The spontaneous course of small abdominal aortic aneurysms. Aneurysmal growth rates and life expectancy

Endoluminal pulse oximetry of the sigmoid colon and the monitoring of the colonic circulation

Colonic ischaemia is a frequently observed serious complication following abdominal aortic reconstruction. For adequate treatment of this disorder, early diagnosis and resection of the diseased colon is essential. The purpose of this study was to evaluate a new method, based on pulse oximetry, to detect colonic ischaemia at an early preclinical stage. During a 7-year period (1989-1995) colonoscopy and pulse oximetry were performed in all patients at risk of colonic ischaemia: complicated acute or elective aortic reconstructions, colostomies with superficial necrosis and in patients who underwent uncomplicated aortic reconstruction and non-ischaemic colonic problems (n = 90). The sensitivity, specificity and positive predictive values, and negative predictive value, were calculated. All patients, except four for whom an acute relaparotomy was necessary, subsequently underwent colonoscopy combined with endoluminal pulse oximetry. Of the 90 patients, 30 had colonic ischaemia according to endoscopy (n = 26) or relaparotomy (n = 4), and in 33 patients the absence of pulsatile signal was detected by means of pulse oximetry. Thus, in three patients, pulse oximetry was falsely positive for colonic ischaemia. The calculated sensitivity and specificity of pulse oximetry were 100 and 95%, respectively. In comparison to other methods used for early detection of colonic ischaemia, pulse oximetry appears to be a promising method for the evaluation and monitoring of colonic ischaemia because it is non-invasive and easy to apply with a high sensitivity and specificity.

Outcome for patients with abdominal aortic aneurysms that are treated non-surgically

BACKGROUND

There are few reports in the literature describing the outcome for patients with abdominal aortic aneurysm who are not treated by surgical repair. This is in spite of the fact that this group of patients often defines the success of surgical treatment. The purpose of this report is to review those patients from St George Hospital Kogarah who have been rejected for surgical therapy and to examine the long-term outcome and mode of demise of these patients.

METHODS

At the end of December 1992 we completed a computerized list of all patients seen at St George Hospital Kogarah with abdominal aortic aneurysm. Since that time we have continued to accrue patients to this list and obtain follow-ups prospectively. End points examined in this study were aortic aneurysm transverse diameter, sex, age, intercurrent illnesses, reasons for not undertaking surgical treatment, length of survival and cause of death.

RESULTS

The mean age of patients in this series was 77 +/- 8.29 years (SD). Survival at yearly intervals for 5 years in our 101 patients were 69, 55, 44, 35 and 33%, respectively. For patients with an abdominal aortic aneurysm of < or = 5 cm, the 5-year survival rate was 42% while for patients with an abdominal aortic aneurysm of > 5 cm, the 5-year survival rate was 25%. There were 66 deaths in this series; 40% were due to cardiopulmonary events and 30% were due to ruptured abdominal aortic aneurysm. The median time between presentation and death was 12 months.

CONCLUSION

The patients from this report were significantly older than those reported from previous series. We believe that it will become increasingly important to develop methods of selection of patients for current and newer modalities of treatment for abdominal aortic aneurysm. It will be increasingly important for groups offering these treatments to be able to explain to patients what their prognosis is likely to be should they not be selected for those treatments.

Interobserver variability in measuring the dimensions of the abdominal aorta: comparison of ultrasound and computed tomography

OBJECTIVES

To examine the interobserver variability in measuring the abdominal aorta by ultrasound (US) and computed tomography (CT).

DESIGN

A prospective clinical study in a university hospital.

MATERIALS

Thirty-three patients whose abdominal aortas were scanned both with CT and US as a part of aneurysm investigation or for a variety of other reasons.

METHODS

Three radiologists measured abdominal aortic diameters by US and CT. The interobserver differences (IOD) in US and CT and intraobserver differences for CT-US-pairs were analysed by various statistical methods. A new concept of "clinically acceptable difference" (CAD) was adopted denoting differences of less than 5mm.

RESULTS

The IOD in US was 2mm or less in 65% of the anteroposterior and 61% of the transverse measurements and 5mm or more in 11% of the anteroposterior and 14% in the transverse measurements in 102 observer pairs for all aortas. The IODs were significantly larger in measuring the aneurysmal aortas compared with normal aortas (p < 0.001). The CAD-value for the aneurysmal aortas was 84% in the anteroposterior and 82% in the transverse directions. In CT the IODs were 2mm or less in 62% of the anteroposterior and 66% of the transverse measurements and 5mm or more in 12% of both anteroposterior and transverse measurements in 94 observer pairs for all aortas. The CAD-value in the aneurysmal aortas was 91% in the anteroposterior and 85% in the transverse directions. There was no significant difference between the US and CT CAD-levels. The absolute CT-US difference of an individual observer was 2mm or less in 54%, 5mm or more in 17% and 10mm or more in 2% of the anteroposterior measurements in the 95 CT-US pairs. In the transverse direction the corresponding figures were: 2mm or less in 63%, 5mm or more 13% and 10mm or more in 2% of the pairs. The diameters obtained by US were smaller in 84% of the cases compared with those of CT in measuring the maximum aortic diameter in anteroposterior direction, whereas the same figure for the transverse measurements was 59%.

CONCLUSIONS

Both US and CT measurements are subject to significant interobserver variability that must be taken into account in the clinical follow-up of small abdominal aortic aneurysms and in screening studies. Neither of these methods can be considered as a 'gold standard'.

Variability in measurement of abdominal aortic aneurysms. Abdominal Aortic Aneurysm Detection and Management Veterans Administration Cooperative Study Group

PURPOSE

The purpose of this study was to report interobserver and intraobserver variability of computed tomography (CT) measurements of abdominal aortic aneurysm (AAA) diameter and agreement between CT and ultrasonography observed in the course of a large, multicenter, randomized trial on the management of small AAAs.

METHODS

CT measurements of AAA diameter from participating centers were compared with measurements made from the same scan by a central laboratory. Blinded central remeasurement of a randomly selected subset of these CT scans was used to assess intraobserver variability. Agreement between AAA measurements by CT and ultrasonography done within 30 days of each other was also assessed.

RESULTS

For interobserver pairs of local and central CT measurements of AAA diameter (n = 806), the difference was 0.2 cm or less in 65% of pairs, but 17% differed by at least 0.5 cm. For intraobserver pairs of central CT remeasurements (n = 70), 90% differed by 0.2 cm or less, 70% were within 0.1 cm, and only one differed by 0.5 cm. Of 258 ultrasound-measured and central CT pairs, the difference was 0.2 cm or less in 44% and at least 0.5 cm in 33%. Ultrasound measurements were smaller than central CT measurements by an average of 0.27 cm (p < 0.0001). Local CT and ultrasound measurements showed a marked preference for recording by half centimeter.

CONCLUSIONS

A high degree of precision is possible in CT measurement of AAA diameter, but this precision may not be obtained in practice because of differences in measurement techniques. Differences between imaging modalities increase variability further. Variations in AAA measurement of 0.5 cm or more are not uncommon, and this should be taken into account in management decisions. Efforts to reduce variation in measurement are warranted and might include (1) seeking agreement between surgeons and radiologists on a precise definition of AAA diameter, (2) limiting the number of radiologists who measure AAAs, and (3) use of calipers and magnifying glass for CT measurements.

Influence of selective management on the prognosis and the risk of rupture of abdominal aortic aneurysms

A total of 199 patients with abdominal aortic aneurysms were followed up to investigate the influence of selective management on the prognosis and the risk rupture of abdominal aortic aneurysms. Decisions to operate or to continue watchful waiting with treatment of risk factors for expansion were based on aneurysm size, expansion rate, aneurysm-related symptoms, and individual operative risk. Rupture occurred in eight cases. All aneurysms were larger than 5 cm, and six were larger than 6 cm in diameter at the last measurement before rupture. The resulting overall 5-year cumulative rate of rupture was 7.3% (Kaplan Meier). The 134 patients who underwent more than one ultrasound examination were observed for an average of 4.0 years (536 patient-years). The expansion rate was significantly correlated with the initial diameter and the diastolic blood pressure (best subset multiple regression analysis: r = 0.403; P < 0.001). A correlation with the systolic blood pressure was found only in univariate analysis (r = 0.236; P = 0.011). Amplitude of blood pressure, serum cholesterol level, low-density and high-density lipoproteins, ratio of low- to high-density lipoproteins age, and the extent of smoking habits were not correlated with the expansion rate. Our conclusion is that larger diameter and higher diastolic blood pressure are important risk factors for expansion of abdominal aortic aneurysms. Selective management of abdominal aortic aneurysms based on aneurysmal size, expansion rate, and patient characteristics may result in a low rate of rupture.