Case of a Slowly Enlarging Pediatric Rib Mass

CASE

A healthy 3-year-old male presented with a progressively enlarging lump on his left posterior torso, present for 8 months but growing rapidly over the past 3 months. There was no associated pain, fever, night sweats, weight loss or prior trauma. The child appeared active and well. Documented vital signs at presentation were: heart rate of 100 beats/minute, temperature of 36.5 °C, weight 17.8 kg (84%, Z = 0.98) and height 98.8 cm (47%, Z = −0.09). On physical examination, there were 2 nontender, nonerythematous, non-mobile masses on his left posterior torso: one measuring 3.0 × 2.5 cm and the other 1.5 × 1.5 cm (Fig. 1). On palpation, the masses were firm and not fluctuant. The remainder of the physical examination demonstrated an active, well-appearing child, with normal heart rhythm and rate, normal work of breathing with good air entry bilaterally, skin without rashes or birthmarks and soft abdomen without masses or distention.

FIGURE 1.

Photograph of 2 masses on mid-axillary/posterior chest wall at time of initial presentation. 

Ultrasound revealed several heterogeneous masses on the posterior aspect of the left 9th rib near the mid-axillary line. CT with contrast showed extensive bone remodeling of the left 9th rib, with osseous sclerosis, hyperostosis and cortical defects. It also revealed a 4.3 × 2.4 × 4.0 cm heterogeneously enhancing soft tissue mass involving the left latissimus dorsi muscle and subcutaneous tissues, extending into the extra-pleural space near the left costophrenic angle and surrounding the rib abnormality, with no lymphadenopathy (Fig. 2). The patient was referred to an oncologist for further evaluation.

FIGURE 2.

CT of chest before biopsy. Axial (left, A) and coronal (middle, B) projections demonstrating extensive bony remodeling of the left 9th rib with sclerotic changes, hyperostosis, and scattered cortical defects/erosions, indicated by straight orange arrows. Coronal projection (right, C) in soft tissue window demonstrating associated ill-defined heterogeneously enhancing soft tissue surrounding the rib with involvement of the muscle and soft tissue into the extra-pleural space (right, C), as show by straight orange arrow. Course calcifications within the mass. No lymphadenopathy or other bony lesions were identified. Differential of chronic infection/osteomyelitis and/or malignancy, with tissue sampling recommended for definitive diagnosis. 

The pediatric oncologist ordered several laboratory tests, including complete blood counts, a complete metabolic panel, inflammatory markers (CRP and ESR), lactate dehydrogenase and uric acid tests, all of which were normal. A biopsy was arranged for mass given unclear diagnosis.

DENOUEMENT

An open bone biopsy was performed, and pathology confirmed osteomyelitis. Cultures grew Methicillin-Resistant Staphylococcus Aureus, and the patient was started on intravenous (IV) vancomycin. Additional workup for immunodeficiency was performed, including neutrophil oxidative burst assay, immunoglobulin levels, lymphocyte subset panel and pneumococcal antibody titers, none of which suggested an underlying immunodeficiency. A nuclear bone scan did not show any other abnormalities. The inpatient course was complicated by an abscess at the biopsy site, requiring incision and drainage; however, no repeat culture was sent. IV vancomycin was continued for 5 days before being switched to IV clindamycin. The patient was eventually discharged on a prolonged oral clindamycin course after continuing to improve on 48 hours of IV clindamycin.

The patient was closely followed by Infectious Diseases to determine the duration of antibiotics. An magnetic resonance imaging (MRI) 5 weeks after discharge showed a chronic abnormality of the left 9th rib and persistent nodular soft tissue masses, the largest measuring 2.5 × 1.2 × 2.0 cm (Fig. 3). At the 6-week follow-up visit, concerns arose that the slow response to treatment, nonhealing of the biopsy site and continued intermittent drainage could indicate he had a possible polymicrobial infection or bacterial superinfection of an, as yet, unrecognized neoplasm. This concern led to a repeat biopsy of the persistent mass at the same location as the prior biopsy, with extraction of several small pieces of tissue. Pathology showed no microorganisms, bone fragments or malignancy, and cultures were negative for AFB, fungi and bacteria. Pathology demonstrated mild chronic active inflammation. Oral clindamycin therapy was extended for another 6 weeks.

FIGURE 3.

Initial MRI chest post-biopsy, 5 weeks post-hospital discharge. Coronal STIR (left, A) and axial T1 post-contrast sequences (right, B) demonstrating diffuse chronic expansile deformity of the rib (see straight orange arrows) with heterogeneous edema and enhancement compatible with inflammatory change, with focal areas of soft tissue nodularity. 

By the 12-week mark from the start of treatment for osteomyelitis, an MRI showed significant improvement: while a chronic deformity of the left 9th rib remained, there was decreased inflammation and reduced axillary lymphadenopathy as compared with prior images (Fig. 4). However, the biopsy site had still not healed, and antibiotics were continued. After a full 6 months from the start of antibiotic therapy, the child achieved complete resolution of the mass, and the biopsy site fully healed. Close to 1 year later, the child remains healthy and off antibiotics, with no recurrence of symptoms.

FIGURE 4.

Follow-up MRI approximately 5 months later demonstrating persistent although decreased inflammatory changes after antibiotic therapy. Coronal STIR (left) and axial T1 postcontrast sequences (right) demonstrating improved but persistent abnormalities of the affected rib. 

Osteomyelitis of the bone can be acute or chronic. Rib osteomyelitis represents only 1% of all osteomyelitis cases, with a pediatric incidence of 8 cases per 100,000 children per year and a higher incidence in children under age 5 years.¹ Risk factors for osteomyelitis include immunodeficiencies, such as CGD, and hemoglobinopathies, such as sickle cell disease.² The typical clinical presentation of rib osteomyelitis in a pediatric patient is a nonhealing abscess with pain at the site. Patients typically present with fevers and increased inflammatory markers.^2–4 Our case demonstrates a rare presentation of a chronic rib osteomyelitis in a child who was afebrile with normal inflammatory markers, no history of trauma and no predisposing risk factors.

Rib osteomyelitis is predominantly associated with hematogenous spread of pathogens, with Staphylococcus aureus being the most common isolated bacteria.^3,5 Less common causes include other bacterial and fungal etiologies. For example, a 2005 literature review of rib osteomyelitis cases found that only 3 cases of 150 were due to streptococcal species.² One case of cryptococcal rib osteomyelitis has been noted in a previously healthy pediatric patient.⁶ Mycobacterium tuberculosis has also been noted as a causative agent of pediatric rib osteomyelitis.⁷

Rib osteomyelitis, especially with an indolent course such as our case, can mimic other diagnoses, such as pneumonia, fracture, neoplasms or costochondritis, resulting in challenges to initial diagnosis.^3,8 Delays in diagnosis can lead to progression of the disease. At initial assessment, our patient was recorded to have had the mass for over 8 months, raising little concern from the mother, as it did not bother the child. Cases in the literature have been noted to have persisted for as long as 3 years.⁸ Making an early diagnosis is essential to counter the significant sequelae of rib osteomyelitis, including fractures, abscesses and bloodstream infection.⁴

Arriving at a final diagnosis may require a combination of repeated physical examination findings, laboratory and pathology results and radiologic imaging, as relying on any given result alone, or at only one time point, can lead to inconsistencies and incomplete information. For example, in a review of 7 cases of pediatric rib osteomyelitis, they found that the patients’ CRP and WBC were not elevated in 2 of 7 cases, a similar nonfinding in our patient.⁸ Further, many patients with osteomyelitis present with fever; however, patients like our case have been afebrile.⁶

While radiographs are indicated for initial osseous evaluation due to low cost and minimal radiation, they can frequently be inconclusive in cases of rib osteomyelitis, given their low sensitivity. CT as an imaging modality can be advantageous in the pediatric population due to fast scanning times, often obviating the need for sedation, and can be helpful for evaluation for bony changes, albeit with some radiation risks.⁴ MRI is complementary to these modalities and serves as the gold standard for imaging to evaluate inflammatory bony, as well as soft tissue changes and offers the highest sensitivity in the diagnosis of osteomyelitis, including in the rib.^3,4 It is further advantageous in this population given its lack of ionizing radiation; however, the need for sedation must be considered due to motion artifact. MRI is helpful for assessment of treatment effectiveness and resolution of infection, especially with chronic osteomyelitis.⁴

The gold standard for diagnosing rib osteomyelitis is blood and/or bone culture as well as histopathology.^3,5 Biopsy is often indicated to distinguish osteomyelitis from other disease processes, including neoplasms, and to identify a causative organism and sensitivity to antibiotics.⁵ The 2 main differentials of note for a progressively expanding costal mass are malignancy, in particular Ewing sarcoma, as well as osteochondroma, a benign entity with very low malignant transformation potential. Ewing sarcoma is of highest concern and commonly involves the ribs.⁹

CONCLUSIONS

Diagnosing a child with a rib mass presents a complex clinical challenge, as the differential diagnosis spans a wide spectrum of conditions, from benign infections to life-threatening malignancies. Unlike masses in more common locations, rib lesions often lack obvious early symptoms, leading to delayed detection. When a child presents with persistent pain, swelling or systemic symptoms like fever, physicians must carefully navigate overlapping features of infectious, inflammatory and neoplastic processes. As this case shows, chronic osteomyelitis can masquerade as a tumor due to its insidious course and subtle inflammatory markers, while primary bone malignancies may initially resemble an infection. Radiographic findings can be equally ambiguous, requiring advanced imaging and, at times, biopsy to distinguish between these possibilities. An early diagnosis utilizing MRI and promptly targeted antibiotics is essential to limit sequelae, including damage to bone and surrounding structures, as well as the risk of infection spread.