Watershed area refers to regions of the body that receive dual blood supply from the most distal branches of two large arteries. During times of blockage of one of the arteries that supply the watershed area, such as in atherosclerosis, these regions are spared from ischemia by virtue of their dual supply. However, during times of systemic hypoperfusion, such as in disseminated intravascular coagulation or Heart failure, these regions are particularly vulnerable to ischemia by virtue of the fact that they are supplied by the most distal branches of their arteries, and thus the least likely to receive sufficient blood.



  1. Splenic flexure of colon border area of superior mesenteric area (SMA) and inferior mesenteric area (IMA).
  2. Distal Sigmoid Colon border area of inferior mesenteric area (IMA) and hypogastric arteries.


  1. Between the cortical territories of the anterior cerebral artery (ACA), middle cerebral artery (MCA), and posterior cerebral artery (PCA).
  2. Between the deep and the superficial arterial systems of the MCA, or between the superficial systems of the middle cerebral artery (MCA) and anterior cerebral artery (ACA).

Spinal Cord

  1. Anterior spinal artery between T7 & T9.
  2. Upper thoracic (T1-T4) and first lumbar (L1)


  1. Proximal tubule and ascending limb of Henle’s loop located in the outer medulla


Hypo-perfusion in watershed areas can lead to Mural and Mucosal infarction in the case of Ischemic Bowel Disease. When watershed stroke occurs in the brain, it produces unique focal neurologic symptoms that aid clinicians in diagnosis and localization.