Polymethyl Methacrylate Cranioplasty Is an Effective Ultrasound Window to Explore Intracranial Structures: Preliminary Experience and Future Perspectives Giannantonio Spena 1 , Francesco Guerrini 1,2 , Gianluca Grimod 1 , Andrea Salmaggi 3 , Lucio Aniello Mazzeo 1 - OBJECTIVE: To evaluate the feasibility of transcranial sonography in patients harboring polymethylmethacrylate cranioplasties (PMMA-CP) and explore whether this ma- terial is a valid sonic window to explore intracerebral structures. - METHODS: In 6 patients, we performed transcranial sonography (TCS), using the PMMA-CP as sonic window. To test the reliability of ultrasound images, we collected several quantitative and qualitative measurements of intracranial structures and compared these sonographic images with standard computed tomography (CT) scan images. - RESULTS: We found that PMMA-CP is a very good sonic window and allowed us to obtain very good quality echographic images of intracranial structures, as shown by the comparison of measurements with CT scan, which were very reliable. The main drawback was related to the shape (i.e., the curvature) of the cranial flap, which hin- dered the ultrasound probe from correctly adhering to the scalp. - CONCLUSIONS: Although limited by the restricted number of cases, this preliminary experience represents the first available data about the serial use of TCS using PMMA-CP as window. These results open the path to the routine use of TCS to longitudinally control patients already harboring PMMA-CP. More, we here discuss its potential role in globally reducing the number of follow-up CT and magnetic resonance imaging scans required in different type of patients and pathologies. INTRODUCTION C raniectomy is a routine procedure that is indicated in different situations, such as for the treatment of refractory intracranial hypertension, traumatic brain injury, hemor- rhagic or ischemic stroke, penetrating head traumas, infections, and tumors. 1 Cranioplasty (CP) aims to restore the integrity of the cranial vault following craniectomy and can be performed with autologous bone or nonbiologic materials such as metal or plastic plates. 2 Brain protection and cosmetic aspects are the major indications to CP as well as the re-establishment of the physiological fluid dynamics of a closed cavity, which are disturbed when the atmospheric pressure directly exerts its in- fluence. Furthermore, CP can help in the recovery of neurologic deficits and neuroimaging alterations that typically follow cra- niectomy. 3 CP can be performed by implanting the previously removed autologous bone flap or by reconstructing the defect with synthetic materials. In some cases, the choice to use a nonbiological implant is mandatory, as for comminuted fractures, penetrating traumas, or bone tumors; in contrast, after decompressive craniectomy for intractable intracranial hypertension, the choice to replace autologous bone with a synthetic one is mainly based on the surgeon’s preferences. Key words - Cranioplasty - PMMA - Transcranial - Ultrasound Abbreviations and Acronyms BF: Bifrontal diameter CP: Cranioplasty CT : Computed tomography IFH: Interfrontal horns MRI: Magnetic resonance imaging PEEK: Polyetheretherketone PMMA: Polymethylmethacrylate TCS: Transcranial sonography TV: Third ventricle diameter From the 1 Unit of Neurosurgery, Department of Neurosciences, A. Manzoni Hospital, Lecco; 2 Unit of Neurosurgery, Department of Surgical, Diagnostic and Pediatric Sciences, University of Pavia, Pavia, Italy; and 3 Unit of Neurology, Department of Neurosciences, A. Manzoni Hospital, Lecco, Italy To whom correspondence should be addressed: Francesco Guerrini, M.D. [E-mail: frague21@gmail.com] Citation: World Neurosurg. (2019). https://doi.org/10.1016/j.wneu.2019.04.026 Journal homepage: www.journals.elsevier.com/world-neurosurgery Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2019 Published by Elsevier Inc. WORLD NEUROSURGERY -: e1-e7, - 2019 www.journals.elsevier.com/world-neurosurgery e1 Original Article