Effect of detethering on bladder function in children with myelomeningocele: Urodynamic evaluation

Abstract

Aim of Work:

To study the effect of detethering of the cord on urodynamic changes in patients with myelomeningocele.

Materials and Methods:

We retrospectively reviewed the urodynamic data of 37 patients. In all of them myelomeningocele primary repair was carried out. The patients were divided into two groups: (1) those who underwent detethering of the cord and (2) those who did not. Neurourological examination, filling cystometry, assessment of bladder management, and fecal continence were studied in all patients.

Results:

Eleven (29.7%) out of 37 patients underwent detethering of the cord. The mean age at presentation was 10.1 ± 4 and 10.8 ± 7 years in groups 1 and 2, respectively (P 0.7). Nocturnal and diurnal enuresis was found in 45% of group 1, while it was found in 69% of group 2. Fecal soiling was detected in 18% in group 1 and in 38.5% in group 2. Mean bladder capacity was 210 ± 125 cc and 199 ± 120 cc for groups 1 and 2, respectively (P 0.8). Uninhibited detrusor contractions were noticed in nine patients (82%) of group 1 and in 21 patients (81%) of group 2. Delta det LPP was lower in group 1 (35 ± 19 cm H₂O) than in group 2 (46 ± 40 cm H₂0).

Conclusion:

Detethering of the cord had a positive impact on patients with myelomeningocele in terms of lowering of det LPP and accordingly decreasing the risk of upper tract deterioration.

Introduction

Tethered cord syndrome (TCS) is a stretch-induced disorder of the spinal cord.[1] It could be primary as in the case of spinal dysraphism,[2] or secondary, following repair of the myelomeningocele.[3] In the primary case, tethering may result from an inelastic structure anchoring the caudal end of the cord as a short and thick filum terminale, while secondary tethering is produced by a scar in the area of the dysraphism resulting from postpartum surgical closure of the lesion,[4] which in turn does not permit normal cranial migration of the conus within the vertebral canal,[2] and leads to axonal anoxia resulting in neural dysfunction.[5] Clinically, this syndrome manifests itself by progressive neurological, urological, and orthopedic signs and symptoms.[6] Many studies have reported an improvement of urodynamic, and clinical variables after the untethering procedure.[3,7–9] However, other studies have raised suspicion about the usefulness of such a treatment in adults.[2,3,6] Improvement of preoperative urological symptoms such as incontinence or abnormal urodynamic findings have been previously reported to be 38 and 100%, respectively, in two different studies.[8,10] The impact of untethering of the cord on fecal incontinence has not gained much attention.[4] The current study is designed to assess the urodynamic abnormalities and urinary symptoms in patients with myelomeningocele, who have undergone detethering of the spinal cord, as compared to those who have not undergone detethering.

Materials and Methods

This is a retrospective analysis of the data of 37 patients, post repair of myelomeningocele, who presented to the Urodynamic Unit between January 1998 and June 2008. The patients were divided into two groups: (1) Those who underwent detethering of the cord, and (2) those who had primary repair only. All the patients were evaluated clinically by history taking and physical examination. Renal and bladder ultrasounds were routinely performed. Retrograde cystogram was also performed using a water soluble contrast and a small caliber Nelaton tube (8 F.) up to the sensation of maximum filling.

Water cystometry was obtained using a 5 or 7 F. dual lumen transurethral catheter. Filling was conducted at room temperature (26°C).The fill rate was 10% of the expected bladder capacity for age per minute(10-20 mL/min). A rectal catheter was inserted to record changes in the intra-abdominal pressure. Detrusor pressure was derived electronically. Simultaneously, skin patch perineal electromyography was recorded. The end point of the filling phase was determined by a sensation of fullness or uretheral leak. Data were presented as the mean ± standard deviation. One way ANOVA was utilized to compare the means.

Results

Thirty-seven patients were enrolled in this study. There were 23 girls and 14 boys. Eleven (29.7%) out of 37 patients underwent detethering of the cord. Mean age at presentation was 10.1 ± 4 and 10.8 ± 7 years in groups 1 and 2, respectively (P 0.7). Nocturnal and diurnal enuresis was found in 45% of group 1 and 69% of group 2. Fecal soiling was detected in 18% of group 1 and 38% of group 2. Urinary tract infections (UTIs) were comparable in both groups (12.5 and 13.6%, respectively). CIC was indicated in 50% of group 1 and in 22.7% of group 2. (CIC was carried out with 8 F Nelaton catheter every 4 hours per day time and once before bed time). Vesicoureteral reflux was noticed in 22.7% of group 2, and none of group 1 had vesicoureteral reflux.

Mean bladder capacity was 210 ± 125 cc and 199 ± 120 cc for groups 1 and 2, respectively (P 0.8). Delta det LPP (the difference between detrosur pressure at leakage and basal detrosur pressure) was lower in group 1 (35 ± 19 cm H₂O) than in group 2 (46 ± 40 cm H₂O). Uninhibited detrusor contractions were noted in nine patients (82%) of group 1 and 21 patients (81%) of group 2.

Discussion

Tethered cord is a terminology commonly used in literature, which refers to a short, thickened, and tight filum terminale, as well as any pathology, which prevents the spinal cord from ascent.[11] Myelomeningocele accounts for more than 90% of all open spinal dysraphisms.[12] Secondary tethering of spinal cord after prior myelomeningocele closure has been found in about 30% of the cases.[13] Myelomeningocele represents the most common etiology of neurogenic bladder dysfunction in children.[14,15] Although MRI is certainly sensitive and is considered the method of choice for the detection of a tethered spinal cord,[1] diagnosis of the tethered cord syndrome (TCS) is a complicated one, because data on the anatomical malformation are not adequate for this task.[16] Recent studies have shown that a combination of an elongated cord and a thick filum terminale, demonstrated by MRI, is no longer an essential feature for the diagnosis of TCS.[16] Moreover, the value of MRI imaging is limited in patients with post repair of myelomeningocele, because most of these patients will show a pattern of tethering.[17] Thus, for TCS diagnosis, emphasis should rather be on its characteristic symptomatology, accentuated by postural changes, since TCS is a functional disorder of the lumbosacral spinal cord.[16] Surgical untethering of the cord is recommended by many authors.[1,3,7–9] However, while patients with lipomyelomeningocele have the most favorable prognosis,[5,18] secondary tethering of the cord have a worse prognosis, and it becomes even worse with surgical treatment, as reported by Grass et al.[4]

In our study, untethered patients showed better outcome in terms of nocturnal and diurnal enuresis after detethering, as compared to those who did not undergo detethering (45% versus 69%). Mean bladder capacity was higher in group 1 than in group 2. This compares favorably to previous reports, in which improvement of urological symptoms has been described.[1,3,7,8] However, none of them, in our study or in the previous studies, became urologically normal.[4] This could be explained by the fact that during complex microsurgery performed in those patients, the conus medullaris and the roots that innervate the lower limbs, bladder, and bowel were inevitably exposed to some degree of damage.[19] Another possibility was the permanent reduction of bladder contractility and increased rigidity in patients with end-stage myelomeningocele.[14]

In pursuing the ideal management of such a malady, an important question yet remains to be answered: When to perform detethering? A vast majority of studies recommend early intervention.[3,18] This suggestion is supported by poor results obtained after surgical correction in adult life.[2,6] Seeking an optimum approach of patient management, bladder management must be considered in adjunction to bowel management.[20] However, little attention has been paid to fecal incontinence, which is also common in patients with tethered spinal cord.[4] Quinones et al., reported (46%) improvement of bowel function after meticulous spinal surgery,[21] another report mentioned an improvement in up to 90% of the cases. Our results show less fecal soiling problems in patients who underwent detethering of the spinal cord (18%) in comparison to those who did not (38%).

Urodynamic testing is an integral part of the initial evaluation and subsequent management of a newborn with myelomeningocele.[15] Based on the McGuire observations, deterioration of the upper urinary tract occurs when intravesical pressure during filling at time of leakage exceeds 40 cm H₂O.[22] Consequently, the accurate measurement of det LPP has evolved to critical importance in the treatment of such patients. Our results have shown an improvement in reduction of det LPP in group 1, as well as more bladder stability after detethering of the spinal cord. Thus, detethering of the cord may prevent deterioration of upper urinary tract in those patients.

Conclusion

Detethering of the spinal cord has a positive impact on patients with myelomeningocele in terms of lowering of det LPP and accordingly in decreasing the risk of upper tract deterioration. It also possibly improves fecal incontinence.