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Surgical Treatment of Scoliosis-Associated with Syringomyelia: The Role of Syrinx Size
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.280648
Keywords: Prophylactic neurosurgery, scoliosis, syringomyelia, syrinx sizeKey Messages: Prophylactic neurosurgery may be beneficial for decreasing the risk of correction surgery in syringomyelia-associated scoliosis patients with large syrinx.
Syringomyelia is a chronic disease defined as a fluid-filled, gliosis-lined cavity within the spinal cord and often associated with Chiari type I malformation (CM I) and scoliosis.[1] The incidence of associated scoliosis in syringomyelia patients was from 25% to 85%.[2],[3],[4] As a common type of neuromuscular scoliosis, syringomyelia-associated scoliosis (SMS) is characterized by back pain, concomitant neurological deficits and atypical curve patterns including early onset, rapid progression, apex left curves, and high prevalence of coronal imbalance.[5],[6],[7] It is clear now that bracing for scoliosis with associated CM I or syringomyelia is ineffective.[8] And correction surgery must be undertaken for those patients with large and/or significant progressive curves.[9] But the treatment of the syrinx prior to correction of the scoliosis remains controversial. Some surgeons thought the neurosurgical intervention of the syrinx should be performed prior to correction to decrease the risk of iatrogenic neurologic injury.[10],[11],[12] Others considered that satisfactory correction of deformity could be achieved and syrinx would not increase the incidence of complications of correction surgery without prophylactic neurosurgery, especially for patients without neurologic symptoms.[5],[9],[13],[14],[15] However, there are limited studies regarding the necessity of neurosurgical intervention of the syrinx in SMS patients according to the syrinx size. Thus, the aim of this study is to evaluate the role of the syrinx size in the management of SMS patients.
This study was a retrospective study of 36 patients with SMS who underwent correction surgery in our department from September 2010 to March 2016. All patients gave their informed consent to be included in this study and this study was approved by ethics committee of Sichuan University. The inclusion criteria were as follows: (1) age ≤18 years, (2) the Cobb angle of the main curve was more than 50°, (3) diagnosis of syringomyelia, (4) more than 1 year of clinical and radiographic follow-up after the last surgery, (5) no congenital spinal deformity. Patients were divided into 2 groups according to the maximal syrinx(S)/spinal cord(C) ratio (the maximal diameter of the syrinx divided by the diameter of the spinal cord at the same level):[16] Group A (small syrinx, S/C ratio ≤0.7) and Group B (large syrinx, S/C ratio >0.7). All the patients of Group B accepted prophylactic surgery of the syrinx (posterior fossa decompression and/or syrinx-shunting) four to ten months prior to scoliosis correction surgery. All patients underwent correction and fusion surgery and all surgical procedures were performed by the same surgeon. The CD HORIZON M8 or Legacy screw-rod system (Medtronic Sofamor Danek Inc., Memphis, TN) was used for fixation. All operations were under neuromonitoring. The Scoliosis Research Society (SRS)-22 scores was used for the evaluation of clinical outcomes before and at last follow-up after surgery. Standing full-length posteroanterior and lateral radiographs by the multipurpose Digital R/F System (Sonialvision Safire 17; Shimadzu Corp., Kyoto, Japan) were obtained at baseline, 1-week and last follow-up after scoliosis surgery [Figure 1]c, [Figure 1]d, [Figure 1]e, [Figure 1]f, [Figure 1]g, [Figure 1]h. The parameters included coronal Cobb angles of the main curve, global coronal balance (the horizontal distance from the C7 plumb line relative to the center sacral vertical line), thoracic kyphosis (TK, the Cobb angle between the upper endplate of T5 and the lower endplate of T12), sagittal vertical axis (SVA, the horizontal distance between the center of the C7 vertebral body and the posterior superior corner of the sacrum). And the preoperative bending radiographs were also obtained to calculate the flexibility of the main curve.
Magnetic resonance imaging (MRI) of the spine and craniocervical junction before and after posterior fossa decompression and/or syrinx-shunting was reviewed in scoliosis patients with syringomyelia [Figure 1]a and [Figure 1]b. The size of the syrinx was expressed as the maximum anteroposterior diameter (mm) of the syrinx cavity, the syrinx length (the number of vertebral levels traversed), and the maximal S/C ratio (the maximal diameter of the syrinx divided by the diameter of the spinal cord at the same level). All of these parameters were measured on the sagittal imagemap of MRI. To avoid the intra-observer bias, all radiological parameters were measured by 2 attending spinal surgeons who were not involved in the surgery, and the average value of their measurements was used for analysis. All data were analyzed by using SPSS software (version 22.0; IBM Corp., Armonk, NY, USA). All values are presented as mean ± standard deviation. Quantitative data were analyzed by using Student's t test or Mann-Whitney U test as appropriate. Categorical data were analyzed by using the χ2 test or Fisher's exact test. Statistical significance was set at P < 0.05.
There were 26 patients in Group A and 10 patients in Group B. The preoperative features of the syrinx in these two groups are listed in [Table 1]. On the initial clinical examinations, no numbness or weakness of the limbs, attenuated abdominal reflex, headache or extremity pain or other neurologic deficits were detected in all the patients. Details of the sex, age, treatment of the syrinx, and the syrinx size of all 10 patients in Group B are showed in the [Table 2].
At the time of the correction surgery, there was no significant difference in sex, age, coronal Cobb angle, flexibility of the main curve, global coronal balance, TK and SVA between the two patient groups [Table 3].
All patients underwent fusion with instrumentation. Twenty-eight patients (28/36, 77.8%) underwent surgical treatment with 1-stage posterior correction and fusion surgery and eight patients (8/36, 22.2%) underwent anterior release internal distraction and posterior spinal fusion surgery. The fusion length of the two groups are comparable [Table 4]. No abnormal signal was detected during the process of neuromonitoring in two groups. Urinary tract infection occurred in two patients of Group A and were successfully treated with antibiotics. And there were no neurologic or other major complications related to the surgery in either group.
The mean follow-up period was 16.8 ± 9.8 months (range, 12–48 months). For Group A, the preoperative coronal Cobb angle was significantly decreased from 71.3° to 17.0° at last follow-up (P < 0.05); for Group B, the preoperative coronal Cobb angle was significantly decreased from 70.7° to 16.7° (P < 0.05). A significant decrease was also observed in TK before and at last follow-up after surgery in the Group A (33.3° to 17.3°, P < 0.05) and Group B (39.3° to 19.3°, P < 0.05). In each group, global coronal balance and SVA were similar before and at last follow-up after surgery (all P > 0.05). The coronal Cobb angle, correction rate, global coronal balance, TK and SVA immediately after surgery and at the latest follow-up examination were comparable in the two groups [Table 4]. All patients completed the SRS-22 outcomes instrument before and at last follow-up after surgery. Analysis of the preoperative and postoperative questionnaire values revealed no differences between groups [Table 5]. Both two groups had significantly improvement in general self-image, satisfaction and total points (P < 0.05).
At present, the necessity of prophylactic neurosurgery of the syrinx in SMS patients remains controversial. Phillips et al.[10] and Yeom et al.[17] concluded that the shunting of the syringomyelia is beneficial for making surgical correction of scoliosis less dangerous and arresting progression of scoliosis in immature patients. Yet, Liu et al.[15] reported that scoliosis associated with syringomyelia may be effectively managed if a surgeon manipulates carefully intraoperatively and perioperative spinal monitoring is practiced. In addition, it was reported that the syrinx would not increase the incidence of postoperative complications without prophylactic neurosurgery. Wang et al.[5] and Zhang et al.[14] found it might be safe and could be an option to leave a syrinx untreated before 1-stage correction surgery for scoliosis patients associated with syringomyelia without neurological deficits. However, few studies have taken the impact of syrinx size into account when evaluating neurosurgical intervention of the syrinx in SMS patients. In this study, patients with a maximal syrinx/spinal cord ratio more than 0.70 were defined as having a large syrinx.[16] Large syrinx was identified in 10 of 36 patients (27.8%). To our knowledge, the syrinx size in our study is the largest compared with prior studies.[6],[13],[18] The average diameter of the syrinx cavity was 11.6mm, the average syrinx length was 9.5 vertebra and the average syrinx/spinal cord ratio was 0.86 in Group B. And the radiographic and clinical outcomes of correction surgery in these 10 patients were evaluated by comparing with other 28 SMS patients. Both Qiu et al.[19] and Godzik et al.[20] have explored the relationship between syrinx morphology and spinal deformity characteristics. And they found no association between syrinx size and curve magnitude. In the current study, the diameter of syrinx and the maximal S/C ratio of patients in Group A were significantly smaller than that of patients in Group B [Table 1]. Yet, there was no significant difference in sex, age, coronal Cobb angle, flexibility of the main curve, global coronal balance, TK and SVA between the two patient groups [Table 3]. Similar to the previous studies,[19],[20] our study revealed no correlation between syrinx size and curve severity. Patients with a multiloculate tensioned syrinx bigger than half of the cross-section area of the spinal cord were with more risk during correction surgery.[5] Also, neuromonitoring difficulties were associated with larger syrinx diameter (>10 mm).[21] Syringomyelia complicated the treatment of the scoliosis, because spinal distraction and instrumentation carried risk of neurological damage, especially when there had been several progressive neurological deficits.[5] Huebert et al.[22] reported a SMS patient who was paraplegic at T12 immediately postoperatively and died 4 weeks postoperatively of a pulmonary embolism. Noordeen et al.[23] reported an 18-year-old patient with scoliosis associated with syringomyelia and Chiari-I malformation whose intraoperative somatosensory-evoked potential (SSEP) spinal cord monitoring detected the decrease of peak amplitude during the correction surgery. Postoperatively, the patient had urinary retention and loss of the right-sided abdominal reflex. At 48 hours, both the ability to void urine and the abdominal reflexes returned to normal. Ferguson et al.[24] reported a SMS patient who had a positive wake-up test with complete paralysis below the waist. She underwent an anterior release and posterior instrumentation surgery for her rigid scoliosis. Her instrumentation was removed with resolution of her symptoms over a 1-week period. The enlarged spinal cord caused by the formation of syrinx was vulnerable during the scoliosis surgery, especially in the process of compression and distraction. Yet, no abnormal signal was detected during the process of neuromonitoring and no patients experienced neurologic or vascular complications in our study. We considered the most important reason of this pleasant outcome was the intervention of syrinx prior to scoliosis correction surgery. The syrinx diameter, syrinx length, and the S/C ratio were significantly decreased after the treatment of syrinx [Table 2]. Accordingly, prophylactic neurosurgery is essential for scoliosis patients associated with large syrinx to minimize the risk of neurologic complication. Some previous studies have shown that progression of the curve following scoliosis surgery was high in SMS patients. Ferguson et al.[24] reported 50% (5/10) of SMS patients had correction loss >10° after fusion surgery with multihook instrumentation. Bradley et al.[25] described 4 (36%) of 11 SMS patients were seen to progress >10° following correction surgery. However, Sha et al.[6] noted that the rate of postoperative progression >10° was 12% (8/69) in SMS patients. They considered that the use of pedicle screw instrumentation in posterior correction and fusion surgery offers effective coronal correction of syrinx-related thoracic curves that can be maintained during the postoperative course. Considering the close link between skeletal immaturity and correction loss,[26] they also attributed the favorable outcomes to older age compared with previous series [24],[25] (15.4y, 13.7y, 11.1y, respectively). In the present study, none of the patients have correction loss >10° in two groups. And postoperative progression of >5° was found in 7.7% (2/26) of the patients in Group A and 10.0% (1/10) of the patients in Group B (P > 0.05). Analyzing this satisfactory outcome, all the patients enrolled in this study were treated with pedicle screws. In addition, the mean age of the patients at the time of surgery in this study was comparable with patients in the prior study.[6] The SRS-22 instrument has been validated to monitor changes in surgically treated adolescent and adult patients with scoliosis.[27] In the current study, SRS-22 pain, general self-image, function/activity, satisfaction, and mental health scores were similar between the two groups, suggesting that SMS patients with large syrinx could obtain similar clinical outcomes of treatment with pedicle-screw-based spinal instrumentation and fusion compared to the patients with small syrinx. Several limitations still exist. First, our study was retrospective and thus had the shortcomings of all retrospective studies. Second, our study had a small number of patients and lacked longer term follow-up time. Therefore, future prospective and longitudinal studies with a larger number of patients and longer follow-up period are needed to evaluate the indications of neurosurgical intervention of the syrinx in SMS patients.
Our study revealed no correlation between syrinx size and curve severity in SMS patients. Prophylactic neurosurgery may be beneficial for decreasing the risk of correction surgery in SMS patients with large syrinx (S/C ratio >0.7). After the intervention of syrinx prior to scoliosis correction, SMS patients with large syrinx could obtain similar clinical and radiographic outcomes of treatment with pedicle-screw-based spinal instrumentation and fusion compared to the patients with small syrinx (S/C ratio ≤0.7). Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Acknowledgements We thank Dr. Lei Wang and Dr. Ganjun Feng for their help in modifying the picture. And we are grateful to Science & Technology Support Project of Sichuan Province (2015SZ0028&2017SZ0046 & 2017SZDZX0021) for supporting our study. Financial support and sponsorship Science and Technology Support Project of Sichuan Province [grant number 2015SZ0028&2017SZ0046 & 2017SZDZX0021]. Conflicts of interest There are no conflicts of interest.
[Figure 1]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]
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