Aneurysms & a Brief Discussion on Embolism
Aneurysms, overview = congenital or acquired dilations of blood vessels or the heart True aneurysms -involve all three layers of the artery (intima, media, and adventitia) or the attenuated wall of the heart e.g., atherosclerotic and congenital vascular aneurysms, as well as ventricular aneurysms resulting from transmural myocardial infarctions false aneurysm (pseudoaneurysm) = extravascular hematoma that communicates with the intravascular space ( pulsating hematoma )
Aneurysms, classification according to shape aortic arch, the abdominal aorta, or the iliac arteries
Aneurysms, pathogenesis Inadequate or abnormal connective tissue synthesis mutations in TGF-β receptors or downstream signaling pathways often rupture, even when small Marfan syndrome deficiency of?? type IV Ehlers-Danlos syndrome defective type III collagen synthesis
Aneurysms, Pathogenesis, cont d The 2 most important causes Excessive connective tissue degradation increased MMPs such as by macrophages in atherosclerotic plaque decreased TIMPs inflammation increased MMPs and decreases TIMPs Loss of smooth muscle cells or change in the smooth muscle cell synthetic phenotype atherosclerosis increases distance of diffusion to inner media HTN decreases blood flow from vasa vasorum to outer media these may cause loss of SM cells, fibrosis, inadequate ECM, accumulation of amorphous proteoglycans, and loss of elasticity in aorta these changes = cystic medial degeneration may be also seen in Marfan & Scurvy
Aneurysms, pathogenesis, cont d HTN ascending aorta more Atherosclerosis abdominal aorta Other causes: -Trauma -Vasculitis -Congenital defects -Infections = mycotic aneurysms
Mycotic aneurysms Mycotic aneurysms result from : (1) embolization of a septic embolus, usually as a complication of infective endocarditis (2) extension of an adjacent suppurative process (3) direct infection of an arterial wall by circulating organisms like Salmonella gastroenteritis Tertiary syphilis is a rare cause of aortic aneurysms predilection for vasa vasorum of ascending thoracic aorta obliterative endarteritis the aneurysm can occasionally involve aortic valve annulus
Abdominal aortic aneurysm (AAA) Atherosclerosis can also affect: common iliac, aortic arch, descending thoracic aorta inflammation and impaired diffusion men smokers after 50 years not only atherosclerosis Marfan syndrome Smoking-related emphysema is associated dysregulated ECM degradation
Abdominal aortic aneurysm, morphology Typically: between the renal arteries and the aortic bifurcation can be saccular or fusiform up to 15 cm in diameter and 25 cm in length In the vast majority: underlying extensive atherosclerosis is present usually with mural thrombus Not infrequently, AAAs are accompanied by smaller iliac artery aneurysms
Clinical consequences of AAA Obstruction of a vessel branching off the aorta renal, iliac etc. Embolism Pressure on ureter, vertebra etc. Palpable pulsating abdominal mass Rupture into peritoneal/retroperitoneal cavity often fatal
AAA rupture Size if <=4cm in diameter: almost never 4-5: 1% per year 5-6: 11% per year >6cm: 25% per year Managed surgically if elective: mortality 5% if emergency: 50%
Thoracic aortic aneurysm Most commonly HTN, Marfan, and TGF-beta defects Clinically: (1) Encroachment on mediastinal structures (e.g., respiratory or feeding difficulties due to airway or esophageal compression, respectively) (2) Persistent cough from irritation of the recurrent laryngeal nerves (3) Pain caused by erosion of bone (i.e., ribs and vertebral bodies) (4) Cardiac disease due to valvular insufficiency or narrowing of the coronary ostia (5) Aortic rupture (5) Patients with syphilitic aneurysms may die of heart failure induced by aortic valvular incompetence
Embolism Thromboembolism systemic or venous Gas embolism Amniotic fluid embolism Fat embolism
Fat embolism Long bone fractures and soft tissue crush injuries <10% are clinically significant Vigorous cardiopulmonary resuscitation mostly asymptomatic If symptomatic: -pulmonary insufficiency -neurologic symptoms -anemia -thrombocytopenia -diffuse petechial rash Fatal in 10%
Fat embolism, mechanisms Both mechanical obstruction and biochemical injury Direct obstruction and platelet aggregation Fatty acid release endothelial injury Granulocyte recruitment and the injury they cause
Amniotic fluid embolism Uncommon Mortality rate: 80%... the most common cause of maternal death in the developed world 85% of survivors suffer some form of permanent neurologic deficit Sudden severe dyspnea, cyanosis, and hypotensive shock, followed by seizures and coma
Amniotic fluid embolism, cont d also may find lanugo hair, fat or mucin If survived initial crisis: -pulmonary edema -DIC (50%) thrombogenic substances from amniotic fluid Robbins basic pathology 9 th edition (Courtesy of Dr. Beth Schwartz, Baltimore, Maryland.)
Air embolism Examples: -bypass surgery coronary artery -neurosurgery cerebral artery -venous such as in obstetric surgery or chest trauma pulmonary -decompression sickness The bends, chokes, and caisson disease