Multidisciplinary approach for improved outcomes in secondary cranial reconstruction: introducing the pericranial-onlay cranioplasty technique.

Secondary cranial reconstruction, often referred to as a cranioplasty, is indicated for cerebral protection, cosmetic appearance restoration, and treatment of the syndrome of the trephined.1–4 A secondary (or delayed) cranioplasty is required for those patients requiring staged reconstruction. This includes patients undergoing decompressive hemicraniectomy for life-threatening conditions such as traumatic brain injury, acute subdural hematoma, intracerebral hemorrhage, and severe ischemic stroke. Several options currently exist for reconstructing a large (> 5 cm2) calvarial defect.5 Historically, bone flaps harvested from dogs was first described in 1670,6 and autologous bone flaps, as opposed to xenogeneic, have since remained the gold standard.7–11 However, because of the morbidity associated with large bone donor sites and occasional bone flap resorption/warping, numerous materials have been developed for secondary cranial reconstruction. The outbreak of World War II resulted in a large number of cranial defects, and the evolution of acrylic resins led to the first use of poly-methyl-methacrylate (PMMA) in humans in 1940.11–18 Since then, PMMA has become the most frequently used alloplastic material for cranial reconstruction.7,8,19–22 It is also associated with decreased rates of exposure and infection compared with bone flaps.23,24 These defects pose a special reconstructive challenge, primarily because of both the skeletal deficit and the corresponding soft tissue deficiency after interval scalp contraction, temporalis malposition/foreshortening, and encephalomalacia with overlying dead space. This is especially deforming in areas with complex convexities such as the pterional region. This area has been shown to have a higher incidence of complications.23 In situations when the bone flap requires removal, there are absent fixation points for the temporalis muscle, leading to muscle foreshortening with caudal displacement and temporal deformity. In these cases, freehand molding of acrylic implants is possible,25 but it is time consuming and technically demanding and may require exposure of the lateral orbit. With the advent of computer-aided design and manufacturing, both metal and acrylic cranial implants can now be designed and manufactured to precisely fit the patient’s defect.26,27 Although the materials and manufacturing have steadily evolved, common techniques for cranial bone flap and implant placement have remained constant. In fact, Booth and Curtis11 described in 1893 secondary cranial reconstruction as simply “elevating the pericranium and scalp flap up with an elevator” and then 19 days later “slipping an aluminum plate under the scalp flap above the dura.” Now, nearly 120 years later, standard techniques still include elevating a full-thickness scalp flap and placing the bone flap or implant directly onto the previously exposed dura or previously placed dural substitute. This is associated with dural inflammation28,29 and exposes the meninges/implant materials to bacterial contamination, especially in cases after bone flap osteomyelitis. At the same time, bone flap fixation has also evolved.30,31 This traditional teaching is to reincise and reelevate the full-thickness scalp flap, similar to the initial neurological procedure, which mandates a dissection along the epidural space. Drawbacks include significant blood loss, potential for dural injury, and unnecessarily exposing the field and materials to bacterial contamination.32 Therefore, we present here a novel approach that preserves the vascularized pericranium as a protective layer against infection. It uses the same horizontal boundaries of the previous scalp incision as a “delayed scalp flap” but divides the full-thickness scalp flap into 2 segments: a lower segment containing a vascularized “pericranial-onlay” and an upper segment consisting of a new galea fasciocutaneous (partial-thickness) scalp flap based on the superficial temporal vessels. This in turn provides a “vascularized sandwich” encasing and protecting the replaced bone flap or implant. This is similar to the mind-set of a plastic surgeon faced with an exposed, infected implant in the setting of alloplastic breast reconstruction, which uses the creation of a “neo-subpectoral pocket.” With the osetomyelitic bone flap acting like an infected implant within the epidural space, one places the bone flap or cranial implant at a second stage using a separate pocket from the previous one and surrounds the area with vascularized tissue as similar to the pericranial onlay being introduced here.33 In this scenario, scalp closure over the bone flap or implant is also critical and can easily be complicated by excessive tension, especially in cases when large scalp concavities exist and when tissue mobility is limited from scalp contraction, scar, and/or irradiation. Therefore, some surgeons use staged tissue expansion, which requires additional time, expense, and potential morbidity.32 Skin dehiscence, whether small or large, is paramount. It allows inoculation of bacteria to the underlying bone flap and/or implant, which may lead to irreversible infection and eventual removal. Therefore, we outline our multidisciplinary approach and case series to suggest decreased morbidity, improved final outcomes, and the ability to avoid unnecessary tissue expansion.