parents were told I was best left alone, as my back was covered by normal skin and I did learn to walk after a fashion. I grew up dealing with lack of enervation to my calf muscles, no sensation in the buttocks area and down the back of my legs, and increasingly deformed feet with hammer toes. I had no sensation to tell me my bladder was full, and I learned to use abdominal muscles to control both bladder and bowel. I fell often and couldn't run, even burned the back of my leg sitting on a hot radiator. I wore corrective shoes which I did under protest and usually worked out how best to do something. If I fell or was hit on the lipoma I had tingling down my legs and more trouble walking.
By the time I was 40-ish I began to have severe pains in my hip and knees, but I was not referred to a neurologist as my doctor thought I had arthritis due to my compensated gait. After losing all bladder control I demanded a referral to a neuro-specialist and I finally found out about my condition. The MRI showed that the lipoma clearly entered the spinal column at L4, L5 and S1 and these vertebrae had no back to them at all. The lipoma was firmly attached to the end of the spinal cord.
Surgery to detether the cord took place when I was 52 and most of the lipoma was removed. My pain was instantly better. The following year, however, the symptoms gradually returned and now I have to use a wheelchair or motorised scooter to get around. My feet are also continuing to contract and so I may be facing a second detethering surgery to stabilise the condition."
I am grateful to my friend for providing this information.