Key words : Early bleeding detection, Imaging modalities, Pediatric liver transplantation, Postoperative hemorrhage

Introduction
Liver transplant (LT) is a complex procedure often associated with postoperative complications, including bleeding events. Early detection of active bleeding is critical for timely intervention and improved patient outcomes. This retrospective observational study aimed to assess the efficacy of 384-slice computed tomography (CT) angiography (CTA) for detection of early postoperative active bleeding events after LT.

Materials and Methods
A retrospective analysis was conducted on data collected from 53 liver transplant recipients from February 1, 2022, to December 26, 2023. Of these patients, 35 had an age range of 7 months to 18 years. All patients underwent 384-slice CTA (Siemens SOMATOM Force Dual Source CT). Arterial, venous, and delayed phases with 0.5-mm slice thickness were obtained. The CT scans were performed for patients with symptoms suggesting bleeding. The contrast material dose was adjusted according to the patient’s weight. The injection rate of contrast material varied between 0.7 and 2 mL/s.

Results
Among our patient group, 34.2% of the all patients experienced bleeding and 28.57% presented with active bleeding complications. In addition, 3.77% of patients had repetitive bleeding events, with 1 patient experiencing 3 episodes and another patient experienced 2 episodes. All bleeding events originated from the perihepatic region near the site of anastomosis, predominantly arterial (97.22%) and only 1 venous (2.78%). The time intervals between the day of surgery and the onset of active bleeding ranged from day 1 to day 14, with a mean time interval of 5.83 days. All patients with active bleeding underwent either conventional angiography or exploratory laparotomy for hemostasis. The site of bleeding was confirmed in all cases. The sensitivity, specificity, and positive predictive value of 384-slice CTA for detection of early postoperative active bleeding were 100%, which indicates that the imaging modality accurately identified all instances of active bleeding and thereby provided a reliable means for prompt intervention.

Multiphase CT in a 7-year-old male patent with postoperative bleeding after living donor LT showed a focal contrast extravasation around the posterior part of the liver graft observed on the arterial phase and more prominently observed in the focal pattern of contrast extravasation on the portal venous phase (Figure 1). Clinical hemostasis was successfully achieved by surgical management.

Multiphase CT in a pediatric patient with auxiliary LT with postoperative bleeding showed hematoma in the lateral aspect of the graft, focal contrast extravasation (type I) from the liver resection site on the arterial phase, and jet-like, contrast media extravasation (type II) on the portal venous phase (Figure 2). The conservative management for clinical hemostasis was primarily attempted with transfusion of 8 units of packed red blood cells, but the patient showed signs of continuous bleeding after 8 hours of active conservative management. Eventually, bleeding control was achieved by surgical hemostasis. A digital subtraction angiogram obtained with selective catheterization and 1 hour of multidetector CT revealed extravasation and extraparenchymal accumulation of extravasated contrast material (Figure 3).

Discussion
Acute postoperative bleeding following LT is a frequent complication and often stems from various aspects of the surgical process, including donor liver procurement, recipient hepatectomy, and vascular anastomosis.¹ In the donor liver procurement procedure, inadequate surgical hemostasis at the cut surface of the partial liver graft, the gallbladder bed, the detachment site of the liver capsule, and undetected small veins draining into the vena cava can serve as potential sources of postoperative bleeding. During recipient hepatectomy, severe adhesions between the diseased liver and the posterior abdominal wall can result in injury to organs or vessels within the peritoneal cavity, such as the adrenal gland, right inferior phrenic, or suprarenal artery, due to rigorous traction and dissection. This can lead to recurrent postoperative bleeding. Additionally, postoperative bleeding may stem from various vascular anastomoses, particularly in patients with compromised initial graft function and inadequate synthesis of coagulation factors.² However, clinical presentation alone often lacks specificity and does not pinpoint the bleeding source, making treatment decisions challenging.

Multiphase CT imaging offers a solution by revealing active contrast extravasation, indicating the site and extent of bleeding, and thus guiding treatment decisions more accurately. Multiphase CT also extends the time frame to observe hemodynamic changes and to track bleeding progression in a single procedure. Katyal and colleagues conducted a study from July 1999 to January 2000, which included 18 patients (16 men and 2 women) with an age range of 35 to 73 years (mean age 61 years). This study demonstrated that CTA of the liver could be a practical noninvasive method for detection of hepatic arterial complications after LT.³

Byun and colleagues explored the role of multiphase CT in patients who experienced acute postoperative bleeding after LT. Their study was a retrospective analysis of multiphase CT images from 270 patients who had undergone LT and subsequently experienced postoperative bleeding from November 2013 to December 2017. Their evaluation with multiphase CT included assessment of contrast extravasation volume, rate, and patterns (focal or stipple vs jet). This analysis proved beneficial for evaluation of the necessity for therapeutic intervention and for determination of the preferred treatment approach for recipients who experience post-LT bleeding.⁴

Many studies have investigated the diagnostic efficacy of CTA for assessment of acute gastrointestinal bleeding. For example, in a prospective study by Martí and colleagues, CTA was conducted in 47 patients with acute lower gastrointestinal bleeding. The study revealed a sensitivity of 100%, specificity of 96%, and accuracy of 93%. To our knowledge, there is a lack of specific studies on the efficacy of CTA for detection of active bleeding events in the pediatric population.⁵

In our study, we categorized the morphologic patterns of active contrast extravasation into focal or stippled types and jet-like types. The contrast extravasation pattern, especially during the portal venous phase, is important for determination of the therapeutic approach.

Furthermore, we observed a significant relationship between the change in the morphologic pattern of contrast extravasation from type I to type II and conservative management failure, which suggests a potential indicator of bleeding dynamics. Specifically, the jet-like extravasation pattern, particularly developed from focal extravasation, may signal faster bleeding progression and indicate the need for active therapeutic intervention. Among the bleeding sites identified by surgery or angiography in patients, bleeding originating from peri-anastomosis was the most common. Despite these insights, our study had limitations. This was a retrospective study from a single institution, and as such it may be subject to selection bias.

Conclusions
The advanced capabilities of 384-slice CTA, including high resolution, noninvasiveness, high sensitivity, specificity, and positive predictive value, advocate for the seamless integration of this tool into routine postoperative surveillance protocols. This incorporation significantly enhances the timely identification and localization of bleeding sites, leading to improved patient outcomes.

References:

1. Nemes B, Gámán G, Doros A. Biliary complications after liver transplantation. Expert Rev Gastroenterol Hepatol. 2015;9(4):447-466. doi:10.1586/17474124.2015.967761
   CrossRef - PubMed
   
2. Nijkamp DM, Slooff MJH, van der Hilst CS, et al. Surgical injuries of postmortem donor livers: Incidence and impact on outcome after adult liver transplantation. Liver Transpl. 2006;12(9):1365-1370. doi:10.1002/LT.20809
   CrossRef - PubMed
   
3. Katyal S, Oliver JH, Buck DG, Federle MP. Detection of vascular complications after liver transplantation: early experience in multislice CT angiography with volume rendering. AJR Am J Roentgenol. 2000;175(6):1735-1739. doi:10.2214/ajr.175.6.1751735
   CrossRef - PubMed
   
4. Byun J, Kim KW, Lee J, et al. The role of multiphase CT in patients with acute postoperative bleeding after liver transplantation. Abdom Radiol (NY). 2020;45(1):141-152. doi:10.1007/S00261-019-02347-Y
   CrossRef - PubMed
   
5. Martí M, Artigas JM, Garzón G, Álvarez-Sala R, Soto JA. Acute lower intestinal bleeding: feasibility and diagnostic performance of CT angiography. Radiology. 2012;262(1):109-116. doi:10.1148/radiol.11110326
   CrossRef - PubMed