INTRODUCTION

 

The general term "spinal dysraphism" refers to those congenital malformations involving any or all of the tissues on the mid-line of the back. It was initially introduced by Lichtenstein in 1940¹. The exact incidence of these lesions is not known with clinical estimate of 4–8/ 10,000 reported in some studies².

Two forms of spinal dysraphism exist: a closed form "spina bifida occulta" and an open form "spina bifida aperta". In spina bifida occulta the skin overlying the spinal anomaly is intact and no neural tissue is exposed. This group includes dorsal dermal sinus, caudal regression syndrome, diastemato-myelia, tight filum terminal, intradural lipoma, syringohydromyelia and anterior sacral meningocele³.

The tethered cord syndrome (TCS) is not some sort of malformation. Instead; it is a clinical syndrome that may ensue as a complication of myelomeningocele repair or as the presentation of occult spinal dysraphism⁴. TCS involves traction on a low-lying conus medullaris with progressive neurologic deterioration due to metabolic derangement⁵.

 

The age of presentation of TCS ranges from early childhood to the elderly. The presentation differs according to the underlying pathology including: back and leg pain, cutaneous signs, weakness, gait deterioration, foot deformities, progressive scoliosis and sphincter dysfunction^6,7.

Early surgical untethering should be considered upon diagnosis of asymptomatic or symptomatic spinal dysraphism. It has the greatest chance of restoration of neurological function^8,9.

These findings prompted us to evaluate our current clinical practice and set out the following study goals. First; to give a detailed description and to analyze the clinical, urodynamic, Somatosensory evoked potential (SSEP) and MRI findings in patients with occult spinal dysraphism. Second, to examine the validity of our multidisciplinary team evaluation in selecting children for untethering before the inception of progressive irreversible neurological deficits.

 

SUBJECTS AND METHODS

 

From January 2006 to January 2011, 10 children with occult spinal dysraphism attributable to various pathological conditions were referred to the department of neurosurgery Suez Canal University Hospital. The following children were included: Asymptomatic children with cutaneous stigmata, or those presented with symptoms and signs of spinal dysraphism; no history of previous surgery; age <12 years.

Pre-operative assessment of Neurological dysfunction (Back pain, sphincter dysfunction, weakness or atrophy of the lower limbs), Orthopedic deformities (Pes cavus, Talipes equines, equinovarus) and Urological dysfunctions (Urinary incontinence, abnormal urodynamic studies, complications of chronic urinary retention e.g. hydronephrosis) were recorded.

Urodynamic tests examination (laborie, Ontario Canada) were done with special attention to bladder hyperreflexia10. In urodynamic tests, compliance and capacity of the bladder, leak point pressure, and uroflowmetry were recorded. Bladder hyperreflexia was considered to be the major indication for surgery.

Somatosensory evoked potential (SSEP) examinations by neurologist (Dantec key Point TM apparatus, Denmark) were evaluated searching for indicated for surgery with relatively normal clinical examination. Posterior tibial SSEP was used. Delay in N22 wave latency, low amplitude, blockade of conduction was considered to be pathological⁸.

MRI was done for all the patients. All had low lying coni medullari.  Tight filum terminal was considered by the presence of a short filum with conus medullaris below L2.  A thick (fatty) filum was defined as a filum diameter >2 mm¹¹ (Figure 1). Fatty lipoma within a thickened filum terminale is a stripe of increased signal intensity on sagittal T1-weighted images. In lipomyelo-meningocele, sagittal T1-weighted image shows high signal intensity subcutaneous lipoma creeping through a wide posterior bony spina bifida into the spinal canal to connect with the low lying spinal cord (figure 2). Dermal sinuses are easily recognized on mid sagittal MRI as a thin hypointense stripe crossing the subcutaneous fat. Associated anomalies such as Chiari malformation, syringomyelia and/or hydromyelia, scoliosis, and vertebral anomalies were also considered⁹.

 

Operative and postoperative outcome:

During surgery and after laminectomy, filum terminal was known as microscopic aspect of the filum including; midline posterior position, tension and retraction after section, thick and fatty aspect, serpentine vessel on its surface, its pallor as compared with the nerve roots, and usually thick than 2mm⁹. Untethering is achieved simply by dividing the tight filum terminale. (Figure 1-F)

For lipomyelomeningoceles, untethering procedures consist of dissecting and debulking the lipoma upon the lumbodorsal fascia, laminectomy on the lower lumbar spine according to the level involved, and opening the Dura for exposing the intradural portion of the lipoma. The junction between the lipoma and the neural placode is dissected and divided for untethering. The lipoma was subtotally excised to allow the neural placode to move freely within the spinal canal, and any tethering arachnoidal adhesions were divided.

After the subtotal resection of the lipoma, the pia was closed if possible and the filum terminale was divided to release any potential tethering (Figure 2). Successful intraoperative untethering is defined as the conus medullaris retracts rostrally for at least one level of lamina. When the cerebrospinal fluid (CSF) space seems inadequate, patches of dural substitute were used. After satisfactory hemostasis, the wound was closed in layers. Post-operative complications were reported.

Post-operative: Patients were maintained in a prone position for 5 days. When the patients had no signs of CSF leakage, they began to mobilize. In case of CSF leakage or infection, further beds redden days were considered till the wound become clean.

During follow-up period; urodynamic and SSEP were evaluated post operatively 6 months while clinical evaluation was extended thereafter for assessment of improvement after surgery. Comparison was made between the pre and post-operative data.

Data were presented as mean ± standard deviation (SD), and considered significant when the two-tailed P value was <0.05. Differences in dichotomous outcomes preoperatively versus postoperatively were assessed using the chi-square test and the Fisher exact test.

 

RESULTS

 

Ten children with tethered cords attributable to various pathological conditions were included. Their ages ranged from 1 month to 7 years. Seven patients (70%) were females and 3 (30%) were males. All had cutaneous stigmata. Five patients did not have primary toilet training; the rest were toilet-trained for various periods of time, but then showed deterioration in their bladder function. Three patients had back pain (30%) and one patient had leg pain (10%). All the patients (except one) had normal motor, sensory and reflex functions in their lower extremities. This patient had distal weakness with equinovarus deformity of foot (Table 1).

Urodynamic tests were performed in nine patients but one patient with dermal sinus was operated early at the age of one month. Bladder hyperreflexia was considered to be the major indication for surgery in five patients (Table 3). Three patients had evidence of delay or block at posterior tibial on SSEP, five were normal, and two had difficulties in recording. Definitive diagnosis was made on MRI. No patient had associated congenital anomalies as syringo-hydromyelia, split notochord syndrome or anterior sacral meningocele.

All the patients had untethering. Resection of the lipoma was incomplete in two patients with transitional type of lipomyelomeningocele but we were able to close pia in one case (Figure 2-D). One case of lipomyelomeningocele needed further dural patches during closure. Although Dura was tightly closed in all cases, we had five children (50%) with CSF leakage. Two patients (20%) had persistent leakage that mandate subcutaneous catheter drainage above the incision line and improved after two weeks. One patient (10%) had skin infection due to primary skin sinus and improved with time, one patient with transient foot drop for two months, and lastly one patient (10%) had transient urine retention due to conus manipulation in case with caudal conus lipoma  (Table 2).

The follow-up period ranged from 6 months to 4 years. During the follow-up, all the patients had either symptoms unchanged (3 patients, 30%) or improved (7 patients, 70%). In 7 patients symptoms totally resolved. No manifestations of recurrent retethering detected in any patient during the follow up period.

 

Table (3) shows the Pre and Postoperative Urodynamic and Somatosensory Evoked Potential (SSEP) parameters. They were done six months post operatively. There was statistically significant improvement in the bladder function capacity, compliance and post voiding residual. Only two patients still had hyperreflexic bladder. Data showed that SSEPs provide more helpful information about the neurophysiological condition of the conus medullaris during the follow-up period after detethering. One patient didn’t improve from leg weakness after surgery and had equinovarus deformity. But SSEP response to untethering showed no significant improvement (P=0.56) as shown in urodynamic.

Table 1. Types of occult spinal dysraphism with main presenting sign or symptom.

 

Type of occult spinal dysraphism "MRI finding"	No	M/F	Age at diagnosis (Years)	Main symptoms and signs	Follow up
Tight filum terminal	3	1/2	5±1	Skin dimple (2) Urine incontinence (3) Constipation (2) Back and leg pain (2)	Improved (2) Stationary (1)
Lipoma of the filum	2	1/1	4	Lipoma of the back (2) Incontinence urine (2) Back pain (1)	Improved (1) Stationary (1)
Lipomyelo-meningocele	4	1/3	0.5±1.5	Lipoma of the back  (4) Equinovarus deformity (1)	Improved (3) Stationary (1)
Dermal sinus	1	0/1	0.1	Lumbosacral dimple (1)	Improved (1)
Total	10	3/7	2.4±0.7		Improved (7) Stationary (3)

 

Table 2. Surgery and complications.

 

Occult dysraphism	Surgery	Dural patches	Complication
Tight filum terminal	Untethering (3)	No	CSF leakage (2)
Lipoma of the filum	Untethering/ lipoma resection (2)	No	CSF leakage (1)
Lipomyelomeningocele	Untethering/ Total resection (2) Subtotal (2)	No (3) Yes (1)	CSF leakage (2) Transient urine retention (1) Foot drop improved on treatment (1)
Dermal sinus	Total removal and untethering (1)	No	Skin infection
Total	10

 

Table 3. Pre and Postoperative Urodynamic and Somatosensory Evoked Potential (SSEP) parameters.

 

Urodynamic and SSEP data	Pre-operative	Post-operative	P-value
Urinary affection / total number investigated	8/9	3/9	0.045*
Daytime incontinence	5/9	3/9	0.56
Constipation	2/9	1/9	0.34
Urinary tract Infection	3/9	-	0.35
Mean bladder capacity ± SD (ml)	104.8±55	150±65	0.023*
Mean compliance ± SD (ml/cm H2O)	5.9±5.6	24.7±20.3	0.005**
No of neurogenic overactivity	5/9	2/9	0.87
Mean ml post residual volume	20.2±1.2	5.3±1.8	0.004**
SSEP: Delay in N22 wave latency, Low amplitude, Blockade of conduction	3/8	1/8	0.56

* Significant at p<0.05 ** Significant at p<0.01

 

Figure 1. Female patient with hyperactive bladder, A) T1 sagittal plane with low lying conus at level of L 4/5 with thin cord and thick filum more than 2 mm, B) T2 sagittal plan the same finding and hyperintensity recognize fat within the cord, C) Axial view with filum relatively iso- to hyper-intense on T1 and hyper-intense on T2, D) Denoting fatty filum, E) Skin dimple is cutaneous finding, F) Intraoperative picture of low lying cord and tight filum terminal.

 

 

Figure 2. A, B) female infant six months TI and T2 sagittal MRI with hyperintensity fat noticed (Lipomyelomeningocele with low lying conus). C) Showed subcutaneous lipoma with central dimple. D) Showed intraoperative A- cord, B- Residual intradural lipoma, C-tethered cord after detethering.

 

 

DISCUSSION

 

Knowledge of the normal embryology allows better understanding of spinal dysraphism defects and the anatomical relationship seen on diagnostic studies. The skin lesions associated with spinal abnormalities include hypertrichosis, dimples, lipoma, angioma and naevi¹². In this study, about 9 cases (90%) had a cutaneous lesion. But only seven patients (70%) had clear skin cutaneous lesions lead to a clinical suspicion of spinal dysraphism³. This situation clarifies why mean age group is relatively higher in tight filum terminal group rather than lipomyelomeningocele dermal sinus.   Nevertheless, patients without apparent neurological deficits or clear skin lesion may have abnormal electrophysiologic or urodynamic studies¹³. This alternate is helpful in early detection of cases which mandate further MRI study¹⁴.

Final diagnosis of spinal dysraphism depends mainly on MRI. Hall et al¹⁵ also found MRI to be the procedure of choice to diagnose a tethered cord and had an excellent correlation between MRI and the surgical findings.  Raghavan et al.¹⁶ concluded that MRI was very useful in visualizing the conus medullaris, assessing the thickness of the filum terminale, and identifying traction lesions in a patient clinically suspected of having tethered cord syndrome (TCS). Associated bony dysraphism was easily evaluated¹⁷.

In the tethered cord syndrome, the distal lumbar spinal cord is fixed at 2 points, first at the site of tethering, and second at the nerve roots exits. During extension, flexion or the abdominal Valsalva maneuver there is a lack of motion and stretching of the cord and roots, which can lead to ischemia and an anaerobic metabolism¹⁰. The clinical spectrum of TCS includes pain, sensorimotor defects of the lower extremities, bladder and bowel dysfunction, and leg atrophy and scoliosis. In this study, 6 (60%) cases had initial presenting symptoms of neurologic and urologic symptoms due to tethering of the spinal cord and 5/6 (83%) had sphincter troubles³. Because the inter-neuronal axon connections require an aerobic metabolism, they are the first affected and clinically this leads to urinary incontinence and a decreased skeletal muscle reflex. In contrast, the long neuronal tracts involving muscular movement are less susceptible to hypoxic injury and, hence, the findings of lower limb weakness with associated hyperreflexia and an upward Babinski reflex are delayed manifestations of neurological impairment¹⁸. Loss of the sacral reflex arc and the development of neurogenic detrusor over-activity are the earliest alterations that can be detected by physical and urodynamic examinations. In this study, patients with bladder hyperreflexia responded favorably to TC release (3/5 60%). (1) Neurogenic detrusor overactivity bladder had the highest response rate for surgery with average 59% - 72%^{10, 19, 20}.

Constipation is not frequently referred in the literatures as associated with tethered cord. In this series, constipation represented 20% of cases. Rosen et al., noted that only 9% of children with spinal cord abnormalities had intractable constipation but TC was the most common association²¹. In another study, constipation was found in 42% of patients, decreased to 25% after surgery¹⁰.

All the patients, except one, had normal motor, sensory, and reflex functions in their lower extremities. Back pain (30%), leg pain (10%), and distal foot weakness and foot deformities (10%) were found in the study. Limb deformities may be associated with abnormal electrophysiology within the spinal cord²² or abnormal innervations of the lower limb^13,20, and therefore, may be unlikely to be responsive to untethering^13,14. Sequential SSEPs through stimulation of the posterior tibia1 nerve, although difficult to perform in infants, can give a better account of the clinical evolution, based on changes in cortical and lumbar amplitudes and latencies²³. Serial SSEP with peroneal or posterior tibial stimulation may reflect deterioration secondary to retethering on follow up. Static rather than deterioration was noticed denoting success untethering^8,24.

Although, we have relatively high incidence of post-operative CSF leakage 50% and one child with skin infection, up to 20% of patients who undergo untethering procedures experience local complications¹. Other reports showed about 3.9-5% of patients manifested neurological deterioration^{14, 25}.

Controversy persists regarding surgery in asymptomatic with TCS. In a given patient, it may be difficult to decide whether there is a likelihood of progression or development of neurological symptoms. Most patients are referred for surgery only after onset or progression of symptoms¹⁸. In this study, 70% of cases improved and 30% were stationary in their symptoms. Many surgeons recommended that if surgery is delayed until the onset of neurological deficits, there is a definite risk of incomplete neurological recovery^{6,9,10,17,23,24}. Furthermore, even if there is neurological recovery after surgery, the orthopedic deformities of the feet which may have developed in the meantime are permanent¹⁷.

In conclusion; Occult spinal dysraphism and the tethered cord syndrome present innumerable challenges to the neurosurgeon and neurologist. Early recognition of symptoms and signs due to tethering of the spinal cord especially cutaneous stigmata should raise suspicion for the disease. Advances in diagnostic imaging, urodynamic study, neurophysiological monitoring, and early surgical release of the tethering element have resulted in proper management of these clinical disorders. Follow up is important to record improvement and tracing occasionally recurrent retethering which mandate re-surgery.

 

[Disclosure: Authors report no conflict of interest]

 

REFERENCES

 

1.      Weprin B, Oakes W. Occult Spinal Dysraphism: The Clinical Presentation and diagnosis. Op Tech Plast Reconst Surg. 2000;  7: 39-52.

2.      Xenos C, Sgouros S, Walsh R, Hockley A. Spinal lipomas in children. Pediatr Neurosurg. 2000;  32: 295-307.

3.      Soonawala N, Overweg-Plandsoen WC, Brouwer OF. Early clinical signs and symptoms in occult spinal dysraphism: a retrospective case study of 47 patients. Clin Neurol Neurosurg. 1999; 101: 11-14.

4.      Warder DE, Oakes WJ. Tethered cord syndrome: the low-lying and normally positioned conus. Neurosurgery. 1994; 34: 597-600.

5.      Rossi A, Biancheri R, Cama A, Piatelli G, Ravegnani M, Tortori-Donati P. Imaging in spine and spinal cord malformations. Eur J Radiol. 2004; 50: 177-200.

6.      Hertzler 2nd DA, DePowell JJ, Stevenson CB, Mangano FT. Tethered cord syndrome: a review of the literature from embryology to adult presentation. Neurosurg Focus. 2010; E1: 29.

7.      Stavrinou P, Kunz M, Lehner M, Heger A, Müller-Felber W, Tonn JC, et al. Children with tethered cord syndrome of different etiology benefit from microsurgery a single institution experience. Childs Nerv Syst. 2011; 27: 803-10.

8.      Selçuki M, Umur AS, Duransoy YK, Ozdemir S, Selcuki D. Inappropriate surgical interventions for midline fusion defects cause secondary tethered cord symptoms: implications for natural history report of four cases. Childs Nerv Syst. 2012; 28: 1755-60.

9.      Cornips EM, Vereijken IM, Beuls EA, Weber JW, Soudant DL, van Rhijn LW, et al. Clinical characteristics and surgical outcome in 25 cases of childhood tight filum syndrome. Eur J Paediatr Neurol. 2012; 16: 103-117.

10.    Guerra L, Pike J, Milks J, Barrowman N, Leonard M. Outcome in Patients Who Underwent Tethered Cord Release for Occult Spinal Dysraphism. J Urol. 2006; 178: 1729-32.

11.    Yamada S, Won DJ, Pezeshkpour G, Yamada BS, Yamada SM, Siddiqi J. Pathophysiology of the tethered cord syndrome and similar complex disorders. Neurosurg Focus. 2007; 23(2):E6.

12.    Davis DA, Cohen PR, George RE. Cutaneous stigmata of occult spinal dysraphism. J Am Acad Dermatol. 1994, 31: 892-6.

13.    Harrison MJ, Mitnick RJ, Rosenblum BR, Rothman AS. Leptomyelolipoma: analysis of 20 cases. J Neurosurg. 1990; 73: 360–367.

14.    Tseng JH, Kuo MF, Tu YK, Tseng MY. Outcome of untethering for symptomatic spina bifida occulta with lumbosacral spinal cord tethering in 31 patients: analysis of preoperative prognostic factors. Spine J. 2008; 8: 630–8.

15.    Hall WA, Albright AL, Brunberg JA. Diagnosis of tethered cords by magnetic resonance imaging. Surg Neurol. 1988; 30: 60-4.

16.    Raghavan N, Barkovich AJ, Edwards M, Norman D. MR imaging in the tethered spinal cord syndrome. Am J Roentgenol, 1989, 152: 843-52.

17.    Gupta SK, Khosla VK, Sharma BS, Mathuriya SN, Pathak A, Tewari MK. Tethered Cord Syndrome in Adults. Surg Neurol. 1999; 52: 362–70.

18.    Pang D, WilbergerJ E. Tethered cord syndrome in adult. J Neurosurg. 1982; 57: 32-47.

19.    Khoury AE, Hendrick EB, McLorie GA, Kulkarni A, Churchill BM. Occult spinal dysraphism: clinical and urodynamic outcome after division of the filum terminale. J Urol. 1990,; 144: 426-8.

20.    Flanigan RC, Russell DP, Walsh JW. Urologic aspects of tethered cord. Urology. 1989; 33: 80-2.

21.    Rosen R, Buonomo C, Andrade R, Nurko S. Incidence of spinal cord lesions in patients with intractable constipation. J Pediatr. 2004; 145: 409-11.

22.    Feldbrin Z, Gilai AN, Ezra E, Khermosh O, Kramer U, Wientroub S. Muscle imbalance in the aetiology of idiopathic club foot: an electromyographic study. J Bone Joint Surg Br. 1995; 77: 596-601.

23.    Cornette L, Verpoorten C, Lage L, Plets C, VAN F. Closed spinal dysraphism: A review on diagnosis and treatment . Euro J of Ped Neurol. 1998; 2: 179-85.

24.    McLone D, La Marca F. The Tethered Spinal Cord:diagnosis, significance, and managment . Ped Neurol. 1997; 4: 192-208.

25.    Pierre-Kahn A, Zerah M, Renier D. Congenital lumbosacral lipomas. Childs Nerv Syst. 1997; 13: 298-335.