Pattern of femoro-popliteal aneurysms in an African population

Femoro-popliteal aneurysms are rare if compared to aortic ones, but they are important because of their thromboembolic or rupture potential and their predictive value for existence of aortic and other extra-aortic aneurysms.1,2 Their site, age and gender distribution display ethnic3 and regional1 variations. In Africa, as atherosclerosis becomes an important disease, its sequelae, including aneurysms, may become increasingly evident.4 Furthermore, there has been recent concern that the number of patients at risk of femoral artery pseudoaneurysm may be increasing in parallel with the extent of intravenous Abstract

drug abuse and the number of cardiac vascular radiological interventional procedures performed each year. 5Nonetheless, reports of femoro-popliteal aneurysms from Africa, including Kenya, are scarce.Data on pattern of aneurysms are important in formulation of prevention and management strategies.This study reports the distribution of femoro-popliteal aneurysms in an African Kenyan population.

Patients and Methods
This was a retrospective cross-sectional study conducted at Kenyatta National Hospital in Nairobi, Kenya, a sub-Saharan African country on the East coast.KNH is a referral and teaching hospital with 80 cardiovascular beds, 8 cardiovascular surgeons and a total in-patient turnover of 80,000 patients per year.The patients are predominantly low to middle class African natives.Ethical approval was obtained from Kenyatta National Hospital-Ethics and Research Committee (KNH-ERC/01/404).Records of African Kenyan patients seen in the hospital over a ten year period from January 1998 to December 2007 with diagnosis of femoral or popliteal aneurysm at discharge or death were examined for presentation, diagnosis, predisposing factors, site, age and gender distribution.Only patients with complete records were included.Those whose records were incomplete or with unconfirmed diagnosis were excluded.The records were divided into those for male and female, and each gender divided into eight age groups, namely 0-10; 11-20, 21-30; 31-40; 41-50; 51-60; 61-70; ≥ 71 years.
The aneurysms were divided into popliteal, common, superficial and deep femoral.Data were analyzed using SPSS 13.0 (IBM, Chicago) and presented using frequency tables.

Discussion
In most series from Western countries with predominantly Caucasian populations, femoro-popliteal aneurysms comprise 70-85% of peripheral aneurysms. 1,6Observations of the present study, showing that they constitute only 34.4%, suggest that peripheral aneurysms in the studied population are more widespread.Distribution of peripheral aneurysms varies with ethnicity, 3 age and etiology. 6,7The involvement of diverse arteries implied in this study suggests a unique profile of risk factors in the population.

Site distribution
There are few studies on combined femoral and popliteal artery aneurysms. 1,6Most studies, mainly case reports, are on either artery separately. 2,8This has rendered comparison difficult.Nonetheless, the popliteal artery is reported to be the most common site of extra-aortic aneurysms in predominantly Caucasian populations. 1,6,8,9Observations of the present study reveal, at variance with this conventional view, that popliteal artery aneurysms account for only just over 10% of peripheral aneurysms.This implies interpopulation variations in the prevalence of these aneurysms, probably dependent on a combination of environmental and genetic factors. 8,10,11In the present study, like in the Japanese one, 12 femoral artery was more affected than the popliteal, further supporting the suggestion that the localization of femoro-popliteal aneurysms varies between populations. 6,7emoral artery aneurysms are rare but usually rated second to popliteal ones. 2,9,10,13Of these, the common femoral artery is the most frequently affected segment, predominantly due to stress and kinking resulting from repeated hip flexion. 1 The rarity of superficial femoral artery aneurysms is attributed to the muscle support and minimal bending stress enjoyed by this artery. 13Observations of the present study that the superficial femoral artery is more affected than the common femoral suggest that other etiological factors are involved.Other studies reported that most femoral artery aneurysms are pseudoaneurysms caused by trauma, catheterization, intravenous injection of drugs, anastomotic leakage or infection. 5,13,14Indeed the superficial femoral artery is a frequent site of vascular injury. 15Accordingly, it is likely that the predominance of superficial femoral artery in the present study is due to the high frequency of trauma observed, and that most of them are pseudoaneurysms.Pertinent to this suggestion is the observation that pulsatile mass and pain, usually ascribed to pseudoaneurysms, 16 were the predominant presenting features.

Risk factor and comorbidities
Most studies reported true and false aneurysms separately, complicating comparison of risk factor prevalences.For true femoro-popliteal aneurysms, however, atherosclerosis is the most common risk factor in Caucasian populations. 8,17In the present study, atherosclerosis constituted over 20% of identifiable risk factors.This implies that, as in another African state, 4 this disease is a substantial cause of morbidity in the black Kenyan population.Control of cardiovascular risk factors such as hypertension and smoking observed in the present study may contribute to reducing the incidence of these aneurysms.
Trauma has been implicated in most pseudoaneurysms. 5,14,15Observations of the current study reveal that trauma, notably from femoral fractures, catheterization and surgery was the most frequent risk factor.This implies that due diligence should be exercised in the management of fractures and during catheterization or surgery in the vicinity of the artery to reduce the incidence of pseudoaneurysms.
Other cases of aneurysms may be caused by infections, 7 as observed in the current study.This suggests that in the black Kenyan population non communicable diseases coexist with infectious conditions, supporting reports that Africa is undergoing an epidemiological transition.

Age and gender distribution
Observations of the current study reveal a mean age of 46 years.This is significantly lower than the widely reported age range of 70-80 years. 1,10,18The observations that over 60% of the patients are aged 50 years and below, however, corroborate Kitchen's view that among Africans, aneurysms occur in younger people 3 and are also concordant with the observation that most of the cases in this study are non-atherosclerotic, being associated more with trauma and, in a few cases, infections.Indeed atherosclerotic aneurysms occur in older people while traumatic and genetic ones occur in younger individuals. 8,19The male predominance observed in the present study is concordant with previous reports. 1,18This supports the widely held view that female hormones may confer a protective role against aneurysms.A pertinent observation of the present study is that the majority of superficial femoral artery aneurysms occur in younger age groups in whom circulating estrogens may still be high.

Conclusion
Femoro-popliteal aneurysms constitute less than 40% of the peripheral aneurysms and the femoral artery is the commonest site.They occur predominantly in males below 50 years and are associated mainly with trauma, and atherosclerosis.Prevalence, site and age distribution of these aneurysms in the Kenyan population differ from those described in studies of Caucasian populations.

Table 3 -
Gender distribution of femoropopliteal aneurysms