Elective Sonolucent Cranioplasty for Real-Time Ultrasound Monitoring of Flow and Patency of an Extra- to Intracranial Bypass

Abstract

Cross-sectional imaging studies or catheter angiogram are the imaging modalities of choice to evaluate bypass patency after extra- to intracranial (EC-IC) bypass surgery. Although providing accurate results, these imaging modalities are time-consuming and/or present radiation risk for the patient. Ultrasound imaging is a fast and widely available imaging modality, but is limited in this setting due to the non-sonolucent autologous bone flap covering the bypass after surgery. The recently FDA approved clear polymethyl methacrylate (PMMA) cranioplasty implant overcomes this limitation by its sonolucent characteristic, but has not yet been used in the setting of EC-IC bypass surgery. Here, the authors describe for the first time the feasibility of an elective sonolucent cranioplasty to monitor flow and patency of an EC-IC bypass in real time using ultrasound. This moyamoya patient underwent a direct superficial temporal artery to middle cerebral artery (STA-MCA) bypass, after which a PMMA implant was used to close the craniotomy defect, instead of reimplanting the autologous bone flap. Immediate postoperative bedside transcranioplasty ultrasound confirmed bypass patency and allowed for quantitative flow measurements as well as for exclusion of postoperative hemorrhage. Postoperative CTA and catheter angiogram confirmed patency of the bypass without complications. This report shows for the first time that this technique is feasible and permits bedside transcranioplasty ultrasound assessment of bypass flow in real time, confirmed with angiography. This technique may permit easy comparison of baseline findings with follow up assessments and facilitate less invasive monitoring of bypass patency.

Conflict of interest statement

The authors have no conflicts of interest to disclose.

Figures

FIGURE 1

Indocyanine green (ICG) angiography color coded flow 800 (A) and microscopic image (B) before STA-MCA bypass after harvest of the STA, craniotomy and dura opening. The marked M4 MCA branch was selected for the bypass as recipient. STA, superficial temporal artery, STA mt, STA main trunk, STA fb, STA frontal branch, STA pb, STA parietal branch. ICG angiography color coded flow 800 (C) and microscopic image (D) after STA-MCA bypass with patent anastomosis and increased flow compared to pre-bypass.

FIGURE 2

The bone flap was used to determine the size and shape of the clear PMMA implant (A) and an approximately 3 × 3 cm cranioplasty implant was cut out (B, C) and fixated over the craniotomy defect using titanium screws and mini-plates allowing enough space inferiorly without compression of the STA graft moving from extra- to intracranial. STA mt, superficial temporal artery main trunk.

FIGURE 3

Transcranioplasty ultrasound confirmed flow in donor STA under the cranioplasty (#) in real-time (A), allowed for quantitative flow measurements of the proximal STA donor vessel (B) and confirmed patency of the anastomosis (C). Postoperative CTA coronal view (D) and catheter angiogram in PA (E) lateral (F-G) planes confirmed bypass patency. ∗ bypass anastomosis, + moyamoya disease vessel occlusion. # transparent PMMA cranioplasty implant.