Liver abscess caused by Parvimonas micra originating from a fish bone: A case report

Abstract

BACKGROUND

Liver abscess is an infectious lesion commonly caused by bacteria, Entamoeba histolytica, or fungi. Although Parvimonas micra (P. micra) predominantly colonizes the orodigestive tract, liver abscesses associated with this bacterium are rarely reported.

CASE SUMMARY

A 52-year-old Chinese male patient presented to our emergency department with intermittent fever, nausea, vomiting, and abdominal distention for 12 days. These symptoms showed no significant improvement following treatment at the primary care hospital. Initial liver ultrasound revealed a 7 cm infectious left lobe lesion. Anaerobic blood cultures and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry performed on admission and 2 days later both identified P. micra, suggesting that the liver abscess may have been caused by a foreign body originating from the digestive tract. Targeted examinations were performed. Abdomen enhanced computed tomography revealed a strip-shaped foreign body in the left outer lobe of the liver, extending to the wall of the pyloric canal. Simultaneous upper endoscopy and endoscopic ultrasonography detected a red scar in the gastric corpus and a 23.5 mm strip-shaped lesion within the liver mass, with one end penetrating the liver. The patient underwent laparoscopic left lateral liver lobectomy of the abscess and gastric perforation repair, during which a 3 cm fish bone was removed. He recovered fully after a targeted antibiotic regimen of penicillin G followed by piperacillin-tazobactam. This case is the first report of a liver abscess caused by P. micra due to ingestion of foreign bodies.

CONCLUSION

The clinical course of this patient highlights that the identification of P. micra and the detection of a foreign body within the liver mass provided pivotal clues for timely diagnosis and appropriate treatment.

Key Words: Liver abscess; Parvimonas micra; Foreign body ingestion; Liver resection; Antibiotics; Case report

Core Tip: Parvimonas micra (P. micra) is an oral and gut commensal rarely causing liver abscess. We report a 52-year-old man who presented to the emergency department with intermittent fever, nausea, vomiting, and abdominal distention for 12 days. On presentation, liver ultrasound revealed a 7 cm hypoechoic lesion in the left lobe. Anaerobic blood cultures and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry performed on admission and 2 days later both identified P. micra, which provided a major diagnostic clue. Subsequent abdomen computed tomography, endoscopy, and endoscopic ultrasound confirmed a 23.5 mm strip-shaped lesion within the liver mass, with one end penetrating the liver. The patient underwent wedge resection of the abscess and repair of the gastric perforation, during which a 3.0 cm fish bone was removed. The clinical course of this patient highlights that pathogen identification is crucial for timely diagnosis and precise treatment.

INTRODUCTION

Liver abscess is an infectious lesion caused by pathogenic microorganisms (including bacteria, Entamoeba histolytica, and fungi) that invade the liver via the biliary tract, portal vein, hepatic artery, adjacent infected organs/tissues, or open hepatic injuries[1]. Bacterial infection is the etiology in approximately 80% of all liver abscess cases[2]. In China, the predominant causative pathogens of liver abscess include the genera Klebsiella, Escherichia, Enterobacter, Staphylococcus, Streptococcus, and Enterococcus[3]. Recent studies reported that the mortality rate of pyogenic liver abscess has less than 1% since 2010 in China[4,5].

Liver abscess secondary to foreign body ingestion leading to gastric perforation and subsequent hepatic infection is occasionally reported[6-8]. Among published cases of gastrointestinal foreign bodies, the most frequently implicated objects are fish bones (33%), toothpicks (27.3%), chicken bones (12.5%), and needles (9.1%)[9]. The stomach, particularly the antrum, is the most common site of perforation, followed by the duodenum and colon[10,11]. Gastric peristalsis may facilitate foreign body penetration through the gastric wall. Given the anatomical proximity of the left liver lobe to the stomach, this region represents the most frequent site of foreign body migration and subsequent abscess formation[12].

Although the liver abscess due to Parvimonas micra (P. micra) has been reported by some studies[13-16], this is the first report describing a liver abscess caused by P. micra originating from a fish bone. P. micra is a gram-positive, anaerobic coccus that was formerly classified as Peptostreptococcus micros (P. micros)[17]. Measuring 0.5-1.0 μm in diameter, this obligate anaerobe thrives at 37 °C and is commonly isolated from the oral cavity, gastrointestinal tract, and genitourinary mucosa as a commensal organism[16]. Being generally non-pathogenic, P. micra can act as an opportunistic pathogen in immunocompromized individuals or following disruption of mucosal barriers, such as after dental procedures or periodontal surgery[18]. It has been increasingly recognized as a causative agent of various deep-seated infections, including brain abscesses[19], pleural empyema[20], and endocarditis[21], often through hematogenous dissemination from its primary colonization sites. The organism typically demonstrates high susceptibility to β-lactam antibiotics, with approximately 90% of strains remaining sensitive to penicillin[22]. Clinical isolation of P. micra should prompt thorough investigation of potential entry portals, including comprehensive dental examination and endoscopic evaluation for occult mucosal perforations, thereby providing critical clues for final diagnosis and efficient treatment.

CASE PRESENTATION

Chief complaints

A 52-year-old male with a 12-day history of fever and abdominal distension presented to our department.

History of present illness

Prior to admission, the patient developed fever (peak temperature 39 °C) with chills and rigors, accompanied by abdominal distension, nausea, retching, decreased appetite, and diarrhea (4-5 yellow watery stools daily with tenesmus). Initial treatment at a local hospital with antibiotics (details unknown) for 8 days failed to alleviate symptoms. Vomiting (gastric contents) with labial herpes developed, prompting transfer to our facility.

History of past illness

The patient had a history of chronic hepatitis B virus (HBV) infection and is maintained on entecavir antiviral therapy. He reported habitual fish consumption but denied ingestion of a fish bone or other sharp objects. He denied a history of diabetes mellitus.

Personal and family history

No significant family history was reported.

Physical examination

On admission, physical examination revealed stable vital signs (temperature 36.3 °C, heart rate 83 bpm, respiratory rate 20/minute, blood pressure 131/90 mmHg). The patient was conscious, with scattered labial herpes lesions and petechiae but no lymphadenopathy. Cardiopulmonary examination was unremarkable. Abdominal assessment showed a soft, non-tender abdomen without rebound tenderness or hepatosplenomegaly, though hepatic percussion tenderness was present. Neurological and extremity examinations demonstrated no edema or focal deficits.

Laboratory examinations

Initial laboratory investigations demonstrated leukocytosis [white blood cell (WBC) count 18.44 × 10⁹/L] with neutrophilic predominance (accounting for 86.2% of the total WBC count; absolute neutrophil count was 15.9 × 10⁹/L), markedly elevated inflammatory markers (procalcitonin 6.130 ng/mL, C-reactive protein 270.00 mg/L), and cholestatic liver enzyme abnormalities (total bilirubin 20.8 μmol/L, alkaline phosphatase 242 U/L, gamma-glutamyl transferase 265 U/L). Serum amylase was normal (31 U/L), and HBV DNA was undetectable, indicating adequate viral suppression under current entecavir therapy. The glycated hemoglobin measured on admission was 6.2%. During hospitalization, the patient's blood glucose changes were monitored: Although fasting blood glucose occasionally exceeded 7.0 mmol/L (normal range 6.4-13.4 mmol/L), the 2-hour postprandial blood glucose after three meals rarely surpassed 11 mmol/L (normal range 7.0-13.3 mmol/L). A consultation with the endocrinology department was requested, and deferring antihyperglycemic therapy was recommended. The anaerobic blood cultures and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) performed on admission and 2 days later both identified gram-positive cocci, subsequently identified as P. micra (Table 1).

Table 1 The anaerobic blood culture results.

Sampling time	Time to positivity	Gram stain	Genus	Species
On admission	47 hours 5 minutes	Positive	Parvimonas	Parvimonas micra
Two days later	41 hours 5 minutes	Positive	Parvimonas	Parvimonas micra

Imaging examinations

The initial liver ultrasound revealed a 7 cm hypoechoic lesion in the left lobe, suggestive of liver abscess (Figure 1A). Contrast-enhanced ultrasound revealed a complex hepatic mass (7.8 cm × 7.7 cm) with < 50% liquefaction, consistent with an evolving abscess formation (Figure 1B). We did not detect foreign bodies, fungal infection (β-D-glucan, galactomannan, and cryptococcal antigen were negative), or malignancy (normal tumor markers). Because P. micra is typically orodigestive in origin[17], a comprehensive re-examination of potential oral and digestive tract entry sites was performed, revealing no evidence of periodontitis or periodontal abscess. To further confirm whether liver abscess was caused by foreign bodies originating from the digestive tract, targeted examinations were performed. Abdomen enhanced computed tomography (CT) revealed a strip-shaped foreign body in the left outer lobe of the liver, extending to the wall of the pyloric canal (Figure 2). Simultaneous upper endoscopy and endoscopic ultrasonography (EUS) detected a red scar in the gastric corpus (Figure 3A) and a 23.5 mm strip-shaped lesion within the liver mass, which invaded the hepatic capsule with extrahepatic extension (Figure 3B-D). These findings were highly suggestive of a hepatic abscess secondary to a penetrating spiculated foreign body.

Figure 1 Liver ultrasound images of the liver lesion. A: Routine liver ultrasound identified a 7 cm hypoechoic lesion in the left lobe; B: Contrast-enhanced ultrasound revealed a complex hepatic mass (7.8 cm × 7.7 cm) with < 50% liquefaction, suggesting evolving abscess formation.

Figure 2 Results of abdomen enhanced computed tomography. A: An irregular hypodense mass shadow in the left lateral lobe of the liver; B and C: A strip-shaped high-density shadow in the left lateral lobe of the liver, with local invasion of the pyloric canal wall.

Figure 3 Results of simultaneous upper endoscopy and endoscopic ultrasonography. A: A red scar was seen in the gastric corpus; B-D: A 23.5 mm strip-shaped lesion within the liver mass, invading the hepatic capsule with extrahepatic extension.

FINAL DIAGNOSIS

The diagnosis was liver abscess caused by P. micra originating from foreign body ingestion, warranting consideration of surgical intervention.

TREATMENT

Initially, antibiotic therapy with intravenous penicillin G was implemented. Upon identification of P. micra in anaerobic blood cultures, the antimicrobial regimen was changed to piperacillin-tazobactam for targeted therapy. Subsequent abdominal CT and EUS suggested hepatic abscess secondary to a penetrating spiculated foreign body. A multidisciplinary team specializing in infectious diseases, gastroenterology, hepatobiliary surgery, anesthesiology, and radiology recommended surgical intervention due to foreign bodies within the mass. The patient underwent laparoscopic left lateral liver lobectomy, foreign body extraction, and gastric repair under general anesthesia. A 3.0 cm fish bone was removed (Figure 4).

Figure 4  A 3 cm fish bone was removed from the liver mass.

OUTCOME AND FOLLOW-UP

Postoperatively, the patient achieved clinical recovery with continued antibiotic therapy and was subsequently discharged.

DISCUSSION

Clinically, percutaneous drainage and broad-spectrum antibiotics are commonly used for treating liver abscesses[23]. For patients without definitive etiologies, particularly those without diabetes or biliary tract disease, clinicians should investigate beyond the apparent pathology to identify the underlying causes. Our patient had no clear recollection of fish bone ingestion. Over 50% of patients with foreign body-induced liver abscesses develop systemic symptoms more than 2 weeks after ingestion[24]. This prolonged latency often leads to overlooked histories.

Our patient atypically presented with fever, abdominal distension, vomiting, and diarrhea but lacked the classic signs of peritonitis or localized pain typically seen in gastrointestinal perforation. Hepatic tenderness on exam suggested chronicity, as the small fish bone and gradual fibrotic encapsulation likely minimized peritoneal leakage, masking the gastrointestinal origin and delaying diagnosis. Blood cultures identified P. micra, which served as a major diagnostic clue, redirecting our investigation toward occult gastrointestinal perforation. Contrast-enhanced abdominal CT revealed a strip-shaped hyperdensity in the left lateral liver lobe extending beyond the hepatic parenchyma. EUS is critical for rapid diagnosis of liver abscesses caused by gastrointestinal foreign bodies[25]. In Leggieri et al’s study[26], only 16% of foreign body-induced liver abscesses were detected by esophagogastroduodenoscopy. This was likely because the foreign bodies had already migrated out of the gastrointestinal tract and penetrated the liver, with the small perforation sites having adhered and healed. In the current case, EGD detected a red scar in the gastric corpus. Concurrent EUS examination identified a hypoechoic mass near the left portal vein branch adjacent to the umbilical vein, containing a hyperechoic strip-shaped structure consistent with a penetrating foreign body. The patient received timely liver surgery and targeted antibiotic therapy, achieving full recovery. His clinical course illustrates the importance of pathogen identification in guiding targeted diagnostic workups.

P. micra, a gram-positive anaerobic coccus formerly known as P. micros[17], is a small (0.5-1.0 μm) obligate anaerobe optimally cultured at 37 °C[16]. While MALDI-TOF MS facilitates its identification[27], conventional culture and susceptibility testing remain challenging. This is likely the main reason why P. micra-related liver abscess has been seldom reported. As a commensal inhabiting the oral cavity, gastrointestinal tract, and genitourinary mucosa, P. micra acts as an opportunistic pathogen in immunocompromised hosts or following mucosal barrier disruption (e.g., post-surgery in periodontal disease)[21]. Clinical isolation should prompt thorough evaluation of potential entry portals, including via dental examination and endoscopic assessment for occult perforations, given P. micra’s propensity for hematogenous spread. Notably, its penicillin susceptibility (90% strains) supports β-lactam therapy, though rising clindamycin resistance (22%) necessitates antimicrobial susceptibility testing-guided treatment[28]. In this case, the targeted antibiotic regimen of penicillin G followed by piperacillin-tazobactam had the desired treatment efficacy.

There are some limitations in this study. Firstly, although P. micra was identified by anaerobic blood cultures and MALDI-TOF MS, the antimicrobial susceptibility testing was not performed due to the laboratory limitations, which increases the risk of antimicrobial resistance. Secondly, the specimens obtained during surgery including aspirated pus, resected liver and fish bone were not subjected to microbiological culture to confirm the causative pathogens.

CONCLUSION

We reported the first case of P. micra-related liver abscess secondary to ingestion of a fish bone. This case highlighted that definitive pathogen identification is always important for certain common diseases. The definitive etiology of liver abscess guided us toward partial liver resection as the first-line treatment. This allowed complete excision of the liver lesion and timely removal of the foreign body to avoid further injury. More precise antibiotic therapy was implemented to promote the full recovery.

ACKNOWLEDGEMENTS

We are thankful to the parents of the patient for the support given in providing the data.