Ultrasound-guided anteroposterior percutaneous catheter drainage for the treatment of psoas abscess: A case series

Abstract

Psoas abscess (PA) is a rare but potentially life-threatening condition that requires prompt intervention. The role of ultrasound-guided percutaneous catheter drainage (US-PCD) via the anterior-posterior (AP) approach warrants further evaluation. This case series retrospectively analyzed 10 patients with PA who underwent US-guided AP-PCD at Beijing Friendship Hospital. Data collected included procedure duration, pre- and postoperative clinical examinations, inflammatory markers, and imaging findings. Technical success was achieved in all cases (median procedure time: 18.5 minutes). Postprocedural Visual Analog Scale (VAS) pain scores decreased within 24 hours. By postoperative day 3, eight patients had normalized body temperature and white blood cell (WBC) counts. Median C-reactive protein (CRP) levels decreased from 151.3 mg/L (range: 58.0–269.4) preoperatively to 49.5 mg/L (range:38.7–186.1) postoperatively. During a follow-up period of 1–6 months, six patients achieved clinical success without further intervention, two required surgical debridement, and two died. This case series demonstrates that US-guided AP-PCD represents a feasible and safe minimally invasive option for selected patients with PA, offering the advantages of real-time guidance and no radiation exposure. However, given the modest success rate (60%) and etiological heterogeneity of this cohort, larger prospective studies are needed to validate its clinical role.

Introduction

Psoas abscess (PA) is an uncommon clinical finding, with an estimated annual incidence of 0.4 cases per 100,000 individuals. ¹ Data on PA remain scarce, and the existing literature consists largely of small case series. ² Owing to its insidious onset and nonspecific clinical presentation, PA is frequently overlooked or misdiagnosed. ³ The disease can progress rapidly, and without timely intervention, it can lead to significant morbidity and mortality. ⁴ Reports indicate that 18% of patients with PA present with septic shock, with an in-hospital mortality up to 12%. ⁵

Conventional treatment ranges from antibiotic therapy alone to computed tomography (CT)-guided or open surgical drainage. ⁶ While effective, open surgery is invasive and carries risks of tissue adhesion and prolonged recovery, especially in vulnerable patients. ⁷ CT-guided percutaneous catheter drainage (PCD) has proven to be a safe and effective first-line treatment for retroperitoneal abscesses.^8,9 However, its broader application is limited by radiation exposure, procedural delays, and higher costs. ¹⁰

Given the deep retroperitoneal location of the psoas muscle and its proximity to critical structures such as the bowel, iliac vessels and femoral nerve, establishing a safe and reliable PCD route remains a clinical challenge. Ultrasound (US)-guided PCD offers distinct advantages, including real-time visualization, minimal trauma, absence of ionizing radiation, and ease of repeated operation, making it an increasingly attractive option for retroperitoneal interventions. ¹¹

Image-guided PCD has become the established first-line minimally invasive intervention for psoas abscess (PA).^7,8 Although US-guided PCD has been described in prior reports, the literature remains limited to small, methodologically heterogeneous case series,^2,11 and a specific evidence gap exists regarding the efficacy and safety of the anterior-posterior (AP) approach under exclusive US guidance. This case series addresses this gap by presenting ten patients treated with US-guided AP-PCD, with particular emphasis on three innovative aspects: (1) exclusive reliance on ultrasound without CT assistance, (2) a standardized patient positioning strategy that optimizes the AP puncture window, and (3) the applicability of this technique in complex postoperative cases involving aortic graft-related infections. By highlighting these distinctive features, this series aims to provide a nuanced contribution to the image-guided management of this deep-seated infection and demonstrate the added clinical value of the US-guided AP approach.

Patients and methods

This retrospective case series reviewed consecutive patients diagnosed with psoas abscess (PA) who underwent ultrasound-guided percutaneous catheter drainage (US-PCD) at Beijing Friendship Hospital between January 2023 and December 2024. No exclusion criteria were applied to ensure a representative sample of real-world clinical practice. This case series was approved on July 2, 2025, by the Ethics Review Committee of Beijing Friendship Hospital (Approval No. 2025-P2-269-01).

The diagnosis of PA was established based on the clinical symptoms (back pain, fever and lower limb dysfunction), blood chemistry tests (white blood cell [WBC] and C-reactive protein [CRP]) and computed tomography (CT) or magnetic resonance imaging (MRI) findings. The inclusion criteria were as follows: (1) confirmed diagnosis of PA by CT or MRI; (2) US-guided PCD was performed; and (3) availability of complete clinical records for review.

Procedure

The patient was positioned supine and evaluated using the Esaote X8 Pro color Doppler ultrasound to determine abscess extent, puncture trajectory, and insertion depth. The skin was disinfected and draped, and local anesthesia was administered with 2% lidocaine. Under real-time ultrasound guidance, gentle probe pressure displaced the adjacent bowel, minimizing puncture distance while avoiding intestinal structures, organs, and major vessels. A 7.0F or 8.5F pigtail drainage catheter was inserted percutaneously via the anterior or lateral abdominal wall using the Seldinger technique. Drainage was confirmed, the catheter secured with adhesive dressing, and connected to a sterile disposable bag. Pus from the initial puncture underwent bacterial culture, and antibiotic therapy was individualized based on sensitivity results.

Technical success was defined as the accurate placement of a drainage catheter into the target abscess cavity under real-time ultrasound guidance, with immediate confirmation of adequate drainage and absence of procedure-related injury. Clinical success was defined as (1) complete and sustained resolution of the abscess on follow-up imaging; (2) resolution of associated symptoms (e.g., fever, back pain); (3) normalization or significant improvement of inflammatory markers (WBC and CRP); and (4) no requirement for surgical conversion or additional invasive intervention.^12,13

Case presentation

Case1

In October, 2024, a woman in her early 60s was admitted to our hospital due to persistent low back pain lasting more than one month. Twenty days prior to admission, her right-sided pain acutely worsened, accompanied by fever (maximum temperature [Tmax]: 38.0°C) and impaired mobility of the right lower limb. Abdominal and pelvic CT revealed swelling of the right psoas major muscle with areas of liquefaction, measuring up to 8.1 cm × 6.6 cm in maximal cross-section, consistent with an abscess (Figure 1(a)). Laboratory findings included a white blood cell (WBC) count of 12.11 × 10⁹/L, neutrophil percentage (NE%) of 79.7%, and C-reactive protein (CRP) level of 144 mg/L. On the day of admission, US-guided AP-PCD of the abscess was performed, and culture of the drained fluid grew Proteus mirabilis. She subsequently received targeted antimicrobial therapy based on susceptibility testing, along with symptomatic and supportive management. Her fever resolved within days, and inflammatory markers progressively normalized over the following weeks. The drainage catheter was removed 28 days later. Follow-up CT demonstrated substantial reduction in abscess size (Figure 2(a)) and absence of local tenderness. During a 6-month telephone follow-up, the patient remained asymptomatic, with no evidence of recurrence or treatment-related complications.

Figure 1.

Computed tomography scan showing psoas abscesses in three representative cases. (a) Case 1 presented with a right psoas abscess. (b) Case 4 exhibited a right psoas abscess. (c) Case 8 was characterized by a left psoas abscess accompanied by an endoleak associated with an abdominal aortic stent graft. White arrows indicate the psoas abscesses.

Figure 2.

Follow-up computed tomography scans after PCD. (a) In Case 1, the abscess cavity decreased in size following drainage. (b) In Case 4, the drainage catheter was successfully positioned via an anterior abdominal wall approach, with shrinkage of the abscess. White arrows indicate the reduced psoas abscesses.

Case2

In April, 2024, a woman in her early 50s was admitted for persistent low back pain lasting over one month and seven days of fever. One month earlier, she underwent hysteroscopic curettage for endometrial hyperplasia and developed right-sided low back pain on the same day, radiating to the right lower extremity, with progressive worsening. At admission, laboratory tests showed leukocytosis (WBC: 12.33 × 10⁹/L), neutrophilia, CRP 269.35 mg/L, and Tmax up to 38.3°C. Contrast-enhanced CT of the lumbar spine revealed right psoas muscle abnormalities consistent with infection. Ultrasound confirmed a fluid collection measuring 8.6 cm × 5.9 cm along the muscle’s course. The following day, US-guided AP-PCD was performed; culture grew Streptococcus anginosus. She received intravenous antibiotics. Symptoms initially improved, with reduced pain, normal temperature, and declining inflammatory markers. However, one week later, fever recurred despite a patent catheter with no output. Repeat CT showed infection extension to the lumbar vertebrae, appendages, and surrounding soft tissues, with intervertebral space destruction, indicating progression. Conservative treatment failed, and surgical debridement was recommended.

Case3

In early 2024, a woman in her early 60s was admitted for persistent lower abdominal pain lasting 11 days and bilateral lumbar pain. Abdominal CT revealed a liver abscess and a left PA measuring approximately 5.8 cm × 3.1 cm. On admission, laboratory tests showed leukocytosis (WBC: 15.08 × 10⁹/L), neutrophilia (86.4%), CRP 193.52 mg/L, and Tmax: 38.3°C. US-guided AP-PCD of the liver abscess was performed several days later. Fever gradually subsided, but lumbar pain persisted. Two days later, US-guided PCD of the left PA yielded 23 ml of purulent fluid. Postoperative ultrasound confirmed near-complete resolution of the abscess cavity. Culture identified Klebsiella pneumoniae. Intravenous antibiotics were initiated. The patient improved clinically, with normal temperature, reduced pain, and declining inflammatory markers. Follow-up CT showed marked reduction in left psoas swelling. During six months of follow-up, no recurrent symptoms or complications occurred.

Case4

In mid-2024, a woman in her late 70s was admitted for fever and low back pain lasting over a month, with worsening symptoms in the prior week. One month earlier, she developed fever without clear cause and was diagnosed at an outside hospital with urinary tract infection and lumbar disc herniation. After anti-infective treatment, her fever resolved and pain improved. Seven days before admission, she had recurrent high fever (Tmax 38.6°C) with right lower limb movement restriction and was transferred to our hospital. Admission lumbar CT revealed a right PA measuring approximately 5.8 cm × 1.6 cm (Figure 1(b)). Initial antibiotic therapy failed to control fever or relieve pain. Several days later, US-guided AP-PCD of the abscess yielded pus; culture grew Escherichia coli. The regimen was then changed to combination intravenous antibiotics. Subsequently, her temperature normalized, inflammatory markers declined, and follow-up abdominalpelvic CT showed marked reduction in right psoas swelling (Figure 2(b)). During four months of follow-up, no infection recurrence or complications occurred.

Case5、Case6 and Case7

All three cases were secondary to lumbar spine surgery, presenting with fever, low back pain, and lower extremity radiating pain. Abdominalpelvic CT confirmed psoas abscesses. Case 5, a women in her late 60s, presented with fever and elevated inflammatory markers. The abscess measured up to 8.2 cm × 5.0 cm in cross-section. Pus culture following drainage grew Staphylococcus aureus; and intravenous antibiotics were initiated. Drainage volume gradually decreased, and the catheter was subsequently removed due to suspected septations limiting further output. Follow-up revealed progressive cytopenia in all three lineages and declining hemoglobin, suggesting possible drug-induced bone marrow suppression. Enhanced lumbar MRI showed findings consistent with bone marrow infection. Multidisciplinary evaluation concluded that medical management failed, and the patient was transferred for surgical debridement.

Case 6 was a female in her late 70s, and case 7 was a female in her mid-70s. Both patients presented with psoas abscesses measuring 9.2 cm × 1.6 cm and 7.2 cm × 2.6 cm, respectively. Microbiological culture identified Staphylococcus aureus in case 6 and Escherichia coli in case 7. Following US-guided AP-PCD and targeted antibiotic therapy, both patients improved significantly, with marked reduction in abscess size and no evidence of recurrence during follow-up.

Case8 and Case9

Case 8 was a male in his early 70s, and case 9 was a female in her early 70s. Both patients developed endoleaks following endovascular stent grafting for abdominal aortic aneurysms, accompanied by perigraft and psoas muscle-adjacent abscesses. The abscesses measured up to 8.0 cm × 5.2 cm (Figure 1(c)) and 11.2 cm × 4.7 cm in maximum cross-sectional area, respectively. Microbiological culture identified Staphylococcus lugdunensis in case 8, while no pathogen was isolated in case 9.

In case 8, US-guided AP-PCD combined with antibiotic therapy led to marked improvement: lumbar pain resolved, body temperature normalized, and fever did not recur. However, the patient subsequently developed massive hematochezia with progressive hemoglobin decline, necessitating emergency repair of the stent graft. Despite resuscitative efforts, the patient died from progression of multifocal infection to septic shock, respiratory failure, and disseminated intravascular coagulation (DIC).

In case 9, after clinical stabilization and exclusion of surgical contraindications, the patient underwent axillary-femoral artery bypass, resection of the abdominal aortic aneurysm, and abdominal aorta–renal artery bypass. Two weeks postoperatively, the patient abruptly developed limb convulsions, loss of consciousness, and hemodynamic shock, with rapid deterioration to critical condition. Given the poor prognosis and to minimize suffering, the family opted against invasive interventions, and the patient passed away shortly thereafter.

Case10

In mid-2024, a woman in her late 50s was admitted for persistent low back pain lasting two months with radiation to the left hip and lower extremity. CT imaging revealed lumbar intervertebral disc protrusion and spinal canal stenosis, as well as gas-containing encapsulated fluid collections in the left psoas major muscle and adjacent pelvic wall. The patient had undergone hysterectomy for endometrial cancer two years prior. To alleviate symptoms, she underwent minimally invasive endoscopic lumbar surgery shortly after admission, with transient postoperative pain relief. However, several days later, her pain worsened, prompting transfer to our service for further management. US-guided AP-PCD was performed for the left PA, and bacterial culture of the drainage fluid identified Proteus mirabilis. Targeted antimicrobial therapy was initiated. Clinical symptoms gradually improved, and follow-up imaging demonstrated marked reduction in abscess size. No recurrence was observed during the follow-up period.

This case series systematically collected clinical data from 10 patients (9 female), with a median age of 69 years (range: 52–77 years), including 4 with primary abscesses and 6 with secondary abscesses (among which 2 were associated with postoperative aortic graft-related infections). Patient baseline characteristics are summarized in Table 1. The median abscess size was 8.1 cm (range: 5.2–11.2 cm). Preoperative laboratory and clinical parameters were markedly elavated.

Table 1.

Baseline characteristics of patients with psoas abscess.

Patient number	Sex	Diabetes	Location	Primary/secondary	VAS	Pre-BT	Abscess size (cm)
1	F	Yes	Right	Primary	8	38.0	8.1
2	F	No	Right	Primary	8	38.3	8.6
3	F	No	Left	Primary	5	38.3	5.8
4	F	Yes	Right	Primary	8	38.6	5.8
5	F	No	Both sides	Secondary to lumbar spine surgery	7	38.7	8.2
6	F	Yes	Left	Secondary to lumbar spine surgery	5	37.6	9.2
7	F	Yes	Right	Secondary to lumbar spine surgery	6	38.9	7.2
8	M	Yes	Left	Secondary to abdominal aortic aneurysm surgery	6	38.5	8.0
9	F	No	Both sides	Secondary to abdominal aortic aneurysm surgery	7	38.1	11.2
10	F	No	Left	Secondary to hysterectomy	7	37.8	5.2

Technical success was achieved in all 10 patients (Figure 3), with a median procedure duration of 18.5 minutes (ranged: 13–40 minutes). Two cases of mild local hematoma occurred and resolved spontaneously; no severe complications were observed. Procedural details and clinical outcomes are summarized in Table 2. Clinical and laboratory outcomes improved rapidly after drainage: Within 24 hours, VAS ¹⁴ pain score decreased from 7 (range: 5–8) preoperratively to 5 (range: 2–6); by postoperative day 3, BT and WBC count had normalized in 8 of 10 patients. The median CRP level declined from 151.3 mg/L (range: 58.0–269.4 mg/L)to 49.5 mg/L (range: 38.7–186.1 mg/L). Following catheter removal (median duration 18 days, range: 2–35days), the median abscess size decreased to 2.4 cm (range: 0–7.6 cm). A complete summary of pre- and post-procedural outcomes is presented in Table 3.

Figure 3.

Illustration of the puncture and drainage procedure. All procedures utilized an anterior or lateral abdominal wall (anteroposterior) approach, with successful placement of drainage catheters into the abscess cavity under imaging guidance. White arrows indicate the needle tract, and red arrows indicate the drainage catheter positioned within the abscess cavity.

Table 2.

Procedural details and clinical outcomes.

Patient number	Operation time	7F/8.5F device used	Bacteria	Antibiotic regimen	VAS (24 hours)	Drainage days	Complications	Abscess size (cm)	Clinical success
1	18	8.5F	P. mirabilis	cefoperazone-sulbactam+metronidazole	5	28	No	2.1	Yes
2	20	7.0F	S. anginosus	imipenem-cilastatin	5	12	No	5.8	No
3	15	8.5F	K. pneumoniae	cefoperazone-sulbactam+meropenem	3	18	No	0	Yes
4	13	8.5F	E. coli	imipenem-cilastatin+tigecycline+linezolid	5	23	No	0	Yes
5	35	8.5F	S. aureus	vancomycin+clindamycin	6	22	Minor hematoma	3.7	No
6	18	8.5F	S. aureus	meropenem c+vancomycin	2	5	No	1.8	Yes
7	40	7.0F	E. coli	Meropenem+moxifloxacin	3	2	Minor hematoma	2.6	Yes
8	15	7.0F	S. lugdunensis	Meropenem+ceftriaxone+vancomycin	4	35	No	3.8	No *
9	19	8.5F	Negative	azithromycin+ rifampicin+meropenem	5	8	No	7.6	No *
10	20	7.0F	P. mirabilis	cefoperazone-sulbactam	5	20	No	1.5	Yes

*Patients 8 and 9 passed away during the follow-up period despite combined drainage and surgical intervention.

Table 3.

Clinical and laboratory outcomes before and after US-guided AP-PCD.

Parameter	Preoperative	Postoperative day 1	Postoperative day 3	Postoperative day 7	After catheter removal
Body temperature (°C)	38.3 (37.6–38.9)	37.7 (37.0–38.0)	37.1 (36.5–37.5)	37.0 (36.2–37.8)	—
WBC count (×109/L)	12.2 (5.2–15.1)	9.8 (5.9-13.4)	8.4 (4.9-13.9)	7.3 (4.0-10.4)	5.4 (2.6-56.4)
CRP (mg/L)	151.3 (58.0–269.4)	105.9 (53.3–226.5)	49.5 (38.7–186.1)	47.3 (5.6–152.3)	28.9 (0.2–171.9)
VAS pain score	7 (5–8)	5 (2–6)	2.5 (2–6)	2.0 (0–5)	—
Abscess size (cm)	8.1 (5.2–11.2)	—	—	—	2.4 (0–7.6)

Data are presented as median (range) unless otherwise specified.

Written informed consent for treatment and publication was obtained from all patients or their legally authorized representatives (in the case of deceased patients), and all patient details were de-identified to ensure anonymity.

Discussion

In recent years, with the advancement of minimally invasive surgical techniques and the adoption of damage control principles, surgical management has increasingly embraced a step-up approach.^15,16 This strategy prioritizes percutaneous catheter drainage (PCD) as the initial treatment, reserving laparoscopic or open surgical exploration for cases in which PCD is ineffective or clinical deterioration occurs. PCD offers several advantages in the management of psoas abscess (PA), including minimal invasiveness, feasibility under local anesthesia, and rapid symptom relief.^9,10 It also enables early collection of pus samples for microbiological analysis, such as polymerase chain reaction (PCR), bacterial culture, and drug sensitivity testing (DST), thereby facilitating targeted antibiotic therapy and potentially reducing the overall duration of treatment.

Yacoub et al. reported a non-surgical management success rate of approximately 90% for PA. ¹⁷ In our series, ultrasound-guided PCD was technically successful in all 10 patients, with positive pus cultures in 9. By the third postoperative day, BT and WBC had normalized in 8 patients, indicating that drainage can rapidly reduce the systemic infectious burden. CRP, with its short half-life, is a sensitive biomarker for assessing infection severity. ¹⁸ The median CRP level decreased from 151.3 mg/L (range: 58.0–269.4 mg/L) preoperatively to 49.5 mg/L (range: 38.7–86.1mg/L) on postoperative day 3, confirming effective control of inflammation.

The clinical success rate of PCD for PA ranges from 71% to 96%, according to several studies.^8,10,19 However, Gupta et al. reported that percutaneous aspiration alone has a recurrence rate of up to 66%. ²⁰ In this case series, based on our predefined criterion of sustained resolution without further surgery, the overall clinical success rate was 60% (6/10). Two patients required surgical debridement due to inadequate response after PCD, and two patients with PA secondary to aortic endograft infection died from sepsis and multiple organ dysfunction syndrome (MODS) despite technically successful drainage and subsequent vascular surgery; both were classified as clinical failures.

Etiology-based outcome analysis and comparison with prior studies

A descriptive subgroup analysis revealed marked outcome differences by etiology. In the primary PA group (n=4), 3 patients (75%) achieved clinical success with PCD alone, aligning with high success rates in the literature. ¹⁹ In contrast, outcomes in the secondary PA group (n=6) were more heterogeneous, with a 50% success rate (3/6). Notably, both patients with endograft-related PA died despite combined drainage and surgical source control, underscoring the poor prognosis associated with this etiology.

The 60% overall success rate in this series is lower than the 71–96% rates reported in several previous studies.^8,10,19 For instance, Cantasdemir et al. reported clinical success in 21 of 22 patients (95.5%) undergoing percutaneous drainage for PA. ⁸ Notably, in their series, all 20 patients with primary abscesses achieved successful outcomes, whereas 1 of the 2 patients with secondary abscesses experienced treatment failure. This pattern closely mirrors our findings and highlights the substantial impact of case mix on reported outcomes. The discrepancy between our overall success rate and those in the literature likely reflects the high proportion of complex secondary abscesses in our cohort (60%)—a particularly challenging etiology consistently associated with poorer outcomes.

These findings highlight that while US-guided PCD is highly effective as definitive therapy for primary PA, its role in secondary PA—particularly those arising from persistent infectious foci such as infected vascular grafts—is often that of a bridge or damage-control procedure. In such complex cases, percutaneous drainage alone is insufficient to eradicate the underlying nidus, and timely, radical source-control surgery is essential. This underscores the importance of considering etiology-specific outcomes when interpreting and comparing results across studies of image-guided drainage for psoas abscess.

Technical considerations

The traditional view suggests that US-guided puncture may be less accurate for deep-located abscesses or those adjacent to surrounding organs and major blood vessels. ²¹ However, technological advances have significantly improved the visualization of deep lesions. US-guided percutaneous drainage combined with appropriate antibiotics is recognized as a safe and effective treatment. ²² In our series, all 10 patients received the anterior-posterior approach following comprehensive evaluation. Utilizing probe compression to displace bowel, this method shortened the needle insertion trajectory, minimized risk to adjacent organs, and achieved 100% technical success.

Limitations

This case series has several limitations. Its retrospective design and small sample size constrain the strength of conclusions. Importantly, the etiological heterogeneity of our cohort—encompassing primary PA, post-spinal surgery PA, and post-endograft infection PA—limits the generalizability of the pooled success rate and complicates outcome interpretation. The underlying pathology and required definitive management differ substantially across these groups. While formal statistical comparison was not feasible, our descriptive subgroup analysis underscores the need for future prospective studies with larger, more homogeneous populations to better define etiology-specific treatment algorithms and to rigorously assess the optimal timing and efficacy of US-guided PCD within the step-up management strategy for lumbar PAs.

Conclusions

Image-guided percutaneous drainage is the cornerstone of initial management for psoas abscess. This case series demonstrates that ultrasound-guided anteroposterior percutaneous catheter drainage is a technically feasible and safe minimally invasive option for carefully selected patients with psoas abscess. It offers real-time guidance, avoids radiation, and enables microbiological sampling. The approach may serve as a valuable initial intervention, particularly in high-risk patients or those with complex secondary abscesses, where it can act as a bridge to definitive surgical source control. Given the modest success rate (60%) and etiological heterogeneity of this cohort, these findings should be considered preliminary and warrant validation in larger prospective studies.