A 64-year-old man underwent a left decompressive frontotemporal craniectomy for a traumatic subdural hematoma. An ePTFE sheet was used to close the dura. After 1 month, cranioplasty was performed using a cryopreserved autologous bone flap. The patient did not suffer any perioperative complications; however, after 5 months, his surgical wound split, and a discharge emanated from it. A staged operation was planned because the infection was resistant to routine antibiotic treatment. In the first operation, the infected bone was removed, and the epidural empyema was irrigated. After the removal of the implanted ePTFE sheet, a subdural empyema was found and irrigated, and the capsule over the brain was debrided. After debridement, no identifiable capsule remained, and small amount of CSF leakage was observed (Figs. 4A, B). Thus, the scalp flap was redraped over the brain and the wound was closed with suction drain to minimize the dead space between the leakage points of brain surface and the scalp. The patient did not show continuous CSF leakage postoperatively. Two months later, cranial reconstruction was performed after it had been confirmed that there were no signs of infection at the surgical site on MRI. The layer that was going to be replaced with a custom-made hydroxyapatite block, which was located between the galea and the pericranium, was dissected without CSF leakage (Fig. 4C). After the cranial reconstruction, the wound healed uneventfully, and no complications occurred during the follow-up period.
Several synthetic materials have been used as dural substitutes. However, the implantation of such materials can lead to infections. Infected synthetic materials should be removed as soon as possible; however, the reconstruction of the resultant dural defects is still a controversial issue among both neurosurgeons and plastic surgeons.2–7 Although the author has identified 2 patterns of abscess formation related to synthetic dura mater substitutes among his patients, the development of epidural abscesses alone (ie, when abscesses develop on the synthetic dura) and the development of a combination of epidural and subdural abscesses (when abscesses develop both on and beneath the synthetic dura), the optimal treatments for these types of abscess have never been discussed. To the best of our knowledge, a report of 12 cases, in which every patient suffered epidural infections, is the largest study of such abscesses to have been reported.4
At about 1 month after the implantation of an ePTFE sheet, a capsule composed of granulation tissue is generally found between the sheet and the brain surface.8 Some previous reports have stated that the capsule should be left as a dural substitute after the removal of infected synthetic dura mater substitutes.4,7 However, another report recommended that contaminated capsules should be removed if abscesses form beneath them.5 The author agrees with both statements. According to the author’s strategy, if the capsule is not contaminated, it should be left intact and no additional dural reconstruction should be performed. A previous report of a large series of cases in which the patients underwent decompressive craniectomy without duraplasty showed that the procedure was technically feasible and safe.9 The latter report also stated that no subpial injuries due to the attachment of the brain to the scalp were noted during the subsequent cranioplasty procedures. The latter study demonstrates that dural defects that are covered with connective tissue do not cause any complications, providing that no CSF leakage occurs. In addition, the fact that the patients in the present study who did not undergo dural reconstruction remained free of complications indicates that the capsules that form underneath synthetic dura mater substitutes act as dural substitutes.
On the other hand, the capsule should be debrided if it is contaminated. Among the patients in the present study whose capsules were debrided, half did not suffer CSF leakage and possessed an identifiable capsule after the debridement. The other half exhibited small amount of CSF leakage and did not have an identifiable capsule. Dural defects should be reconstructed with autologous tissue if CSF leakage occurs. If a postcraniotomy infection develops in the early stages before capsule formation, dural reconstruction is necessary after debridement. There is a consensus among reconstructive surgeons that vascularized tissue is preferable to nonvascularized tissue for reconstructing defects after local wound infection. In fact, the author experienced a case (before 2006) in which a recurrent infection developed after dural reconstruction using a fascia lata graft, that is, nonvascularized tissue, following debridement of the infected capsule.7 A free vascularized skin or muscle flap with or without fascial tissue is often used for dural reconstruction after the removal of an infected synthetic dura mater substitute2,3,5,10,11; however, using such a free flap results in a lengthy operation and poor cosmetic results.12 The only other reported option for dural reconstruction is the transposition of a pericranial flap from a neighboring site.6 Of course, autologous pericranial tissue is generally recommended as a dural substitute in neurosurgery,13 and pericranial flaps are more useful than pericranial grafts; however, they are not always available, and their vascularity is not always reliable. On the other hand, leaving pericranium on the brain surface is always a possibility during secondary cranial reconstruction, and the pericranium has reliable vascularity. Accordingly, dural defects produced by debridement of the capsule do not need immediate reconstruction. And it is common that small amount of CSF leakage will stop after redraping the scalp if cranial reconstruction is not carried out simultaneously.
There is no consensus regarding the optimal time to perform delayed cranial reconstruction after treatment for an infected synthetic dura mater substitute.12,14,15 The author recommends that the interval should be within 3 months following an evaluation of the surgical site using MRI. Early cranial reconstruction might reduce the risk of complications associated with the syndrome of the trephined. When skin tightness is anticipated after wound closure, especially in patients with compromised scalps or large bone defects, it is better to wait approximately 3 months until the scar is matured. Although closure can be aided with a local flap, tissue expansion, or free flaps, the prefabrication of custom-made artificial bone implants with reduced curvatures is another option. This method is preferable for defects affecting the temporal and parietal regions, rather than the frontal region, because of cosmetic considerations. The author considers that this method is also useful for patients with ventricular shunts because the epidural spaces of these patients are likely to remain after cranial reconstruction, and the resultant dead space can increase the risk of postoperative infections or hematomas.16 Although high rates of brain re-expansion and gradual resolution of the epidural space below the implant after cranial reconstruction have been reported,17,18 large dead spaces can become infectious foci, especially in patients with ventricular shunts.19,20 Moreover, adjusting the pressure or occluding the ventricular shunt tube is also recommended to reduce the risk of potential complications, including epidural hematoma, effusion, and infection.21,22 The pressure of ventricular shunt should be maximized at least 1 or 2 days before the cranial reconstruction even if the patient’s consciousness permits. And temporary ligation of the shunt tube is another option to make brain expand sufficiently if maximizing the shunt pressure does not have enough effect. After cranial reconstruction, the pressure of ventricular shunt should be decreased to a normal level following confirmation of decreased epidural fluid collection. Although the use of free tissue transfers before cranial reconstruction to obliterate endocranial dead space remains controversial,17 the author recommends temporarily adjusting the shunt pressure before performing cranial reconstruction as a primary choice because this encourages brain expansion and reduces the size of the extradural space.
Staged cranial reconstruction after the removal of an infected synthetic dura mater substitute using an algorithmic approach is feasible and safe, produces satisfactory cosmetic results, and is not associated with any complications.
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© 2014 American Society of Plastic Surgeons
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