Letter: First Experience With Postoperative Transcranial Ultrasound Through Sonolucent Burr Hole Covers in Adult Hydrocephalus Patients.

Abstract

To the Editor: We were captivated by the recent cover article by Lee et al1 titled “First Experience With Postoperative Transcranial Ultrasound Through Sonolucent Burr Hole Covers in Adult Hydrocephalus Patients.” The authors presented their initial experience with 37 patients who received a sonolucent burr hole cover during ventriculoperitoneal shunt placement or endoscopic third ventriculostomy and subsequently underwent ultrasonography. They found no significant difference in infection and revision rates of these 37 patients compared with 57 historical controls.1 The authors presented multiple ultrasound images of ventricular anatomy and showed comparisons with computed tomography (CT). We commend the authors for their innovative efforts in bringing new technology to the operating room, neurosurgical intensive care unit, and neurosurgical clinic. However, we would like to add a historical perspective on the use of transcranial ultrasound through sonolucent cranioplasty implants. The first clinical publication on transcranioplasty ultrasonography was published in 2018 by Mursch et al.2 Here, the authors demonstrated in 2 patients that frontoparietal polyetheretherketone (PEEK) cranioplasties enabled sonographic imaging of intracranial parenchymal and vascular structures. After this study, Spena et al3 published a 2019 case series comparing sonographic images with CT in 6 patients with polymethyl methacrylate (PMMA) cranioplasties. Belzberg et al quickly followed these with both preclinical and clinical examples comparing porous-polyethylene, PEEK, opaque PMMA, and clear PMMA.4,5 Various case series and bench top studies were subsequently published,6-9 including groups focused on polyolefin cranioplasties.10,11 The largest case series to date was an early outcome analysis of 55 patients with clear PMMA cranioplasties by Shay et al.8 Applications for this technology so far have included hydrocephalus, subarachnoid hemorrhage, traumatic brain injury, tumor, arterial bypass, and intracerebral hemorrhage. In fact, our institution is currently leading a prospective clinical trial for the application of transcranioplasty ultrasonography after minimally invasive intracerebral hemorrhage evacuation.12 This clinical trial is using the same FDA-approved clear 2-cm PMMA cranioplasty implants (Longeviti). Therefore, it has been helpful to review Lee et al‘s techniques, including ultrasound protocol and image standardization. There are certain limitations to the use of point-of-care ultrasound in neurosurgery. First, unless performed in a pediatric patient with open fontanelles, transcranioplasty ultrasonography requires a “bone window” to allow ultrasound waves to penetrate the source. There are costs associated with the cranioplasty procedure to create this window. Furthermore, even with a window, the ultrasound view is limited by the location of the cranioplasty and may not be easily comparable with the typical axial, sagittal, and coronal views. Still, there are numerous benefits of transcranioplasty ultrasound. Compared with transcranioplasty ultrasound, CT poses cumulative radiation risks and MRI is expensive. Ultrasound provides point-of-care imaging which is already used widely in emergency departments and obstetrics. Just as the Focused Assessment with Sonography in Trauma is used to emergently assess for intraperitoneal fluid, it is reasonable to assess for intracranial bleeding using transcranioplasty ultrasound.13 This imaging technology may alleviate the burden of CT and provide the option of point-of-care imaging. Multicenter randomized controlled trials are needed to further assess the diagnostic capabilities, imaging techniques, ideal biomaterials, and health care costs of this technology.