Introduction: Previously, sonographic evaluation of the intracranial contents has been limited to either intraoperative use following bone flap removal or in neonates with open fontanelles, secondary to the impedance of cranial bone. Therefore, we hypothesized that cranial bone replacement (i.e. cranioplasty) with sonolucent implants may represent a “window into the brain” by allowing trans-cranioplasty ultrasound (TCU) to serve as a novel bedside imaging modality.To examine the potential sonolucency of commonly-used cranial implants made of various biomaterials and to evaluate this imaging modality in a live human patient requiring cranioplasty reconstruction.
Methods: A three-phase study was comprised of 1) cadaveric evaluation of trans-cranioplasty ultrasound (TCU) with various cranioplasty implants of varying materials, 2) intraoperative TCU during right-sided cranioplasty with clear implant made of poly-methyl-methacrylate (PMMA), and 3) bedside TCU on postoperative day 5 after cranioplasty.
Results: TCU through clear PMMA, polyether-ether-ketone (PEEK), and opaque PMMA cranial implants revealed implant sonoluceny, in contrast to autologous bone and porous-polyethylene. In a live human patient, intraoperative ultrasound via the clear PMMA implant revealed recognizable ventricular anatomy. Furthermore, postoperative bedside ultrasound revealed comparable ventricular anatomy and a small epidural fluid collection corresponding to that visualized on an axial computed tomography (CT) scan.
Conclusion: Sonolucent cranial implants, such as those made of clear PMMA, hold great promise for enhanced diagnostic and therapeutic applications previously limited by cranial bone. Furthermore, as functional cranial implants are manufactured with implantable devices housed within clear PMMA, the possibility of utilizing ultrasound for real-time surveillance of intracranial pathology becomes much more feasible.