The Laryngoscope Lippincott Williams & Wilkins, Inc. © 2006 The American Laryngological, Rhinological and Otological Society, Inc.
Dural Defect Repair with Fascia by a CO2 Laser System in a Porcine Model Boaz Forer; Tamar Vasilyev; Tamar Brosh; Naam Kariv; Leonor Leider Trejo; Ziv Gil; Abraham Katzir; Dan M. Fliss
Hypothesis/Objectives: We tested the effectiveness of a temperature-controlled CO2 laser soldering system on a porcine model for dural defect reconstruction using a fascial patch. Methods: A dural patch was excised and then reconstructed with fascia by a CO2 laser system in vitro in 27 animals and in vivo in five animals. Results: After dural reconstruction, the average burst pressure of the soldered patch in vitro, as measured by a custom-made pressure detector, was 258.5 cm H2O. All five pigs in the in vivo group showed no neurological complications or cerebrospinal fluid leak, and the underlying brain tissue showed no thermal injury. Conclusion: The CO2 laser system created a watertight bond and did not cause thermal injury to the brain. The procedure is potentially faster than conventional repair, and wound healing may also be more rapid. Key Words: CO2 laser, dura, reconstruction, fascia, pig, albumin, in vivo. Laryngoscope, 116:1002–1006, 2006
INTRODUCTION The dura can be damaged by trauma or excised during tumor surgery. The result of incomplete dural closure can be life-threatening meningitis or tension pneumocephalus. Dural reconstruction must be able to support cerebrospinal fluid (CSF) pressure. The conventional suturing technique has inherent drawbacks: CSF might leak through the suture holes or between the sutures themselves (particularly noticeable in older patients or in patients who had undergone radiotherapy), and the sutures can produce a foreign body reaction, which might slow the healing process.
From the Department of Otolaryngology Head and Neck Surgery (B.F., Z.G.) and Pathology (L.L.T.), Tel-Aviv Sourasky Medical Center, the School of Physics and Astronomy, Sackler Faculty of Exact Sciences (T.V., A.Z.), the Goldschlager School of Dental Medicine (T.B.), and the Animal Research Laboratory, Sackler Faculty of Medicine (N.K.), Tel Aviv University, Tel Aviv, Israel. Editor’s Note: This Manuscript was accepted for publication February 21, 2006. The research project was partially supported by the Israeli Cancer Foundation. Send Correspondence to Boaz Forer, MD, Department of Otolaryngology Head and Neck Surgery, Barzilai Medical Center, 3rd Histadrut Street, Ashkelon, Israel. E-mail:
[email protected] DOI: 10.1097/01.mlg.0000217241.01388.2d
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Laser soldering is an alternative technique for tissue bonding. Albumin is applied onto the approximated edges of the tissue and is heated by a laser beam. This technique does not involve a foreign body such as suture. The potential advantages of laser compared to conventional suturing are that (1) it can be applied endoscopically, (2) it generates a watertight bond, (3) the time to wound healing might be shorter, and (4) there is relatively little scar formation. The mechanism of laser soldering is not fully understood, although it appears to be a heating-induced protein denaturation-renaturation process.1 Review of the literature revealed only two reports on dural reconstruction using lasers. In the first report, a diode laser with albumin solder was used to close dural cuts in rats.2 No temperature control was applied, and the soldering resulted in thermal damage to the underlying brain tissue. The second report described brainstem dural defect reconstruction in dogs,3 which was not watertight in six of seven animals. Our group has carried out experimental studies on laser soldering of skin, urinary bladder, blood vessels, and cornea.4 – 6 The results of these experiments showed that laser soldering resulted in good closure, less inflammatory reaction, and very little scarring.7,8 Temperature control is essential to achieve optimal soldering results and to avoid thermal damage to the underlying tissue. Based on these experiments, we created a model for the reconstruction of a dural defect with fascia using a CO2 laser system. Farm pigs were chosen for this study because their brain size and dural thickness were suitable for surgical manipulation. The purpose of this study was to create a model for dural reconstruction using a temperature-controlled CO2 laser system.
MATERIALS AND METHODS Laser Soldering System The Applied Physics group at the Tel Aviv University (Israel) developed a unique temperature-controlled CO2 laser system. The main idea is to apply biologic solder (i.e., albumin) on the approximated edges of a cut and heat the albumin and underlying tissue to a narrow temperature range (65 ⫾ 3°C). The CO2 laser was chosen because its radiation is highly absorbed by water and hence does not penetrate deeply into the tissue.16
Forer et al.: Porcine Dural Defect Laser Repair with Fascia
Fig. 1. The laser soldering system is based on a CO2 laser, an infrared (IR) detector, two silver halide fibers, and a personal computer (PC). One of the fibers delivers energy from the CO2 laser to the tissue and heats it. The warm tissue irradiates IR waves, which are transferred through the second fiber to an IR detector. A computer program continuously adjusts the laser energy according to the IR fiber input to maintain a constant temperature on the tissue surface.
The system is based on a CO2 laser, an infrared detector (IRD), two silver halide fibers, and a personal computer (Fig. 1). One of the fibers delivers energy from the CO2 laser to the tissue and heats it. The warm tissue emits infrared radiation, which is transferred through a second fiber to an IRD. A computer program continuously adjusts the laser output according to the IRD input to maintain a constant temperature on the tissue surface. Aqueous 47% bovine albumin (Sigma Chemical, St. Louis, MO, U.S.A.) was used as a solder in all experiments.
Animal Model and Surgical Procedure: In Vitro Experiments For this part of the study, we used juvenile farm pigs (7–19 kg) that died of natural causes in the Institute of Animal Research, Kibutz Lahav, Israel. A circular 8 mm dural patch located approximately 10 mm off the midline and midway between the anterior and posterior ends of the brain was excised through a wide craniotomy. Reconstruction was done with the fascia investing the longissimus et lumborum muscle (located under the skin on the animal’s back). This fascia is tightly adhered to the muscle fibers on its inner “muscular” side. Its outer “fatty” side facing the skin, however, is loose and covered by a thin fat layer. The fascia was separated from the muscle and excised. A circular 15 mm fascial patch was inserted between the dura and brain tissue, resulting in an overlapping area. The albumin solder was spread over the dura-fascia junction line and the tissue was heated by the laser system to 65 ⫾ 3°C. At the end of the procedure, a wide dural patch with the soldered area in the middle was excised and taken for burst pressure measurement, using the system described below.
Burst Pressure Measurements The dural patch was attached to the top of a holding device shaped like a drinking glass, which was custom-made for this purpose. Fluid was driven into the holding device by a computerized system (Instron, model 4502, Buckingamshire, UK) and the pressure inside the device was continuously measured by a pressure detector. With increasing pressure, the weakest point of the soldered dura-fascia line eventually disconnected, resulting in fluid leak though the opening and a rapid drop in pressure. The burst pressure of the reconstructed dura was defined as the peak pressure (Fig. 2).
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Fig. 2. Burst pressure measurement. The pressure in the holding device was continuously measured up to a certain pressure at which the weakest point of the soldered dura-fascia line disconnected and fluid leaked though the opening. The peak pressure was defined as the burst pressure of the reconstructed dura (271 cm H2O in this particular experiment).
In Vivo Experiments In vivo experiments on five live pigs weighing 12 kg each were carried out according to the regulations of the animal care and use committee at Tel Aviv University. General anesthesia was achieved with pentobarbital 30 mg/kg (Nembuthal). Ceftriaxone (Teva, Petah Tikva, Israel) 50 mg/kg once a day was given perioperatively for 2 days. The surgical procedures were performed using sterile equipment. A small circular craniotomy was performed over the parietal lobe. Dural excision and reconstruction were done at the same place and in the same manner as described for the in vitro model. Soldering was done under microscopic magnification. The circular craniotomy bone was secured back in place using bone cement. The animal was scheduled for euthanasia 10 days after surgery. Until then it was observed daily by the Institute of Animal Research staff who noted food intake, neurologic status, and wound condition. At the end of the observation period, the animal was anesthetized, the surgical wound was re-opened, and the soldered area was checked for CSF leak. En bloc excision of the dura containing the soldered area with the underlying brain was then performed. The specimen was fixated using 4% formaldehyde solution and stained by hematoxilin-eosin. The anesthetized animal was killed with an intracardiac injection of pentobarbital.
RESULTS Burst Pressure Measurements: In Vitro Model We used 27 pig corpses divided into three groups: the first group consisted of nine pigs, which were operated on without the use of magnification (direct vision soldering [DVS]). The second group consisted of eight corpses, and soldering was done under microscopic magnification with the outer “fatty” side of the fascia facing the dura (microscopic fatty side soldering [MFSS]). In the third group, 10 animals were operated on under a microscope with the inner “muscular” side of the fascia facing the dura (microscopic muscular side soldering [MMSS]). Burst pressure measurements were carried out using the computerized system discussed earlier. The results are displayed in Table I. DVS produced the lowest burst pressure results (mean 120.1 ⫾ 61.8 cm H2O). MFSS yielded an intermediate bonding strength (mean 139.6 ⫾ 51.7 cm H2O). MMSS resulted in the highest burst pressure (mean 258.5 ⫾ 117.3 cm H2O), which was significantly higher than both DVS (P ⫽ .001) and MFSS (P ⫽ .008), and more than Forer et al.: Porcine Dural Defect Laser Repair with Fascia
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TABLE I. In Vitro Burst Pressure Measurements, Done Using a Computerized System. Direct Vision Soldering (DVS)
Microscopic Fatty Side Soldering (MFSS)
Serial No.
Animal Weight, kg
Burst Pressure, cm H2O
1 2 3 4 5 6 7 8 9
7 11.5 19.5 7 7 7 13 13 13
160 114 57 55 192 159 193 124 27
Mean pressure 120.1 ⫾ 61.8
Serial No.
Animal Weight, kg
Burst Pressure, cm H2O
10 11 12 13 14 15 16 17
7 7 7 7 7 12 8 7
50 113 175 164 116 131 226 142
Mean pressure 139.6 ⫾ 51.7
10 times higher than the physiologic intracranial pressure (approximately 20 cm H2O).
Dural Reconstruction: In Vivo Experiments The surgical procedure was done as described above in five live animals. When the craniotomy was reopened after a 10-day observation period, the soldered area was seen to be covered by granulation tissue (Fig. 3). No CSF leak was detected. The dura-to-fascia bonding was strong and the soldered area could not be separated by manipulation (i.e., prodding by a blunt instrument). To verify a watertight seal, a lumbar puncture was then performed and blue dye was injected through the lumbar puncture
Fig. 3. After a 10-day observation period, the surgical wound was re-opened. A wide craniotomy was performed. Blue dye was injected intrathecally and the CSF pressure was raised to 30 cm H2O for 30 minutes. Bulging of the soldered area due to elevated CSF pressure can be seen, without CSF leak. Black arrow is pointed at the margin of the previous small craniotomy. The dura and soldered area at this site were covered by granulation tissue. White arrow is pointed at the margin of the wide craniotomy.
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Microscopic Muscular Side Soldering (MMSS)
Serial No.
18 19 20 21 22 23 24 25 26 27
Animal Weight, kg
Burst Pressure, cm H2O
7.5 192 7.5 165 9 104 10.5 377 9 258 9 271 7 122 9 291 7 327 7 478 Mean pressure 258.5 ⫾ 117.3
needle. The CSF pressure was raised to 30 cm H2O by saline injection through the needle and maintained for 30 minutes. During this time, the blue dye was visible under the dura and no leak was detected. The soldered area and underlying brain tissue were resected en bloc at the end of the experiment. The microscopic appearance of the soldered area is presented in Figure 4.
Fig. 4. Histologic appearance of the soldered area after 10 days. The fascia (F) and dura (D) show mild fibroblast infiltration with no signs of necrosis. On the inner “fatty” side of the fascia fat cells can be seen (arrows). The outer surface of the dura and fascia shows hyaline material representing the albumin layer (A) and lymphocyte infiltration. The dura-fascia junction line is tightly adhered. The arachnoid, pia, and brain tissue (B) show no signs of thermal damage. The neurons and glial cells appear normal.
Forer et al.: Porcine Dural Defect Laser Repair with Fascia
DISCUSSION Repair of dura following trauma or tumor extirpation is conventionally done by synthetic suture materials that can cause local inflammatory reaction and slow the healing process. Moreover, the reconstruction is not watertight and fluid can leak in-between the sutures themselves or through the suture holes. Laser heating offers an alternative technique that could generate a watertight seal and good tensile strength. The absence of sutures allows a faster healing process without foreign body reaction. Two previous studies described the use of laser soldering for dural reconstruction.2,3 The first described the use of diode laser soldering for dural repair in Lewis rats. The results showed that soldering yielded better bonding strength than sutures (mean leak pressure of 34 cm H2O vs. 12.3 cm H2O, respectively).2 Thermal damage to brain tissue was observed on histologic examination. The burst pressure value of the soldered tissue was much lower than our results. Deep penetration of diode laser radiation compared to CO2 wavelength and the lack of temperature control may be responsible for the brain tissue damage and weaker bond. In the second report,3 CO2 laser without temperature control was used for dural reconstruction in dogs. The authors observed CSF leakage immediately after the procedure in most animals. They also found that fibrin glue supported more than 50 cm H2O of CSF pressure, emerging as being superior to both laser and sutures. In our experiments, a much higher bonding strength (mean, 258.5 ⫾ 117.3 cm H2O) was observed using laser soldering. The lack of precise temperature control might be the reason for the weak and not watertight bond in this study. In our study, we have successfully bonded fascia to dura both in an in vitro setting and in live animals and showed that no thermal damage was inflicted on the soldered tissue or the underlying brain. This report is the first successful attempt to reconstruct a dural defect with fascia by a CO2 laser. The rationale for the use of a CO2 laser is its high absorption rate in water. The laser energy heats only the top layer (roughly 20 m) and does not penetrate deep into the tissue. We chose a porcine model because the pig brain is relatively large, thus providing a wide surgical field for dural excision and reconstruction, and its dura and the fascia are relatively thick compared to those of smaller animals (i.e., rats or rabbit), making them easier to manipulate. We decided to use a patch that was larger than the hole and to bond the fascia to the dura in an end-toside fashion because placement of a fascial patch that will exactly match the hole is technically difficult and had reportedly produced inferior bonding results in preliminary experiments.9 The mechanism of tissue soldering is not fully understood, although protein denaturation-renaturation seems to be the biologic process involved.10 The use of fascia as the reconstruction material would appear to be a “natural” choice, since it is protein rich and is the tissue of choice for dural reconstruction in humans by many authors. 11–15 The use of the muscular side of the fascia, which is rich in protein and has an irregular, large surface area, proved to produce significantly stronger bond than the fatty side of Laryngoscope 116: June 2006
the same fascia. This result supports the assumption that soldering involves protein-based bonding. We believe that the current report is the first to compare soldering with and without magnification. The use of an operating microscope for magnification significantly improved our soldering results by enabling the surgeon to see tissue’s reaction to heating (i.e., shrinkage and movement) under the albumin solder, which is very difficult to see without magnification. In our soldering experiments, the albumin layer was sometimes too thick or the laser fiber movement too fast, which resulted in heating of the superficial albumin layer but insufficient heat conduction into the tissue and a weaker bond. When this problem was observed under the microscope, the procedure was stopped and the necessary adjustments made so that optimal heating was achieved at every point along the dura-fascia junction line. For soldering of the muscular side (MMSS), the mean burst pressure (258.5 cm H2O) was more than 10 times the physiologic CSF pressure (approximately 20 cm H2O). These encouraging results support the assumption that laser soldering of fascia to dura can withstand CSF pressure without the risk of leak. Even the lowest value that we recorded for MMSS (104 cm H2O) was sufficient for all practical applications. In the in vivo experiments, the animals were observed for 10 days and no neurologic or surgical complications (e.g., CSF leak) were noted. Histologic examination of the surgical specimen showed a watertight seal with no evidence of brain tissue damage. Furthermore, bonding of the fascia and dura was complete, without necrosis or excessive inflammation. Our laser system has the potential to be used in endoscopic surgery; hence, laser soldering offers an alternative to fibrin glue for endoscopic dural reconstruction. Moreover, soldering can be done in deep and narrow areas of the skull base (e.g., sphenoid and sellar region) were suture placement is difficult, therefore providing the surgeon with another tissue bonding technique for dural reconstruction in those areas.
CONCLUSIONS Temperature-controlled laser soldering is a reliable technique for the reconstruction of dural defects. It is easy to apply and creates a watertight bond and better wound healing. Laser tissue soldering might replace conventional techniques in dural reconstruction in difficult to reach skull base areas and in endoscopic surgery.
Acknowledgments Esther Eshkol is thanked for editorial assistance.
BIBLIOGRAPHY 1. Bass LS, Moazami N, Pocsidio J, et al Changes in type i collagen following laser welding. Lasers Surg Med 1992;12: 500–505. 2. Foyt D, Johnson JP, Kirsch AJ, et al. Dural closure with laser tissue welding. Otolaryngol Head Neck Surg 1996;115: 513–518. 3. Hadley MN, Martin NA, Spetzler RF, et al. Comparative transoral dural closure techniques: a canine model. Neurosurgery 1988;22:392–397.
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4. Barak A, Eyal O, Rosner M, et al. Temperature-controlled CO2 laser tissue welding of ocular tissues. Surv Ophthalmol 1997;42Suppl 1:S77–81. 5. Cohen M, Ravid A, Scharf V, et al Temperature controlled burn generation system based on a CO2 laser and a silver halide fiber optic radiometer. Lasers Surg Med 2003;32: 413–416. 6. Eyal O, Scharf V, Katzir A. Fiber optic pulsed photothermal radiometry for fast surface-temperature measurements. Applied Optics 1998;37:5945–5950. 7. Shumalinsky D, Lobik L, Cytron S, et al. Laparoscopic laser soldering for repair of ureteropelvic junction obstruction in the porcine model. J Endourol 2004;18:177–181. 8. Simhon D, Brosh T, Halpern M, et al. Closure of skin incisions in rabbits by laser soldering: I: Wound healing pattern. Lasers Surg Med 2004;35:1–11. 9. Gil Z, Shaham A, Vasilyev T, et al Novel laser tissuesoldering technique for dural reconstruction. J Neurosurg 2005;103:87–91. 10. Schober R, Ulrich F, Sander T, et al Laser-induced alteration
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11.
12.
13.
14.
15.
of collagen substructure allows microsurgical tissue welding. Science 1986;232:1421–1422. Fliss DM, Gil Z, Spector S, et al. Skull base reconstruction following anterior subcranial resection. Neurosourgical Focus 2002;12:1–7. Sekhar LN, Nanda A, Sen CN, et al. The extended frontal approach to tumors of the anterior, middle, and posterior skull base. J Neurosurg 1992;76:198–206. Cansiz H, Cambaz B, Papila I, et al. Use of free composite graft for a large defect in the anterior skull base. J Craniofac Surg 1998;9:76–78. Fliss DM, Zucker G, Cohen A, et al. Early outcome and complications of the extended subcranial approach to the anterior skull base. Laryngoscope 1999;109:153–160. Fukuda S, Sakai N, Kamata SE, et al. Surgical results of skull base surgery for the treatment of head and neck malignancies involving skull base: Multi-institutional studies on 143 cases in Japan. Auris Nasus Larynx 2001; 28Suppl:S71–75.
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