In this retrospective study, over a 9-year period (1999–2008), 65 subsequent patients received detethering surgery in the conus cauda region. All the operations were performed by a single surgeon (EWH).

The mean age of the patients was 22.0 years (median 11.5 years, range 0.1–72.7 years). Sex distribution showed 24 males (37%) and 41 females. All patients were diagnosed with a tethered cord due to spinal dysraphism. A HRG was identified for patients with LMC and/or a SCM, sometimes in combination with a tight filum terminale (TFT). The HRG contained 40 patients (Table 1). Of the remaining patients, two were diagnosed with a myelomeningocele (MMC), ten with a TFT, five with a dermoid sinus, and three patients had a combination of a TFT and a filum lipoma. Another five patients had been diagnosed with other combinations (two TFT + syringomyelia, one MMC + syringomyelia, one MMC + TFT, one dermoid + TFT).

Of all patients, 77% were symptomatic with a TCS (n = 50). Neurological deficits were present in 32 patients (64% of symptomatic patients) (Table 2). Urological deficits were present in 27 patients (54% of symptomatic patients). A group of 14 patients presented with orthopedic deficits, consisting of scoliosis, and 28 patients experienced pain (28% of symptomatic patients and 56% of symptomatic patients respectively). A combination of these symptoms was present in 34 patients (70% of all symptomatic patients).

For intraoperative neurophysiological assessment, two modalities were applied on all patients. The modalities used were transcranial electrical stimulation and direct root stimulation. Both consist of recorded evoked muscular motor potentials (mMEP) that were evoked by either transcranial electrical stimulation (TES) or by direct stimulation of nerve roots in the surgical exposed area. The bulbocavernosus reflex (BCR), a third IONM modality to monitor the sacral sensory roots and neural circuitry, was later added to the protocol but was not considered in this study. Direct spinal stimulation has been used to exclude motor function of the surgically identified filum terminale or other tethered structures, whereas TES-mMEP was recorded for monitoring the integrity of sacral motor roots and neural circuitry in the lower spinal cord.

At the start of this study, 11 patients were sedated with halogenated agents (sevoflurane). This had a profound depressing effect on TES-MEP responses. In six out of eight patients receiving halogenated agents as sole sedative, it was impossible to obtain responses. In three patients receiving halogenated agents for induction, TES-MEP was feasible after switch to TIVA. Hence the anesthetic regime was changed to TIVA. Direct root stimulation was possible in all patients and reliable measurements could be obtained.

The pre- and postoperative scores of three scoring parameters were presented (Table 3). Postoperative changes in orthopedic scores were not expected. Neurologically four out of 65 patients improved, 60 patients remained stable (Table 4). Urological score showed one patient with improvement and 63 patients remaining stable. Both urological and neurological deterioration occurred only in one MMC patient. Pain score showed that 20 patients improved, 44 patients remained stable, and one patient deteriorated.

Neurological outcome showed three patients with a single step improvement in scoring and one patient with a two step improvement (Table 5). Only one patient showed a single step deterioration in scoring. The urological score showed one patient with an improvement of one step. Another patient showed a deterioration of three steps. Improved pain score by a single step occurred in 14 patients, in five patients by two steps, and in one patient even by three steps. These patients were predominantly adults (mean age 34.5 years, range 1–72 years). A single patient in pain experienced an increase in pain scoring by one step.

The mean follow-up of all 65 patients was 4.6 years (SD 2.5 years, median, 4.1 years, range 9.2 years, min–max 1.1–10.3 years). Scoring of deficits directly after surgery and at maximum follow-up has been compared. Neurological outcome showed that 60 patients remained stable and one patient deteriorated (Table 7). The scoring of four patients improved. Urological outcome showed that 57 patients remained stable, two patients deteriorated, and six patients improved. All patients with deterioration of urological function were below 10 years of age. Orthopedic outcome showed that three patients deteriorated and one patient improved. The other 61 patients remained stable. The pain score remained stable in 63 patients, and the score improved in two patients. The scoring difference per patient is shown in Table 7. All symptomatic patients showed a general deterioration in a scoring of 8% at maximal follow-up (n = 50). General deterioration at maximal follow-up occurred only in patients aged younger than 18 years.

IONM is a method which has been proven to be technically feasible even in younger age [¹¹, ¹²]. Responses can always be obtained when no halogenated agents are administered and patients do not have severe neurological deficits [¹³, ¹⁴]. In our series, both transcranial electrical stimulation and direct electrical root/ nerve stimulation appear to be technically feasible, even in very young children. Technical adjustments like double-train stimulation may be required more often in young children. The presence of immature myelinated corticospinal fibers in this group of patients may desynchronize the transportation of action potentials on their way to the motor neurons. This often results in failure to elicit muscle MEPs. Conditioning by double-train stimulation compensates the relative hyperpolarisation of motorneurons resulting in stable MEP responses with high amplitudes [¹⁵, ¹⁶]

The responses of the anal sphincter muscles are generated by the lower sacral nerves S2–5, and they represent the integrity of the bladder function as well. This type of monitoring of urological function in our series appears to be effective in maintaining bladder function in most patients, both postoperatively and during follow-up. Only one patient deteriorated with three steps to incontinence. This patient had a myelocystocele and was operated at the age of 1 month. This diagnosis is a separate entity in the spectrum of spinal dysraphism [¹⁷, ¹⁸]. During surgery, the nerve roots could easily be recognized along the wall of the sack, but its handling and repositioning into the spinal canal appeared to be hazardous. IONM was of limited value during surgical detethering since all nerve roots could be saved at least anatomically.

The continuous use of the BCR has not been used in a standard fashion at that time of surgery in this series. BCR might have had an additional value by indicating deterioration of functions of the sacral nerves in this particular young patient with myelocystocele. Currently BCR is also used in our standard IONM set-up of tethered cord surgery.

No direct postoperative neurological and/or urological deterioration was found in all 40 patients of the HRG while only one patient suffered from an increase in pain. The absence of neurological and urological deterioration in this technically challenging group illustrates a potential beneficiary effect of the use of IONM to the safety of the procedure [⁸]. In the nHRG, only one patient deteriorated postoperatively in both neurologic and urologic function. As expected for the nHRG positive, results were found similar to the HRG [¹¹, ¹⁹].

In our series, a technique of partial resection of the lipoma was used. Recently Pang et al. compared the postoperative neurological deterioration in a historical group with partial resection and a more recent total resection group with the use of IONM. The neuro-urologic complication rate appeared to be similar in both groups, 4.2% and 5.2%, respectively [²⁰, ²¹]. The postoperative results in our series are at least comparable to these figures.

Pain can effectively be treated as a symptom of TCS especially in adult patients [³]. The improvement of pain directly postoperatively in 36% of all symptomatic pain patients corroborates this in our series. Only one patient deteriorated progressively after surgery. This patient had a lipoma and was aged 60 years old. The patient had suffered from progressive neurological and urological deterioration before surgery. Peroperatively only a partial resection of the lipoma with a partial detethering could be accomplished. This partial detethering might have resulted in increased strain and tension in the caudal nerve roots with the subsequent increase in pain. In this case, the technique of total resection of the lipoma, as proposed by Pang, might have resulted in a better outcome.

Remarkably 20% (13 patients) of the patients improved during follow-up. This included four patients with neurological improvement and six with urological improvement, both not only confirmed by questionnaire but also by physical neurological exam and video urodynamics. A majority of these patients belonged to the HRG (10/13). At maximum follow-up, six patients had deteriorated. Of these six patients, four belonged to the HRG. No neurological deterioration had occurred in the HRG. The overall deterioration was less than expected for the HRG. The absence of neurological deterioration may imply that no retethering has occurred and lasting effective detethering has been achieved in this technically challenging group. Although our FU is relatively short and our series is small, our results indicate the maintenance of neurological function. This promising outcome may be related to a beneficial contribution of IONM in spite of the partial resection of the lipoma. Maximal detethering may protect the patient for recurrent symptoms. The prophylactic group did not show any neurological deterioration during follow-up (seven HRG/eight nHRG). Pang et al. identified in his series the young asymptomatic patients to benefit most of radical resection. One should strive for a large cord sack ration in these patients. In our much smaller series, we focused on maximal detethering without maximal resection of the lipoma. This strategy appears also to be effective.

^a34 patients had multiple symptoms

VU video urodynamics

^aThis deterioration in scoring occurred in one patient

HRG high-risk group, nHRG non-high-risk group

HRG high-risk group, nHRG non-high-risk group