Posterior Fossa Sinking Skin Flap Syndrome Presenting With Orthostatic Vertigo After Decompressive Craniectomy: A Case Report

Sinking skin flap syndrome (SSFS) is an uncommon complication of cranial defects and is rarely described after posterior fossa decompression. We report a case of chronic phase posterior fossa SSFS presenting with positional vertigo and vomiting, successfully treated with delayed cranioplasty. A 40-year-old man presented with subarachnoid hemorrhage caused by a ruptured vertebral artery dissecting aneurysm involving the left posterior inferior cerebellar artery (PICA). He underwent an occipital artery (OA)-PICA bypass and trapping of the aneurysm, followed by decompressive suboccipital craniectomy without immediate cranioplasty. Progressive ventriculomegaly developed, and a ventriculoperitoneal (VP) shunt (Codman Hakim, Integra Japan, Tokyo, Japan) was placed. He was later readmitted with vertigo and vomiting that worsened in the upright position and improved when supine, accompanied by a conspicuous depression and postural change of the scalp flap over the defect. Posterior fossa SSFS was diagnosed, and cranioplasty was performed, leading to rapid and sustained symptom resolution. SSFS should be considered in patients with large posterior fossa defects who develop posture-dependent symptoms, particularly when local soft-tissue support is limited; timely cranioplasty may be therapeutic.