Cerebrovascular disease capillary bed separates arteries from veins, which protects the veins from the higher blood pressures that occur in arteries. In arteriovenous malformations, arteries are directly connected to veins, which increases the risk of venous rupture and hemorrhage. Arteriovenous malformations in the brain have a 2–4% chance of rupture each year. However, many arteriovenous malformations go unnoticed and are asymptomatic throughout a person's lifetime. A germinal matrix hemorrhage is bleeding into the brain of premature infants caused by the rupture of fragile blood vessels within the germinal matrix of premature babies. The germinal matrix is a highly vascularized area within an
Smallest cardiac veins Smallest cardiac veins The smallest cardiac veins (or Thebesian veins) are minute valveless veins in the walls of all four heart chambers. The veins are sometimes accurately referred to as vessels, but they are frequently confused with a distinct set of artery connections eponymously referred to as the "vessels of Wearn". In his 1928 publication, Wearn himself referred to the arterio-cameral connections (vessels of Wearn) as thebesian. However, Wearn's 1933 and 1941 publications emphatically described the thebesian veins as distinct from arterio-cameral vessels. The thebesian veins are reportedly most abundant in the right atrium and least in the left ventricle.