Miscellaneous Abdomen Diseases

Chapter 31

Miscellaneous Abdomen Diseases

Beverly L. Harger

Lisa E. Hoffman

Richard Arkless

ABDOMINAL AORTIC ANEURYSM

ACUTE ABDOMEN

HYDATID DISEASE

Abdominal Aortic Aneurysm

Definition

Focal dilatation of the infrarenal abdominal aorta of at least 150% of the normal diameter (range, 1.4–3 cm; average, 2 cm) is the usual definition of an aneurysm.19 Therefore, aortic dilatation larger than 3 cm indicates a possible aneurysm. Some sources state that 4 cm is clearly diagnostic.19,11 Consultation with an experienced surgeon is indicated when the dilatation reaches a diameter of 5 cm (some say 5.5 cm).

Rupture (Rates and Mortality)

Each year in the United States, more than 15,000 deaths, many of which are preventable, are attributed to AAA.5 The natural history of most aneurysms is one of gradual enlargement; growth rates have been estimated to average 0.2 cm/year for aneurysms smaller than 4 cm and 0.5 cm/year for those larger than 6 cm.19 Although impossible to predict for a given individual, the risk of AAA rupture increases with larger initial aneurysm diameter, hypertension, and chronic obstructive pulmonary disease. Expansion rates of AAAs for men 65 years of age are listed in Table 31-1.12 Rupture of AAA is considered essentially inevitable if the patient lives long enough.15 When rupture occurs, massive intraabdominal bleeding usually occurs and is fatal, with a mortality rate of 80% to 90% unless prompt surgery can be performed.1,4,5,9 A relatively low risk of rupture is seen for asymptomatic, slow-growing AAA smaller than 6 cm. Table 31-2 lists the estimated annual rates of rupture related to AAA.10,19

TABLE 31-1

EXPANSION RATE OF ABDOMINAL AORTIC ANEURYSM BASED ON INITIAL SIZE

Initial Size Measured on Ultrasonography (cm) Expansion Rate Per Year (cm)
2.6–2.9 0.09
3.0–3.4 0.16
3.5–3.9 0.32

TABLE 31-2

ESTIMATED ANNUAL RATES OF RUPTURE RELATED TO ABDOMINAL AORTIC ANEURYSM SIZE

Size of Abdominal Aortic Aneurysm (cm) Annual Rate of Rupture (%)
4.0–4.9 1
5.0–5.9 3
6.0–6.9 9
≥7.0 25

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Risk Factors

The underlying cause of AAA is multifactorial, including such factors as smoking, hypertension, diabetes, and inflammation that may lead to dilatation and subsequent plaque deposition.8 Other uncommon possible causes include infection, inflammatory disease, increased protease activity within the arterial wall, genetically regulated defects in collagen and fibrillin, and mechanical factors.8 An individual’s risk is increased 12-fold if a first-degree relative has an AAA.7 In addition to family history of aneurysms, increasing age and male gender are established risk factors. Understanding the established as well as possible risk factors assists the clinician in determining an index of suspicion for the presence of AAA (Table 31-3). AAA is best repaired as an elective, not emergency, procedure.

TABLE 31-3

RISK FACTORS FOR DEVELOPING ABDOMINAL AORTIC ANEURYSM

Established Risk Factors Comments
Increasing age Most studies focus on ages 65–80 years
Male gender More frequent and at an earlier age than in women. The male-to-female ratio for death from abdominal aortic aneurysm (AAA) is 11 : 1 between ages 60 and 64 years and narrows to 3 : 1 between 85 and 90 years.
Family history of aneurysm Increases individual’s risk twice, especially first-degree male relative
Possible Risk Factors Comments
Tobacco use Long-term smoking increases individual’s risk five times over the baseline
Systemic atherosclerosis disease Including peripheral arterial disease, cerebrovascular disease, history of coronary artery bypass, history of myocardial infarct have modest correlation; less association with smaller AAA than with larger AAAs
Chronic obstructive pulmonary disease Difficult to establish as an independent risk factor
Hypertension Weak correlation
Hypercholesterolemia Weak correlation, specifically related to hypertriglyceridemia
White race AAAs are uncommon in African Americans, Asians, and Hispanics

From Ebaugh JL, Garcia ND, Matsumura JS: Screening and surveillance for abdominal aortic aneurysms: who needs it and when, Semin Vasc Surg 14(3):193, 2001; Lederle FA, Simel DL: Does this patient have abdominal aortic aneurysm? JAMA 281:17, 1999; U.S. Preventive Services Task Force: Guide to clinical preventive services, ed 2, Washington, DC, 1996, U.S. Department of Health and Human Services, Office of Disease Prevention and Health Promotion.

Imaging Findings

Ultrasonography reaches almost 100% accuracy19 for detecting AAA, making it ideal for screening, diagnosis, and follow-up studies in suspected cases.3 Obesity and excessive bowel gas may interfere with ultrasound imaging.15 Approximately 50% of AAAs may be seen as cyst-like calcifications on plain film radiography resulting from the calcium content of atherosclerotic plaques (Figs. 31-1 to 31-11).15

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FIG 31-1 Abdominal aortic aneurysm. Lateral view demonstrates a calcified wall of a fusiform abdominal aorta (arrows). Plain film visualization is possible because of the calcium content of atherosclerotic plaques. Most abdominal aortic aneurysms occur between the renal artery and iliac bifurcation.
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FIG 31-2 Abdominal aortic aneurysm presenting in an anteroposterior lumbar projection. Note the characteristic thin rim of curvilinear calcification (arrows). The location to the right of the spine indicates an extremely large aneurysm. Courtesy Cynthia Peterson, Toronto, Ontario, Canada.
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FIG 31-3 A, Abdominal aortic aneurysm: computed tomography with intravenous contrast. This scan shows a large, partially calcified abdominal aortic aneurysm anterior to the spine. Within the aneurysm is a region of increased density (asterisk) that corresponds to the functional lumen of the aneurysm; the remaining low-attenuated region represents a large thrombus (arrows). Note the renal cyst (curved arrows). B and C, The same imaging methods applied to a different patient reveal abdominal aortic and iliac aneurysms (arrows). B and C, Courtesy Julie-Marthe Grenier, Davenport, IA.
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FIG 31-4 Axial computed tomography scan of a large aortic aneurysm with minimal wall calcification (arrows). Generally, the larger the aneurysm and the older the patient, the more likely it is to rupture. Rupture may mimic a variety of presentations, including disc herniation, acute myocardial infarction, sepsis, appendicitis, and strangulated inguinal hernia. Courtesy Michael Buehler, Carol Stream, IL.
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FIG 31-5 Abdominal aortic aneurysm measuring 4.7 cm on the lateral 40-inch focal-film distance lateral lumbar projection. Any measure larger than 3.0 cm is suspicious of aneurysm, and values over 4.0 cm warrant further investigation with ultrasonography. In this case, the ultrasound examination validated the presence of an aneurysm. Note the faint linear radiodensity of the anteroposterior margin of the vessel (arrowheads). Interpreters are cautioned not to assume that wall calcification is requisite to aneurysm formation. Any suggestive linear shadows, as seen in this case, warrant consideration for an ultrasound examination.
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FIG 31-6 The aorta is calcified but not enlarged (arrowheads). No evidence of aneurysm is present in this case. The sole finding of vascular wall calcification of the abdominal aorta does not warrant further investigation.
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FIG 31-7 A and B, Two cases of an expanded aorta (arrowheads) consistent with aneurysm.
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FIG 31-8 A 12.5-cm aneurysm seen in prominently in the anteroposterior projection (A) and only faintly in the lateral projection (B, arrowheads). Courtesy Robert C. Tatum, Davenport, IA.
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FIG 31-9 A 74-year-old man exhibiting prominent calcification of the anterior and posterior walls of the abdominal aorta. A focal dilatation of 4.7 cm is noted (arrowheads), consistent with aneurysm. In addition to the overall size of the vessel, aneurysms often exhibit a focal bulge, disrupting the parallel continuity of the walls of the vessel. For instance, the focal nature of the budge seen in this case would represent a concern for aneurysm regardless of its size.
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Feb 2, 2016 | Posted by in RESPIRATORY IMAGING | Comments Off on Miscellaneous Abdomen Diseases
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