PIK3CA Somatic Mosaicism in a Skull Base Intraosseous Slow Flow Vascular Malformation

Skull base intraosseous vascular malformations are rare, with poorly understood pathophysiology and limited treatment options. We report a 12-year-old female with right-sided pulsatile tinnitus and hypoglossal nerve palsy caused by a destructive mass of the right clivus, occipital condyle, and hypoglossal canal. After near-total resection, histopathology showed capillary-type vascular channels. Following recurrence, sirolimus therapy achieved sustained radiographic and clinical stability. Genetic testing later identified somatic PIK3CA mosaicism. This represents a novel skull base intraosseous slow-flow vascular malformation with PIK3CA mosaicism. A consistent mutational pattern could refine the classification of PIK3CA -related vascular anomalies. We highlight phosphoinositide 3-kinase/protein kinase B/mechanistic target of rapamycin inhibition as a less invasive potential therapy for malformations in which resection carries significant risk of morbidity.