Diagnostic Challenges and Surgical Outcomes of Miyazaki Syndrome: A Report of Two Cases and a Systematic Review

Miyazaki syndrome is a rare and underrecognized complication of long-standing cerebrospinal fluid (CSF) diversion. It usually occurs in patients with chronic CSF overdrainage and is caused by enlargement of the cervical epidural venous plexus, which may compress the spinal cord and cause progressive myelopathy or radiculopathy. Because symptoms develop slowly and may resemble degenerative cervical myelopathy or other neurological conditions, diagnosis is often challenging. We report two illustrative cases from our institution. The first patient was a 57-year-old man with a ventriculoperitoneal (VP) shunt placed at birth for neonatal intraventricular hemorrhage (IVH), who developed progressive spastic paraparesis, sensory ataxia, and increasing wheelchair dependence over several years. MRI showed chronic intracranial hypotension with marked cervical venous engorgement and upper cervical cord compression. He underwent shunt revision with the addition of an anti-siphon device, followed by radiological resolution of venous engorgement and partial clinical improvement. The second patient was a 44-year-old woman with congenital hydrocephalus treated with shunting since childhood, who presented with worsening gait disturbance, recurrent falls, impaired hand coordination, orthostatic headaches, and radicular pain. Imaging showed venous congestion at C2 with cord compression and chronic CSF hypotension. Her shunt was revised with placement of a Codman CERTAS® Plus programmable valve and anti-siphon device (Integra LifeSciences, Princeton, NJ, USA), resulting in improved venous drainage, cord decompression, and meaningful clinical recovery. To place these cases in context, we performed a Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA)-guided systematic review - registered in the International Prospective Register of Systematic Reviews (PROSPERO; CRD420251048122) - of case reports and case series on Miyazaki syndrome or overshunting-associated myelopathy through May 2025 using PubMed, the Cochrane Library, and Google Scholar. Study quality was assessed with Joanna Briggs Institute tools, and data were extracted on patient characteristics, shunt type, valve configuration, anti-siphon device use, symptom latency, imaging findings, treatment, and outcomes. Thirty-one studies, including 37 patients, met the eligibility criteria. The mean age was 43.9 years, and VP shunts were the most common shunt type. The most consistent imaging finding was cervical epidural venous plexus engorgement with cord compression, often associated with pachymeningeal enhancement and slit ventricles. The median interval from the last shunt procedure to symptom onset was 14 years, and valve adjustability did not significantly influence this latency. Most patients were treated by correcting CSF overdrainage through valve pressure adjustment, conversion to a programmable valve, and/or addition of an anti-siphon or gravitational device. All patients treated with an anti-siphon device improved, and earlier treatment was associated with better outcomes. These findings emphasize that Miyazaki syndrome should be considered in shunted patients with progressive myelopathy and imaging signs of intracranial hypotension or CSF overdrainage. Early recognition and correction of siphoning through valve optimization and anti-siphon device placement may reverse venous congestion, improve neurological function, and prevent permanent spinal cord injury.