Management of asymptomatic popliteal aneurysms: the use of a Markov decision tree to determine the criteria for a conservative approach

Natural history, growth rates, and treatment of popliteal artery aneurysms

BACKGROUND

The natural history of a cohort of patients monitored for popliteal artery aneurysms (PAAs) has not been well described. A prevailing uncertainty exists regarding the optimal surveillance strategies and timing of treatment. The primary aim of the present study was to describe the care trajectory of all patients with PAAs identified at two tertiary vascular centers, both in surveillance and eventually treated. The secondary aim was to define the PAA growth rates.

METHODS

A retrospective, multicenter cohort study was performed of all patients with PAAs at two vascular centers in two countries (Sweden, 2009-2016; New Zealand, 2009-2017). Data were collected from electronic medical records regarding the comorbidities, treatment, and outcomes and analyzed on a patient- and extremity-specific level. Treatment was indicated at the occurrence of emergent symptoms or considered at a PAA threshold of >2 cm. The PAAs were divided into small (≤15 mm) and large (>15 mm) aneurysms. The mean surveillance follow-up was 5.1 years.

RESULTS

Most of the 241 identified patients (397 limbs) with a diagnosis of PAAs had bilateral aneurysms (n = 156). Most patients were treated within the study period (163 of 241; 68%), and one half of the diagnosed extremities with PAA had been treated (54%; 215 of 397). Among those who had undergone elective repair, treatment had usually occurred within 1 year after the diagnosis (66%; 105 of 158). More small PAAs were detected in the group that had required emergent repair compared with elective repair (6 of 57 [11%] vs 12 of 158 [8%]; P < .001). No differences were found in the mean diameters between the elective and emergent groups (30.1 mm vs 32.2 mm; P = .39). Growth was recorded in 110 PAAs and on multivariate analysis was associated with a larger index diameter (odds ratio, 1.138; 95% confidence interval, 1.040-1.246; P = .005) and a concurrent abdominal aortic aneurysm (odds ratio, 2.553; 95% confidence interval, 1.018-6.402; P = .046).

CONCLUSIONS

The present cohort of patients represented a true contemporary clinical setting of monitored PAAs and showed that most of these patients will require elective repair, usually within 1 year. The risk of emergent repair is not negligible for patients with smaller diameter PAAs. However, the optimal selection strategy for preventive early repair is still unknown. Future morphologic studies are needed to support the development of individualized surveillance protocols.

Bilateral Vein Compression by Popliteal Artery Aneurisms Mimicking Post-Thrombotic Syndrome

PURPOSE

To report a case of a 79-year-old man who presented a bilateral popliteal artery aneurysm compressing both popliteal veins mimicking signs and symptoms of post-thrombotic syndrome.

CASE REPORT

A 79-year-old male patient, was seen in the ambulatory clinic with a 2-year history of bilateral leg swelling, calf pain, chronic ulceration, and hyperpigmentation. Upon physical examination, lower extremities were edematous, with a 3 cm suppurative ulcer on each leg. Image studies showed a popliteal right arterial aneurysm of maximum diameter of 41.7 mm, extrinsically compressing the ipsilateral popliteal vein. Likewise, on the left leg, a popliteal arterial aneurysm of maximum diameter of 47.9 mm was encountered triggering the same phenomenon. Bilateral endovascular treatment deploying stent grafts was auspiciously performed. At 36-months follow up, his symptoms are completely resolved, and his ulcers healed. US follow up showed exclusion of the aneurysms with progressive shrinkage of both residual sacs.

CONCLUSION

Popliteal artery aneurysm compressing and constraining flow in the popliteal vein must be included as a differential diagnosis among the causes of chronic venous syndromes. Prompt diagnosis with its appropriate treatment is needed for reducing severe complications caused by PAA, such as the venous disorder our patient had.

Contrast-enhanced ultrasound (CEUS) in the diagnostic evaluation of popliteal artery aneurysms, a single-center study

BACKGROUND

Popliteal artery aneurysms (PAA) are the most common peripheral artery aneurysms. Most common cause is arteriosclerosis. Acute thromboembolic limb ischemia and rupture of the PAA depict severe complications. Diagnostic tools for identifying PAAs are (Doppler) ultrasound, CT/MR angiography and DSA.

PURPOSE

The aim of the present retrospective single-center study is to assess the application and safety of CEUS for assessing untreated and treated PAAs.

MATERIALS AND METHODS

13 patients were included in this study on whom CEUS was performed between 2007-2016. CEUS examinations were performed and interpreted by an experienced single radiologist (EFSUMB Level 3).

RESULTS

CEUS allowed for the detection of PAAs in all cases. CEUS allowed for detection of partial thrombosis of PAA in 7/8 of untreated patients, proper exclusion of PAA upon femoro-popliteal bypass in 3 patients, incomplete exclusion of PAA upon femoro-popliteal bypass in 1 patient and ruling out of in-stent stenosis in 1 patient.

CONCLUSION

CEUS is a useful and safe tool for in real-time evaluation of PAAs in the pre-/post-treatment status. In addition to conventional (Doppler) ultrasound and as an alternative tool to more elaborate imaging modalities, CEUS might be integrated in the future diagnostic work-up and follow-up of PAA patients.

Contemporary Treatment of Popliteal Artery Aneurysms in 14 Countries: A Vascunet Report

OBJECTIVE

Popliteal artery aneurysm (PAA) is the second most common arterial aneurysm. Vascunet is an international collaboration of vascular registries. The aim was to study treatment and outcomes.

METHODS

This was a retrospective analysis of prospectively registered population based data. Fourteen countries contributed data (Australia, Denmark, Finland, France, Hungary, Iceland, Italy, Malta, New Zealand, Norway, Portugal, Serbia, Sweden, and Switzerland).

RESULTS

During 2012-2018, data from 10 764 PAA repairs were included. Mean values with between countries ranges in parenthesis are given. The incidence was 10.4 cases/million inhabitants/year (2.4-19.3). The mean age was 71.3 years (66.8-75.3). Most patients, 93.3%, were men and 40.0% were active smokers. The operations were elective in 73.2% (60.0%-85.7%). The mean pre-operative PAA diameter was 32.1 mm (27.3-38.3 mm). Open surgery dominated in both elective (79.5%) and acute (83.2%) cases. A medial surgical approach was used in 77.7%, and posterior in 22.3%. Vein grafts were used in 63.8%. Of the emergency procedures, 91% (n = 2 169, 20.2% of all) were for acute thrombosis and 9% for rupture (n = 236, 2.2% of all). Thrombosis patients had larger aneurysms, mean diameter 35.5 mm, and 46.3% were active smokers. Early amputation and death were higher after acute presentation than after elective surgery (5.0% vs. 0.7%; 1.9% vs. 0.5%). This pattern remained one year after surgery (8.5% vs. 1.0%; 6.1% vs. 1.4%). Elective open compared with endovascular surgery had similar one year amputation rates (1.2% vs. 0.2%; p = .095) but superior patency (84.0% vs. 78.4%; p = .005). Veins had higher patency and lower amputation rates, at one year compared with synthetic grafts (86.8% vs. 72.3%; 1.8% vs. 5.2%; both p < .001). The posterior open approach had a lower amputation rate (0.0% vs. 1.6%, p = .009) than the medial approach.

CONCLUSION

Patients presenting with acute ischaemia had high risk of amputation. The frequent use of endovascular repair and prosthetic grafts should be reconsidered based on these results.

Ruptured popliteal artery aneurysms

Background

Rupture is a recognised complication of ruptured popliteal artery aneurysms that requires emergency intervention. There is little evidence collating the presentation, intervention and outcomes of ruptured popliteal artery aneurysms.

Objective

The primary aim of this study was to deduce the sequelae following different management modalities of ruptured popliteal artery aneurysm.

Methods

We performed a systematic review of all available cases reports of ruptured popliteal artery aneurysms in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analysis Protocol.

Results

We identified 48 cases taken from 35 case reports and series. Men were more commonly affected ( n = 96%), and mean age was 71 years. Acute limb ischemia was the commonest presentation (32%) whilst incidental deep vein thrombosis was found in 43% of patients. The mean aneurysm size was 8.2 cm (range, 2.7 to 13.3 cm). Management consisted of open surgery (58%), endovascular treatment (25%) and ‘other’ treatment (evacuation of haematoma, ligation of aneurysm, amputation or palliation) (17%). The perioperative mortality rate in the whole cohort was 13%. Perioperative mortality was similar between comparing the open and endovascular surgery groups. Re-intervention rate amongst endovascular patients was 25% over an average follow-up period of 14 months. There was one re-intervention in the re-constructive group (3%) over a follow-up period of 17 months and none in the ‘other’ group.

Conclusion

Popliteal artery aneurysm rupture is a serious complication associated with significant morbidity and mortality. Open surgical reconstruction and endovascular repair are both feasible for the treatment of ruptured popliteal artery aneurysms; however, open surgery is less likely to require further re-intervention.

Femoral artery transposition is a safe and durable option for the treatment of popliteal artery aneurysms

OBJECTIVE

A suitable ipsilateral great saphenous vein (GSV) autograft is widely considered the best material for arterial reconstruction of a popliteal artery aneurysm (PAA). There are, however, cases in which such a GSV is absent, diseased, or of too small diameter for this use. Alternatives to GSV are synthetic conduits, but with a reduced long-term patency, in particular for infragenicular bypass; other venous autografts of marginal use; and stent grafts still in the first stages of their evaluation. However, a sufficiently long segment of the ipsilateral superficial femoral artery (SFA) is often preserved in patients with a PAA. Such a segment may be used as an autograft for popliteal reconstruction. Moreover, the morphometric characteristics of the SFA often optimally match those of the distal native popliteal bifurcation. SFA autografts (SFAAs) have therefore become our choice when the ipsilateral GSV is not suitable. We herein present the long-term results of SFAA for the treatment of PAA in the absence of a suitable GSV.

METHODS

Within this single-center study, all cases during the last 26 years were retrospectively reviewed. Demographics, risk factors, comorbidities, morphometrics of the PAA, and preoperative and follow-up data were intentionally sought.

RESULTS

From 1997 to 2017, there were 67 PAAs treated with an SFAA. The mean age of the patients was 67.67 ± 12 years, and 98% were male. Symptoms included intermittent claudication in 25% (17), critical limb ischemia in 7% (5), and acute ischemia in 10% (7) of the patients; 51% (34) of the patients were asymptomatic. The mean aneurysm diameter of the treated PAA was 29 ± 11 mm (12-61 mm). The mean operative time was 254.8 ± 65.6 minutes (140-480 minutes), with a mean cross-clamp time of 64.5 ± 39 minutes (19-240 minutes). The median length of stay was 9 ± 6.4 days (5-42 days). There were no early amputations or deaths in the series. During a mean follow-up of 47.91 ± 48.23 months, there were 2 anastomotic stenoses, 11 thromboses, 1 infection, and 1 aneurysmal degeneration of the graft; 6 patients died of unrelated causes. The 1-, 3-, 5-, and 10-year primary and secondary patency rates were 93% and 96%, 85% and 90%, 78% and 87%, and 56% and 87%, respectively.

CONCLUSIONS

These data suggest that SFAA use to treat PAA is a safe and durable option. A prospective and comparative work is necessary to confirm these results and to determine the interest of this technique as a first-line strategy.

Markov chain decision model for urinary incontinence procedures

Purpose Urinary incontinence (UI) is a common chronic health condition, a problem specifically among elderly women that impacts quality of life negatively. However, UI is usually viewed as likely result of old age, and as such is generally not evaluated or even managed appropriately. Many treatments are available to manage incontinence, such as bladder training and numerous surgical procedures such as Burch colposuspension and Sling for UI which have high success rates. The purpose of this paper is to analyze which of these popular surgical procedures for UI is effective. Design/methodology/approach This research employs randomized, prospective studies to obtain robust cost and utility data used in the Markov chain decision model for examining which of these surgical interventions is more effective in treating women with stress UI based on two measures: number of quality adjusted life years (QALY) and cost per QALY. Treeage Pro Healthcare software was employed in Markov decision analysis. Findings Results showed the Sling procedure is a more effective surgical intervention than the Burch. However, if a utility greater than certain utility value, for which both procedures are equally effective, is assigned to persistent incontinence, the Burch procedure is more effective than the Sling procedure. Originality/value This paper demonstrates the efficacy of a Markov chain decision modeling approach to study the comparative effectiveness analysis of available treatments for patients with UI, an important public health issue, widely prevalent among elderly women in developed and developing countries. This research also improves upon other analyses using a Markov chain decision modeling process to analyze various strategies for treating UI.

Long-term results of open repair of popliteal artery aneurysm

INTRODUCTION

Popliteal artery aneurysms (PAA) are rare. Different surgical techniques for open surgical repair are possible. This study presents a single centre experience using open surgical repair with a medial approach (MA) and outlines differences between symptomatic (SLS) and asymptomatic (ALS) legs.

METHODS

Data collection was performed retrospectively. The investigation period was from 1 January 1996 to 1 January 2013. Patients presented in the Outpatient Department and received a questionnaire concerning their quality of life. Data are presented as mean ± standard deviation. Mann-Whitney test and Cochran-Armitage test for trend was used for data analysis. Kaplan-Meier method was used to calculate limb salvage rates. p < 0.05 was considered statistically significant.

RESULTS

We analyzed 16 ALS and 26 SLS with an average age of 63.5 ± 10 years. Preoperative ankle-brachial index (ABI) was 1.0 ± 0.2 for ALS (on control examination: 1.12 ± 0.24) and 0.08 ± 0.18 for SLS (on control examination 0.94 ± 0.14) (p < 0.05). Limb salvage rate was 100% for ALS and 86.7% for SLS (overall 93.3%). Primary patency rate for SLS was 85%, for ALS rate of 100%, respectively (overall 92.5%). ALS reached an average of 13.1 ± 2.7 points (SLS 11.4 ± 2.8) on a numeric point scale.

CONCLUSION

Open surgery is therapy and prevention of acute ischaemia all in one, especially for asymptomatic patients and delivers good long-term results. Endovascular therapies offer an alternative but long-term results are pending. Open surgery should still be considered as a gold standard therapy.

Peripheral arterial aneurysms: open or endovascular surgery?

Peripheral arterial aneurysms are uncommon; for some aneurysm types, data are limited to case reports and small case series. There is no Level A evidence in most cases to determine the choice between open or endovascular intervention. The evolution of endovascular technology has vastly improved the armamentarium available to the vascular surgeon and interventionalists in the management of these rare and unusual aneurysms. The choice of operative approach will ultimately be determined on an individual basis, dependent on the patient risk factors, and aneurysm anatomy. After consideration, some aneurysms (femoral, subclavian, carotid and ECAA) fare better with an open first approach; renal, splenic and some visceral artery aneurysms do better with an endovascular first approach. In our practice PAAs are treated with an endovascular first approach. For these rare conditions, both open and endovascular therapy will continue to work in harmony to enhance and extend the capabilities of modern surgical management.

Update on aneurysm disease: current insights and controversies: peripheral aneurysms: when to intervene - is rupture really a danger?

Peripheral artery aneurysms are rarer than abdominal aortic aneurysms (AAA), although the true prevalence is not well known. They often coexist with aortic and other peripheral artery aneurysms. In contrast to AAA, where the principal risk is that of rupture, thromboembolism is more common, contributing a bigger risk in the more common lesions. Although rupture does occur, with incidence related to anatomical site, aneurysm diameter cannot be used to guide management with the same confidence as in AAA. In addition, the rarity of these lesions results in a paucity of evidence with which to guide intervention. Consequently they are difficult lesions to manage, and numerous aneurysm and patient factors must be considered to provide treatment individualised for each case. We discuss popliteal, femoral, carotid, subclavian, upper limb, visceral and false aneurysms, focussing on the risk of rupture and thromboembolism, and current thresholds for intervention, based on the available published literature.

Nonoperative versus surgical management of small (less than 3 cm), asymptomatic popliteal artery aneurysms

Popliteal artery aneurysms represent a common pathology that vascular surgeons are often confronted with. However, several issues remain incompletely understood, including indications for intervention and optimal methods of treatment. In the following article, our discussants debate the appropriate management of small popliteal artery aneurysms. Further complicating this discussion is the unclear relationship between popliteal artery aneurysm diameter and subsequent complications. Whereas with abdominal aortic aneurysms diameter is linked to rupture risk, it is less clear with popliteal artery aneurysms where complications are more likely to include thrombosis, embolization, and compression whether aneurysm diameter is accurately predictive. Perhaps other anatomic features should be included in our management algorithms? Regardless, our debaters will try to convince us whether small popliteal artery aneurysms warrant repair or not.

Endovascular treatment of peripheral vascular disease

Peripheral arterial disease (PAD) affects about 27 million people in North America and Europe, accounting for up to 413,000 hospitalizations per year with 88,000 hospitalizations involving the lower extremities and 28,000 involving embolectomy or thrombectomy of lower limb arteries. Many patients are asymptomatic and, among symptomatic patients, atypical symptoms are more common than classic claudication. Peripheral arterial disease also correlates strongly with risk of major cardiovascular events, and patients with PAD have a high prevalence of coexistent coronary and cerebrovascular disease. Because the prevalence of PAD increases progressively with age, PAD is a growing clinical problem due to the increasingly aged population in the United States and other developed countries. Until recently, vascular surgical procedures were the only alternative to medical therapy in such patients. Today, endovascular practice, percutaneous transluminal angioplasty with or without stenting, is used far more frequently for all types of lower extremity occlusive lesions, reflecting the continuing advances in imaging techniques, angioplasty equipment, and endovascular expertise. The role of endovascular intervention in the treatment of limb-threatening ischemia is also expanding, and its promise of limb salvage and symptom relief with reduced morbidity and mortality makes percutaneous transluminal angioplasty/stenting an attractive alternative to surgery and, as most endovascular interventions are performed on an outpatient basis, hospital costs are cut considerably. In this monograph we discuss current endovascular intervention for treatment of occlusive PAD, aneurysmal arterial disease, and venous occlusive disease.

Treatment of popliteal aneurysms by femoral artery transposition: long-term evaluation

A multicentric retrospective study was carried out on 29 operations (28 patients) to evaluate the long-term results of the treatment of popliteal artery aneurysms by transposition of the superficial femoral artery (SFA). This treatment consisted in proximal and distal ligation and bypass grafting or endoaneurysmorrhaphy followed by reconstruction of the popliteal artery. This surgery was always performed when the homolateral SFA could be used. After surgery, every patient was prescribed a long-term antiplatelet treatment. Mean follow-up was 39.2+/-28 months. Actuarial primary patency was 100% at 1 year and 92% at 3 years. No patients presented with either aneurysmal evolution of arterial graft or septic complication of prosthetic bypass. SFA can be used to treat isolated popliteal aneurysms with satisfying long-term results. This technique is an alternative to the use of autologous saphenous vein.

Popliteal Artery Aneurysm Surgery: The Role of Emergency Setting

The aim of this study was to compare the outcomes of emergent surgery caused by acute complications versus elective surgery of popliteal artery aneurysms (PAAs) and to evaluate the advantages of elective repair related to limb salvage and bypass patency rates. Fifty PAAs were operated on in 40 patients from January 2000 to December 2004. Surgery was elective in 34 cases (68%) and emergent in 16 (32%). Emergent repair was performed because of acute complications. All patients were treated surgically. Early results in terms of limb salvage, primary patency, and assisted patency were assessed. Follow-up consisted of clinical and/or ultrasonographic examinations at 10 days and 1, 3, 6, and 12 months and yearly thereafter. Long-term limb salvage and bypass patency rates were analyzed. The mean follow-up was 17 months. The 1-year limb salvage rate in the elective group was 97.1% versus 56.3% in the emergent group ( P = .0007). The bypass patency rate at 1 year was 94.1% in the elective group versus 66.7% in the emergent group ( P = .03). In this study, the outcomes of the PAA repair were significantly better in the group operated electively and without acute symptoms at presentation compared with the group with acute complications, operated on emergently, especially related to limb salvage and bypass patency rates.

History of the management of popliteal artery aneurysms

Management of popliteal aneurysms remains controversial. Debate continues as to when an asymptomatic popliteal aneurysm should be treated and, with concerns regarding the fate of a bypassed popliteal aneurysm and the advent of intravascular stents, what procedure is best. This paper reviews the history of popliteal artery aneurysm management with particular emphasis on treatment and results before the modern era of arterial reconstruction. The aim of treatment then was to induce thrombosis. Now it is to prevent thrombosis.

Deep vein thrombosis and pulmonary embolus associated with a ruptured popliteal aneurysm - a cautionary note

Popliteal artery aneurysms representing 80% of peripheral artery aneurysms rarely rupture (a reported incidence of 0.1-2.8 %) and second commonest in frequency after aorto-iliac aneurysms. They usually present with pain, swelling, occlusion or distal embolisation and can cause diagnostic difficulties. We report a 78 year old man who was previously admitted to hospital with a pulmonary embolus secondary to deep venous thrombosis. He was heparinized then warfarinised and was readmitted with a ruptured popliteal aneurysm leading to a large pseudo aneurysm formation. The pulmonary embolus had been due to popliteal vein thrombosis and propagation of the clot. A thorough review of literature identified only one previously reported case of ruptured popliteal artery aneurysm and subsequent large pseudo aneurysm formation. We feel it is important to exclude a popliteal aneurysm in a patient with DVT. This may be more common than the published literature suggests.

Long-term Results of Surgical Repair of Popliteal Artery Aneurysm

OBJECTIVE

To determine the long-term outcome of surgical repair of popliteal artery aneurysms (PAA).

METHODS

A retrospective review of consecutive patients who underwent surgical PAA repair in two vascular surgery units between 1988 and 2006 was performed. Primary and secondary graft patency, limb salvage and patient survival rates were determined using Kaplan-Meier methods.

RESULTS

48 patients underwent repair of 63 PAAs (ligation and bypass=45, interposition grafting=18). The 5-year primary graft patency, secondary graft patency, limb salvage and patient survival rates were 75%, 95%, 98% and 81%, respectively. The 10-year primary graft patency rates were significantly lower for emergency cases (59%) compared with elective cases (66%) (p=0.0023). Thirteen patients (16 PAAs) required a total of 20 late re-interventions. Duplex ultrasound was available in 33 of 45 PAAs treated by ligation and bypass. Five (15%) PAAs demonstrated perfusion of the aneurysm sac at median (range) follow up of 75 (1-246) months after primary repair and two of these required emergency re-operation.

CONCLUSIONS

These data demonstrate that surgical PAA repair is associated with excellent long-term durability and provide an important benchmark with which to compare results of endovascular PAA repair. Patients treated using the ligation and bypass technique should be enrolled in an aneurysm sac surveillance program.

Popliteal aneurysms: from John Hunter to the 21st century

Popliteal aneurysms are rare and tend to occur in older men with significant co-morbidity. Historically, management of popliteal aneurysms can be considered in three broad groups: (i) the technique of Antyllus; (ii) techniques relying upon a collateral circulation; and (iii) techniques involving maintenance or restoration of circulation. Bypass and exclusion is currently been challenged by endovascular techniques which show promise in selected cases. Current controversies in popliteal aneurysms management are: when to repair asymptomatic aneurysms, what operation to do and how to manage acute thrombosis. These have been addressed by studying, prospectively, 73 patients presenting with 116 popliteal aneurysms. Diameter greater than 2 cm is often stated as being an indication for elective operation in asymptomatic popliteal aneurysms. However, distortion of the aneurysm appears to be at least as important as size in determining whether symptoms are likely to develop. Of 17 popliteal aneurysms followed for a median of 34 months with a diameter 2-3 cm and distortion less than 45 degrees , none thrombosed. This is no worse than patency following elective bypass (P = 0.064). Popliteal aneurysms greater than 3 cm in diameter in patients who are unfit or who declined an operation were significantly more likely to develop thrombosis or any other symptom (P = 0.01 and P = 0.004, respectively). Popliteal aneurysms less than 3 cm in diameter with distortion less than 45 degrees can safely be managed by ultrasound surveillance. Popliteal aneurysms with greater diameter or distortion are best operated upon. Bypass, combined with proximal and distal ligation of the aneurysm, resulted in 5-year graft patency of 78% and 65% for popliteal aneurysms originally patent or thrombosed, respectively, with good long-term exclusion of the aneurysm. In addition to the general complications of intra-arterial thrombolysis, acute deterioration of the limb during lysis appears to be a particular problem when dealing with thrombosed popliteal aneurysms. It occurs in about 13% of cases which compares with 2% when dealing with thrombosed grafts or native arteries. Intra-arterial thrombolysis for thrombosed popliteal aneurysms is associated with unacceptably high numbers of complications and thrombolysis should be reserved for intra-operative use only.

Early complications and long-term outcome after open surgical treatment of popliteal artery aneurysms: is exclusion with saphenous vein bypass still the gold standard?

BACKGROUND

Popliteal artery aneurysms (PAAs) are rare, but thromboembolic complications may result in limb loss. To define complications and outcomes after open surgical repairs, we reviewed our experience.

METHODS

Clinical data of patients with PAA seen between 1985 and 2004 at Mayo Clinic, Rochester, Minnesota, were reviewed and outcomes in 289 patients with open revascularization were analyzed. Kaplan-Meier method with log-rank tests, chi(2), and Wilcoxon rank sum tests were used for analysis.

RESULTS

A total of 358 PAAs were treated in 289 patients, consisting of 281 (97%) men and eight (3%) women. There were 133 (46%) unilateral and 156 (54%) bilateral PAAs with a mean diameter of 2.9 cm (range, 1.5 to 9 cm). Abdominal aortic aneurysm (AAA) was more frequent with bilateral than unilateral PAAs (65% [101/156] vs 42% [56/133] P = .001). There were 144 (40%) asymptomatic limbs (group 1), 140 (39%) had chronic symptoms (group 2), and 74 (21%) had acute ischemia (group 3). Great saphenous vein (GSV) was used in 242 limbs (68%), polytetrafluoroethylene (PTFE) in 94 (26%), and other types of graft in 22 (6%). Early mortality was 1% (3/358), all in group 3 (4% [3/74]). Six of seven patients with perioperative myocardial infarctions belonged to group 3 (8%). The 30-day graft thrombosis rate was 4%, with 1% in group 1 (1/144), 4% in group 2 (5/140), and 9% in group 3 (7/74). All six early amputations (8%) were in group 3, five with failed bypass (4 PTFE, 1 GSV). Mean follow-up was 4.2 years (range, 1 month to 20.7 years). The 5-year primary and secondary patency rates were 76% and 87%, respectively, higher with GSVs (85% and 94%) than PTFE (50% and 63%, P < .05). Seven recurrent PAAs (2%) required reintervention. The 5-year freedom from reintervention was 100% after endoaneurysmorrhaphy vs 97% after ligations (P = .03). Five-year limb salvage rate was 97% (85% in group 3). There was no limb loss in group 1 and none in group 2 with GSV. In group 3, preoperative thrombolysis reduced the amputation rate in class II patients with marginally threatened limbs (96% vs 69%, P = .02).

CONCLUSION

Acute presentation of PAA continues to carry high mortality and cardiac morbidity; although preoperative thrombolysis appears to improve results, the 8% early and 15% late amputation rates remain ominous. Early elective repair is recommended because these patients had no surgical mortality, a low rate of complications, and asymptomatic patients had no limb loss at 5 years. GSV and endoaneurysmorrhaphy continues to be the gold standard for open repair of PAA.

Mid-term outcomes of endovascular popliteal artery aneurysm repair

OBJECTIVE

This study documents mid-term outcomes of a series of endovascular popliteal aneurysm repairs compared with concurrent results of open surgical repair.

METHODS

A retrospective chart review was done of all popliteal artery aneurysm repairs since January 1, 2000. Patency was defined as continued presence of palpable pulses or maintenance of postoperative ankle-brachial index +/- 0.15. Statistical methods included chi(2), t test, Fisher's exact test, and Kaplan-Meier plots with log-rank comparison.

RESULTS

A total of 56 popliteal artery aneurysm repairs were performed. All endovascular popliteal aneurysm repairs (EVPAR, n = 15) were performed using Viabahn endoprostheses. Patients with open repair (OR, n = 41) underwent surgical bypass and aneurysm exclusion with great saphenous vein (n = 26), short saphenous vein (n = 3), or polytetrafluoroethylene (n = 12), through either a medial (n = 28) or posterior (n = 13) approach. All urgent cases received open repair. Technical success was 100% in both groups. Mean follow-up was 16.5 +/- 3 months (range, 0.5 to 56 months). Aneurysm size, location, and outflow were similar between groups. Primary patency, secondary patency, and survival did not differ between groups. Endoleaks were observed in three (20%) of 15 endovascular cases, and type I and III endoleaks were treated with additional endografts.

CONCLUSION

To our knowledge, this represents the largest United States series of EVPAR to date. Early mid-term results of elective endovascular repair of popliteal artery aneurysms are encouraging. Further studies are warranted to define optimal indications for EVPAR and to generate long-term outcomes for this technique.

Outcome following bypass, and proximal and distal ligation of popliteal aneurysms

Background

The aim of this study was to describe early and late results of proximal and distal ligation for popliteal aneurysm (PA), combined with bypass, with particular reference to the fate of the excluded aneurysm.

Methods

Of a cohort of 116 patients with PAs, 66 were treated with bypass and ligation. Graft patency was determined by duplex surveillance. In addition, 17 patients with bypassed PAs underwent a total of 33 duplex scans to determine flow within the aneurysm and change in size.

Results

For initially patent PAs, 3-, 5- and 8-year primary bypass graft patency was 78, 78 and 51 per cent respectively. These rates were not statistically significantly different from those following bypass for thrombosed PA, 3- and 5-year primary patency being 72 and 65 per cent respectively. No PA produced further symptoms after bypass and ligation. No flow was seen in any aneurysm at follow-up. Only one showed an increase in size.

Conclusion

Proximal and distal ligation with bypass produced satisfactory long-term patency with good exclusion of the PA.

Endovascular Treatment of Peripheral Vascular Disease

An estimated 10 million people in the U.S. have symptomatic peripheral arterial disease (PAD); 20 to 30 million have asymptomatic PAD. The prevalence of intermittent claudication increases with age, affecting >5% of patients over 70. The incidence of claudication doubles or triples in patients with diabetes. As people grow older, symptoms from peripheral vascular disease increasingly limit daily activity. Until recently, vascular surgical procedures were the only alternative to medical therapy in such patients. Today, advances in minimally invasive percutaneous interventions have made endovascular procedures the primary modality for revascularization in most patients. Compared with open surgical procedures, endovascular interventions offer comparable or superior long-term rates of success with very low rates for morbidity and mortality. Furthermore, most of these interventions are performed on an outpatient basis, reducing hospital stays considerably. In this monograph we discuss current endovascular interventions for treating occlusive PAD, aneurysmal arterial disease, and increasingly common venous occlusive diseases.

MANAGEMENT OF POPLITEAL ARTERY ANEURYSMS

BACKGROUND

Popliteal artery aneurysms (PAA) are the most common peripheral aneurysm and are recognized as 'the silent killer of the leg circulation'. The timing and type of interventions used in their treatment is still controversial. This review examines the published data on the natural history, epidemiology, clinical presentation and management options available. The aim of this study is to try and reach a consensus with regards to the best management of PAA.

METHOD

A systematic review of data in the English published works since 1980.

RESULTS

The authors include 53 studies containing 2854 patients with 4291 PAA. Most published data involves retrospective studies and personal experience, with one multicentre study. No randomized controlled studies exist regarding the management of PAA.

CONCLUSIONS

1. Although most PAA are of atherosclerotic origin in old patients, trauma, infection and family history are the main causes in young patients. 2. Great vigilance is needed for diagnosis as only approximately five patients are seen each year by a major vascular centre. There is no place for screening programmes to detect PAA. 3. Approximately 45% of patients are asymptomatic at the time of initial diagnosis. Aortic aneurysms are found in 40% and bilateral PAA in 50% of patients. More than 95% of patients are men with a mean age of 65 years and 45% have hypertension. 4. Surgical reconstruction is recommended for all symptomatic and asymptomatic aneurysms larger than 2 cm. Five-year graft patency rates after surgical repair range from 30 to 97%, with 5-year limb salvage ranging from 70 to 98%. Patient survival rates at 5 and 10 years are 75 and 46%, respectively. 5. If carried out carefully, intra-arterial thrombolysis can safely prepare patients presenting with acute ischaemia from occluded PAA, for surgical revascularization to restore distal run-off. 6. Endovascular repair of a PAA is a feasible option, although little evidence is yet available. 7. Lifelong, careful patient surveillance is essential to detect and treat new aneurysms at other sites.

Endovascular Popliteal Aneurysm Repair: Are the Results Comparable to Open Surgery?

INTRODUCTION

The aim of this study was to review our experience of popliteal aneurysms using endovascular techniques.

METHODS

Thirty popliteal aneurysms in 25 patients were treated over an 11-year period. Median aneurysm diameter was 26 (16-48) mm. Five were symptomatic and 25 asymptomatic. Patients were treated with the Haemobahn/Viabahn stent-graft (26), Passager (two), Aneurx (one), and PTFE homemade device (one). Data were assessed using life table analysis, and expressed as cumulative patency rates and standard error (SE).

RESULTS

Median follow-up was 24 (range 1-95) months. Primary patency was 92.9% (SE 4.5%), 84.7% (SE 6.8%), 80% (SE 8.2%), 74.5% (SE 9.4%) and 74.5% (11.3%) at 1, 6, 12, 24 and 36 months, respectively. Cumulative secondary patency was 96.5% (SE 3.3%), 88.7% (SE 6.0%), 88.7% (SE 8.6%), 83.2% (SE 8.0%) and 83.2% (SE 9.8%) at 1, 6, 12, 24 and 36 months, respectively.

CONCLUSION

Endovascular treatment of popliteal aneurysms in this series achieved patency rates similar to open surgery. Aneurysm repair was performed without peroperative deaths and the risks associated with open surgery.

Impact of duplex arteriography in the evaluation of acute lower limb ischemia from thrombosed popliteal aneurysms

Acute limb-threatening ischemia from thrombosis may be the initial presentation of popliteal artery aneurysms (PAA) and is associated with amputation rates of 20-30%. Since contrast angiography may miss the diagnosis, the authors suspect that thrombosis of PAA may be an underappreciated cause of acute ischemia. Routine use of duplex arteriography (DA) may aid in the diagnosis and may help identify the outflow vessels with improved results. One hundred and nine patients (group 1) from 1994 to 1997 and 201 patients from 1998 to 2001 (group 2) presenting with acute limb-threatening ischemia were studied. None of the group 1 patients underwent preoperative DA and no diagnosis of acute popliteal artery aneurysm thrombosis was made. Ten patients with acute ischemia due to thrombosed popliteal artery aneurysms were identified in group 2 when preoperative DA was routinely performed. Urgent revascularization based on the results from DA was performed with use of autogenous saphenous vein in all patients. Six patients had functioning bypasses with a mean follow-up of 15.6 months. There were 3 deaths, 2 within 30 days and 1 after 2(1/2) years with functioning grafts. One patient was lost to follow-up. No major amputations were performed. Incidence of thrombosed popliteal artery aneurysms as the cause of acute limb-threatening ischemia is probably underestimated. Routine use of DA may provide the diagnosis and identifies the available outflow vessels. Contrary to previously published reports, urgent revascularization of an acutely ischemic extremity from thrombosed popliteal aneurysm can provide excellent rates of limb salvage.

Popliteal Aneurysms: Distortion and Size Related to Symptoms

OBJECTIVES

To examine size and distortion of popliteal aneurysms (PA) in relation to symptoms produced at presentation.

METHODS

A prospective study of all PA presenting to a single unit 1988-1994. Wherever possible patients underwent angiography, duplex scanning and measurement of both PA diameter and the most proximal angle of distortion. Symptoms and measurements were noted at the time of first presentation.

RESULTS

Seventy-three patients presented with 116 PA. At initial diagnosis 44 PA (38%) were asymptomatic and 39 (34%) produced acute ischaemia. As the PA increased in diameter so did the degree of distortion (p < 0.0001). Size and distortion were greater in PA producing acute ischaemia or acute thrombosis than in asymptomatic PA (p < 0.01). Degree of distortion differentiated symptomatic from asymptomatic PA (p = 0.0066). Size was not significantly different between these two groups. For PA 3 cm or larger in diameter with greater than 45 degrees distortion sensitivity, specificity and positive and negative predictive values for thrombosis were 90, 89, 83 and 94%, respectively.

CONCLUSION

Distortion and size can differentiate between PA producing different symptoms. Combining the two provides a reliable method of differentiating PA which should be managed by early elective repair.

Popliteal aneurysms: controversies in their management

Popliteal artery aneurysms (PAs) occur in older men with significant comorbidity and limited life expectancy. This needs to be remembered when planning elective operation for asymptomatic aneurysms. In the absence of significant distortion PAs <3 cm in diameter can be managed by sequential ultrasound scanning. Their rate of thrombosis is no worse than that of grafts after elective bypass. Intra-arterial thrombolysis for acute thrombosis should be restricted to intra-operative usage to clear run off.

Is Assessment of Popliteal Artery Diameter in Patients Undergoing Screening for Abdominal Aortic Aneurysms a Worthwhile Procedure

PURPOSE

The aim of this study was to assess whether screening of popliteal arteries in patients undergoing ultrasound screening of their abdominal aortas was worthwhile.

METHODS

All male patients undergoing ultrasound screening for abdominal aortic aneurysm (AAA) during the period February 2000 to June 2002 were offered scanning of their popliteal arteries. All scans were performed by a single, trained operator using a Sonosite 180.

RESULTS

Four hundred and forty-nine patients underwent screening and thus 898 popliteal arteries were assessed. The mean aortic diameter was 2.1 standard deviations (SD) 0.5 cm and the upper limit of normal (2 SD) was 2.7 cm. The mean diameter of the popliteal arteries was 0.74 SD 0.11 and the upper limit of normal was 0.96 cm. Thirty patients had aortic diameters greater than 2.5 cm (ectatic or aneurysmal aortas) but based on a popliteal diameter of 2 cm, no popliteal aneurysms were detected. However, 39 (4.3%) popliteal arteries measured > or = 1 cm (> mean+2 SD); 3/60 (5%) in the ectatic/AAA subgroup and 36/838 (4.3%) in the non-AAA subgroup.

CONCLUSIONS

This study has shown that, using conventional definitions, the imaging of popliteal arteries during screening for AAAs does not detect any popliteal aneurysms and is thus of limited value. However, if a definition of popliteal aneurysm of > or = 1 cm (based on mean+2 SD) is used then 39/898 (4.3%) of arteries would be regarded as having abnormal diameters and may require surveillance.

Expansion Rates of Asymptomatic Popliteal Artery Aneurysms

OBJECTIVES

In the absence of symptoms the decision to operate on popliteal artery aneurysms (PA) is often made on PA diameter. Little information exists on growth rate and therefore optimum scanning intervals. The aim of this paper is to define growth rate of PA managed conservatively.

METHODS

A prospective study of patients with asymptomatic PA was carried out. Patients were invited for ultrasound scanning at 6-12 months intervals. Diameter changes between consecutive pairs of scans were measured. A decision to operate was made in fit patients if PA became symptomatic and/or had a diameter above 3 cm.

RESULTS

Twenty-one men (24 aneurysms) with a median age of 69 years (46-86) underwent 78 scans. Sixteen PA were on the right and eight on the left. Eighteen patients had bilateral aneurysms, 15 of which were complicated on one side at presentation and were dealt with surgically on that side. The median size at first scan was 19 mm (14-36). The median time interval to the first follow-up scan was 9 months and subsequent scans were 12 months. The mean rate of expansion at aneurysm sizes below 20 mm diameter was 1.5 mm/year. PA grew by 3.0 mm/year at sizes 20-30 mm and by 3.7 mm/year at sizes >30 mm. Among the risk factors analysed, hypertension appeared to increase the risk of aneurysm growth.

CONCLUSION

The expansion rate of PA increases with increasing size of the PA. This rate of growth in relation to size at previous scan and threshold diameter for intervention should be borne in mind when planning surveillance intervals.

Surgery of popliteal artery aneurysms: a 12-year experience

BACKGROUND

Management of asymptomatic popliteal aneurysm is controversial, and the prognosis for acutely thrombosed aneurysm is notoriously poor. We evaluated the management and outcome for popliteal aneurysm.

PATIENTS AND METHODS

A retrospective review of all patients with popliteal aneurysm between 1988 and 2000 was carried out. Fifty-two limbs were operated on in 41 patients. Data collected included findings at presentation, operative details, graft patency, limb salvage, complications, and 30-day mortality.

RESULTS

Initial findings included acute ischemia (n = 14), no symptoms (n = 29), acute rupture (n = 2), chronic ischemia (n = 5), and symptoms of nerve or vein compressive (n = 2). All patients with symptomatic aneurysms and 22 patients with asymptomatic aneurysms (21 larger than 2 cm in diameter, 1 with thrombus at duplex ultrasound scanning) underwent surgery as first-line treatment. Of the 7 patients with asymptomatic aneurysm managed with surveillance with duplex ultrasound scanning, acute ischemia developed in three, 1 aneurysm ruptured, compressive symptoms developed in 1, and 2 remained asymptomatic but required surgery because of aneurysm enlargement (>2 cm). Of the 17 patients with acute ischemia, 13 had neurologic signs and underwent immediate thromboembolectomy (trifurcation alone in 8, ankle-level arteriotomy in 4) and bypass grafting (n = 12) or inlay grafting (n = 1), and the other 4 underwent intra-arterial thrombolysis initially. Of these 4 procedures, 2 were successful and had elective surgery; the other 2 required urgent surgery because of secondary distal embolism and failure of recanalization. Thirteen of the 17 grafts were to the crural vessels. Bypass grafting (medial approach) was used in 16 of the 17 patients with acute ischemia, all 5 patients with chronic ischemia, and the 8 patients with no symptoms. An inlay technique (posterior approach) was used in 16 patients with no symptoms, the 3 patients with symptoms of nerve or vein compression, and 1 patient with acute ischemia. The distal anastomoses were to the below-knee popliteal artery in 35 patients and the crural arteries in 15 patients, using autologous vein. Two of the patients with rupture underwent ligation alone, the other undergoing bypass grafting in addition. The overall 5-year primary patency rate was 69%, secondary patency rate was 87%, and limb salvage rate was 87%. Limb salvage was achieved in 14 of the 17 patients with acute ischemia. Patients with asymptomatic aneurysms had better secondary graft patency (100%) compared with symptomatic aneurysms (74%; P <.01). Acute ischemia, technique used, and crural artery grafts were not predictors of graft failure with either univariate or multivariate analysis. Symptomatic aneurysms were associated with more postoperative complications and greater 30-day mortality (4 of 28 vs 0 of 24).

CONCLUSION

Thromboembolectomy followed by crural bypass grafting is an effective treatment for popliteal aneurysm with severe acute limb ischemia. Outcome is better with surgical management of asymptomatic popliteal aneurysm compared with symptomatic aneurysm.

Management of popliteal aneurysm

BACKGROUND

The best management of patients with a popliteal aneurysm has yet to be established. This paper describes an experience of managing both patent and acutely thrombosed popliteal aneurysms.

METHODS

A prospective study was carried out of all patients who presented with a popliteal aneurysm from January 1988 to December 2001. Since 1993 asymptomatic popliteal aneurysms less than 3 cm in diameter without distortion have been managed conservatively. Ultrasonography was repeated at 6-month intervals. These results were compared with conservative management of popliteal aneurysms greater than 3 cm in diameter in patients who declined or were unfit for operation, and with the outcome of patients who underwent elective bypass of a popliteal aneurysm.

RESULTS

Fifty-eight patients (two women) presented with 92 popliteal aneurysms. Some 39 had a thrombosed aneurysm and these patients were significantly more likely to have bilateral aneurysms (P < 0.001). Of patent popliteal aneurysms managed conservatively, none below 3 cm in diameter thrombosed. The risk of postoperative complications was greater after repair of a thrombosed than a patent aneurysm (P < 0.005). Preoperative lysis for a thrombosed popliteal aneurysm was associated with more complications than operation and on-table lysis (P < 0.05).

CONCLUSION

Careful monitoring of asymptomatic popliteal aneurysms less than 3 cm in diameter is safe. Preoperative lysis is associated with increased risks compared with operation alone in patients with a thrombosed popliteal aneurysm.

Aggressive treatment of acute limb ischemia due to thrombosed popliteal aneurysms

OBJECTIVE

The absence of infra-popliteal runoff in patients with acute limb ischemia and thrombosed popliteal aneurysms carries a high risk of amputation. A combined treatment method involving thrombolysis and surgery is reported.

MATERIAL AND METHODS

Information regarding six patients was reviewed. Ankle brachial indices and degree of ischemia were recorded. All patients underwent digital subtraction angiography. In five patients thrombus dissolution was achieved using a combination of mechanical and pharmacologic therapy. One patient was judged incapable of withstanding any delay in reperfusion and was treated with isolated limb perfusion using a thrombolytic agent. All patients underwent surgical revascularization. Follow-up (1-3 years) consisted of duplex examinations at 6 months and yearly thereafter.

RESULTS

Five patients had no measurable ankle brachial index (ABI), while one patient had an ABI of 0.4. Initial angiography noted all patients to have no runoff in continuity to the pedal arch. Following thrombolytic therapy, an adequate bypass vessel was noted in all cases, with reconstitution of the plantar arch in five patients. Distal revascularizations included one peroneal, and five below knee popliteal arterial bypasses. Fasciotomies were performed in four of the six patients. There were no amputations. One patient developed a persistent foot drop. Two patients developed bypass grafts occlusions; one of which required therapy.

CONCLUSION

The pre-operative use of thrombolytic therapy is a safe and effective method to achieve limb salvage in this patient population. Patients must be capable of withstanding an additional period of ischemia allowing for reconstitution of distal runoff. Isolated limb perfusion is of use when a delay to reperfusion cannot be tolerated.

Popliteal aneurysms: a 10-year experience

BACKGROUND

Popliteal aneurysms account for 70% of peripheral arterial aneurysms and, if untreated, pose a serious threat to the affected limb. Debate continues about the best form of treatment especially for asymptomatic lesions.

METHOD

We reviewed the computer records and charts of patients seen at this department with a diagnosis of popliteal aneurysm over the last 10 years. Patients who had not been seen within the last year were followed-up through their G.P.

RESULTS

Twenty-four patients (M 23/F 1) presented with 40 popliteal aneurysms. The mean age was 63.5 +/- 9 years. Symptoms were present in 23 of the affected limbs while 17 were asymptomatic. Thirty were treated surgically and 10 followed with regular ultrasound. The mean diameter of the repaired aneurysms was 3.3 +/- 1 cm. Aneurysms < 2 cm were more likely to be asymptomatic. No limbs were lost in patients undergoing elective repair of popliteal aneurysms. The secondary patency and limb salvage rates at 3 years were 84% and 96% respectively. Conservative management of asymptomatic lesions < 2 cm was not complicated by the development of symptoms.

CONCLUSIONS

Elective repair of popliteal aneurysms by exclusion and bypass is a safe, effective and durable technique. Small asymptomatic lesions can be safely managed with close follow-up.

Decision analysis in surgery

BACKGROUND

The technique of decision analysis is often applied to clinical policy and economic issues in surgery. Because surgeons may be unfamiliar with such work, this article catalogues decision analysis studies in the surgical specialties.

METHODS

We reviewed the medical literature (1966 to 1994) to identify surgical decision analysis studies and to assess trends over time. Each article was categorized according to the type of journal (surgical, other clinical, or technical) in which it was published and content, including surgical specialty, clinical topic, article focus (individual patient decision making, clinical policy, or cost-effectiveness), and primary findings.

RESULTS

Publication rates of surgical decision analysis have increased dramatically over time. Of the 86 total studies only six were published before 1980. In contrast, 44 studies appeared between 1990 and 1994. Although 77% were published in nonsurgical journals, decision analyses have begun to appear more regularly in surgical forums. Studies addressing all of the surgical specialties were found, although more than one half addressed topics in general surgery (34%) or cardiothoracic surgery (22%). The most frequent topics were gallstones (11 articles), head and neck cancer (five articles), coronary artery disease (four articles), and cerebral arteriovenous malformations (four articles). Articles focusing on clinical policy (i.e., those assessing surgical efficacy for broad groups of patients) now account for large majority of published decision analyses.

CONCLUSIONS

The use of decision analysis in surgery is growing steadily. Because decision analysis is being used to influence clinical policy, it is important for surgeons to be aware of these studies and to be able to review them critically.

Cost effectiveness analysis: a review

Medical treatments and strategies are increasingly being subjected to evaluations of economic efficiency. Although the reasons for this are many, it is becoming ever more important for physicians to have an understanding of the uses and limitations of such evaluations. Cost effectiveness analysis (CEA) is a technique that measures the cost of medical technology per unit of a defined health output, usually life years saved with an adjustment for quality of survival. CEA is a popular method of economic evaluation for policy markers, because it can provide direct comparisons among many medical technologies, resulting in a ranked order of procedures based on economic efficiency. The proper interpretation of a CEA requires an understanding of the component parts of the analysis, their theoretical bases, and their limitations. The components of a CEA include the determination of relevant costs, an appropriate analysis viewpoint, the use of discounting for both costs and benefits, and a sensitivity analysis of the assumptions and probabilities that drive the analysis. Marginal and incremental CEAs are techniques that help to address the cost effectiveness of different amounts of a particular treatment and the differential costs and benefits of competing strategies, respectively. A review is presented of the theoretical basis of CEA and its component parts. Emphasis is placed on generating an understanding of the method rather than providing a step-by-step protocol for the undertaking of such studies.