A research center studying cardiovascular pathology is conducting trials in which experimental rabbits are fed sweet peas containing substances that alter connective tissue synthesis and maturation. The animals are monitored for several weeks prior to euthanasia. Autopsy shows myxomatous degeneration with pooling of proteoglycans in the media layer and an intact intima layer in large arteries. The pathologic findings seen in the experiment are most similar to which of the following conditions?

Question

A research center studying cardiovascular pathology is conducting trials in which experimental rabbits are fed sweet peas containing substances that alter connective tissue synthesis and maturation.  The animals are monitored for several weeks prior to euthanasia.  Autopsy shows myxomatous degeneration with pooling of proteoglycans in the media layer and an intact intima layer in large arteries.  The pathologic findings seen in the experiment are most similar to which of the following conditions?

Quizplus · Accepted Answer

11ec160b_38b1_0897_9249_cb824f9a9c3a_MD0001_00 Myxomatous changes in the media of large arteries is found in cystic medial degeneration, a form of pathologic weakening of connective tissue that occurs in large arteries. Medial degeneration is characterized by the fragmentation of elastic tissue and separation of the elastic and fibromuscular components of the tunica media by small, clefted spaces that become filled with amorphous extracellular matrix (ie, mucopolysaccharide). Marfan syndrome is a frequent cause of cystic medial degeneration in younger patients. It is characterized by an autosomal dominant defect in the extracellular glycoprotein fibrillin-1, which is a major component of the extracellular matrix microfibrils that form the scaffolding for elastic fibers. Mutation of the fibrillin-1 gene results in elastic tissue fragmentation, which predisposes affected patients to aortic aneurysms (with an intact intima) and dissections (with an intimal tear). Beta-aminopropionitrile (a chemical found in certain kinds of sweet peas) causes inhibition of lysyl oxidase, an enzyme responsible for cross-linking elastin fibers and collagen fibers. Ingestion of this compound can cause connective tissue disruption in the aorta that mimics the myxomatous degeneration seen in patients with Marfan syndrome. (Choice B) Atherosclerosis is the formation of intimal atheromas in response to chronic or repetitive endothelial injury. Myxomatous degeneration does not play a significant role in the pathogenesis of atherosclerosis. (Choice C) The pathogenesis of berry aneurysms is multifactorial. Contributory factors include hemodynamic stress, hypertension, and certain connective tissue disorders. Type IV Ehlers-Danlos syndrome (which results in abnormalities in type III collagen) predisposes patients to the development of berry aneurysms. Myxomatous degeneration is not associated with berry aneurysms. (Choice D) A false aneurysm, or pseudoaneurysm, is the result of a breach in the continuity of all the layers of a blood vessel, leading to blood leakage outside the vessel wall (eg, hematoma). The intima would not be intact in a false aneurysm. (Choice E) Giant cell arteritis involves granulomatous inflammation of the media and fragmentation of the internal elastic lamina, perhaps due to autoimmunity to elastin. It is not related to myxomatous changes of the arterial wall. (Choice F) Hyperplastic arteriolosclerosis of the renal arterioles is associated with malignant hypertension. It results from concentric lamellar reduplication of the intimal smooth muscle cells ("onion-skinning"). Myxomatous degeneration is not a contributing factor. Educational objective: Myxomatous changes, with pooling of mucopolysaccharides in the media layer of large arteries, are found in cystic medial degeneration, which predisposes affected patients to the development of aortic aneurysms. Medial degeneration in younger individuals is frequently due to Marfan syndrome. __________ References: Histological pattern and changes in extracellular matrix in aortic dissections. (http://www.ncbi.nlm.nih.gov/pubmed/3537014) Cystic medial necrosis: pathological findings and clinical implications. (http://www.ncbi.nlm.nih.gov/pubmed/21881719)

A Research Center Studying Cardiovascular Pathology Is Conducting Trials in Which