Dural And Skull Base Reconstruction To Eliminate Postoperative Complications Related To Cerebrospinal Fluid Leakage: Technical Nuances And Surgical Outcomes

BACKGROUND: Cerebrospinal uid (CSF) leakage is a common complication associated with neurosurgical procedures, and eliminating postoperative CSF leaks remains challenging. OBJECTIVE: Unique applications of free or vascularized aps for watertight dural and skull base reconstruction are presented. METHODS: A total of 512 cases of cranial surgeries were examined focused on the postoperative complications that required revision surgery. These cases were divided into skull base (SB) lesions and non-SB lesions according to the site of dural opening. The postoperative complications were analyzed according to their relationship to the CSF. A free ap, including fascial, myofascial, or pericranial ap, is routinely prepared for later use in dural closure in all cranial surgeries. A pedicled vascularized pericranial ap (VPF) is also used for SB dural reconstruction in extended surgical procedures. RESULTS: There were 434 cases of SB lesions and 78 cases of non-SB lesions. Of the 512 surgical cases, 27 (5.3%) required revision surgery due to patients’ postoperative conditions or complications. There were 9 cases (1.8%) of CSF-related and 18 cases (3.5%) of non-CSF-related complications. Eight of nine cases of CSF-related complications (88.9%) were seen in posterior fossa surgery. Postoperative CSF leaks that required revision surgery were seen in 4 cases (0.8%). SB reconstruction using a VPF was performed in 40 cases of SB surgeries. No postoperative infection was seen in these 40 cases, and only 1 case (2.5%) of pseudomeningocele, which required revision surgery, occurred. CONCLUSION: Dural reconstruction using a fascial ap or VPF plays an important role in achieving successful surgery. in 1, three-inch, lazy-S incision in 2, four-inch linear incision in 1, a large rectangular incision in 1). These results indicate that a wide range of subperiosteal detachment from the bone with the existence of a CSF leak from the dural gap may cause the formation of a postoperative pseudomeningocele.


Introduction
Postoperative cerebrospinal uid (CSF) leaks or subcutaneous uid collections (pseudomeningocele) are among the most common complications in neurosurgery, especially in skull base (SB) surgery. A CSF leak may cause deterioration of a patient's activity, a prolonged hospital stay, and surgical site or intracranial infection. To prevent postoperative CSF leaks or pseudomeningocele, watertight dural closure is absolutely essential. We have used a fascial graft for secured dural closure and reconstruction. In any SB case that requires an extended or invasive SB approach, reconstruction of the SB using a vascularized pericranial ap (VPF) is needed. Our unique use of a fascial ap or VPF in neurosurgical interventions is presented, and the surgical outcomes are analyzed.

Material And Methods
Patients' characteristics Page 3/15 A total of 512 cases of intracranial surgery, including tumor, vascular, traumatic, and functional surgeries, operated by the rst author from 2008-2018 were examined, focusing on the postoperative complications that required revision surgery. These postoperative complications were divided into CSFrelated and non-CSF-related. CSF leakage was characterized by rhinorrhea, otorrhea, and leakage from the operative wound. Patients were divided into those with SB lesions and those with non-SB lesions according to the site of dural opening. The SB lesions included anterior SB, middle SB or infratemporal fossa (ITF) lesions, and posterior SB or craniovertebral junction (CVJ) lesions. Postoperative CSF-related complications, which did not respond to conservative care, required additional surgical manipulation, including revision surgery for dural repair or plasty, wound opening, debridement or irrigation.
Conservative procedures such as continuous lumbar drainage placement with pressure dressing on the surgical site were not included as revision surgeries. The Institutional Review Board for Clinical Research approved this retrospective study. All patients had previously given informed consent for the surgery and all diagnostic and therapeutic interventions/techniques applied; the Review Board ruled that additional patient consent for inclusion into this retrospective study was not required.

Fascial graft (free ap)
We routinely prepare a fascial, myofascial, or pericranial ap, which is harvested at the surgical site, for later use in watertight dural closure in all cranial surgeries, especially in posterior fossa surgery. The skin incision is made through the subcutaneous fat layer, and then the skin is undermined widely to expose the surface of the musculofascial layer (Video 1). An incision is made through the musculofascial layer to elevate a thin musculofascial ap without any laceration from the muscle layer [9]. This ap is used as an autologous graft for dural closure. An inlaid ap, which is larger than the dural opening in size, is applied to cover all needle holes of suturing from inside of the dura (hole-cover technique) (Fig. 1). The inlaid ap reduces small CSF leaks from the needle holes by tight contact with the dura. A leak test using the Valsalva maneuver and physiological saline water infusion is performed to con rm watertight closure. Dural closure is reinforced by using brin glue (Bolheal®) (Teijin, Tokyo, Japan) and Surgicel® (Ethicon US, LLC, Cincinnati, OH, USA), followed by bone ap xation by a titanium plate and screw.

Vascularized pericranial ap (pedicled ap)
A VPF is used for the SB dural reconstruction mainly in extended and invasive surgical procedures. The scalp is elevated by sharply dissecting the true galea off from the subgaleal loose areolar connective tissue, which lies over the pericranium (Fig. 2, Video 2). The non-ap-side scalp edge is undermined, and the pericranium is elevated from the undermined deep end. The VPF and the fascia are sharply elevated as a large ap is separated from the temporal muscle and the sternocleidomastoid muscle (SCM). A thin portion of the SCM and the temporal muscle may be elevated together with the fascia to maintain continuity with the pericranium and for good vascularity. A wide VPF can be cut freely to provide vascular tissue to secure the closure of the dural incision or to cover the opened air sinuses, or to ll a dead space due to a bony defect or large tumor cavity.

Skull base reconstruction
When the SB dura mater is partially removed with a tumor, an appropriate size of abdominal fascia is applied for the primary dural closure. Then, the SB side of the fascia is xed onto the bone surface of the SB at some points by one or two titanium microplates and screws (microplate-bridge technique) [18] (Fig.   3, Video 2). The dural side of the fascia can then be sutured easily to the dura watertightly. Some abdominal fat grafts cut into multiple narrow strips are placed on the edge of the SB side fascia in multilayered fashion with brin glue to compress the gap between the SB bone and the fascia. The VPF is brought to the extradural space through an incision made on the temporal muscle and then sutured on the dura widely to cover the reconstructed area. Additional fat grafts are applied onto the sutured VPF to eliminate any dead spaces.

Type of surgeries
There were 434 cases of SB lesions and 78 cases of non-SB lesions ( Of the 512 surgical cases, 27 (5.3%) required revision surgery due to the patient's postoperative condition or complications (Fig. 4). There were 9 cases (1.8%) of surgical site infection (SSI), 5 cases (1%) of pseudomeningocele, 5 cases of intracranial hemorrhage, and others ( Table 2). These complications were divided into CSF-related and non-CSF-related complications. The 9 cases (1.8%) of CSF-related complications included 5 cases of pseudomeningocele and 4 cases of CSF leaks requiring revision surgery. Eight of 9 cases (88.9%) of CSF-related complications were seen in posterior fossa surgery. The overall rate of CSF-related complications in posterior fossa surgery in the present series was 2.6% (8/306). Non-CSF-related complications were seen in 7 cases in the posterior SB, 5 in the non-SB, 2 cases in the anterior SB, and 1 in the middle SB. CSF; cerebrospinal uid, SSI; surgical site infection. * A patient who presented with a CSF leak from the wound developed to the SSI. SB reconstruction using a VPF was performed in 30 cases of posterior SB, 7 cases of middle SB or ITF, and 3 cases of anterior SB surgeries. No postoperative infection was seen in these 40 cases, and only 1 case (2.5%) of pseudomeningocele occurred that required revision surgery.

Infection
Nine cases (1.8%) of SSI, which did not respond to antibiotics, required revision surgery. SSI was divided into CSF-related infection (1 case) and non-CSF-related infection (8 cases). All cases required removal of the bone ap and irrigation or wound debridement if necessary. The CSF-related infection occurred in 1 case subsequent to a CSF leak. Non-CSF-related infections were seen in 4 cases of posterior SB, 3 cases of non-SB, and 1 case of anterior SB.

CSF leak
Four cases (4/512; 0.8%) of CSF leak, which did not improve by lumbar drainage (rhinorrhea in 2, wound leak in 2) required revision surgery. All CSF leaks were seen in posterior SB surgeries (4/306; 1.3%). Two cases of rhinorrhea occurred in the retrosigmoid approach, 2 cases of wound leak were seen in the combined retrolabyrinthine and retrosigmoid approach, and the midline suboccipital approach.

Pseudomeningocele
Some pseudomeningoceles regressed spontaneously with a pressure dressing with or without lumbar drainage. Revision surgery was required in 5 cases (5/512; 1%) of pseudomeningoceles (posterior SB 4, non-SB 1). Dural plasty using an additional fascial graft and re-suturing of a loosened stitch were performed in three cases of pseudomeningocele, which occurred in the posterior fossa. A ventriculoperitoneal shunt was done for an intractable pseudomeningocele, which was seen in the case of a huge calvarial meningioma with a wide-ranging skull bone and dural defect.
Previously, we reported our surgical outcomes and complications of a consecutive series of 410 cases of vestibular schwannomas [21]. There were signi cant differences in the incidence of CSF leaks by surgeon. When dural closure was performed by residents, the incidence of CSF leaks was 13.9%. However, when closure was performed by faculty or experienced surgeons, the rate of CSF leaks decreased to 5.5%. In the present series, 2 of 4 cases (50%) of CSF leaks and 2 of 5 cases (40%) of pseudomeningoceles occurred after dural closure by residents. Although 8 of 9 cases (88.9%) of CSFrelated complications were seen in posterior SB surgery, their overall incidence in the 306 cases of posterior SB surgery was 2.6%. Furthermore, all CSF leaks were seen in posterior SB surgeries (4/306; 1.3%), which is relatively lower than in past reports (6.6%-13%) [4,5,8].
Throughout the surgery, the re ected dural ap dries up and shrinks easily by coagulation for hemostasis or heat from the illumination of the microscope. Moreover, the posterior fossa dura is generally thin and friable. In such situations, to pull back the shrunken dural ap to the original position for closure is not easy, and the putting of a needle on it or tying suture easily causes dural tears, which makes a watertight closure impossible. Closure using a fascial ap reduces the tension on the shrunken dura. An inlaid fascial ap, which is incised larger than the dural incision, will cover the stitch hole from inside. Moreover, the fascial ap will be compressed to the inner surface of the dura by the pressure of the CSF, which will make dural closure tighter. Furthermore, an autologous tissue is easy to stick on to the dura mater.
We routinely use a two-inch, lazy-S-shaped skin incision in the retrosigmoid approach. A pressure dressing, which may contribute to reducing dead space to create a pseudomeningocele or a direct conduit for CSF to reach the skin, is applied postoperatively for 72 hours for all retrosigmoid cases. Interestingly, all pseudomeningoceles occurred in cases in which the skin incision was larger than two inches (threeinch, postauricular C-shaped incision in 1, three-inch, lazy-S incision in 2, four-inch linear incision in 1, a large rectangular incision in 1). These results indicate that a wide range of subperiosteal detachment from the bone with the existence of a CSF leak from the dural gap may cause the formation of a postoperative pseudomeningocele.
Vascularity is a critical element for adherence between the tissues in the process of wound healing and for prevention of infection. Reconstruction with vascularized autologous tissue is preferred where watertight closure of the dura is required, and signi cant potential for infection exists. It has been well established to use a vascularized tissue ap for the repair of large SB defects [10][11][12][14][15][16][17]19,20,22,29]. In other words, aggressive surgical approaches for the treatment of SB tumors are warranted with the availability of reconstructive techniques using the VPF, which minimize postoperative morbidity [29]. In cases of a recurrent situation, where a ap has already been used, the transfer of a VPF from an untouched area remains the ultimate procedure. For this reason, in cases of re-do surgery for SB tumor recurrence, a skin incision much larger than the previous one should be made to effectively obtain the VPF (Fig. 5).
There are several limitations to this study. The rst is that this study included only a few cases of malignant neoplasms of the anterior SB or nasofrontal region, or extensive traumatic fractures that involve the paranasal sinuses, which may result in large bone defects with the potential to lead to much higher complication rates than other regions. Therefore, the lower rate of postoperative infection in this study cannot be compared simply with that of other studies of anterior SB reconstruction [11,12,14,24,29]. Second, the distribution of the lesions was not equal, and the types of surgery varied.

Conclusion
We believe that the incidence of CSF-related complications is simply a re ection of the surgeon's skill, attention, experience, and the way of reconstructing the dura mater. The present surgical outcomes demonstrated that dural reconstruction using a fascial ap and SB reconstruction using a VPF would signi cantly reduce the risk of postoperative CSF leakage and infection. Therefore, synthetic materials, as potential dural substitutes, should only be used when the autologous grafts are not available.  Large vascularized pericranial aps in skull base surgeries (cadaveric specimen). A: A photo showing a large and thick VPF that consists of loose areolar connective tissue, pericranium, and the true temporal fascia in the left-side combined petrosal approach. B: The VPF is much larger than the skin incision. C:

Abbreviations
Additional incisions (white dotted lines) on the VPF make the ap longer in the right-side frontotemporal approach. VPF: vascularized pericranial ap Skull base reconstruction in the right-side combined petrosal approach. A: An abdominal fascial graft is sutured with temporal and presigmoid dura with stitches. A microtitanium plate, which is cut and contoured, is secured with a couple of titanium screws to the temporal bone. B,C: A large piece of fat is placed over the suture line between the fascial graft and the dura and over the microplate and mastoid cavity, with brin glue for a multilayered closure. D: The vascularized pericranial ap, which is harvested at the beginning of the operation, is applied to cover the fat grafts and is xed on the temporal dura with additional stitches and brin glue. EAC: external auditory canal, SS: sigmoid sinus, VPF: vascularized pericranial ap Figure 4 The chart shows the number of revision surgeries divided into CSF-related and non-CSF-related complications. The most common location of where the CSF-related complication occurred was the posterior skull base. CSF: cerebrospinal uid Video.220210616.mp4