Editing Aneurysms (section)

== Classification: ==

* Size:
** Defined as 'a permanent localised dilatation of an artery having at least a 50% increase in diameter compared with the expected normal diameter of the artery in question.'
** 'Physical forces of wall tension are dictated by the absolute radius rather than by any ratio to a standardised normal size.'
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* True vs false
** True: dilatation of the entire vascular wall
** False: locally contained haematoma resulting from disruption of the vessel (i.e. pseudoaneurysm). The wall is effectively connective tissue formed in reaction to the contained haematoma. Aetiology - vascular trauma or peri-anastomosis.
** Note that in many cases it doesn't really matter whether it's true or false in determining treatment, except in the case of pseudoaneurysms formed as a result of vascular interventions, which tend to have a narrow neck, amenable to injectable thrombotics.
* Location and extent
** Ectasia - Enlarged, but <50% greater than normal.
** Arteriomegaly - diffuse, continuous enlargement of multiple arterial segments, dilated to >50% of normal. This is a descriptive term, rather than a specific diagnosis. 
** Aneurysmosis - multiple aneurysms at several different locations, or the combination of aneurysmal degeneration in the setting of arteriomegaly.
* Morphology
** Fusiform - generalised increase in the entire diameter of the affected vessel. More often seen with true degenerative aneurysms.
** Saccular - localised, often eccentric in shape. Can arise from a focal ulcer or weakness in the arterial wall due to trauma or infection. Can be eccentric (pseudoaneurysms, renal, intracranial/cerebral aneurysms) or concentric. Saccular morphology aneurysms have less well-characterised risks, and therefore may be seen as an indication for intervention at a lower threshold than fusiform aneurysms. Saccular are often easier to treat endovascularly because of their focal nature.
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