Pubic osteomyelitis complicated by a rectus abdominis abscess and urethral fistula: a rare case report

Abstract

Background

Pubic osteomyelitis is an uncommon condition that is typically reported in patients with a history of pelvic surgery or immunosuppression. Its clinical presentation, which often includes lower abdominal pain and persistent fever, is nonspecific, making its diagnosis challenging. Advanced imaging modalities, particularly computed tomography (CT), are essential for accurate diagnosis.

Case presentation

An 85-year-old woman initially diagnosed with a urinary tract infection was referred for clinical deterioration. Contrast-enhanced CT revealed a large abscess in the rectus abdominis and osteolytic changes in the pubic bones. Contrast instillation via the drainage catheter demonstrated communication between the abscess cavity and urethra, which was confirmed by the appearance of indigo carmine dye in the urethral meatus. The patient improved with drainage and antibiotic therapy and was transferred for rehabilitation on hospital day 42.

Conclusions

This case highlights that pubic osteomyelitis can develop even in the absence of typical predisposing factors such as pelvic surgery or immunosuppression. It also highlights that chronic tract infections may serve as a potential source, possibly leading to complex complications such as urethro-abscess fistulas.

Clinical trial number

Not applicable.

Background

Pubic osteomyelitis is a rare but clinically significant condition that is occasionally reported after trauma, athletic injury, urogynecological surgery, or pelvic radiation therapy [1]. It accounts for < 1% of all osteomyelitis cases; however, its true incidence may be underestimated because of diagnostic challenges [2]. This disease primarily affects adults. Both sexes are susceptible, and it is more frequently observed in athletes, postoperative patients, and individuals with chronic comorbidities. Given the anatomical proximity of the pubic symphysis to the urogenital and gastrointestinal tracts, infections often spread contiguously [3, 4]. Nonspecific symptoms, such as persistent fever and lower abdominal pain, often delay diagnosis unless advanced imaging modalities are employed [5]. While most reported cases involve identifiable risk factors such as recent surgery or immunosuppression, spontaneous cases remain exceedingly rare [1, 6]. Here, we present an unusual case of pubic osteomyelitis complicated by a rectus abdominis abscess and urethral fistula in an older adult patient without prior pelvic surgery or known immunocompromised status, highlighting the potential role of chronic urinary tract infections in facilitating contiguous spread.

Case presentation

An 85-year-old woman presented with a high fever and gross hematuria. According to the referral letter from the previous hospital, her medical history included recurrent urinary tract infections associated with a neurogenic bladder, and she had been residing in a long-term care facility, as well as bilateral bipolar hip arthroplasty. She had no history of urogenital malignancy, pelvic trauma, pelvic radiation therapy, or prior pelvic or endoscopic urological surgery. In addition, she did not have a chronic indwelling urinary catheter. She was initially diagnosed with a urinary tract infection and treated with cefazolin (CEZ); however, urine culture and susceptibility testing were not performed prior to antibiotic administration. Her symptoms persisted for six days, and her oral intake declined, necessitating hospital admission.

Upon admission, the patient was afebrile but reported mild lower abdominal pain without flank pain. Laboratory findings revealed the following elevated inflammatory markers: white blood cell count, 10,610/µL; C-reactive protein (CRP), 21.85 mg/dL; and procalcitonin, 0.39 ng/mL. Contrast-enhanced computed tomography (CECT) demonstrated fluid accumulation, widening of the pubic symphysis joint space, increased bone marrow density, osteolytic changes in the pubic bone, and a rectus abdominis abscess (Fig. 1a and b), suggesting pubic symphysis osteomyelitis and/or septic arthritis. There were no signs of pyelonephritis, including pelvic dilatation or perinephric fat stranding.

Fig. 1.

CECT showing an abscess in rectus abdominis. a) The arrow indicates increased bone marrow density and osteolytic changes in the pubic bone. b) The abscess in rectus abdominis is highlighted with a circle

Blood cultures obtained after antibiotic therapy at another hospital yielded negative results. Urine cultures revealed a small number of Candida species. Owing to clinical deterioration, the antibiotic regimen was escalated to piperacillin-tazobactam (TAZ/PIPC). Under ultrasound guidance, a drainage catheter was placed, which yielded a white purulent fluid. The abscess culture was obtained directly from the purulent material at the time of the initial puncture, prior to prolonged catheter placement. The abscess extended from the suprapubic region into the rectus abdominis (Fig. 2a). Contrast imaging via the catheter demonstrated fistulous communication between the urethra and the abscess cavity (Fig. 2b). There was no evidence of gastrointestinal tract involvement. Indigo carmine, instilled through the catheter, emerged at the urethral meatus, confirming the fistula (Fig. 3).

Fig. 2.

Contrast imaging via the drainage catheter. a) The abscess extended to rectus abdominis from the suprapubic region (highlighted with a circle). b) A fistulous communication between the rectus abdominis and the urethra is shown. The circle indicates leakage of contrast medium

Fig. 3.

Indigo carmine test confirming fistulous communication. The red circle indicates the leakage of indigo carmine from the urethral meatus, confirming the presence of a fistulous tract

The drainage catheter was removed on hospital day 11 after drainage ceased, and a follow-up Computed Tomography (CT) demonstrated a reduction in the abscess size. Abscess fluid culture revealed the presence of Escherichia coli, Streptococcus constellatus, Bacteroides thetaiotaomicron, Bacteroides fragilis, and Actinomyces turicensis. Based on susceptibility testing, the antibiotic regimen was switched to ceftriaxone and metronidazole on day 13.

On day 30, a small amount of purulent discharge was observed at the drainage site. A CT scan revealed a residual abscess near the pubic symphysis. By day 34, the abscess had enlarged, prompting reinsertion of a drainage catheter. Repeat contrast injection revealed no persistent communication between the abscess and urethra. The catheter was removed on day 40. The patient showed clinical improvement and was switched to oral antibiotics (amoxicillin/clavulanate). The total duration of antimicrobial therapy, including treatment at the referring hospital, was 48 days. She was transferred to a rehabilitation facility on hospital day 42.

Discussion and conclusions

Pubic osteomyelitis is an infrequent diagnosis, comprising < 1% of all osteomyelitis cases [1]. The present case is particularly noteworthy because of the absence of typical risk factors such as prior pelvic surgery [7–9] or immunosuppressive therapy [10]. Although the patient had no history of immunosuppressive therapy or known immunocompromised conditions, advanced age itself may have contributed to disease progression through immune senescence, characterized by age-related decline in immune function. Moreover, the simultaneous presence of a rectus abdominis abscess and urethral fistula is exceedingly rare and, to our knowledge, has not been previously reported.

This report highlights several important diagnostic and pathological considerations. The polymicrobial nature of an abscess, characterized by organisms typically associated with both urogenital [11] and gastrointestinal flora [12], complicated the identification of the primary source of infection. Despite the presence of gastrointestinal anaerobes, the imaging and clinical findings excluded gastrointestinal tract fistulas. The detection of scant Candida species in the urine was most likely indicative of colonization rather than infection, particularly given the prior exposure to antibiotics and the absence of Candida growth in the abscess aspirate. Although urine culture was not obtained prior to the initiation of antimicrobial therapy at the referring hospital, subsequent urine culture collected after antibiotic exposure yield only scant Candida species. In contrast, culture of the abscess aspirate obtained at the time of initial drainage revealed polymicrobial growth dominated by uropathogenes. The presence of E. coli in the abscess suggested a urinary tract origin, potentially enabling bacterial translocation and osteomyelitis. Previous literature supports cystitis as a possible precursor of pubic bone infection [13]. A limitation of this case is that urine culture and susceptibility testing were not performed prior to the initiation of antimicrobial therapy at the referring hospital, which limited definitive identification of the primary infectious source.

The spontaneous resolution of the urethral fistula in our patient was particularly remarkable. Urethral fistulas are typically resistant to nonsurgical management, particularly in cases of ongoing infection or tissue fragility [14, 15]. In this case, early and effective source control through catheter drainage combined with targeted antibiotic therapy likely prevented epithelialization of the fistulous tract, thereby allowing for spontaneous closure and resulting in a rare and clinically significant outcome.

The discrepancy between the urine and abscess culture results also underscores the diagnostic complexity. Candida detection in the urine might reflect transient colonization related to the patient’s neurogenic bladder, while the predominance of uropathogens in the abscess culture supports a urinary origin. While blood cultures are obtained after the initiation of antibiotics, which likely reduces the yield, early antibiotic administration prior to blood culture collection is a common challenge in clinical practice. Additionally, Actinomyces spp. which are known for their propensity to form chronic suppurative infections and fistulas [16], may also have contributed to fistula development.

From a diagnostic standpoint, this case reaffirms the critical role of multimodal imaging, including CECT and dynamic contrast studies, in identifying atypical infection pathways and fistula formation. The use of indigo carmine dye instilled via a drainage catheter was particularly valuable for confirming urethral fistulous communication and providing direct visual evidence of the urethral meatus. This simple yet effective technique can serve as a practical adjunct in situations in which conventional imaging may yield equivocal findings. The use of ultrasound-guided drainage and real-time contrast monitoring is essential for establishing a diagnosis.

In conclusion, this case illustrates a unique triad involving pubic osteomyelitis, rectus abdominis abscess, and urethral fistula in the absence of standard predisposing factors. Chronic urinary tract infections should be recognized as a potential source of pubic osteomyelitis, even in patients without obvious immunosuppression or a recent surgical history. Early recognition, comprehensive imaging, and appropriate antimicrobial therapy are essential for achieving favorable clinical outcomes.

Abbreviations

CT

Computed tomography

CECT

Contrast-enhanced computed tomography

Author contributions

YI, KS, KT, TY, and OS treated the patient. KS provided clinical advice. YI drafted and revised the manuscript critically. All of the authors have read and approved the final version of the manuscript.

Funding

There was no funding source for this article.

Data availability

Data is provided within the manuscript.

Declarations

Ethics approval and consent to participate

Ethics approval or consent to participate was not applicable.

Consent for publication

Written informed consent was obtained from the patient for publication of their personal and clinical details along with any accompanying images.

Competing interests

The authors declare no competing interests.