Traumatic Splenic Artery Pseudoaneurysm Managed With Percutaneous Histoacryl (N-butyl-2-cyanoacrylate) Embolization: An Alternative to the Conventional Transcatheter Approach

Introduction

Splenic injury is one of the most frequent solid organ injuries encountered in the setting of blunt trauma [1]. Associated vascular injuries are not uncommonly seen; these are reportedly present in up to 1 in 5 patients with splenic injuries [2]. In the context of splenic injury, a recent longitudinal study by Koskinen et al found the incidence of early contained vascular injury, defined to include pseudoaneurysms and arterio-venous fistulae, to be 8.3% [3]. Splenic artery pseudoaneurysms (SAPs) are best diagnosed with computed tomography (CT) or ultrasound [4] In patients diagnosed with traumatic SAP, guidelines from the World Society of Emergency Surgery suggest consideration of angiography and embolization if the patient is hemodynamically stable [5].

Active management of traumatic SAP is necessary due to the substantial risk of spontaneous rupture if left untreated [6]. Spleen-preserving embolization is preferred if feasible, over the undesirable alternative of surgical repair, which entails higher morbidity and mortality rates [7].

Embolization of pseudoaneurysms via a transcatheter approach is not always possible. For example, transcatheter embolization may be hindered by splenic artery tortuosity, preventing cannulation [8]. Narrow-necked pseudoaneurysms may be intermittently perfused and hence non-visualized during catheter angiography [9], precluding precise cannulation and embolization. In such cases, a transabdominal percutaneous approach may be considered; this entails accessing the pseudoaneurysm directly with a needle under ultrasound guidance, followed by injection of the embolic agent [10].

Current literature on the efficacy and safety of such an approach is sparse, with available literature on such limited to a few case reports. For example, Foo et al employed an ultrasound-guided percutaneous approach in embolizing multiple traumatic SAPs in a single patient with injection of thrombin [11]. Alternatively, a recent publication by Almasri et al demonstrated the safe use of Glubran2 cyanoacrylate glue in direct percutaneous embolization of idiopathic SAP [12].

The present report describes the case of a 10-year-old boy with traumatic splenic artery pseudoaneurysm managed with percutaneous histoacryl (N-butyl-2-cyanoacrylate) embolization after an unsuccessful attempt via the conventional transcatheter approach. As current literature on the efficacy and safety of such an approach remains limited, we aim to illustrate that such a technique is a viable alternative. A successful outcome can be accomplished by taking into consideration imaging clues, technical steps (modality of guidance, needle approach, choice of embolic), and strategies to minimize complications.

Case Report

Our patient was a previously healthy 10-year-old boy who was brought to the hospital following a fall from a 1.5-meter high platform at a playground. He had landed on the ground with impact on the left side of his face and abdomen. Thereafter, he was conveyed to the hospital due to persistent vomiting and complaint of left-sided abdominal pain.

Upon arrival at the Children’s Emergency Room, he was found to be hemodynamically stable but with tenderness over the left upper and lower abdominal quadrants. A bedside point-of-care ultrasound showed intra-abdominal free fluid, and he was urgently admitted to the surgical department. Analgesics and antiemetics were given, and he was kept nil per os on his first day of stay. He subsequently reported resolution of pain and vomiting the next morning.

Formal ultrasound of the abdomen performed after admission revealed an avascular cystic structure in the inferior pole of the spleen (Figure 1A) with slight heterogeneous echogenicity of the surrounding splenic parenchyma. There was trace perihepatic and perisplenic fluid with additional findings of a moderate volume of free fluid in his pelvis. This pelvic free fluid contained extensive internal echoes in the dependent aspect (Figure 1B). Overall findings were compatible with splenic laceration with hemoperitoneum, given the clinical context of trauma.

Recommendations for further evaluation with contrast-enhanced CT were declined by the patient’s parents as the child had good relief of symptoms and stable vitals. Consensus was made for close outpatient follow-up with interval ultrasound.

Repeat ultrasound of the abdomen performed 2 weeks later demonstrated 2 focal splenic abnormalities. An irregular hypoechoic focus corresponding to the known splenic laceration was seen (Figure 2A) – it remained stable in size. There was a well-defined structure with heterogeneous echogenicity, adjacent to the laceration and in close proximity to the splenic hilum (Figure 2A). On color doppler interrogation, there was arterial flow in its posterior aspect and pulsatile waveform in the central region (Figure 2B). Overall findings were worrisome for a pseudoaneurysm associated with splenic laceration.

The patient was urgently recalled for contrast enhanced CT of the abdomen and pelvis. This was performed in the late arterial and portal venous phases using a split-contrast bolus technique. The late arterial images revealed a nodular enhancing focus within the splenic laceration which appeared to be supplied by a branch arising from the splenic artery (Figure 3). Delayed-phase imaging showed reduced attenuation of this nodular focus with attenuation similar to blood pooling. Overall findings were suggestive of a splenic pseudoaneurysm.

The imaging findings and the potential risk of spontaneous pseudoaneurysm rupture resulting in massive hemorrhage were explained to the patient’s parents, and they were counselled on treatment options. They decided on angioembolization of the splenic artery pseudoaneurysm. Informed written consent was obtained.

The embolization procedure was performed with the patient under general anesthesia. Ultrasound-guided access was obtained via the right common femoral artery. A 4 French angiographic catheter and 0.035-inch hydrophilic guidewire were used to cannulate the splenic artery under fluoroscopy guidance. The pseudoaneurysm of concern was not unequivocally visualized on digital subtraction angiography (DSA) in various obliquities (Figure 4). Coaxial advancement of a microcatheter into the distal splenic artery to obtain more selective DSAs also did not delineate the pseudoaneurysm.

The pseudoaneurysm was confidently identified on our on-table ultrasound, on both grey scale and color doppler imaging. A safe needle trajectory could be marked out; hence, the decision was made to access the pseudoaneurysm percutaneously. It was targeted with a 21-gauge needle (AccuStick; Boston Scientific, Marlborough, United States) under ultrasound visualization (Figure 5A). Back bleed was observed upon removal of the needle stylet. DSA was done to confirm and characterize the pseudoaneurysm origin (Figure 5B) in relation to the supplying splenic artery and other collateral branches, neck location and size, and flow dynamics. After ascertaining that there was no contrast flow into crucial nontarget vessels, histoacryl (B Braun, Melsungen, Germany) was diluted with lipiodol (Guerbet, Paris, France) to a 33% concentration, and instilled into the pseudoaneurysm under continuous fluoroscopy. This mixture was also injected along the needle track during needle withdrawal to achieve track embolization.

Post-embolization cone-beam CT showed satisfactory glue cast within the pseudoaneurysm sac, albeit with inadvertent glue cast in the splenic vein as well (Figure 5C). As the latter was small and flat in morphology relative to the vessel lumen, it was likely non-occlusive, and the decision was made for conservative management. Post-procedure recovery was uneventful, save for mild tenderness in the left upper abdominal quadrant. He was discharged in good health on the evening of the procedure.

Follow-up ultrasound was performed 1 week later. There was interval stability of the size of the pseudoaneurysm and resolution of color doppler flow within it, confirming stable thrombosis. Echogenic content within the pseudoaneurysm was in keeping with glue cast and thrombus formation. The splenic volume and parenchymal vascularity were preserved. The splenic vein was patent on color doppler (Figure 6). The patient remained asymptomatic at the subsequent 6-month clinic review. Interval repeat ultrasound showed that the splenic pseudoaneurysm remained completely thrombosed.

Discussion

Our case demonstrates that direct percutaneous access with histoacryl injection is a viable technique for traumatic SAP embolization when selective transcatheter access is not feasible. While there is some evidence suggesting that children may not benefit from angioembolization due to the relative frequency of spontaneous thrombosis [5], we opted to proceed with embolization due to persistence of the pseudoaneurysm on both ultrasound and CT at 2 weeks post-injury.

An endovascular approach is typically adopted for embolization of visceral pseudoaneurysms. In our case, angiography did not reveal the pseudoaneurysm, preventing selective cannulation. Current literature is inconclusive on the safety of proximal splenic artery embolization in such situations [5,13]. As the pseudoaneurysm was readily visualized on ultrasound, we decided to attempt percutaneous access and embolization. DSA after successful access of the pseudoaneurysm did not show brisk antegrade flow into any crucial vascular structure, hence a liquid embolic like histoacryl was considered. In addition, when diluted with lipiodol, its radio-opacity allows for real time fluoroscopic visualization to guide injection. The embolization procedure was technically successful and the post-procedural recovery uneventful.

A recent systematic review of splenic artery pseudoaneurysm embolization by Alomar et al revealed a low failure rate at 5.3%, with relatively low rates of major complications, including rebleeding (4.8%), infarction (4.6%), and abscess formation (4.0%) [14]. However, the majority of these studies focused on embolization performed via a transcatheter approach. While a few papers suggest a percutaneous approach as a viable alternative [10,15], to our knowledge, there is scarcity of information regarding the success and complication rates of this approach. For example, while Giurazza et al showed in a multicenter review that the percutaneous approach to pseudoaneurysm embolization is safe and effective in a range of arteries in the thorax, abdomen, and limbs, the studied patient population had a wide heterogeneous range of involved arteries, with splenic arteries forming only 2 out of 54 cases included [16]. Other available literature comprises a small number of case reports, eg, by Huang et al [8] and Krueger et al [17]. While the patient in the former case report was found on imaging to have possible splenic infarcts 4 months post-procedure, the patients in both case reports remained asymptomatic, with subsequent imaging showing resolution of their respective pseudoaneurysms. Similar successes were reported when this technique was employed in pseudoaneurysms arising from other intra-abdominal visceral arteries, eg, pancreaticoduodenal artery [18], a branch of a segmental renal artery [19], and the internal iliac artery [20].

Even less is known about the specific safety consideration of children undergoing embolization of splenic artery pseudoaneurysms. This is despite the importance of splenic preservation, given its immune function against life-threatening infections (eg, pneumococcal, meningococcal) which children are particularly vulnerable to [21]. Similar to reported studies on adult patients, current literature on pseudoaneurysm embolization amongst children is largely focused on embolizations performed via conventional transcatheter approaches [22,23]. We opted for a liquid embolic, histoacryl, with the aim of treating the inflow-supplying vessel of the pseudoaneurysm, in turn securing better hemostasis. Our patient had a non-occlusive glue cast extending into the splenic vein on post-embolization scan which suggests inadvertent embolization into a fistulous venous communication.

This is a known risk of liquid embolics, but one which is usually asymptomatic and inconsequential, with no prolongation of recovery [7,16]. However, this underlines the importance of scrutinizing the pre-embolization angiograms for proximity to and communications with crucial vessels. In the present case, we did not detect any arteriovenous fistula on either planning scans or angiograms.

There is also a shortage of literature regarding the efficacy of histoacryl in angioembolization of pseudoaneurysms. Thrombin was used in the previously mentioned case report by Foo et al [11]; this was found to have higher recanalization rates, thromboembolic complications, and allergic reactions [24], compared with N-butyl-2-cyanocacrylate (NBCA), of which histoacryl is a type. It is also thought that NBCA, being more viscous and having a short polymerization time [25], comes with reduced risk of embolization of non-target vessels compared with thrombin [26]. Almasri et al, like us, performed a percutaneous SAP embolization using Glubran2, which is NBCA combined with metacryloxysulpholane. This is said to produce a more pliable polymer with a milder exothermic reaction, and less inflammation and histotoxicity [27]. In our case, histoacryl proved successful in achieving SAP embolization with subsequent uneventful clinical recovery. Further research regarding the safety of histoacryl injection in such situations would be valuable for future practice.

While NBCA has been an available option for years [15], there are several challenges associated with the use of this liquid embolic. Firstly, NBCA rapidly polymerizes upon contact with plasma, necessitating brisk administration in a single push rather than repeated intermittent boluses to avoid catheter blockage or adhesion of the catheter to the vessel wall due to glue cast formation [25]. Additionally, imprecise control or overly forceful injection of liquid embolic materials risks non-target embolization [15]. While there are novel embolic agents being developed to address such shortfalls, eg, poly(propylene glycol) diacrylate with pentaerythritol tetrakis (3-mercaptopropionate) (PPODA-QT), which has a more adjustable and predictable polymerization rate vis-à-vis histoacryl, current trials are largely limited to animal models [25].

To mitigate nontarget embolization, we opted for a low dilution histoacryl/lipiodol solution, which polymerizes more rapidly and forms a cast more proximally to the injection site [28]. The injection of embolic should also be monitored in real time under fluoroscopy.

As embolization of traumatic splenic pseudoaneurysms remains relatively uncommon, further evidence on its efficacy and risks will be helpful in tackling visceral pseudoaneurysms.

Conclusions

Traumatic SAP, albeit uncommon, should be promptly recognized and treated due to the substantial risk of hemorrhage. Our case demonstrates that direct percutaneous embolization can achieve rapid, effective exclusion of traumatic splenic pseudoaneurysm with preservation of splenic function, particularly when selective transcatheter access is not feasible.