Choroid Plexus Papilloma

A 1-year-old infant presents with rapidly increasing head circumference crossing percentiles, bulging anterior fontanelle, split sutures, and the "sunset sign" of downward gaze. Examination reveals macrocephaly and a positive Macewen's cracked-pot sign. MRI brain with contrast shows a lobulated, cauliflower-like intraventricular mass at the atrium of the left lateral ventricle with frond-like papillary projections, isointense on T1, iso-to-hyperintense on T2, and showing intense homogeneous gadolinium enhancement with prominent vascular pedicles. Marked biventricular hydrocephalus is noted out of proportion to mechanical obstruction. The structure marked **C** in the diagram is responsible for the disproportionate hydrocephalus in this case primarily through which mechanism?