This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
[{'content': 'In aortic dissection, blood enters in - \nSelect and explain. \nA. Intima, B. Media, C. Adventitia, D. Any of the above layer', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Aortic dissection \n\nAortic dissection is a catastrophic illness characterized by dissection of blood between and along the laminar planes of aortic media.\nBlood enters inside the arterial wall (in the media layer) and leads to the formation of blood-filled channels within the aortic wall, which often ruptures outward causing massive haemorrhage.\nThe most frequent pre-existing histologically detectable lesion is cystic medial degeneration.\nIn aortic dissection, there is an intimial tear through which the blood enters into the media.\nUsually, the tear is within 10 cms of the aortic valve.\nThe dissecting hematoma spreads characteristically along the laminar planes of the aorta, usually between the middle and outer third.\nSome times, blood ruptures into the lumen distally, i.e. there is the second tear distally. So that a complete new vascular channel is formed inside the media of aortic wall. Blood enters from proximal tear into the media and comes out into the lumen from the distal tear.\nThis is called double - barrel aorta with a false-channel in the media.\nLater on, this false channel becomes endothelized → chronic dissection.\n\n\xa0 Classification of Aortic dissection\n\nThe risk and nature of serious complications of dissection depend strongly on the level of aorta affected, with the most serious complications occurring from the aortic valve to the arch.\nThus aortic dissections are generally classified into two types -\n\n1. Proximal lesion (Type A)\n\nMore common and more dangerous.\nInvolve either the ascending portion only or both ascending and the descending portion of aorta.\n\n2.\xa0\xa0 Distal lesion (Type B)\n\nInvolve only descending part distal to the subclavian artery.', 'role': 'assistant'}]