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Posterior fossa decompression with and without duraplasty for the treatment of Chiari malformation type I—a systematic review and meta-analysis

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Abstract

The treatment of Chiari malformation type 1 (CM-I) with posterior fossa decompression without (PFD) or with duraplasty (PFDD) is controversial. Our aim is to compare the clinical outcome between the two methods for the treatment of CM-I. In this paper, the authors report a systematic review and meta-analysis of operation time, clinical improvement, and complications of PFD compared with PFDD for the treatment of CM-I. Randomized or non-randomized controlled trials of PFD and PFDD were considered for inclusion. Twelve published reports of eligible studies involving 841participants meet the inclusion criteria. There is significant difference in the operative time [mean difference = −74.63, 95 % CI (−83.02, −66.25), p < 0.05] in favor of PFD compared with PFDD. There is significant difference in overall complication rates [mean difference = 0.34, 95 % CI (0.19, 0.60), p < 0.05] and rates of CSF leak [mean difference = 0.24, 95 % CI (0.07, 0.78), p < 0.05] in favor of PFD groups. However, there is significant difference in the clinical improvement rate in favor of the PFDD group [mean difference = 0.85, 95 % CI (0.73, 0.99), p < 0.05]. Although PFDD is related with longer operation time and higher CSF leak rate, it can still be considered as a preferable treatment option for most CM-I patients for its higher improvement rate. More evidence from advanced multi-center studies are needed to provide illumination for the surgical decision making of CM-I.

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Correspondence to Ting Lei.

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Luca Massimi, Rome, Italy

The treatment of Chiari type I malformation continues to raise interest and debate. A well-known issue concerns the management of asymptomatic/poorly symptomatic subjects. A further and still disputed one concerns the best surgical operation. Actually, many kind of surgical treatments are adopted in different centers, ranging from the bony decompression of the posterior cranial fossa alone (craniectomy with or without C1 laminectomy) to the coagulation of tonsils passing through the expanding decompressive craniotomy, the dural delamination, and the duraplasty. All these surgical approaches seem to ensure good clinical results with some differences as far as the radiological outcome and the complications are concerned. On these grounds, an updated systematic review and meta-analysis of the literature was needed.

The review proposed by Xu and coworkers is focused on the “dilemma” between posterior fossa decompression alone (PFD) or with duraplasty (PFDD). As expected, PFD showed lower operating times and lower rates of complications compared with PFDD. However, PFDD showed better clinical outcome and lower risk of recurrence. Similar results were collected by Durham and Fjeld-Olenec in a previous meta-analysis on pediatric patients [8]. The confirmation provided by Xu et al. in a larger and mixed population (children and adults), therefore, would allow the neurosurgeons to definitely identify the PFDD as more effective than PFD, though more risky. Nevertheless, as stressed by the authors, several biases burden the study, as the different criteria for indication and evaluation of the results adopted by the authors of the analyzed papers, the use of retrospective series, the extent of bone decompression, the length of follow-up, or the materials used for the duraplasty. In addition, the inability to achieve a systematic correlation between clinical and radiological findings deprives this meta-analysis of information on the trend of the CSF dynamics in the posterior fossa (cisterna magna re-expansion) and the spinal cord (decrease of syringomyelia). This reinforces the need for multicenter randomized trials.

The goal of the surgical treatment of Chiari type I is to restore the CSF spaces at the craniocervical junction. In spite of the obtained results, the authors do not solve the dilemma about the best solution between PFD and PFDD. They propose intraoperative ultrasounds as the method to evaluate the restoration of the cisterna magna and, consequently, the need for a duraplasty. Such a strategy is already used by many authors (including the author of the present comment) and gives reasons of some results found in the literature and some possible biases. Indeed, intraoperative MRI, utilized for the same purpose in a recent prospective series, demonstrated an improvement of the CSF flow with the prone position alone so good that it was not significantly enhanced after PFD (Bond AE et al., J Neurosurg 122: 1068–1075, 2015). This observation, unfortunately, offers a further intraoperative bias. For these reasons, the surgical management of Chiari I should continue to be tailored on the single patient based on preoperative clinical and radiological criteria (PFD for poorly symptomatic patients without syringomyelia, PFDD for clearly symptomatic ones with syringomyelia) other than on intraoperative radiological criteria. Similarly, children should be differentiated from adults. Actually, pediatric patients do not infrequently show a moderate tonsillar herniation that is hard to be correlated with the clinical picture and that is not associated with syringomyelia (or is associated with thin hydromyelia). In these instances, also due to the residual potential of growth of the posterior fossa and the increased risk of CSF leakage in children, PFD alone should be considered.

Jörg Klekamp, Quakenbrück, Germany

The authors of this paper propose to leave the dura open after decompression of the foramen magnum for patients with Chiari I malformation in order to avoid problems with dura grafts and formation of arachnoid adhesions between dura or duragraft and underlying cerebellar and spinal cord tissue. This is a concept originally used by Gardner in his paper from 1965. Bernard Williams adopted this strategy fearing reobstruction of CSF pathways by arachnoiditis when dura grafts are used. He was convinced that duraplasties should be avoided whenever creating a sustained CSF passage was part of the surgical strategy. I had many personal discussions with him on this subject without ever agreeing on this issue. While working in Hannover, a number of patients were actually operated leaving the dura open. Their results, however, were considerably worse compared to patients operated with duraplasties, so this technique was quickly abandoned:

1. Leaving the dura open allows breakdown products of blood or muscle proteins to contaminate the subarachnoid space. This causes a severe arachnoiditis. If such areas are reopened surgically a few months or years later, the entire area usually appears covered by a thick, whitish membrane. It is no longer possible to identify any blood vessels on the cord surface or caudal cranial nerves lateral of the cervical cord and medulla oblongata. If the foramen of Magendie is closed by this membrane, any attempt of opening it is extremely dangerous for lack of any anatomical landmarks. When this technique had been used in the spinal canal, the CSF passage was regularly found to be obstructed due to this arachnoiditis upon reopening.

2. Leaving the dura open puts patients at risk to develop superficial siderosis, which is a potentially life-threatening complication related to repeated contaminations of CSF with blood. Bernard Williams operated on a woman with Chiari I malformation in Hannover during an instructional course in 1990 leaving the dura open. The patient did well postoperatively for about 1 year when she started to demonstrate signs of this disease causing severe gait and hearing problems.

3. With time, bulging of neck muscles may lead to a progressive decrease of the subarachnoid space at the foramen magnum even to the point of complete obstruction of CSF flow. Although I have seen such cases presented in scientific meetings by British neurosurgeons, who widely adopted Williams’ technique in the 1980s and 1990s, this late complication has not been published to my knowledge.

Therefore, I cannot agree with the authors of this paper and strongly advise against the technique of leaving the dura open for patients with Chiari decompressions or other pathologies.

Giannantonio Spena, Brescia, Italy

In this interesting paper from Xu et al., the authors perform a meta-analyis of the last two decades literature in order to clarify if posterior fossa decompression with (PFDD) and without (PFD) duroplasty shows differences in terms of outcomes.

The quest for the perfect intervention on Chiari I malformation (CMI) has led many authors to try many different approaches. By looking at the last decades, surgery for CMI has become more minimally invasive with the aim to reducing complications. In fact, intraarachnoid manipulation, although performed with success by several authors, intrinsically exposes the patient to risks. Moreover, adding tonsillar and arachnoid manipulation does not seem to bring further improvement to outcomes. Proposing an osseous decompression without duroplasty has become the natural consequence of chasing the most atraumatic surgery. Unfortunately, as pointed out in this meta-analysis, leaving the dura mater intact can potentially augment the number of redo surgery due to an insufficient decompression and eventually scarce symptom relief. We routinely perform PFD with duroplasty in all subjects. This said, PFD without duroplasty is still the preferred treatment in children and adolescents since the CSF dynamics follows completely different rules in young patients leading to higher numbers of external fistulas. In our opinion, this strategy is also preferable in those rare elderly patients where the aim is to guarantee relief of symptoms while avoiding any possible complications and reducing operative times.

One aspect that should be regarded with interest is that, despite different technical nuances, recent literature demonstrates that a certain percentage of patients does not benefit from decompression. It is difficult sometimes to predict clinical result, but today, it is clear that one of the first causes of unsatisfying results is an incomplete diagnosis. This implies not only to mistake a cerebellar tonsils’ ecotopia with CMI but also to neglect many other structural alterations (craniocervical-associated malformations, instability, cerebrospinal fluid’s dynamic alterations) which require sometimes different or multiple treatments.

Hao Xu, LinYang Chu, Rui He and Chang Ge contributed equally to this work.

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Xu, H., Chu, L., He, R. et al. Posterior fossa decompression with and without duraplasty for the treatment of Chiari malformation type I—a systematic review and meta-analysis. Neurosurg Rev 40, 213–221 (2017). https://doi.org/10.1007/s10143-016-0731-x

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