Angiofibroma bleeds excessively because -

The characteristic of JNA is that the vessels are just endothelial - lined spaces with no muscle coat. As the contractile component (muscle coat) of vessels is absent, vessels have no ability to contract, i.e. vasoconstriction does not occur, and this accounts for :- Severe and recurrent epistaxis Bleeding cannot be controlled by application of adrenaline, a potent vasoconstrictor.