Craniotomy bone flaps are often frozen or stored in the subcutaneous layer of the abdominal wall after decompressive craniectomy for intracranial hypertension from traumatic brain injury, cerebrovascular disease, or other causes. Bone flap restoration will be needed once the acute issues have resolved. There is no consensus regarding the optimal timing of bone flap replacement.1–4Replacements can be performed from as little as 2 weeks to more than 1 year after injury.5,6
Indications
Sufficient abatement of swelling has occurred with the brain noted on clinical or radiological examination to be “sunken” or not significantly protruding beyond the defect.
There is no indication of systemic or local infection, or evidence of significant decubitus ulcers in proximity to the cranial defect or incision.
Increasing lethargy or new focal deficit is present on examination and not otherwise attributed to metabolic or structural abnormalities. Such deficits are potentially due to the effects of altered cerebrospinal fluid (CSF) dynamics or atmospheric pressure on the brain.
There may be significant brain depression at the defect and computed tomography (CT) may reveal brain shifting to the contralateral side. Evidence suggests that earlier restoration of cranial integrity can improve neurologic deficits in addition to helping those patients who exhibit early signs of communicating hydrocephalus.5,7,8
Preprocedure Considerations
Radiographic Imaging
CT is essential to evaluate the condition of the brain and its relationship with the defect prior to performing reconstruction (Fig. 25.1).
Fig. 25.1 Preoperative computed tomography study indicating a large left cranial defect. The brain is largely flush with the bone edges.
Medication
The author prefers vancomycin and gentamicin for antibiotic prophylaxis, provided the patient does not have renal failure or other contraindications. Often patients have been hospitalized for significant periods of time and there is a possibility for the skin to be colonized with methicillin-resistant Staphylococcus aureus.
Diphenylhydantoin is administered at 15 mg/kg in nonallergic patients who are not on standing antiepileptic medication. Levetiracetam can be used alternatively at a 1000-mg loading dose.
Operative Field Preparation
Alcohol prep is performed before povidone iodine or chlorhexidine application.
The incisions are marked and infiltrated with 1% lidocaine with epinephrine 1:100,000.
FigureFig. 25.2Procedural Steps(a) Patient positioning. The head is turned approximately 60 degrees in the contralateral direction and the prior frontotemporoparietal scalp incision is exposed and prepared.(b) The abdominal incision housing the subcutaneously placed bone flap is exposed and prepared.Pearls• While this chapter discusses subcutaneously placed autogenous bone grafts as opposed to those stored in a freezer, the techniques of reopening the craniotomy incision and bone flap replacement remain the same. For the commonly performed hemicraniectomy or frontotemporoparietal (occipital) defect, the patient is positioned in the supine position with the head turned approximately 60 degrees in the contralateral direction. The head is placed on a donut and a roll is placed under the ipsilateral shoulder. For bifrontal craniectomies, the patient is placed supine, head straight position; the subcutaneous dissection described forthwith is essentially the same (see Chapter 26).
FigureFig. 25.3Procedural Steps(a) The incision is made with a no. 10 blade from the superoanterior frontal region first and opened in progressive fashion. The bone edge is palpated under the incision. If there is no bone edge, a straight clamp is used to separate the pericranium from the galea to provide protection from the knife blade when bone cannot be palpated underneath the incision.(b) The incision is opened in stages starting with the frontal, superior portion, placing galeal clamps when this layer has been properly separated. The plane between the pericranium and galea is developed with sharp dissection. The scalp layer can be properly reflected forward by developing the plane between the vascularized pericranium and the galea.Pearls• In cases where the pericranium was elevated with the scalp during the initial procedure, this layer is virtually unscarred. The galea–pericranial plane is developed with a Metzenbaum scissors. Unscarred planes can also be developed with blunt dissection using a gauze sponge. The pericranium will cover the defect as the new “pseudodural” plane. If the pericranium is intact, the defect area will be well-vascularized and the underlying duraplasty or brain tissue will not be seen.
FigureFig. 25.4Procedural StepsAfter dissection becomes limited, the skin is opened further. Progressive alternation of skin opening and galeal–pericranial plane dissection is completed until the wound is completely reopened and the entire scalp flap has been reflected. Galeal clamps are placed for hemostasis. The scalp flap is then retracted anteriorly with scalp hooks or 2-0 braided nylon sutures attached to rubber bands and clamps. Hemostasis is achieved with mono-and bipolar cautery.Pearls• Maintaining vascularized tissue in the epidural plane can help combat potential infections and promote osteoinduction.9Surgeons who have previously performed a duraplasty with collagen or allo/xenographic dural substitutes may choose to dissect the pericranial–dural plane. However, if the cranioplasty is performed prior to sufficient incorporation of the dural graft material, the resulting dural layer may not yet have sufficient vascularity.
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