Additional Assessment of Developed Occipital Sinus Using Intraoperative Indocyanine Green Videoangiography for a Safe Foramen Magnum Decompression-Technical Case Report

Background and importance Although foramen magnum decompression (FMD) with expansive duraplasty is a popular procedure for treating chiari malformation (CM), the common Y-shaped dural incision can lead to a life-threatening cerebral venous circulation disturbance in patients with a developed occipital sinus. Here, we describe the effectiveness of intraoperative indocyanine green video angiography (ICG-VA) for a CM type 1 (CM1) patient with a highly developed unilateral occipital sinus. Clinical presentation A 40-yr-old woman presented with sensory disturbance on the left side of the body. Magnetic resonance imaging (MRI) revealed cerebellar tonsil herniation into the foramen magnum with cervical syringomyelia, and computed tomography additionally revealed skull anomalies: fontanel closure insufficiencies, cranial dysraphism, thin cranial bone, and dentition abnormalities. We diagnosed as symptomatic CM1 with syringomyelia associated with cleidocranial dysplasia, which is a dominantly inherited autosomal bone disease. Cerebral angiography revealed a developed right occipital sinus and hypoplasia of the bilateral transverse sinus. We performed FMD, paying special attention to the developed occipital sinus using ICG-VA to ensure a safe duraplasty. The angiography clearly highlighted a right-sided occipital sinus with a high contrast ratio, and no left-sided occipital sinus was visible. After a dural incision in a unilateral curvilinear fashion was safely completed, expansive duraplasty was performed. The sensory disorders experienced by the patient disappeared postoperatively. Postoperative MRI revealed elevation of the cerebellar tonsil and decreasing of the syringomyelia. Conclusion Additional assessment using intraoperative ICG-VA provides useful information for a safe FMD, particularly in patients with complicated cerebral venous circulation anomalies.