on 02-Feb-2021 (Tue)

， 审丑节制， 创作理念与文本呈现之间的辩证关系， 个体经验更 新与叙事技术升级之间的矛盾统一等等， 都结

en mycotic aneurysms occur during the course of IE, manifestations of the underlying disease may be evident. Peripheral middle cerebral artery aneurysms constitute 2.5% to 6.2% of all intracranial aneurysms 826–830,852 and usually are secondary to infection. Intracranial mycotic aneurysms are usually clinically silent.

Contrary to popular belief, most intracranial hemorrhages associated with IE were found to be caused not by ruptured mycotic aneurysms but by septic necrotic arteritis. 828

Visceral artery aneurysms are uncommon but when present are almost uniformly caused by infection 835 or by polyarteritis nodosa. The most common location is in the superior mesenteric artery. Although superior mesenteric artery aneurysms account for only 8% of visceral artery aneurysms overall, most are of infectious origin. 856 Symptoms include colicky abdominal pain of acute onset, but the presentation is variable. Hepatic artery aneurysms may produce colicky right upper quadrant pain, fever, jaundice, and gastrointestinal hemorrhage 857 or hemobilia. 858 More than 190 cases of this entity have been reported in the literature; 75% were extrahepatic, and 25% were intrahepatic. Ruptured mycotic aneurysm of the celiac artery may manifest as hemoptysis or hemothorax. 859

If the external iliac artery is involved, a triad of clinical signs may be present: (1) pain in the lower extremity (especially the anterior aspect of the thigh) with quadriceps muscle wasting and a depressed knee jerk; (2) arterial insufficiency of the extremity with coolness, pallor, and depressed pulses; and (3) bacteremia. 860

Distal aneurysms (e.g., affecting the femoral artery) occasionally have unusual presenting manifestations, including arthritis and purpura in the affected limb.

In users of illicit drugs, the brachial, radial, or carotid arteries or arteries of the lower extremity may be involved. 822 Only 50% of these patients are febrile on admission. 822 A superimposed septic arthritis also may be present. 861

Although most infected aortic atherosclerotic aneurysms occur in elderly men, no pathognomonic findings exist to separate these patients from patients with bland, uninfected aneurysms. Fever is the most helpful differentiating sign (present in >70% of patients), because it is uncommon in patients with bland aneurysms. Back pain or abdominal pain occurs in about one-third of the cases. A draining cutaneous sinus may be present.

Differentiation of an infected aneurysm from the entity of inflammatory abdominal aortic aneurysm may be difficult. Inflammatory abdominal aortic aneurysms first were described in 1935 and account for 5% to 10% of abdominal aortic aneurysms; the lesions are usually infrarenal and often lead to ureteral obstruction, owing to the densely adherent fibrotic mass surrounding the vessel. 862 In a large series of 2816 patients undergoing repair of abdominal aortic aneurysms, 127 (4.5%) had inflammatory abdominal aortic aneurysms. 863 Most patients (123 of 127) were men and heavy smokers. Inflammatory abdominal aortic aneurysms are associated with an elevated erythrocyte sedimenta- tion rate (73% of cases), weight loss, symptoms (back or abdominal pain in 30%–50%), and a high operative mortality rate.

Continuing bacteremia despite “appropriate” antimicrobial therapy in an elderly (especially diabetic) patient who has no signs of IE suggests an infected intravascular site. The aneurysm is palpable in 50% to 60% of the cases. 824,835 In most cases, the onset is insidious, and a low-grade fever may be present for several months before diagnosis. The nonspecificity of the clinical manifestations is reflected by the 75% preoperative rupture rate for this entity. Rupture may occur into the retroperitoneal space or peritoneal cavity (56%), pleural cavity (9%), duodenum (12%), esophagus (6%), mediastinum (3%), or pericardium (3%). The most common site of aortoenteric fistula is between the aorta and the third portion of the duodenum. Short periods of herald bleeding are common warning signs before exsanguinating hemorrhage occurs. 864 Severe pain and the rapid onset of shock usually accompany rupture of the aneurysm.

CT is not sufficiently sensitive for the detection of intracranial mycotic aneurysms 828,829 ; however, these lesions are not likely when the appearance on CT scan is completely normal. Diagnosis of intracranial mycotic aneurysm can be established by four-vessel cerebral arteriography, although 2D and 3D helical CT angiography, 865 magnetic resonance angiography, 829,866 and the less dangerous and invasive procedure of intravenous digital subtraction angiography 867 are promising. Magnetic resonance angiography may detect aneurysms only 2 to 3 mm in diameter, but false-negative results occur in 8% to 10% of such studies; this modality cannot substitute for selective angiography, although techniques and resolution are evolving.

Patients with infected aortic aneurysms usually have a leukocytosis (65%–83%), but this is nonspecific and may be present even if the aneurysm is bland. Bacteremia is found in 53% to more than 90% of the cases, is continuous, and usually does not clear with antibiotic therapy alone. Evidence for a primary source of bacteremia (e.g., pneumonia, osteomyelitis) may be present but is absent in 46% of the cases. 823 The abdominal aorta is noted to be calcified on abdominal radiographs in 47%, 825 and anterior vertebral body erosion has been shown in 18%. A lack of calcification suggests infection, because 70% to 80% of bland aneurysms show calcification on abdominal radiographs.

Gas in the aortic wall is diagnostic but rare.

Although the sensitivity is unknown, 67 Ga- and 111 In-labeled leukocyte imaging have been used to localize intraarterial infections. 872 Occult infected aneurysms have been identified in patients with fever of unknown origin and negative results on CT or MRI studies with gallium 873 or leukocyte scintigraphy, 874 and these procedures may enable seroma or hematoma to be distinguished from adjacent infection. Leukocyte imaging with 99m Tc-labeled cells also seems promising, but false-positive results have been noted. 875 Positron emission tomography labeled with 18 F-fluorodeoxyglucose shows great potential for the detection of endarteritis and infected vascular grafts and will likely become the nuclear medicine study of choice for this group of diseases.

Nevertheless, preoperative angiography often is preferred to delineate precisely the extent of aneurysmal involvement. 876 This information may alter the operative approach and may minimize complications.

Before the antibiotic era, mycotic aneurysms associated with IE usually were caused by the more “virulent” organisms, such as the β-hemolytic group A streptococci, pneumococci, or H. influenzae. With the decline of these organisms as causal agents in IE, most are now due to streptococci or staphylococci (≥60% of cases).

When bacteria seed a preexisting atherosclerotic vessel, the etiologic agents are markedly different from those found in mycotic aneurysms associated with IE. Gram-positive organisms cause approximately 60% of these lesions, but gram-negative bacilli (chiefly salmonellae) are isolated in 35%. Staphylococci are implicated in 40% of the cases overall, 825 and more than two-thirds of these are S. aureus.

The risk for vascular infection in adult patients with non-Typhi Salmonella bacteremia has been reviewed. 880 Salmonellae cause 20% of the cases and involve, in order of frequency, the aorta and femoral and iliac arteries. Only 1 in 24 such cases reported before 1974 was above the renal arteries. 881 Lumbar osteomyelitis due to Salmonella was present in one-third of cases. The presumed portal of entry is the gastrointestinal tract. 882 S. enteritidis strains are isolated in 40% of cases, which is proportional to their overall rate of isolation in the United States. S. enterica serotype Choleraesuis, an uncommon clinical isolate, seems to be particularly pathogenic for this condition, because this species was isolated in 32% of the cases. 883 S. enterica serotype Typhi rarely is implicated in this disorder. Salmonella infections of aortic aneurysms first were reported in 1948.

The predilec- tion for involvement by this organism is not understood, but salmonellae tend to seed abnormal tissues during bacteremia (e.g., hematomas, malignant tumors, cysts, gallstones, bone infarcts, altered endothelium, aortic aneurysms). It has been estimated that 25% of patients older than 50 years with Salmonella bacteremia have an intravascular focus of infection. 884,885

Fungal mycotic aneurysms are rare in the intracranial compartment, and only 13 definite cases had been reported by 1981. 897

Fungal mycotic aneurysms tend to involve larger, more proximal vessels at the base of the brain (11 [61%] of 18 cases were carotid or basilar), compared with those involved in bacterial cases of IE, 898 and may complicate intracranial surgery.

Fungi also may cause endarteritis in the aorta or on aortic grafts, including Aspergillus or Bipolaris spp. 899,90

Pseudoaneurysms resulting from intraarterial or perivascular injection of illicit street drugs, often in addicts with sclerosed veins due to repeated intravenous inoculation, are associated with contiguous abscesses. The causative agents are S. aureus (in 76% of cases), P. a e r u g i n o s a (in 18%), and many others.