Introduction

Chest wall masses are uncommon clinical presentations that encompass a wide range of differential diagnoses, including benign and malignant tumors, inflammatory lesions, and infectious processes [1]. Among these, chest wall abscesses are particularly rare, especially when they occur without an apparent source of infection. They may arise secondary to direct extension from pulmonary, pleural, or mediastinal infections, or following trauma or thoracic surgery [2, 3]. In contrast, primary chest wall abscesses occurring in the absence of any adjacent or systemic infectious focus are exceedingly uncommon and can cause a significant diagnostic dilemma [2, 3].

The clinical presentation of a chest wall abscess may mimic that of a soft-tissue tumor, particularly when typical signs of infection such as fever, erythema, and tenderness are absent [4]. Radiologic findings can also be misleading, as both infections and malignancies may demonstrate overlapping features [5].

Given these overlapping clinical and imaging features, establishing an accurate diagnosis is crucial to avoid unnecessary surgical intervention and ensure timely antimicrobial therapy [1]. Here, we present a case of an elderly man with Diabetes Mellitus (DM) and chronic kidney (CKD) disease who developed a rapidly growing large right anterior chest wall mass that demonstrated aggressive bone invasion. This case highlights a critical diagnostic challenge where clinical and imaging profiles strongly mimicked an advanced malignancy, overshadowing an underlying pyogenic infection.

Case report

A 68-year-old man with underlying DM and  CKD presented to our institute with a complaint of swelling over his right anterior chest wall for the past 4 months. He had experienced weight loss of approximately 12 kg, along with a poor appetite. He reported no history of fever. He denied any history of trauma, recent infections, tuberculosis exposure, or previous thoracic surgery.

On examination, he appeared chronically ill but not in acute distress.. A non-tender mass measuring 10 × 10 cm was noted over the right anterior chest wall. There was no punctum (small cutaneous opening indicating a possible draining sinus), erythema, or fluctuance. No palpable lymph nodes were detected in either axillary or cervical regions. Laboratory investigations showed an inrease of white blood cell (WBC) count of 26 × 109/L (normal range: 4.0 - 11.0 × 10⁹/L) and a C-reactive protein (CRP) level of 105 mg/L(normal range:<5mg/L). Renal function was at baseline for CKD. Urine and blood culture, urine analysis and chest radiograph showed no evidence of infection.

Two months earlier, the patient had sought treatment at our hospital. Ultrasound of the chest wall at that time revealed a solid–cystic mass) at the right chest wall, extending towards the right upper shoulder region, without obvious intrathoracic extension. The mass was avascular and demonstrated echogenic debris within the mass with differential diagnoses of chest wall collection or infected cyst [Figure 1]. The patient was scheduled for excision and drainage; however, he defaulted on treatment as he lived far from the hospital and represented 2 months later with marked progression of the mass size.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                Computed tomography (CT) of the thorax later revealed a huge heterogeneously enhancing solid–cystic mass over the right anterior chest wall, extending from the right first to the fifth rib, measuring approximately 6.7 cm × 20.5 cm × 14.2 cm (AP × W × CC). There was an intrathoracic extension with erosion of the right anterior first rib [Figure 2 and 3]. At that stage, the clinical features and imaging favoured a soft tissue tumour rather than an abscess, with undifferentiated pleomorphic sarcoma (UPS) or fibrosarcoma considered the most likely diagnosis. Given the highly aggressive presentation on CT with bone erosion and intrathoracic extension, the clinical objective shifted directly towards radical surgical intervention for simultaneous diagnostic tissue sampling and therapeutic local control. Consequently, a preoperative image-guided needle biopsy was omitted out of concern for delaying definitive surgical management. Additionally, obtaining a preoperative Positron Emission Tomography-Computed Tomography (PET-CT) was logistically unfeasible because our regional centre does not have a PET-CT scanner. Transferring the patient to the nearest tertiary facility would have required a 9-hour drive, dangerously delaying the urgent intervention needed for this rapidly growing mass.

Fig. 1
Fig. 1
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Figure 1: Ultrasound evaluation of the right anterior chest wall mass. (a) Grey-scale (B-mode) ultrasound showing an ill-defined cystic mass with internal debris abutting the pleural lining and adjacent rib. (b) Colour Doppler ultrasound demonstrating the mass is avascular, favouring an infectious collection over a hypervascular soft-tissue tumour

(Figure 3A 3B) favoured a 

Fig. 2
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CT thorax in sagittal view demonstrates a large, ill-defined heterogeneously enhancing mass (*) over the right anterior chest wall extending from the right 1 st rib through the right 5th rib with minimal extension into the intercostal spaces

Fig. 3
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CT thorax with contrast in axial soft tissue window (A) and bone window (B) shows the cystic component within the right chest wall mass (long arrow). There is also an extension into the intrathoracic cavity (*) together with rib erosion (short arrow)

The patient was scheduled for definitive surgical exploration and excision. Intraoperatively, however, copious pus was encountered, and the procedure was immediately converted to extensive surgical debridement of the abscess cavity and the infected bone. Histopathological examination demonstrated features of an abscess with acute-on-chronic inflammation and prominent histiocytic infiltration, without evidence of malignant cells (Fig. 4). Formal bone tissue biopsy was not obtained, but surrounding histopathology confirmed pyogenic soft-tissue infection adjacent to the costal bone rather than histological osteomyelitis. Pus culture grew Staphylococcus aureus, which was sensitive to common antibiotics, including beta-lactams. Post-operatively, broad-spectrum intravenous Tazocin (piperacillin/tazobactam) and Unasyn (ampicillin/sulbactam) were administered to cover potential polymicrobial and nosocomial superinfections given the patient’s high-risk background of DM and CKD. Unfortunately, he developed a nosocomial infection complicated by septicaemia, requiring intensive care unit (ICU) admission, and succumbed to death 3 weeks after surgery.

Fig. 4
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Histopathological examination of the chest wall lesion showing (A) tissue densely infiltrated by inflammatory cells composed of foamy macrophages and neutrophils (Hematoxylin & eosin 100 × magnification) (B) in areas, abscess presence is noted (Hematoxylin & eosin 100 × magnification) (C) occasional multinucleated giant cells with groups of lipid laden macrophages ((Hematoxylin & Eosin 200 × magnification)

Discussion

Chest wall abscesses are rare clinical entities that may present either primary or secondary lesions [1, 3]. Primary abscesses arise via haematogenous spread, whereas secondary abscesses usually result from contiguous spread of infection from the lung, pleura, or mediastinum, or following trauma or surgery [1, 3]. In the present case, no predisposing factors or concomitant sites of infection were identified, suggesting a primary chest wall abscess. Primary chest wall abscesses without a clear infectious source are exceedingly uncommon, with only isolated reports in the literature, such as Escherichia coli costochondritis described by Sakran et al. [1] and a trauma-associated abscess reported by Yamaoka et al. [3].

The absence of fever in our patient is noteworthy. Infections are often expected to manifest with pyrexia; however, certain groups including the elderly, infants, patients with chronic kidney disease, and those receiving corticosteroids may instead present with hypothermia or remain afebrile [5, 6]. In our case, the patient’s comorbidities of DM and CKD likely contributed to the atypical presentation. A possible explanation is haematogenous seeding from an unrecognised or transient focus, such as the skin, urinary tract, or oral cavity. Even brief episodes of bacteraemia can result in microbial colonisation, particularly in immunocompromised hosts. Patients with diabetes and chronic kidney disease are predisposed to such infections due to impaired neutrophil chemotaxis, phagocytosis, and intracellular killing, reducing their ability to contain bacterial invasion [4, 5]. Minor or unnoticed trauma to the chest wall may also create a favourable microenvironment for infection by disrupting tissue integrity. In this case, Staphylococcus aureus was isolated, a pathogen well recognised for its ability to adhere to tissues and form abscesses through virulence factors such as coagulase and protein A [1, 3, 5]. These findings suggest that haematogenous seeding, compounded by impaired host defences, was the most likely mechanism of abscess formation in our patient.

Clinically, abscesses are typically painful, fluctuant, and associated with overlying erythema [7]. In our case, the lesion was firm, non-fluctuant, and without skin changes, further complicating clinical assessment. While the markedly elevated WBC count and CRP supported an inflammatory process, these markers are non-specific and may also be elevated in other conditions including trauma, surgery, inflammatory bowel disease, and malignancy [6]. Indeed, CRP has been associated with various cancers, including those of the breast, gastrointestinal tract, pancreas, kidney, and lung, limiting its diagnostic specificity [6].

Imaging played a pivotal role but also contributed to diagnostic confusion. The initial ultrasound findings of a solid cystic mass with internal debri was consistent with an abscess or infected cyst. In contrast, CT imaging later revealed a large, heterogeneously enhancing mass with bone erosion and intrathoracic extension- features more suggestive of malignancy. Abscess generally appears as a cystic lesion with peripheral rim enhancement without solid component in CT imaging, whereas tumour often demonstrates heterogenous enhancement and necrosis [8]. Myxoid tumours such as myxomas, myxoid liposarcoma and myxofibrosarcomas may further mimic abscesses radiologically as these tumours commonly show pseudocystic appearance [8]. Thus, imaging alone cannot always distinguish between infection and neoplasm. In situations of diagnostic uncertainty, image-guided aspirations or biopsy can provide diagnostic clarity and may prevent unnecessary extensive surgery; however, in our case, a preoperative biopsy was omitted out of concern that it might delay urgent radical management for a presumed high-grade sarcoma. Furthermore, as demonstrated in recent thoracic imaging literature, inflammatory and infectious processes affecting costal structures frequently present with focal swelling, sclerosis, and extensive reactive soft-tissue thickening, directly simulating the aggressive bone invasion typical of malignant lesions [9]. Thus, imaging alone cannot always distinguish between infection and malignancy. As multiple distinct pathologies can manifest within the exact same anatomical site with overlapping radiological features, a meticulous multimodality imaging approach remains essential [9]. In situations of diagnostic uncertainty, image-guided aspiration or core needle biopsy can provide vital diagnostic clarity and prevent unnecessary extensive surgery; however, in our case, a preoperative biopsy was omitted out of concern that it might delay urgent radical management for a presumed high-grade sarcoma.

Advanced imaging modalities such as Magnetic Resonance Imaging (MRI) and PET-CT play a vital role in the diagnostic work-up of complex chest wall masses [2]. MRI provides superior soft-tissue contrast, allowing for precise delineation of anatomical planes, intercostal muscle involvement, and neurovascular bundle invasion [2]. On MRI, a chest wall abscess typically demonstrates characteristic peripheral rim enhancement on T1-weighted contrast-enhanced sequences and profound central restricted diffusion on diffusion-weighted imaging (DWI), which serves as a key discriminator from necrotic malignancies [10]. Conversely, PET-CT is highly valuable for systemic staging and identifying occult primary malignancies or synchronous infectious foci [11]. However, clinicians must note that both high-grade sarcomas and active infectious processes exhibit marked hypermetabolism with intense fluorodeoxyglucose (FDG) avidity [11]. Therefore, while PET-CT excels at demonstrating the metabolic activity and extent of a lesion, its specificity can be limited when differentiating an aggressive infectious abscess from a malignant chest wall tumour [11]. Chest wall tumours, although uncommon, represent approximately 5% of all thoracic malignancies, with more than half being malignant [1, 2]. Primary malignant tumours may arise from bone or soft tissue, whereas secondary tumours result from invasion of adjacent structures, most commonly breast, lung, or pleural cancers [2]. Undifferentiated pleomorphic sarcoma (UPS) is the most common primary malignant soft tissue tumour of the adult chest wall [1, 2]. On CT, UPS typically presents as a large, heterogeneously enhancing mass with local invasion; a pattern closely mimicked our case [1, 2].

Management of chest wall abscesses generally involves a combination of surgical drainage and targeted antibiotic therapy. As in our case, although pus culture confirmed S. aureus sensitive to standard antibiotics, the post-operative broad-spectrum regimen consisting of Tazocin and Unasyn was clinically justified to provide empirical coverage against potential hospital-acquired polymicrobial superinfections in this vulnerable host with DM and CKD. However, the diagnostic delay and subsequent hospital-acquired infection were decisive factors in the fatal outcome. This case therefore highlights the importance of maintaining clinical suspicion for infection in any enlarging chest wall mass and of initiating empiric antibiotic therapy once infection is reasonably suspected.

Ultimately, this case illustrates how an a typical clinical presentation combined with aggressive radiological features can obscure an underlying infectious process. While radical surgery was initially prioritised to avoid delaying treatment for a presumed high-grade malignancy, the unexpected intraoperative finding of an abscess underscores the diagnostic value of early tissue sampling. Recognizing these diagnostic pitfalls is essential for optimizing clinical management and preventing adverse outcomes in similar challenging cases.

Conclusion

This case underscores the diagnostic difficulties posed by atypical presentations of primary chest wall abscesses, particularly in immunocompromised individuals. The absence of classical signs of infection, combined with progressive enlargement and aggressive radiological features, may closely mimic malignancy and delay appropriate management. . This case highlights a critical clinical learning point: when an enlarging chest wall mass presents with diagnostic uncertainty, an early image-guided needle biopsy or aspiration should be strongly considered. Timely histological and microbiological identification enables prompt initiation of targeted antimicrobial therapy, potentially averting extensive surgical debridement and reducing the risk of life-threatening nosocomial complication.