Beyond Remission: Radiation-Induced Moyamoya Syndrome After Childhood Skull-Base Rhabdomyosarcoma

Introduction

Moyamoya syndrome is a progressive steno-occlusive arteriopathy of the terminal internal carotid arteries and circle of Willis. Cranial irradiation is a recognized cause, particularly following childhood treatment involving the parasellar region. Most reported pediatric cases occur after CNS tumors; radiation-induced moyamoya following treatment of skull-base rhabdomyosarcoma is rarely described.

Case Presentation

A 20-year-old woman treated in early childhood for skull-base head and neck rhabdomyosarcoma (surgery, chemotherapy, radiation) developed progressive left-sided deficits and recurrent cerebral ischemia. MRI showed acute and subacute right hemispheric infarctions with extensive collaterals. Angiography demonstrated chronic bilateral internal carotid artery occlusion with moyamoya collateralization, long-segment narrowing of the left cervical internal carotid artery, and severe bilateral posterior cerebral artery stenosis. Right-sided revascularization was pursued. Intraoperatively, the recipient cortical arteries were too small and fragile for direct anastomosis, so an indirect extracranial-to-intracranial revascularization using the superficial temporal artery with dural inversion was performed. Postoperatively, delayed awakening prompted imaging revealing a large right hemispheric infarction involving middle and posterior cerebral artery territories with edema and mild midline shift. She required neurocritical care with blood-pressure augmentation, hyperosmolar therapy, intracranial pressure monitoring, mechanical ventilation, and continuous EEG, which demonstrated severe encephalopathy without seizures. Neurologic examination subsequently showed gradual improvement.

Discussion

This case extends a phenomenon described almost exclusively after CNS tumors to a skull-base sarcoma survivor. The convergence of childhood skull-base irradiation, progressive bilateral terminal carotid occlusion, and extensive collateralization strongly supports RIMS (Radiation Induced Moyamoya Syndrome), in which delayed endothelial injury, intimal proliferation, and fibrosis drive progressive stenosis. Reported median latency is approximately 40 months but ranges to 20 years, highlighting the importance of treatment history in adult survivors. This case also illustrates recognized perioperative vulnerabilities in advanced moyamoya. Preoperative ischemic events and posterior cerebral artery involvement are associated with increased postoperative stroke risk; posterior circulation disease may compromise leptomeningeal collateral reserve. Indirect revascularization was necessitated by unsuitable recipient vessels but depends on gradual neoangiogenesis and does not provide immediate flow augmentation. Consequently, meticulous perioperative preservation of cerebral perfusion through avoidance of hypotension, hypovolemia, hypoxemia, and hypocapnia is critical.

Conclusion

Radiation-induced moyamoya should be considered in young adults with cerebrovascular ischemia and remote childhood cranial or skull-base irradiation, including survivors of non-CNS malignancies. Recognition of prior radiation exposure, posterior circulation involvement, and recent ischemia can inform revascularization planning and perioperative risk assessment.