26 Techniques of Alloplastic Cranioplasty



10.1055/b-0035-121772

26 Techniques of Alloplastic Cranioplasty

Erin N. Kiehna and John A. Jane Jr.

Introduction


When an autologous cranioplasty is not an option—whether from contamination, infection, fragmentation, bony reabsorption, or growth in the cranial vault (in children)—neurosurgeons often have to turn to implantable synthetic cranioplasties. The goals of a cranioplasty remain the same: lasting repair of the cranial defect with good anatomic contour. This can be performed at any time point following a reduction in brain swelling. 1 Since the 1600s, neurosurgeons have experimented with several different constructs in the quest for the perfect cranioplasty. 2 Recent developments in computer-aided design and manufacturing, tissue engineering, and osteoinductive capabilities allow for the fabrication of an alloplastic implant with excellent aesthetics that withstands biomechanical stresses and allows for tissue integration. 3



Indications




  • Sufficient abatement of swelling has occurred when neuroimaging demonstrates that brain is not protruding beyond the defect and lacks any evidence of systemic or local infection.




    • Unsuitability of autologous cranioplasty



    • Bone was fragmented (primary injury was a depressed skull fracture)



    • Bone was contaminated at the time of injury (foreign body contamination or open fractures)



    • Bone flap infection/osteomyelitis



    • Significant disproportion between the skull and the bone flap resulting in aesthetically unpleasing outcome




      • Bony reabsorption following initial autologous cranioplasty ( Fig. 26.1 ).



      • Bony remodeling



      • Significant growth of the cranial vault (in children)



    • Growing skull fractures and traumatic defects in the skull ( Fig. 26.2 )



Preprocedure Considerations



Radiographic Imaging




  • Neuroimaging is required prior to any cranioplasty to evaluate the condition of the brain, its relationship with the cranial defect, any degree of hydrocephalus, external hydrocephalus, and/or leptomeningeal cysts.



  • Magnetic resonance imaging (MRI), while not necessary, allows for more detail of the brain; it also may be more suitable for children when there is a goal to limit radiation exposure.

Fig. 26.1 Three-dimensional CT scan of bony reabsorption following cranioplasty in an infant.
Fig. 26.2 Growing skull fracture in an infant.



  • Computed tomography (CT) allows for visualization of the thickness of the bone to determine the “splitability” in children.



  • A three-dimensional anatomic CT is necessary for construction of custom, implantable cranioplasties.



Medication




  • Antibiotic prophylaxis includes the standard preoperative dose 30–60 minutes prior to skin incision. Some neurosurgeons also provide 24 hour antibiotic prophylaxis postoperatively.



  • Antiepileptic prophylaxis may be considered in patients who are not on standing antiepileptic medication. Our institution utilizes phenytoin or levetiracetam.



Operative Site Preparation




  • The skin incision used for the decompressive craniectomy or craniotomy site is typically sufficient.



  • Incisions should be made as cosmetic as possible, staying behind the hairline and preserving blood flow to the scalp flap.



  • Approximately 1–2 cm of hair clipping may be performed.



  • The skin is prepped as per physician preference, with the recommendation that alcohol is used during a stage of the skin cleansing process.



  • The incisions are marked and infiltrated with 0.2% ropivacaine with epinephrine 1:100,000.



  • Algorithm for cranioplasty selection ( Fig. 26.3 ).

Fig. 26.3 Algorithm for cranioplasty selection. HA, hydroxyapatite; PMMA, polymethylmethacrylate.


Operative Procedure



Positioning Unilateral Craniectomy (Fig. 26.4)

Figure Fig. 26.4 Procedural Steps For most cranioplasties, it is sufficient to place the head on a donut or horseshoe with a roll placed under the ipsilateral shoulder for relief of strain. The head is turned approximately 60 degrees in the contralateral direction and the prior frontotemporoparietal scalp incision is exposed and prepared. Pearls • For cranioplasties that extend to the occipital region, it may be necessary to “pin” the patient to optimize the surgical field.


Positioning for Bifrontal Craniectomy (Fig. 26.5)

Figure Fig. 26.5 Procedural Steps For bifrontal cranioplasties, the patient is positioned supine with the head in a neutral position on either a gel donut or three-point fixation. Pearls • For bilateral hemicraniectomies it may be necessary to do one side at a time, reprepping and redraping in between.


Skin Incision Unilateral (Fig. 26.6)

Figure Fig. 26.6 Procedural Steps The incision is made with a no. 10 blade from the superoanterior frontal region first and opened in progressive fashion until the temporalis muscle is reached. 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. Care should be taken to open the scalp flap separately from temporalis muscle. The incision is made with a no. 10 blade from the sagittal suture down to the zygoma bilaterally. Pearls • Alternatively, one can open with a monopolar electrocautery with a needle tip cautery.


Subcutaneous Dissection (1) (Fig. 26.7)

Figure Fig. 26.7 Procedural Steps The incision is opened in stages starting with the frontal, superior portion, and wrapping around to the temporalis, placing galeal clamps when this layer has been properly separated. The plane between the pericranium and galea is developed with sharp dissection (Metzenbaum scissors or no. 15 blade scalpel). The scalp layer can be properly reflected forward by developing the plane between the vascularized pericranium and the galea. Pearls • The galea–pericranial plane may also be developed with a no. 10 or no. 15 blade scalpel, or with monopolar electrocautery. • In cases where the pericranium was elevated with the scalp during the initial procedure, this layer is virtually unscarred and may be dissected bluntly, leaving the pericranium against the dura.

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Jun 13, 2020 | Posted by in NEUROSURGERY | Comments Off on 26 Techniques of Alloplastic Cranioplasty

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