AAO is an uncommon clinical entity, and most of reports are small series over extended time periods or case reports. However, the general consensus regarding AAO is that the prognosis is devastating due to the high mortality caused by reperfusion injury [5,6,9–11]. Our series is a relatively large series about AAO, and we determined the prognosis and risk factors associated with mortality.
Due to the rarity of AAOs, the diagnosis of AAO is difficult, and this disease entity can easily go unrecognized, which results in prolonged ischemia. In addition, patients with AAOs usually had varying degrees of motor/sensory deficits on presentation. Patients are often referred to a neurologist or neurosurgeon, particularly patients with flaccid paraplegia, even if a physical finding of absent femoral pulses is identified, leading to misdiagnosis and a loss of valuable time. Meagher et al.  reported that 4 of the 8 patients with AAOs were referred for neurologic evaluation at the time of presentation, and Babu et al.  reported a delay of over 10 hours in 29.2% (14/48) of patients who presented with clinical signs other than limb ischemia, such as neurologic deficits, abdominal pain and acute hypertension. These findings are similar to our series, in which 41.7% (10/24) of patients were initially evaluated for neurologic problems at presentation due to varying degrees of motor/sensory deficits.
In our series, the level of aortic occlusion was infrarenal in the majority of patients and only 1 patient presented with suprarenal aortic occlusion below the superior mesenteric artery. However, 20.8% (5/24) of patients presented with complete paraplegia, which is similar to a study by Crawford et al. , in which 27.6% (8/29) of patients with AAOs presented with complete paraplegia. The principle radicular artery is known as the greater radicular artery of Adamkiewicz, and it most commonly arises from the left intercostal artery between T9 and T12 . Occlusion of this artery can result in acute spinal cord infarction. Aortic dissection and reparative vascular surgery are well established causes of spinal cord ischemia. In contrast, there are few reports in the literature concerning paraplegia associated with acute infrarenal aortic occlusion [7,8]. Currently, translational research has developed a collateral network concept, which is a model for understanding and optimizing spinal cord perfusion during and after thoracic aortic surgery . This concept emphasizes the important contribution of collaterals to the net spinal cord blood supply, which includes vascular territories supplied by the intercostal, lumbar, subclavian, and hypogastric arteries. In addition, the abovementioned radicular artery is occasionally discontinuous or stenotic in patients with AAOs due to preexisting atherosclerosis . In these patients, acute paraplegia may occur after acute infrarenal aortic occlusion due to the sudden occlusion of the lumbar collaterals and hypogastric perfusion, which act as major sources of blood supply to the spinal cord. Therefore, AAO may initially present as complete paraplegia, and this may obscure the classic signs of arterial occlusion. Thus, vascular examinations should always be performed in every patient presenting with lower limb neurologic deficits, and treating physicians should be on alert for this entity, particularly in patients with a clinical history of peripheral vascular disease.
Currently, the etiology of AAO is changing, and the frequency of thrombotic AAO has increased over the last few decades. In a report by Dossa et al.  on a 40-year experience of AAOs from 1953 to 1993, the frequency of thrombotic AAOs was 35.0%, and embolic occlusion accounted for 65.0% of cases. However, in accordance with a recent series by Crawford et al.  that evaluated 29 patients, the etiology was aortoiliac thrombosis in 22 cases, embolic occlusion in 2 cases, and indeterminate in 5 cases. The authors concluded that the dominant etiology of AAOs is now thrombotic occlusion. In our series, thrombotic occlusion was considered the primary cause of AAO similar to recent series.
However, the association between the etiology of AAO and postoperative mortality is controversial. In their series, Surowiec et al.  reported that the postoperative mortality of patients with embolic occlusion was higher than that of patients with thrombotic occlusion. Similarly, in a recent series by Crawford et al. , the post-procedural 30-day mortality of a group of patients with a large proportion of thrombotic AAOs was 15.0%; the authors suggested that this may have been the result of improved critical care or the high number of thrombotic occlusions in their series. The reason for lower postoperative mortality in patients with thrombotic AAOs than in those with embolic AAOs may be because these patients have had the advantage of forming collaterals and developing and exuberant collateral system, which may improve their survival by reducing reperfusion injury to the musculature and improving collateral circulation. However, Dossa et al.  reported there was no difference in-hospital mortality between the two groups. Moreover, the in-hospital mortality in our series tended to be higher in patients with thrombotic AAOs than in those with embolic AAOs (43.8% for thrombotic occlusion vs. 14.3% for embolic occlusion; P=0.345), and patients who underwent by bypass surgery demonstrated higher mortality than patients who underwent thromboembolectomy.
According to our series, age, preoperative renal function and combined iliac arterial occlusive disease were associated with in-hospital mortality. After revascularization of an AAO, systemic metabolic consequences, such as myonephropathic syndrome can develop and affect the life and viability of limbs. Muscle cell ischemia and cell death leads to the release of myoglobin, potassium, and lactic acid . Consequently, AKI can occur, and HD becomes necessary. In addition, when renal function is not maintained, the excessive potassium released by the ischemic muscle cannot be cleared, and hyperkalemia becomes an additional problem. Therefore, preoperative renal function is important for the prognosis of patients with AAOs, and as a result, postoperative AKI is also associated with in-hospital mortality, as was found in our series.
Another interesting finding in our series was that combined iliac and femoropopliteal arterial occlusion was surprisingly high. In patients with AAOs, this kind of combined arterial occlusion further impairs the blood supply to lower extremities, and the resultant ischemia can be severe. Although this finding was not statistically significant, the proportion of EIA occlusions in patients with thrombotic AAOs tended to be higher than in those with embolic AAOs (76.0% vs. 43.0%; P=0.122). Furthermore, the frequency of combined femoropopliteal arterial occlusion in patients with thrombotic AAOs was significantly higher than in patients with embolic AAOs (94.0% vs. 43.0%, P=0.003). This combined peripheral arterial occlusion may be a preexisting lesion or a newly developed lesion that occurred concurrently with AAO. However, peripheral arterial occlusion is expected to be more frequent in patients with thrombotic occlusion than in patients with embolic occlusion because of preexisting atherosclerotic disease . In any case, combined arterial occlusion is an additional obstacle to the blood supply to the lower limbs and intensifies ischemic damage and increases reperfusion injury. This finding may be another explanation for the differences in postoperative mortality in patients with AAOs of different etiologies.
The major limitation of this study was its retrospective design. Additionally, the small patient sample size that was monitored over a long period might have resulted in patient selection and treatment bias. Furthermore, although we included all patients with AAOs who were admitted to our department, some patients who presented to the emergency department who were in poor general condition with high comorbidities may have died without treatment because their families refused treatment. This particular limitation prevented us from assessing the exact rate of in-hospital mortality; thus, selection bias might have been present.
In conclusion, AAO is a rare disease that is associated with high mortality. In our series, 42.0% of the patients are mistakenly evaluated for a central nervous system lesion, leading to a delay in diagnosis. Thus, vascular examinations should always be performed in every patient presenting with lower limb neurologic deficits. Age, perioperative renal dysfunction, and combined iliac arterial occlusion were associated with in-hospital mortality. Treating physicians need to pay attention to risk factors and these patients should be managed more closely.