Abstract
Purpose:
Symptomatic intraspinal extradural cysts of the cervical subaxial spine are rare, but usually require surgery. Conventional posterior decompression is the gold standard. However, there is increasing experience with endoscopic surgical techniques. The purpose of the study is to evaluate the technical implementation and outcomes of a full-endoscopic uniportal technique via the posterior approach in patients with symptomatic intraspinal extradural cysts of the cervical subaxial spine.
Methods:
Seven consecutive patients with a subaxial location of symptomatic intraspinal extradural cysts were decompressed in a full-endoscopic uniportal technique via the posterior approach between 2009 and 2015. Imaging and clinical data were collected in follow-up examinations for 18 months.
Results:
In all cases, the cyst was completely removed and adequate decompression was achieved using the full-endoscopic uniportal technique. One patient developed a dural leak that was sutured and covered intraoperatively. No other complications requiring treatment were observed. All patients had a good clinical outcome with stable regression of the radicular and central nerve pain or neurological deficits. The imaging follow-up showed sufficient decompression in all cases. No evidence was found of increasing instability during the follow-up period.
Conclusion:
The full-endoscopic uniportal operation with a posterior approach allows the resection of the cyst and can minimize trauma and destabilization and has technical benefits and a low complication rate. It is an alternative surgical method that can offer advantages and is considered by the authors to be the surgical technique of choice for cervical subaxial intraspinal extradural cysts.
Keywords
Introduction
Symptomatic intraspinal extradural cysts occur relatively rarely and are most often located in the lumbar spine, followed by the cervical and thoracic spine. 1 –5 If they become symptomatic, they can cause radicular or central nerve pain or neurological deficits. If nonsurgical measures fail, if pain is intolerable, or if there are neurological deficits, surgery may become necessary. In the subaxial cervical spine, this involves individual degrees of lamina resection and cyst resection using posterior techniques with or without additional posterior stabilization. 1,3,6 –11
For operations of lumbar and cervical herniated discs and spinal canal stenoses, sufficient results and advantages for full-endoscopic uniportal surgical techniques under continuous irrigation have been described. 12 –17 In the lumbar spine, intraspinal extradural cysts are resected using this technique. 18 In the cervical spine, the posterior access is used for foraminotomies. 14,19 This study evaluates the technical implementation and outcomes of a full-endoscopic uniportal technique via the posterior approach in patients with symptomatic intraspinal extradural cysts of the cervical subaxial spine, taking specific advantages and disadvantages and literature into consideration.
Materials and methods
Patient characteristics
The routinely collected prospective data of all full-endoscopic posterior operations of the cervical spine were evaluated retrospectively in compliance with the guidelines of the responsible ethics committee. The research protocol for this study has been reviewed and approved by the Hospital Institutional Review Board. A specific patient consent was not required regarding federal data privacy act because this retrospective study is on the basis of intradepartmental medical records. Seven consecutive patients (two women, five men, age between 51 and 74) with a subaxial location of a symptomatic intraspinal extradural cyst were included and had undergone a cyst resection in a full-endoscopic uniportal technique via a posterior approach between 2009 and 2015. The patient characteristics are summarized in Table 1.
Patient characteristics.
DMARD: disease-modifying anti-rheumatic drug; CT: computed tomography.
Full-endoscopic instruments
The endoscope used has an oval shaft cross section measuring 5.9 × 5 mm2 and is introduced through a sheath. The view angle is 25°. For a uniportal technique, an intra-endoscopic working channel with a diameter of 3.1 mm is needed. A bipolar articulating probe is used that applies the radiofrequency current of 4 MHz, which reduces the transmission of heat to adjacent tissue structures. 20 The endoscopic system is used as an open system, 12,15,16,19 so that for the length of the working sheath, a maximum pressure of the irrigation fluid of 9.6 mmHg can be reached. On average, the cerebrospinal fluid (CSF) pressure in the high cervical region is 15.5 mmHg. 21 All surgical and optical instruments are products of RIWOspine (RIWOspine GmbH, Knittlingen, Germany).
Surgical technique
The operation is performed under general anesthesia in prone position with the head fixated in a Mayfield (Integra LifeSciences, Saint Priest, France) skull clamp. The level to be operated is marked and approximately 7-mm-long skin incision is made over the lateral mass on the respective side. The dilator is introduced bluntly to the vertebral joint; the surgical sheath is inserted via the dilator and through it the endoscope. The further procedure is full-endoscopic uniportal technique (Figure 1). Bone resection is begun at the cranial lamina and at the medial edge of the descending facet if necessary. Resection in cranial direction can be carried out until hemilaminectomy is achieved or beyond. The necessary extent of the bone resection depends on the size of the cyst. The ligamentum flavum is resected, the dura exposed, and then the cyst is dissected. The cyst is opened and emptied, and the wall of the cyst is resected. The recess and if necessary, the foramen is decompressed and exposed until the affected spinal nerves can be seen. The spinal cord is decompressed up to the opposite side, possibly in over-the-top technique. Free floating of the dura mater in the irrigation fluid is a sign of sufficient decompression. No drainage is placed; the skin incision is closed.
Cervical full-endoscopic uniportal technique with posterior approach.
Follow-up
The data were routinely recorded pre- and postoperatively and after 6 weeks, 6 months, and 18 months. The patients came to follow-up in person. Because of the complexity of the symptoms (central/peripheral), various measuring instruments were necessary. In addition to clinical and radiological parameters, the visual analog scale for neck and arm pain and the Japanese Orthopedic Association (JOA) score for the patients with myelopathy were used. X-ray images in two planes and MRI or computed tomography (CT) scans were made routinely. All seven patients were available to follow-up in the designated period.
Results
Surgical technique/intraoperative findings
In all cases, the cyst was completely removed and sufficient decompression was achieved. Because of the endoscopic technique with a 25° view angle and continuous irrigation, visibility was good with the corresponding field of vision and working area; no problems due to epidural bleeding occurred. In two patients with radicular symptoms, a partial foraminotomy was performed. In both cases, no more than the medial third of the joint facets was removed. No patient required additional stabilization due to this slight surgery-induced destabilization.
Intra- and perioperative data/complications
The intra- and perioperative parameters are presented in Table 2. The intraoperative blood loss was so low that it could not be measured due to the continuous irrigation. All patients were mobilized immediately depending on the general anesthesia; no medication for surgery-related pain was required. No other more serious problems requiring treatment such as postoperative epidural bleeding, operation-induced damage to the spinal cord or spinal nerves, wound healing disorders, infections, and thrombosis occurred. No recurrence of a cyst was detected in the follow-up period.
Intra-/perioperative data/complications.
OP: operation.
Clinical and radiological outcome
All patients had a good clinical outcome with regression of the myelopathy or radicular symptoms. Mean JOA increased from 11.2 to 14.7 after 18 months. The patients with radicular symptoms were painless and achieved complete recovery of radicular deficits. These outcomes remained stable in the follow-up period. No operation-related increase in neck pain was reported. The imaging follow-up showed sufficient decompression in all cases (Figure 2(a) to (d)). No evidence of increasing instability was found during the follow-up period.
(a) and (b) Preoperative sagittal and transversal MRI images show the intraspinal extradural cyst (arrows) with compression of the spinal cord. (c) and (d) Postoperative sagittal and transversal MRI images show decompression of the spinal cord (arrows).
Discussion
The cervical spine symptomatic intraspinal extradural cysts are usually found at level C7/T1, 3,9,10 which was also the case in our study. Although increased strain at the junction to the more rigid thoracic spine is assumed, the exact mechanism or cause of the greater number at this location is not known. 9,22 The overall incidence increases with age, 2 in our study, the average age was 61.8. Different theories are discussed regarding the pathogenesis. 23,24 Instability, repetitive stress, and degeneration triggering an inflammatory reaction or expansion of the synovia have been associated with cyst formation. 2,25 In this study, all patients showed degeneration of the vertebral joints and the disc; one patient also had rheumatoid arthritis as an underlying disease.
If cervical cysts become symptomatic, they can cause radicular or central nerve pain or neurological deficits due to compression, depending on the location. 3,10 Spontaneous remissions have been described, 26,27 but most symptomatic cysts appear to require intervention. Overall, a more aggressive method appears to be required for cysts in the cervical spine than for those in the lumbar spine, as the spinal cord is located here and there is thus a risk of central nerve damage with progressive myelopathy, limiting management through conservative treatment. 28 In the subaxial cervical spine, cysts are always resected via the posterior access. 1,3,6 –11 No recurrences in the cervical spine have been described in the literature, but the necessity of a complete resection has been pointed out with this possibility in mind. 3,9,24,29 According to other results, a resection as sparing as possible appears to be sufficient, 9 which can have advantages for minimizing surgery-induced trauma. In the full-endoscopic uniportal posterior technique, the cyst was removed completely in all patients. This is consistent with the experience of other full-endoscopic posterior operations on the cervical spine and cyst resections in the lumbar spine. 14,18,19 The full-endoscopic technique under continuous irrigation has the proven technical advantages known from arthroscopies or other endoscopic spine operations such as an enlarged visual field due to the 25° view angle, excellent illumination and visualization, reduced bleeding due to continuous irrigation, low complication rates, and so on. 12 –17 The intraoperative blood loss is too low to be quantified due to the continuous irrigation. No surgery-induced neck pain was observed immediately postoperatively or in the follow-up period. The operation does not require a prolonged hospital stay. No cyst recurrences were observed and none have been described in the literature 3,9,24,29 ; however, this could be due to the generally only medium-term investigation periods.
The necessity for additional stabilization is not precisely specified; however, it is recommended in the case of preoperative instability or iatrogenic destabilization and to prevent recurrences. 1,3,6 –11 In the full-endoscopic technique, in two cases, a maximum of one-third of the medial vertebral joint was resected; much less was necessary in the other cases (Figure 3(a) and (b)). It has been described that only resection of more than 50% of the vertebral joint is associated with increased postoperative instability or segment mobility. 30,31 Surgery-induced instability was also not found in the full-endoscopic posterior foraminotomy to operate cervical disc herniation, and no additional laminectomies were performed for this. 14,19 Based on these results and in view of the minimal trauma and destabilization using this full-endoscopic technique, the authors will continue to attempt to use surgical decompression for the symptoms of intraspinal extradural cysts and avoid performing additional stabilization.
(a) and (b) The postoperative computed tomography (CT) scan shows the hemilaminectomy (arrow) with a preserved vertebral joint.
The good clinical and radiological outcomes in this study confirm the technically sufficient decompression and are consistent with those in published studies. 3,11,24,29 Full-endoscopic posterior decompression is a real minimally invasive procedure that can reduce surgery-induced trauma and has technical advantages and a low complication rate. The possibilities for comparison are limited due to the low number of cases and the fact that most publications are available only as case reports. For the operator, the uniportal technique with an angled visual field can be unfamiliar at first. The same applies to the two-dimensional work at the monitor. One general disadvantage for endoscopic procedures is the steep learning curve, 32 which, however, can be overcome with new or modified techniques. No other technical disadvantages were noted in the pathologies operated on in this study.
Conclusion
Symptomatic intraspinal extradural cysts of the cervical subaxial spine are rare, but usually require more aggressive treatment. One problem is the risk of central nerve damage with progressive myelopathy. If surgery is necessary, conventional posterior decompression is the gold standard. The full-endoscopic uniportal technique with a posterior approach described here allows sufficient resection of the cyst and minimizes trauma and destabilization, has technical advantages, and a low complication rate. It is an alternative surgical technique with advantages.
Footnotes
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.