ARTERIAL

The main determining factor in this type of lesions is the reduced (for some Authors beyond 50%) arterial flow  to the tissues, with decresed or absent nutrient and oxygen input and resulting tissue hypoxia, until ischemia and necrosis.
Vascular occlusion, a consequence of thrombo-embolic phenomena, can be associated with increased endothelium permeability, interstitial fluid accumulation and fibrin aggregation to form some sleeves around the microcirculatory system vessels, with resulting reduction of gas and nutrient exchanges between the circulatory system and the tissue.
At the same time, the activation of the inflammation process stimulates the aggregation of blood components (especially platelets) with further worsening of microcirculation, until the obstruction of smaller caliber vessels.
Skin lesions forming because of necrotic processes usually appear on the extremities, like well-demarcated, small ulcers tending to confluence, with scarcely secreting bottom and covered by necrotic material and/or fibrin.
Perilesional skin is usually atrophic, with absent or dystrophic annexes.
In the advanced stages, the necrotic process can expand to one or more segments (foot, leg), with gangrenous presentation (wet or dry).
Very intensely painful symptoms are typical and they are exacerbated by the offloading position of the extremities (for the additional reduction of arterial flow).