Report on two neonatal cases with iliopsoas abscess, diagnostic and microbiological challenges during ongoing sepsis therapy: A Case Report

Authors

Abstract

Introduction Ilio-psoas abscess (IPA) is a deep-seated infection that is rarely reported in neonates. The underlying condition in most cases remains unknown, a history of prior systemic infection has been identified in only a few cases. The insidious onset and non-specific initial symptoms often lead to delayed diagnosis and an increased demand for surgical intervention.
Case Presentation Here, we present two neonatal cases of iliopsoas abscess with the symptoms of ipsilateral lower limp pain that developed during the treatment of sepsis. In one of the cases, the pathogens responsible for sepsis and IPA were different.
Conclusion IPA can develop concurrently with neonatal sepsis, whether caused by the same or different pathogens. Therefore, in neonates undergoing sepsis treatment who develop lower limb pain and swelling, IPA should also be considered.

Keywords

Introduction

Ilio-psoas abscess (IPA) has been rarely reported in neonates, and its clinical presentation is often insidious, frequently mimicking septic arthritis or osteomyelitis.^1,2 In previously described neonatal cases, IPA has usually presented as an isolated condition and has rarely been reported as part of a systemic infectious process.^1,3,4 Here, we present two neonatal cases of IPA diagnosed based on lower limb findings emerging during ongoing sepsis treatment.

Case Presentation

Case 1A female infant weighing 2170 g was born as a twin by caesarean section at 34 weeks’ gestation to a 25-year-old primigravida. She was referred to our hospital due to prematurity and respiratory distress. Antenatal history was uneventful, with no premature rupture of membranes. On admission, physical examination was unremarkable except for respiratory distress, which improved with non-invasive support over five days. In the absence of perinatal risk factors and with normal laboratory results, including blood culture, empirical antibiotics were not initiated. On day 13, she developed fever and irritability. Evaluation revealed no clear infection focus, except elevated C-reactive protein (CRP, 156 mg/dl). Empirical meropenem and amikacin were started, and vancomycin was added after blood culture grew methicillin-resistant Staphylococcus aureus (MRSA). Meanwhile, decreased movement of the right leg and pain on manipulation were observed. Initial ultrasonography (US) showed no fracture or septic arthritis. Although CRP decreased after two days, mild swelling of the right medial thigh appeared. Repeat US detected fluid collection in the right psoas muscle, and magnetic resonance imaging (MRI) confirmed a 26 × 13 mm cystic collection in the right iliopsoas muscle (Figure 1). US-guided aspiration yielded 1 cc of purulent fluid, which cultured MRSA. A second aspiration was deferred, and antibiotic therapy was continued. Intravenous antibiotics were administered for 28 days, resulting in complete clinical and radiological resolution.
Case 2A male infant weighing 2100 g was born via caesarean section at 38 weeks of gestation, from the second pregnancy of a 26-year-old mother. He was referred to our hospital due to small-for-gestational-age, respiratory distress, and hypoglycemia. Apart from intrauterine growth restriction, the antenatal history was unremarkable, with no premature rupture of membranes or maternal glucose metabolism disorders. However, it was later informed that the mother had developed a surgical wound infection. The infant was started on supplemental oxygen and intravenous glucose infusion, with strict monitoring of blood glucose levels. Empirical antibiotic therapy was not considered at admission, upon being informed about maternal infectious status, serial evaluation for neonatal infection was initiated. The respiratory distress and hypoglycemia were resolved by the fifth day and the second week of life, respectively. On the 12th day of hospitalization, the infant's condition acutely deteriorated due to sepsis caused by Klebsiella pneumoniae, which was sensitive to commonly used antibiotics. Intravenous fluids, catecholamine support, platelet transfusion, and wide-spectrum antibiotics (meropenem and amikacin) were administered. Clinical improvement was observed, with a decrease in CRP levels (from 238 mg/dl to 83 mg/dl), and generalized edema began to resolve. However, on 10 days of the treatment, asymmetrical swelling of the whole left leg was noticed, with mild limitation of hip mobility. The thigh circumference difference between the legs was 2.8 cm, and the values of CRP rose again to 91 mg/dl. Doppler US showed normal arterial and venous blood flow of the left lower extremity, and the hip joint appeared normal on US. Based on the experience from the previous case, targeted US of the ilio-psoas muscle was performed, revealing an abscess formation in the left ilio-psoas muscle, along with several small reactive lymph nodes on the left inguinal and femoral region (Figure 2). The abscess was aspirated percutaneously under US guidance, and MRSA was isolated from the purulent fluid. Vancomycin was added to the ongoing treatment and continued for at least 14 days until complete clinical, biochemical, and radiological resolution was achieved.
Ethical ApprovalThis study did not require ethical approval according to the relevant guidelines.
Reporting GuidelinesThis case report is presented in accordance with the CARE guidelines.

Discussion

Ilio-psoas abscess is rare in infants and young children, and even more uncommon in neonates.¹ It may occur either as a primary or secondary infection. Primary IPA typically results from hematogenous or lymphatic spread of a causative pathogen from a distant site, while secondary IPA arises from direct extension of a nearby inflammatory or infectious process into the muscle compartment.^1,3 Primary IPA is more commonly reported in neonates, whereas secondary IPA constitutes the majority of cases in adults.¹ Despite the predisposing factors leading to abscess formation in the iliopsoas in neonates have not been fully understood, it has been speculated that a hemorrhage within the psoas muscle during birth and a bacteremic episode in the perinatal period may serve as initiating events.^1,3 Intramuscular injections or repeated skin punctures can provide a portal of entry for skin or hospital flora. Two cases presented here had undergone frequent skin punctures, particularly in the lower extremities, for capillary blood gas analysis and blood glucose monitoring. Since S. aureus is a common component of the skin’s resident flora, the disruption of skin integrity may facilitate its spread via hematogenous or lymphatic routes, potentially settling into the previously affected iliopsoas muscles and leading to abscess formation. Interestingly, the most reported cases of neonatal IPA usually present with symptoms between two and three weeks after birth, an interval sufficient for the formation of a clinically significant abscess.³
The clinical presentation of IPA may initially be non-specific, and fever may not be a prominent symptom. As the abscess enlarges, localized signs such as pain, decreased leg movement, and swelling in the groin or the lower limb develop gradually, shifting medical attention to a more specific area.^3,4,5 The insidious onset and non-specific early symptoms often contribute to delayed diagnosis and an increased demand for surgical intervention.⁶ The cases presented here, sepsis was the initial manifestation, with fever as the most prominent symptom, which disappeared in the subsequent days. During ongoing sepsis treatment, the diagnosis of IPA was made based on the emergence of lower limb symptoms. At this stage, the differential diagnosis includes septic arthritis, osteomyelitis, inguinal hernia, thrombotic events, and superficial skin and soft tissue infections. In the literature, septic arthritis is the most common initial diagnosis.^1,2 Therefore, the initial imaging modalities may fail to definitively diagnose IPA, and a high index of clinical suspicion is required to prompt appropriate imaging studies aimed at detecting occult sites of infection, particularly in the iliac fossa. In addition to point-of-care US, computed tomography or MRI are highly sensitive for confirming the diagnosis of a deep-seated abscess, such as IPA.^1,5 In the second case, the edema of the entire left leg was likely a result of the compression of the vascular structures in the iliac fossa by the abscess.
Unlike the two cases presented here, in which sepsis preceded the development of IPA, most cases of isolated IPA show only mild increases in acute phase reactants and white blood cell count, which don’t specify the diagnosis.^1,7 In addition to the delayed onset and non-specific early symptoms, the high tendency to start empirical antibiotics in sick neonates and the treatment of underlying infections without a definitive diagnosis may contribute to the underdiagnosis and underreporting of IPA. As seen in the present cases, if the decrease of CRP levels is slower than expected or shows a pause despite appropriate sepsis treatment, a localized infectious focus should be suspected. S. aureus is the most commonly isolated pathogen from pus cultures, while the isolation of the causative pathogen from blood cultures has been reported only in a few cases.^1,5 In the first case, the pathogen was isolated from both blood and pus cultures, whereas in the second case, the different pathogens were identified. This finding emphasizes the importance of diagnostic aspiration under US guidance when an abscess is detected, even if the patient is already being treated for sepsis caused by a previously isolated pathogen.
The management of IPA involves systemic antibiotic therapy combined with the drainage of the abscess, either percutaneously under US guidance or, if necessary, via open surgical drainage.^1,5 The drainage of the abscess is of critical importance both for identification of the causative pathogen and for minimizing the duration of antibiotic therapy, as demonstrated in the present cases. With early diagnosis and effective drainage, the prognosis is quite good, without disability or recurrence.¹ However, a delay in the diagnosis may be fatal.⁸

Limitations

In the first case, MRI was able to demonstrate sensitivity sufficient to confirm the diagnosis of IPA; however, the relatively low image quality and limited spatial resolution may potentially compromise the illustrative value of the case.

Conclusion

This report highlights that IPA can develop concurrently with neonatal sepsis, whether caused by the same or different pathogens. Therefore, in neonates undergoing sepsis treatment who develop lower limb pain and swelling, IPA should also be kept in mind, such as septic arthritis or osteomyelitis. The point-of-care US and aspiration of the abscess with pus culture are essential for the diagnosis and optimal treatment.

Declarations

Abbreviations

CARE: case report guidelines
CRP: c-reactive protein
IPA: ilio-psoas abscess
MRI: magnetic resonance imaging
MRSA: methicillin-resistant staphylococcus aureus
US: ultrasonography

References

1. Akın MŞ, Ağaçkıran D, Ünal E, Yavuz ÖÖ, Yiğit Ş. Neonatal iliopsoas abscess presenting with transient cyanosis of a single extremity: a case report and review of the literature. Turk J Pediatr. 2020;62(1):160-164. doi:10.24953/turkjped.2020.01.025
   Article PubMed Google Scholar
2. Okan F, Ince Z, Coban A, Can G. Neonatal psoas abscess simulating septic arthritis of the hip: a case report and review of the literature. Turk J Pediatr. 2009;51(4):389-391.
   PubMed Google Scholar
3. Edgar EA, Schlesinger AE, Royster RM, Deeney VFX. Ilo-psoas abscess in neonates. Pediatr Radiol. 1993;23(1):51-52. doi:10.1007/BF02020223
   Article PubMed Google Scholar
4. Andreou A, Karasavvidou A, Papadopoulou F, Koukoulidis A. Ilio-psoas abscess in a neonate. Am J Perinatol. 1997;14(9):519-521. doi:10.1055/s-2007-994326
   Article PubMed Google Scholar
5. Yano T, Takamatsu H, Noguchi H, et al. Iliopsoas abscess in the neonate. J Pediatr Surg. 2004;39(7):e13-15. doi:10.1016/j.jpedsurg.2004.03.080
   Article PubMed Google Scholar
6. Song J, Letts M, Monson R. Differentiation of psoas muscle abscess from septic arthritis of the hip in children. Clin Orthop Relat Res. 2001;391:258-265.
   PubMed Google Scholar
7. Han YM, Kim AY, Lim RK, et al. Neonatal iliopsoas abscess: the first Korean case. J Korean Med Sci. 2015;30(8):1203-1206. doi:10.3346/jkms.2015.30.8.1203
   Article PubMed Google Scholar
8. Sham M, Singh D. Neonatal ilio-psoas abscess: report of two cases. J Neonatal Surg. 2014;3(1):4. doi:10.52783/jns.v3.68
   Article PubMed Google Scholar

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About This Article

Received:

January 16, 2026

Accepted:

March 31, 2026

Published Online:

April 3, 2026