Spontaneous intracranial hypotension (SIH) is a rare disease that has been increasingly diagnosed in recent years.1–3 Spinal CSF leaks are the most prevalent cause of SIH.4 Currently, three types of spinal CSF leaks are differentiated.5 While ventral (type 1) and lateral (type 2) leaks are treated surgically, direct CSF venous fistulas (type 3) can be treated surgically as well as using endovascular techniques.6
Recently, we showed that spinal CSF leaks can be sealed through a single open posterior approach no matter where on the 360° surface of the dura mater the leak is located.7 The basis for successful surgical treatment is the exact localization of the spinal CSF leak.5,8–15 Over the years, less-invasive approaches for spinal surgery have been developed, with the goal of minimizing access-related morbidity and mortality.16–20 The combination of our posterior transdural approach to the 360° aspect of the dura and minimally invasive surgical techniques in conjunction with advanced imaging techniques for precise localization of the leak enables highly targeted minimally invasive neurosurgical approaches with small nonexpandable tubular retractors. Thus, we have applied the principle of minimally invasive spine surgery and the use of tubular retractors for para- and transdural closure of spinal CSF leaks.
The objective of the current study was to describe the technique and to report the safety and efficacy of minimally invasive microsurgery using tubular retractors for the treatment of spinal CSF leaks in a consecutive series at a highly specialized center.
Methods
Patients
This single-center, retrospective study was conducted in consecutive patients treated between April 2019 and December 2020. Inclusion criteria were: 1) SIH according to the International Classification of Headache Disorders,21 2) a confirmed spinal CSF leak, and 3) surgical treatment by our minimally invasive technique. Patients with post–dural puncture orthostatic symptoms were excluded. Demographic data as well as pre- and postoperative neurological findings were recorded in all patients. All patients were evaluated following a standardized CSF leak protocol.8 Because of the complexity of diagnosing SIH and localizing the spinal CSF leak, we would like to refer to recently published reviews.3,22
The primary outcome was the frequency of successful dura sealing via a minimally invasive approach. Secondary outcomes were the occurrence of any surgery-related complications and patient outcome at discharge categorized into unchanged, improved, and rebound hypertension. In addition, patients were contacted by a brief survey in March 2022. We asked the following questions to assess their outcome: "Did you benefit from the surgery with respect to your orthostatic symptoms?" and "Can you remain in the upright position for longer since the operation?" Intraoperative switch to an open approach was also recorded.
Ethics
The study was approved by the local ethics committee. All consecutive patients treated surgically for SIH from April 2019 to December 2020 were included if they signed the informed consent for data collection.
Minimally Invasive Surgical Technique
All patients were placed prone under general anesthesia. After fluoroscopic localization of the spinal segment of the CSF leak using C-arm imaging, a 2.5-cm midline skin incision was performed. The autochthonous musculature was then bluntly dilated unilaterally, and a nonexpandable tubular retractor system (METRx, Medtronic) with a 20-mm diameter was inserted and aimed toward the leak (Figs. 1 and 2A). Under microscopic magnification, a facet-preserving partial hemilaminectomy and flavectomy were performed. The position of the tube is centered between the two adjacent pedicles of the respective surgical level including the lateral margin of the thecal sac (Fig. 2B). The thecal sack was exposed and opened by a dorsolateral durotomy targeting the lateral border of the spinal cord (Fig. 2B and C). Using microsurgical bayonet instruments, the spinal cord was mobilized after transection of the denticulate ligament (Fig. 2D). To identify the spinal CSF leak and minimize spinal cord mobilization, it is helpful to pull the ventral aspect of the thecal sac laterally with the aid of the microsurgical suction tube (Fig. 2E). Ventral spinal CSF fistulas were disconnected by severing transdural membranes and sealed by freeing the dural breach of all arachnoid membranes, removal of osteophytes, and introducing a TachoSil patch (Takeda) from the extradural and intradural space (Fig. 2F and G). Thereafter, the dorsolateral durotomy was sutured using 5-0 nonresorbable sutures (Fig. 2H). Lateral leaks were treated by reducing the nerve root cyst and wrapping the targeted nerve root with a TachoSil patch and applying a clip at its proximal part. In direct CSF venous fistulas, all peridural veins were coagulated and disconnected, followed by clip application at the proximal nerve root.
Inserted 20-mm nonexpandable tubular retractor at T10–11 on the left side. The working channel is centered over the intervertebral disc.
Schematic workflow of transdural sealing of a ventral spinal CSF leak. A: The nonexpendable tubular retractor is aimed toward the leak. B: The tube should be placed between the two adjacent pedicles and expose the lateral margin of the thecal sac. C: Dorsolateral opening of the dura. D: Disconnection of the dentate ligament and mobilization of the spinal cord. E: Exposure of the spinal CSF leak by lateral displacement of the ventral aspect of the thecal sac. F: Introduction of the extrathecal TachoSil patch. G: Inward pulling of the extrathecal TachoSil patch and introduction of the intrathecal TachoSil patch. H: Closure of the dorsolateral durotomy. © Department of Neurosurgery, Freiburg Medical Center; published with permission.
Initially, intraoperative neuromonitoring was used routinely. After uneventful microsurgical closure of more than 100 leaks by the first author, intraoperative neuromonitoring was considered dispensable for standard cases and only performed in selected CSF leaks.
Results
We included 58 patients (38 female [65.5%] and 20 male [34.5%]), and performed 63 surgical procedures at 72 surgical levels. The median patient age was 46 years (IQR 36–55 years). During the study period, 158 patients were treated with conservative means.
Thirty-eight patients (65.5%) had ventral leaks, 17 patients (29.3%) had lateral leaks, and 2 patients (3.4%) had CSF venous fistulas; in 1 patient (1.7%), the leak could not be identified intraoperatively and the patient did not undergo reoperation. All ventral CSF leaks were located at a single level. In 25 (65.8%) of the patients with a ventral leak, a microspur was identified intraoperatively as the cause of the spinal CSF leak.
In patients with lateral CSF leaks, we targeted the surgery at a single site in 11 patients, at 2 sites in 5 patients, and at 5 sites in 1 patient.
We performed a minimally invasive procedure with a nonexpandable tubular device in all procedures. In most procedures (n = 56), we used a tube measuring 20 mm in diameter. In 1 patient each we used 16- and 18-mm-diameter tubes. Details regarding the tubular device used in 5 cases were unavailable.
After April 2019, no "open" approaches were performed, and there was no need for conversion from minimally invasive to open surgery.
Sealing of the CSF Leak
In surgeries for ventral leaks (n = 40) (Fig. 3A), surgical access was achieved via a transdural approach and closure by an intra-/extradural sandwich patch using a fibrin sealant patch (TachoSil). In 1 patient, the spinal CSF leak was closed with a suture.
Nonexpandable tubular retractor approach displaying a ventral leak (type 1) and microspur (arrow) via a transdural approach (A). A lateral leak (arrow, type 2) (B). *Tubular retractor; §exiting nerve root.
Lateral leaks (Fig. 3B) were mostly closed by clipping the respective thoracic nerve root (13 patients). In the remaining 4 patients with lateral CSF leaks, closure included surgical techniques such as direct suture, plugging, and a TachoSil sandwich patch including a transdural approach.
The overall median surgical time was 110.5 minutes (IQR 92–135.5 minutes). The median surgical time was 110 minutes (IQR 92.8–136 minutes) for patients with ventral CSF leaks, 111 minutes (IQR 95–141 minutes) for patients with lateral leaks, and 59 and 130 minutes for the 2 patients with direct CSF venous fistulas. Intraoperative neuromonitoring was performed in 15 procedures (24%).
Complications
In 2 patients, the leak could not be identified at the targeted level. In the first patient (patient 1), the neuroradiological workup localized the leak at C6–7, yet surgery at C6–7 did not reveal the leak. This patient underwent surgery at an external hospital where the leak was identified at C7–T1 and sealed. For the second patient (patient 2), the initial neuroradiological workup showed the spinal CSF leak at T9–10. However, surgery at this level did not reveal the leak. After a repeat diagnostic workup, the spinal CSF leak was observed at T1–2, where it was then microsurgically identified and sealed during reoperation. Two other patients (patients 3 and 4) had to undergo reoperations because of persisting or reopened leaks 3–4 months after the initial surgery. In both patients, revision surgery was performed from the contralateral side. One (patient 5) underwent reoperation because of suspicion of a persisting leak within 11 days after initial surgery, which turned out to be a seroma. Another patient (patient 6) underwent revision surgery because the suture of the dorsal durotomy was insufficient. In total, 5 patients underwent surgery twice at our department. In 1 patient (patient 7), paresis of the interosseous muscle and opponens pollicis muscle (Medical Research Council [MRC] grade 3) occurred after clipping of the T1 nerve root. During follow-up, a mild weakness (MRC grade 4) of the opponens pollicis muscle persisted (Table 1). Therefore, the rate of permanent neurological deficits was 1.7%, the revision rate for persisting or recurring leak was 3.4%, the overall revision rate including second surgery at an external hospital was 10.3%, and the overall complication rate was 12.1%.
Complications
| Pt No. | Age (yrs), Sex | Type of Leak | Complication | Resolution |
|---|---|---|---|---|
| 1 | 36, F | Ventral | Wrong level | 2nd surgery at external hospital |
| 2 | 52, F | Ventral | Wrong level | Revision surgery at 2nd level T1–2 |
| 3 | 39, F | Ventral | Persisting/recurrent leak | Revision same level |
| 4 | 54, F | Ventral | Persisting/recurrent leak | Revision same level |
| 5 | 34, F | Ventral | Seroma | Superficial wound revision |
| 6 | 35, F | Ventral | Insufficiency of dorsal durotomy suture | Revision |
| 7 | 58, F | Lateral | Paresis of the interosseous muscle & opponens pollicis muscle (MRC grade 3 to MRC grade 4) | None |
Outcomes
The primary outcome, the frequency of successful dura sealing via a minimally invasive technique, was achieved in 56 of 58 patients (96.6%). In these patients, the targeted leak/fistula could be identified and sealed during a single surgical procedure. Outcome at discharge after initial surgery was unchanged in 14 patients and improved in 25 patients, and 19 patients had signs of rebound hypertension. The patient in whom surgery was performed at the wrong level (patient 2) showed no improvement after the initial surgery, yet she experienced improvement after revision surgery. The two patients with persisting spinal CSF leaks (patients 3 and 4) had rebound hypertension after definite closure of the CSF leak. At a median follow-up of 21.5 months (IQR 16–28 months), 8 patients were lost to follow-up. Forty-five of 50 patients reported to have benefited from the surgery with respect to their orthostatic symptoms, and 46 of 50 patients replied that they can remain in the upright position for longer after the surgery.
In addition to the aforementioned complications, we noted transient deficits in 9 patients. In 3 patients who underwent surgery for a ventral leak, we noted a transient postoperative hypo-/dysesthesia at the dermatome related to the surgical access, one of whom had a transient paresis of the triceps muscle (MRC grade 4−). Two further patients with ventral leaks showed wound secretion that was treated conservatively with a course of antibiotics. Four patients who underwent surgery for lateral leaks had a hypoesthesia or dysesthesia according to the dermatome of the clipped nerve root.
Discussion
Minimally invasive surgery with nonexpandable tubular retractors using para- and transdural approaches allowed sufficient visualization for safe closure of all types of spinal CSF leaks in patients with SIH. We have completely replaced open approaches with minimally invasive procedures in the treatment of SIH. According to our experience, minimally invasive approaches offer the advantages of shorter surgery times and less postoperative pain. The rate of permanent neurological deficits was low (1.7%).
Until recently, there has been a lack of a generally accepted surgical approach to the anterior dura. Different approaches to the anterior dura were mainly described for the therapy of thoracic disc herniation.23 With this development, many possible approaches (posterior approaches via laminectomy or hemilaminectomy; transpedicular and transfacet pedicle-sparing approaches; costotransversectomy; and lateral extracavitary, transthoracic, thoracoscopic, and transsternal approaches) have been described and discussed.23 The complication rate associated with these approaches was approximately 30% and included lung-related complications, medullary complications, intercostal neuralgia, and dural breaches.23
For spinal CSF leaks, several surgical approaches have been described.7,24–29 Ventral approaches include cervical and thoracic discectomy or single- or multilevel corpectomies.25,27–29 Because of the difficulty of visualizing ventral leaks, extensive ventral approaches, including sternotomies and thoracotomies, have been utilized.25 The most commonly used dorsal approaches are multilevel laminectomies, which may be associated with an increased risk of postoperative instability and the need for fusion surgery.30–32 Even with these extensive approaches, it has been often difficult to find and visualize the leak and then to seal or suture the leak. Recently, we showed that spinal CSF leaks anywhere on the 360° circumference of the thecal sac could be treated via a posterior approach.7 In that first series, all patients underwent surgery via an open approach, and the surgical complication rate was 28%. With increasing experience and caseload, we have advanced our surgical technique. In our department, minimally invasive techniques have been routinely used for the treatment of lumbar disc herniation, spinal stenosis, and the minimally invasive transforaminal lumbar interbody fusion approach, as well as for the resection of small intradural pathologies such as meningiomas or schwannomas.16,17,33–35 By introducing this technique for the treatment of spinal CSF leaks, we were able to seal the CSF leaks effectively and reduced our complication rate and surgical time while increasing patient comfort. With respect to a successful closure of the spinal CSF leak, 25 patients reported an improvement at discharge. However, an additional 19 patients presented signs of rebound hypertension at discharge, indicating successful closure of the leak. In the longer-term follow-up, even more patients reported improvement of their clinical situation. Cases of revision surgery highlighted the utmost importance of precise preoperative localization of the spinal CSF leak and the correct side of the surgical access. In ventral leaks, the latter is of importance due to the limited space available for intradural manipulation. In the current series, the neuroradiological workup yielded a wrong level and resulted in an unsuccessful initial operation in 2 patients. This, however, should not be attributed as a failure of the minimal invasive approach. Minimally invasive surgery is now our standard to treat spinal dural CSF leaks, and we advocate that minimally invasive surgery should be the method of choice in highly specialized centers.
The limitations of the study are its retrospective design, single-center approach, and limited patient numbers.
Conclusions
Increasing experience, a higher caseload, and better imaging in addition to minimally invasive surgery by nonexpandable tubular retractors utilizing the para- and transdural approach allows safe visualization and closure of spinal CSF leaks in SIH while reducing the complication rate compared to open approaches. Neuroradiological diagnostic workup with exact localization of the leak is of utmost importance. Considering its safety, efficacy, and the advantages of less-invasive techniques, we propose minimally invasive surgery to be the method of choice for the surgical treatment of spinal CSF leaks.
Disclosures
The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.
Author Contributions
Conception and design: Fung, Beck. Acquisition of data: Fung, Roelz, Kraus, Volz. Analysis and interpretation of data: Fung, Hubbe, Klingler, Kraus. Drafting the article: Fung, Hubbe, Roelz. Critically revising the article: Fung, Hubbe, Klingler, Volz, Lützen, Urbach, Kieselbach. Reviewed submitted version of manuscript: Fung, Beck, Hubbe, Roelz, Kraus, Volz, Lützen, Urbach, Kieselbach. Approved the final version of the manuscript on behalf of all authors: Fung. Administrative/technical/material support: Fung, Beck. Study supervision: Fung, Beck.
Supplemental Information
Previous Presentations
Portions of this work were presented as a poster presentation at The International Headache Congress, International Headache Society and European Headache Federation, September 8–12, 2021, held virtually; as an oral presentation at the European Association of Neurosurgical Societies, October 3–7, 2021, held virtually; and as an oral presentation at the 72nd Annual Meeting of the German Society of Neurosurgery, June 6–9, 2021, held virtually.
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