In posterior cranial vault distraction（PCVD）, it is necessary to accurately determine the direction of the venous sinus. A three-dimensional fluoroscopic composite image was created from the venous cava by MRI and the cranial bone on CT using SYNAPSE VINCENT®. Four patients who underwent PCVD for craniosynostosis at our hospital between 2019 and 2020 were analyzed. As a measurement of the accuracy of the composite image, the distance from the intersection of the suture lines during the operation to the lower edge of the osteotomy（λ-A）and the distance from the intersection of the suture lines on postoperative CT to the lower edge of the osteotomy（λ-B）were measured. The average of the difference（A-B）was 0.5 mm. As a measurement of the accuracy of setting the cutting line, the average distance between the lower edge of the osteotomy line and the upper edge of the sinus was 9.4 mm. The three-dimensional fluoroscopic composite image was an accurate indicator. The setting of the bone-cutting line was appropriate. If images of different modalities are synthesized and examined, three-dimensional fluoroscopic composite images are considered a useful method in PCVD.
