Spinal intradural arachnoid cysts (SIACs) are cerebrospinal fluid (CSF) sacs formed by arachnoid membranes. They may be idiopathic or acquired. Treatment is resection, fenestration, or cyst drainage. A 40-year-old female patient presented with myelopathy symptoms and complaints. Magnetic resonance imaging (MRI) revealed a T6-T10 dorsal intradural arachnoid cyst. A T6-T10 laminectomy was performed and an arachnoid cyst was excised under a microscope. The cyst contained a clear liquid that was surrounded by a transparent membrane. At 7 weeks postoperatively, the patient experienced severe headache, excessive sleepiness, vomiting, loss of coordination, difficulty walking, and difficulty concentrating. A head computed tomography (CT) scan showed marked ventricular dilation that was diagnosed as delayed hydrocephalus. The patient underwent ventriculoperitoneal shunt (VPS) placement one day after admission. This is a rare condition of hydrocephalus that develops due to CSF leakage after SIAC surgery.