A 13-Year-Old Boy with Chest Wall Actinomycosis Mimicking Ewing Sarcoma on Imaging

Background

Actinomycosis is an uncommon yet clinically significant bacterial infection caused by Actinomyces species. These filamentous, branching, and anaerobic gram-positive bacilli typically constitute the normal microbial flora in various human anatomical sites, including the oral cavity, gastrointestinal tract, and urogenital tract [1,2]. Actinomyces species possess the potential to become opportunistic pathogens, leading to manifestations in diverse anatomical regions throughout the body, such as the cervicofacial, abdominopelvic, pulmonary, and pelvic areas [3]. Factors that predispose individuals to thoracic actinomycosis include underlying respiratory disorders, poor oral hygiene, dental disease, and facial or dental trauma [3]. Furthermore, various chronic debilitating diseases and conditions, such as diabetes mellitus, neurologic and psychiatric diseases, malnutrition, drug abuse, and hiatal hernia, can facilitate respiratory tract infection and increase susceptibility to this condition [3].

Depending on the affected anatomical site, actinomycosis can present with various symptoms, including local pain, swelling, fever, and systemic manifestations [1,2]. Chest wall involvement is a rare presentation [3]. Chest wall lesions in childhood encompass a broad spectrum of conditions, including benign lesions like lipomas, neurofibromas, and hemangiomas, as well as malignant tumors such as neuroblastoma and rhabdomyosarcoma [4]. Additionally, infectious etiologies like tuberculosis and manifestations of systemic diseases such as leukemia and lymphoma should be considered [4–6]. This report describes the case of a 13-year-old boy with chest wall actinomycosis that presented with imaging findings mimicking Ewing sarcoma.

Case Report

A 13-year-old previously healthy boy presented to the Emergency Department with increasing chest pain 1 week after a minor fall while playing sports. The pain was localized to the left side of the chest and worsened with movement. The patient denied experiencing any associated symptoms, such as fever, weight loss, or fatigue. Importantly, there was no history of significant medical conditions, immune suppression, poor dentition, trauma, or malignancy in either the patient or his family.

On physical examination, the patient appeared well and showed no signs of acute distress. Vital signs were within normal limits. Mild swelling and tenderness were noted over the left anterior chest wall upon examination. No visible signs of trauma or abnormalities in the skin were observed. Auscultation of the lungs revealed clear breath sounds bilaterally, and the cardiovascular examination was unremarkable.

A computed tomography (CT) scan of the chest was performed to evaluate the rib cage and adjacent structures. The imaging revealed a large tumor involving the lower left chest wall, extending from the level of the left 6th rib to the left 12th rib. The tumor exhibited both soft tissue and bone components. The soft tissue component appeared ill-defined and hyper-vascularized, and demonstrated heterogeneous enhancement. It extended from the subcutaneous region anteriorly and reached deep/posterior to the adjacent ribs. The bony component of the mass mainly involved the anterior aspect of the left 7th, 8th, and 9th ribs, showing expansion and significant periosteal reaction. The overall measurements of the mass, including the soft tissue and bony components, were approximately 8.0×4.4×11.8 cm in maximum dimensions (Figure 1). Additionally, 2 ill-defined nodular lung lesions were noted, 1 in the left upper lobe measuring 1.1 cm and 1 in the left lower lobe measuring 1.2 cm, suggestive of possible lung metastasis (Figure 2). Multiple left hilar lymph node enlargements were also observed, with the largest measuring approximately 1.8×1.0 cm, indicative of metastatic lymph nodes. These findings raised suspicion for Ewing sarcoma.

To further investigate the chest wall lesion, a core needle biopsy was performed under image guidance. Surprisingly, the histopathological examination revealed a distinctive presentation of granulomatous inflammation. The granulomas contained sulfur granules composed of filamentous gram-positive bacilli. These bacilli were surrounded by intensely eosinophilic material, contributing to the formation of characteristic asteroid bodies. The affected area showed notable infiltration of neutrophils (Figure 3). These findings, when considered in conjunction with clinical correlation and microbiological cultures, confirmed the diagnosis of actinomycosis. The specific Actinomyces species responsible for this infection was identified as Actinomyces israelii.

Considering the diagnosis of actinomycosis of the chest wall, the patient was promptly initiated on intravenous penicillin G at a dosage of 100 000 units/kg/day, divided into 4 doses every 6 h for 4 weeks.

Following a 4-week course of therapy, a repeat CT scan demonstrated a marked and favorable response in the soft tissue and bone lesion involving the lower left chest wall, with extension now limited to the level of the left 7th to 9th ribs (Figure 4). The overall dimensions of the mass, encompassing the soft tissue and bony components, showed a notable reduction, measuring approximately 5.6×2.0×6.4 cm at its maximum extent. Furthermore, the 2 previously noted ill-defined nodular lung lesions exhibited complete healing, and a reduction in size was observed in the multiple left hilar lymph node enlargement.

After the initial treatment, the patient continued with maintenance therapy, transitioning to oral amoxicillin at a dosage of 40 mg/kg/day, divided into 3 doses every 8 h, for the entire 12-month course. Throughout this period, the chest wall mass showed complete resolution, and no significant adverse events or complications were observed.

Discussion

In this case report, a compelling clinical presentation of thoracic actinomycosis involving the chest wall is illustrated. This case offers valuable insights into the diverse clinical manifestations of actinomycosis, emphasizing the importance of considering this rare condition in the differential diagnosis of patients with unresolving chest wall symptoms. Actinomycosis of the chest wall is a rare entity [7]. The case described here is particularly noteworthy due to its unusual presentation and the initial suspicion of Ewing sarcoma, which is more commonly encountered in pediatric patients [4].

Actinomycosis is primarily caused by Actinomyces israelii, although other Actinomyces species can also be implicated. It typically occurs as a result of endogenous spread from the oral cavity or gastrointestinal tract, often following local tissue damage or a breach in the mucosal barriers [7].

Actinomycosis often manifests with suppurative and granulomatous features, frequently resembling malignancies or infections [8]. The presentation in our case, characterized by a large tumor-like mass comprising both bone and soft tissue components, initially prompted concerns of Ewing sarcoma. Similarly, Yilin et al [9] documented an instance involving an 11-year-old child with a chest wall mass and discomfort, initially leading to suspicion of a malignant tumor such as Askin tumor. However, a chest wall biopsy ultimately unveiled actinomycosis, underscoring the diagnostic complexity of this rare condition. Similar to our case, the young age of the patient and the initial suspicion of malignancy based on radiological findings highlighted the difficulty in distinguishing actinomycosis from more common conditions.

The clinical presentation of chest wall actinomycosis can be diverse and nonspecific, making diagnosis challenging [8]. Patients often present with pain, swelling, and tenderness, which can mimic various conditions, including trauma, malignancy, or infectious processes [9]. Radiological imaging, such as CT, plays a crucial role in evaluating the extent of the lesion and identifying associated complications, such as bone involvement [3]. In our case, the CT scan revealed a large tumor involving the lower left chest wall with both soft tissue and bone components, simulating a malignant neoplasm.

Differentiating actinomycosis from malignancy, such as Ewing sarcoma, can be challenging due to overlapping clinical and radiological features [10,11]. However, there are certain features that may raise suspicion for actinomycosis. In chest wall actinomycosis, the presence of abscesses or sinus tracts can aid in the diagnosis. Moreover, while malignancies often demonstrate aggressive growth with infiltrative margins, actinomycosis can exhibit a more indolent growth pattern with ill-defined margins and variable enhancement on imaging [10,11].

The management of chest wall actinomycosis typically involves a combination of antibiotics and, in some cases, surgical intervention [11,12]. Antibiotic therapy plays a central role in eradicating the infection, with penicillin or amoxicillin being the agents of choice. Surgical intervention may be necessary in cases with extensive involvement, abscess formation, or complications such as fistulae [10,11]. Regular follow-up and repeat imaging are essential to monitor treatment response and ensure resolution of the infection [1,2].

Conclusions

This case underscores the importance of expanding the range of possible diagnoses when evaluating pediatric patients with chest wall masses, and it highlights the importance of considering uncommon conditions such as chest wall actinomycosis. The diagnostic complexities associated with this rare condition emphasize the need for a comprehensive evaluation strategy incorporating histopathological examination and imaging. The effective diagnosis and treatment of this case underscore the vital contributions of a multidisciplinary medical team. This case serves as a valuable reminder of the collaborative effort required to address complex medical conditions in pediatric patients.