Multimodal ultrasound evaluation of an infectious internal iliac artery pseudoaneurysm complicating perforated infantile appendicitis: a case description

Introduction

Acute appendicitis is the most common pediatric surgical emergency; however, it is exceedingly rare in infancy, with an estimated incidence of only 1–2 cases per 10,000 children aged 0–4 years (1). Despite its rarity, appendicitis in this age group has a risk of perforation exceeding 80%, largely due to its nonspecific clinical manifestations and delayed diagnosis (2).

Vascular complications secondary to appendicitis are exceptionally rare and are predominantly reported in adults (3,4). Recently, the clinical course and computed tomography angiography (CTA) findings of a 7-month-old infant with perforated appendicitis complicated by an infectious pseudoaneurysm of the right internal iliac artery were briefly reported in a cardiovascular imaging vignette (5). However, the ultrasound features of this rare complication, including grayscale findings, Doppler hemodynamic characteristics, and the diagnostic pathway leading to its recognition, have not been described. Therefore, the present report focuses on the multimodal ultrasound evaluation of this case and highlights the potential role of ultrasound in the early detection of occult vascular complications associated with infantile appendicitis.

Case presentation

A 7-month-old boy presented with a 9-day history of persistent fever (peak 40.1 ℃) and a 1-day history of hematochezia. Initial evaluation at an outside hospital revealed leukopenia (2.90×10⁹/L) and markedly elevated high-sensitivity C-reactive protein (CRP; 95.01 mg/L). Cerebrospinal fluid examination and an initial abdominal ultrasound were unremarkable, and the fever persisted despite empirical antimicrobial therapy.

One day prior to admission, the patient experienced repeated episodes of hematochezia, with clots accompanied by pallor and lethargy. On admission, he appeared critically ill with tachycardia (172 beats/min). His blood pressure was 85/53 mmHg. Physical examination revealed an acutely ill infant with a Glasgow Coma Scale score of 7 (E2M4V1). The abdomen was soft and non-distended without signs of peritonitis, including guarding, rebound tenderness, or rigidity. The extremities were pale and slightly cool, with a capillary refill time of less than 2 seconds. Laboratory tests demonstrated leukocytosis (16.4×10⁹/L), severe anemia (hemoglobin 58 g/L), and coagulopathy.

Ultrasound played a pivotal role in the initial diagnosis. Grayscale ultrasound identified an abnormal sac-like structure measuring approximately 1.8 cm × 1.5 cm adjacent to the right internal iliac artery, surrounded by an abscess with adjacent bowel wall thickening. Further magnified grayscale interrogation revealed a focal 2-mm defect communicating between the sac and the parent artery. Subsequent targeted color Doppler evaluation demonstrated turbulent arterial flow and arterial spectral waveforms within the sac, findings highly suggestive of a pseudoaneurysm (Figure 1). CTA was subsequently performed for anatomical characterization and surgical planning, demonstrating a pseudoaneurysm arising from the proximal right internal iliac artery within a gas- containing pelvic abscess measuring approximately 4.0 cm × 3.1 cm. Collectively, the imaging findings suggested perforated appendicitis complicated by an infectious pseudoaneurysm.

Figure 1 Bedside grayscale and color Doppler ultrasound findings. (A) Grayscale ultrasound showed an anechoic mass (red arrows) measuring 1.8 cm × 1.5 cm adjacent to the right internal iliac artery (blue arrows), surrounded by a hypoechoic area (yellow arrows), representing an abscess with an adjacent thickened, ill-defined bowel wall. (B) Grayscale ultrasound revealed a pseudoaneurysm (red arrows) arising from the right internal iliac artery (blue arrows) and communicating with the parent artery through a 2-mm defect (green arrow). (C,D) Color Doppler imaging demonstrated turbulent intralesional flow with an arterial pulsatile pattern in the pseudoaneurysm (red arrows: pseudoaneurysm; blue arrows: right internal iliac artery).

Given the presence of ongoing gastrointestinal hemorrhage, severe anemia, coagulopathy, and a pseudoaneurysm within a pelvic abscess, emergency laparotomy was performed immediately following imaging evaluation. Surgery confirmed perforated suppurative appendicitis with inflammatory involvement of the right internal iliac artery and pseudoaneurysm formation. Pseudoaneurysm resection, right internal iliac artery ligation, and appendectomy were successfully performed. Histopathology examination demonstrated suppurative appendicitis and inflammatory destruction of the arterial wall (Figure 2). The patient recovered uneventfully and was discharged one week later.

Figure 2 Histopathological findings. (A) Hematoxylin-eosin staining demonstrated transmural suppurative inflammation of the appendix extending from the mucosa to the serosa, with dense inflammatory cell infiltration (red arrows). (B) The wall of the right internal iliac artery showed necrosis of fibrous and smooth muscle components with marked acute and chronic inflammatory cell infiltration (red arrows; hematoxylin-eosin staining). Scale bars, 100 µm (large image) and 30 µm (small image).

All procedures in this study were performed in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patient’s guardian for the publication of this article and the accompanying images. A copy of the written consent form is available for review by the editorial office of this journal.

Discussion

Vascular complications associated with appendicitis are exceedingly rare. Most reported cases occur in adults and typically involve the iliac, femoral, or visceral arteries (3,6). Pediatric cases are extremely rare and have largely been described in older children (7). Infection-related pseudoaneurysms are believed to result from direct bacterial invasion and inflammatory degradation of the arterial wall, mediated by cytokines and matrix metalloproteinases, ultimately leading to focal arterial rupture and pseudoaneurysm formation (3). In the present case, operative and histopathological findings supported a mechanism of contiguous infectious erosion from the adjacent pelvic abscess, resulting in inflammatory destruction of the arterial wall and subsequent pseudoaneurysm formation.

The 9-day interval from symptom onset to hemorrhage highlights the insidious course of infantile appendicitis. Laboratory findings are often nonspecific: leukocytosis has a reported sensitivity of only ~18% within 24 hours, and CRP cannot reliably distinguish appendicitis from other abdominal pathologies (1,8). In this case, initial leukopenia and a non-diagnostic ultrasound contributed to delayed diagnosis. The clinical presentation was further confounded by the absence of localizing signs on physical examination. The pseudoaneurysm was not palpable on physical examination, likely due to its deep pelvic location, small size, and encasement within the pelvic abscess. These diagnostic challenges underscore the critical role of imaging in recognizing both occult appendicitis and its uncommon complications.

The clinical course, CTA findings, and surgical management of this patient were recently reported in a brief cardiovascular imaging report by Wang et al. (5). The present report is intended to complement that publication by focusing on the ultrasound perspective, including the grayscale morphology, Doppler hemodynamic characteristics, and diagnostic workflow that led to recognition of the pseudoaneurysm prior to CTA. These sonographic findings were not described in the previous publication and may provide practical diagnostic clues for sonographers and pediatric imaging specialists encountering similar presentations.

Ultrasound remains the first-line imaging modality for infants with suspected abdominal pathology; however, appendiceal non-visualization is common because of anatomical and physiological factors. Consequently, indirect findings often serve as more reliable indicators of appendicitis than direct visualization of an enlarged appendix, particularly the presence of a right lower quadrant abscess (9). In the present case, grayscale ultrasound not only detected the associated inflammatory collection but also identified a vascular sac communicating with the right internal iliac artery, while Doppler interrogation demonstrated turbulent arterial flow characteristic of a pseudoaneurysm. These findings prompted further vascular evaluation with CTA and ultimately guided timely surgical management. This case illustrates how a stepwise imaging strategy, beginning with conventional ultrasound and escalating to Doppler and CTA when indicated, can facilitate recognition of rare vascular complications while supporting appropriate imaging utilization.

Open surgical management was required due to active infection, the risk of pseudoaneurysm rupture, and the technical limitations of endovascular therapy in a 7-month-old infant. Although internal iliac artery ligation is generally well tolerated because of pelvic collateral circulation, ischemic complications have been reported (10); thus, longitudinal follow-up is warranted.

The combination of fever and hematochezia in infants is nonspecific and may mimic several conditions. Intussusception is a common cause of gastrointestinal bleeding in this age group and typically exhibits the classic “target sign” on ultrasound. Necrotizing enterocolitis may also present with hematochezia, particularly in critically ill infants, and is characterized by pneumatosis intestinalis or portal venous gas on imaging. Meckel’s diverticulum represents another important cause of lower gastrointestinal bleeding, although bleeding is usually painless and not associated with systemic sepsis. Further, severe sepsis may independently precipitate gastrointestinal hemorrhage through systemic coagulopathy and ischemia-induced disruption of the intestinal mucosal barrier (11). In the present case, the identification of a pelvic abscess adjacent to the right internal iliac artery, together with a vascular sac demonstrating arterial flow, directed attention toward an infectious pseudoaneurysm secondary to perforated appendicitis. No direct arterial-enteric communication was observed intraoperatively. The hematochezia was therefore most likely multifactorial, resulting from a combination of local inflammatory injury to the bowel wall adjacent to the abscess, sepsis-related coagulopathy, and microcirculatory dysfunction leading to mucosal barrier disruption.

This case highlights several clinical implications. In infants with persistent fever and nonspecific abdominal symptoms, early imaging evaluation is essential, as clinical and laboratory findings may be misleading. When the appendix is not clearly visualized, meticulous sonographic interrogation of the right lower quadrant, with attention to indirect signs such as peri-appendiceal or pelvic collections and other complication-related findings, is critical for identifying occult appendiceal disease. In the setting of sepsis or unexplained gastrointestinal bleeding, occult appendiceal or other intra-abdominal pathology should remain in the differential diagnosis. Moreover, recognition of unusual vascular findings on ultrasound, including perivascular sac-like structures with arterial flow, may facilitate early detection of rare infectious vascular complications. Given the potential for rapid clinical deterioration, a stepwise imaging strategy coupled with timely multidisciplinary management may facilitate the early recognition of severe complications and improve outcomes.

Conclusions

In infants presenting with persistent fever, sepsis, or unexplained gastrointestinal bleeding, careful evaluation of the appendiceal region and heightened awareness of indirect sonographic signs and complication-related findings are essential for detecting occult appendiceal disease and its associated complications. A rational stepwise imaging strategy, beginning with ultrasound and escalating to Doppler evaluation and CTA when indicated, can facilitate timely diagnosis and guide appropriate management.

Acknowledgments

We extend our gratitude to Wei Jiang from the Department of Pathology, West China Second University Hospital, Sichuan University, for invaluable assistance in pathological diagnosis. We also thank the Department of Pathology at West China Second University Hospital, Sichuan University, for providing the pathological images used in this study.

Footnote

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-2026-0537/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patient’s guardian for the publication of this article and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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