The Bleeding Edge

Question:   A 16 year old male presents with unilateral left sided epistaxis for 3 months. The severity has increased substantially over the last few weeks. Endoscopy reveals a unilateral posterior nasal mass that bleeds easily on manipulation. You suspect a vascular tumor; what is the most common type and site of origin?  [Answer will be posted with next week's new question]

Answer to last week's question, Can You Smell That Smell (January 11, 2016): 

Given the location and mechanism, the patient likely suffered a shearing injury to the olfactory fibers passing through the cribriform plate.