Introduction
Pseudoaneurysms are caused by some forms of arterial injury, which include perivascular inflammatory reactions or infections, direct vascular trauma or iatrogenic factors (1,2). With the advancement of complex surgical operations, iatrogenic pseudoaneurysms are relatively commonly encountered in clinical practice. Patients may present with sentinel bleeding or delayed hemorrhage, which may be easily overlooked (3). These pseudoaneurysms, with the lack of complete vascular wall structure, gradually increase in size and are under a growing strain with the continuous impact of blood flow, eventually resulting in burst and sudden bleeding.
The overall incidence of pseudoaneurysms following abdominal and pelvic surgery or radiological intervention is relatively low (4,5). If appropriate treatment is not undertaken in a timely fashion, pseudoaneurysm may be associated with high morbidity and mortality. Visceral artery pseudoaneurysms (VAPA) refer to pseudoaneurysms occurring in the celiac artery, superior mesenteric artery, or inferior mesenteric artery and their branches. VAPA may manifest as gastrointestinal hemorrhage (hematemesis, hematochezia) or abdominal hemorrhage (hematoma, abdominal hematoma), which is frequently evident as continuous hemorrhagic fluid from the abdominal drainage tube. A pseudoaneurysm from the pelvic internal iliac artery may also manifest as abdominal and pelvic hemorrhage or hematoma. A pseudoaneurysm may be particularly life-threatening among patients with thrombocytopenia or consumptive coagulopathy and therefore, these patients require rapid clinical evaluation and treatment (6,7).
Ultrasound with doppler and contrast-enhanced techniques are commonly used as an initial screening tool for pseudoaneurysm (8). However, CT angiography (CTA) and digital subtraction angiography (DSA), are the formal diagnostic tools for pseudoaneurysm (9). On CTA, a pseudoaneurysm may be seen as a bubble-shaped (saccular), irregular nodule budding from the lateral wall of the artery. DSA may not only clearly show the location, size and shape of the pseudoaneurysm but also its relationship with the parent artery (10,11). Pseudoaneurysms are conventionally managed by surgery, including surgical ligation, aneurysm resection and even the removal of affected organs. More recently, endovascular embolization has gradually become the preferred option of treatment instead of surgery, given that it may be rapidly applied to hemodynamically unstable patients while avoiding major surgical trauma, particularly among patients with extensive comorbidities. Several studies have also indicated high success and low recurrence rates of pseudoaneurysm treated by endovascular embolization, justifying the expansion of its applications in clinical practice (12-14).
The present study provided a retrospective review, reporting on the practice and experience of endovascular embolization at the Affiliated Hospital of North Sichuan Medical College (Nanchong, China). The clinical effectiveness and safety of this treatment for secondary pseudoaneurysm following abdominal and pelvic surgery or radiological percutaneous abdominal procedure were investigated.
Discussion
Pseudoaneurysm is usually caused by the disruption of arterial wall continuity. Such a disruption may be secondary to direct injury during an abdominal procedure or surgery or various endovascular treatments, or an indirect injury from post-operative peri-vascular inflammation or infections (18-20), resulting in the formation of pseudoaneurysm. The majority of patients in the present study had received hepatobiliary/gastric surgery. Such predilection may have been due to corrosion of the arteries around the pancreas by the pancreatic juice, causing pseudoaneurysm formation and delayed bleeding (11,21). The use of electrocautery and ultrasonic scalpel in the process of clearing the lymph nodes around the artery and removing its adventitia in addition to clamping of vessels during surgery may also lead to vascular injury and subsequent pseudoaneurysm formation (22). Therefore, it is not surprising that in radical hepatobiliary/gastric surgery, the elevated incidence of surgical complications was correlated with an increase in mortality rate associated with bleeding and pseudoaneurysm (22-25).
The risk of spontaneous rupture of a pseudoaneurysm is high and sentinel bleeding is generally regarded as a precursor of massive hemorrhage (3). Therefore, rapid and accurate diagnosis is crucial, with CTA having a sensitivity and accuracy rate of 95% (26,27). CTA is able to indicate the size and location of the aneurysm and its relationship between the parent artery and neck. One of the patients of the present study had a false-negative result on CTA, and DSA was used in this instance as a diagnostic adjunct to CTA. It also offers the possibility of therapeutic interventional therapy at the same time. During DSA, attention should be paid to the observation angle, flow rate and injection pressure of contrast agents to avoid missing small aneurysms. When necessary, magnification and multi-angle angiography should be performed (26-28).
Acute torrential hemorrhage from pseudoaneurysm may be treated by open surgical exploration/ligation or endovascular embolization (29). The following factors may affect the clinician's choice of different treatment methods: i) the time of bleeding and pseudoaneurysm; ii) comorbidities and complications, such as inflammation and infection; and iii) hemodynamics. Ligation, aneurysm resection and removal of an involved organ are the major methods of surgical treatment. Compared with the open surgical approach, endovascular therapy prevents any potential risk of serious complications caused by re-operation while minimizing further stress to impair the patient's organ function (13,17). Furthermore, the present study suggested that endovascular embolization was highly effective, that there was no further bleeding following the single intervention and no recurrence of pseudoaneurysm was observed in any of the patients.
The endovascular approach to pseudoaneurysm consists of either covered stent implantation or embolization. Endovascular graft exclusion with a covered stent may completely isolate the pseudoaneurysm immediately, prevent the rupture and bleeding of the pseudoaneurysm and reconstruct the parent artery without affecting the anatomical blood flow (30). This is suitable for pseudoaneurysm that has sentinel hemorrhage without rupture. However, a covered stent is usually not the first choice due to the risk involved and the technical difficulty of stenting in a visceral artery, in addition to the contraction of the parent artery caused by the use of vasoconstrictive drugs. Furthermore, economic and medical insurance factors are also reasons for its limited application. Therefore, endovascular embolization is widely used in clinical practice, including the Affiliated Hospital of North Sichuan Medical College, as reported in the present and previous studies (31-34). For VAPA, due to the anastomosis of digestive arteries and abundant collateral circulation, liquid embolic materials should be carefully selected to prevent the occurrence of missed embolization, and solid embolic agents generally do not cause serious ischemia and necrosis (5). The present study demonstrated that coil embolization is a safe therapy for pseudoaneurysm and no serious complications were encountered.
The selection of embolization techniques is mainly based on the location, size and the neck of the pseudoaneurysm (35). At the Affiliated Hospital of North Sichuan Medical College, if the pseudoaneurysm occurs at the main visceral artery and has a high risk of rupture, two-end embolization (isolation technique) is used, which entails embolization of the proximal and distal parent artery. In general, this technique is associated with less serious complications such as large-area organ necrosis and infection (31), and this was not observed among the patients included in the present study. According to our experience, if the GDA stump has a beak-like shape and the hepatic artery is not damaged, no further treatment is required. However, if the stump exhibits sac-like or bag-like structure, intervention is required to prevent rupture regardless, of its length. If the stump is long, the microcatheter may be inserted into the neck of the sac. In this way, embolization with microcoils does not affect the blood flow of the liver. If the stump is short or irregular, isolation embolization or stent-assisted coil embolization should be performed.
Embolization of VAPA may be technically challenging, as the visceral artery is frequently small in caliber due to the bleeding, decreased systemic blood pressure and the use of vasoconstrictive drugs. This may be improved by hemodynamic stabilization with volume replacement and discontinuation of vasoconstrictive drugs. A large-diameter coil may then be selected for embolization, as small-diameter coils used for embolization may migrate to the efferent artery to cause rebleeding. In the present study, distal coil migration occurred in one case. The present experience conforms to the principle of 120-150, according to which the ratio of the coil diameter to the diameter of the parent artery or pseudoaneurysm should be at least 1.2-1.5, which is similar to the ‘spaghetti technique’ (36).
For technical considerations of VAPA embolization, it may be recommended to construct the coil with a low packing density while ensuring it is stably located in the neck of the pseudoaneurysm. According to certain scholars, a solid embolic agent such as coils may increase the risk of aneurysmal rupture due to the weak sac and damaged arterial wall, so that the sac packing technique should be selected with caution (37), while other studies recommend the sandwich technique or covered stent implantation for pseudoaneurysm secondary to mechanically injured visceral arteries to avoid the potential risk of massive bleeding during the procedure (38,39), particularly among patients with pancreatic fistula after PD. In recent years liquid embolic materials have been used for pseudoaneurysms, but the risk of undesired ectopic embolization is higher than that of a coil. The combined use of the two materials may, however, bring a higher benefit (40,41).
There were certain limitations to the present study. First, it was a retrospective, observational study with no case-control cohort for comparative analysis to determine the true effectiveness and safety of endovascular embolization over the conventional surgical approach. In addition, the sample size was relatively small due to the rarity of VAPA. Of note, the nature of the patient's medical insurance, economical status and the preference of family members are important factors that influence the choice of treatment. Additionally, the majority of patients prefer the conventional approach in China (19,31).
In conclusion, the present study indicated that endovascular embolization is a safe and effective treatment for pseudoaneurysm in the abdomen and pelvis. Several techniques of embolization were presented and discussed. The endovascular approach to VAPA should be considered as a preferred treatment option in most cases.