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I am having trouble understanding the visual and structural differences between these vascular lesions.

I know that purpura is elevated and that spider angiomas (easly recognizable) refill from the center to the periphery when pressure is applied.

However, in the telengiectasias from Rendu Osler disease I am unsure if these lesions cannot be considered petechiae too because they are less than 3mm in diameter.

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Purpura and petechiae are both the results of extravasated blood under the skin - essentially bleeding causing a small pool of blood. The distinction between purpura and petechiae is arbitrary at <3mm = petechiae and >3mm = purpura. Large (>10 mm) bleeding is called an ecchymosis. A bruise is simply an ecchymosis resulting from trauma.

Purpura is not necessarily palpable or elevated. When it is this is a different clinical entity with a different list of causes, predominantly vasculitic.

Telangiectasia is a different pathology. These are malformed, typically widened, capillaries and small venules which are visually prominent due to their proximity to the skin surface and relative engorgement with blood. They are neither petechiae, purpura or ecchymoses.

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  • @JWC Throw a clickable resource for that info in there and I'll upvote for an excellent answer!! I am guessing you're a professional of some branch of the medical field, and although it's kind of a pain at first, you'll get used to adding a reference - which allows others to do additional reading and is part of how this site works. We welcome you! Check out our Meta for how we're developing the site. – DoctorWhom Jun 20 '18 at 23:53

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