thrombose       
verb [ I  ]  medical specialized uk/θrɒmˈbəʊz/ us/θrɑːmˈboʊz/
 形成血栓
to be affected by thrombosis (= a medical condition in which the flow of blood in the body is blocked by a partly solid mass of blood called a clot)
  Haemorrhoids are not usually painful unless they thrombose. 痔疮通常不疼,除非形成血栓。 
  - More examples
 - We observed thrombosis and infections with thrombosing tendencies.
 - Distension may become so severe that his sigmoid colon presses on his left iliac vein and may make it thrombose.
 - External haemorrhoids may thrombose spontaneously, possibly secondary to straining at stool or heavy lifting.
 - Because of the immaturity of the sinuses, these venous "lakes" thrombose spontaneously and cause venous brain infarction.
 - One advantage of this procedure is that when one vessel has thrombosed the other vessel functions as a safety valve.