Dominant Occipital Sinus Complicating Surgery of a Fourth Ventricular Mass

BACKGROUND: We describe a case of a fourth ventricular mass requiring a modified approach to its management owing to a rare variation of the occipital sinus (OS). CASE DESCRIPTION: A 32-year-old female presented with persistent headache and nausea. Magnetic resonance imaging revealed a fourth ventricular mass and hydrocephalus. Venous sinus anatomy appeared unusual, and thus magnetic resonance venography was performed, which identified the OS as the main drainage pathway for the entire brain, providing the sole drainage between the superior sagittal sinus and the jugular veins through the marginal sinus. Both the transverse and sigmoid sinuses were hypoplastic, and flow through the straight sinus was diminished. Thus, endoscopic third ventriculostomy and biopsy were performed as the first step. Postoperatively, the patient's nausea persisted and biopsy results were inconclusive, and thus a second surgery was planned. The dural opening was tailored so as not to damage the OS and marginal sinus, and the tumor was resected subtotally through the limited dural opening. Histopathological analysis identified a low-grade glioma. CONCLUSIONS: Rare variations of the venous/sinus anatomy may fundamentally change the surgical management plan, and recognizing such variations is crucial to minimizing the risk of potentially fatal complications.