Working Diagnosis:
Left femur osteomyelitis with Brodie's abscess
Left thigh soft tissue abscesses – medial, posterior, and lateral

Treatment:
When relaying results to the patient, he reported he had spontaneous fluid drainage from his lateral thigh while sleeping. Patient was admitted to orthopedics, started on IV antibiotics, and underwent surgical debridement with antibiotic-impregnated calcium sulfate (AICS) beads. After surgery, the patient was given a 6-week PO antibiotic course and placed on crutches given the amount of osseous debridement. He was seen by an ID specialist 10 days post-op and reportedly complied with protected weight bearing, home exercise program, and antibiotic therapy. The patient shortly thereafter moved to Indiana and has been followed by an orthopedic surgeon and ID specialist there. Case Photo #4

Outcome:
Return to activity was based on infection resolution and imaging in conjunction with restoration of full function. He received serial x-rays, which showed slow closure and healing of the bone cavity. The patient completed rehabilitation with progressive strengthening and mobility work. By 6 months, he returned to full activity with no pain.

Author's Comments:
Brodie's abscess can be diagnostically complex, initially presenting in this case as thigh cellulitis with persistent knee effusion and a negative culture on arthrocentesis. Upon re-review, the abscess was present on initial x-ray, mistaken for bone contour. This infection likely started in the bone and spread to the soft tissues. Patient deferral of MRI delayed definitive identification of subacute osteomyelitis. Brodie's abscess can mimic benign and malignant bone abnormalities, emphasizing the need for advanced imaging when symptoms persist despite antibiotic therapy. Early intervention with target antimicrobial therapy is critical to prevent chronic infection or functional impairment.

Editor's Comments:
The case illustrates the complexities surrounding the evaluation and diagnosis of a Brodie’s abscess in subacute osteomyelitis. Brodie’s Abscess is common in children and adolescents but can be seen in early adulthood. It is most commonly caused by Staphylococcus Aureus. The diagnosis can be elusive as subtle abnormalities may be missed on initial imaging, and systemic symptoms may be minimal or absent. In this case, not only was the initial xray interpreted as normal, but the arthrocentesis was initially negative for infection. Advanced imaging is very helpful in differentiating Brodie’s Abscess from osteoid osteoma, nonossifying fibroma, giant cell tumor, eosinophilic granuloma, chondroblastoma, fibrous dysplasia, and primary bone malignancy. MRI demonstrates the "penumbra sign" which is a discrete rim of granulation tissue that is relatively hyperintense on T1 surrounding the abscess cavity, which is a helpful discriminating feature for subacute osteomyelitis.

Brodie’s Abscess is treated with a combination of surgical curettage/drainage, with bone grafting for larger lesions, plus antibiotics (anti-staphylococcus) typically up to 6 weeks.

References:
Chin J, Naito T, Hon K, Lomiguen C. Challenges in the Diagnosis of Brodie's Abscess in Subacute Osteomyelitis. J Orthop Case Rep. 2020 May-Jun;10(3):1-4. doi: 10.13107/jocr.2020.v10.i03.1722. PMID: 33954124; PMCID: PMC8051581.

Salik M, Mir MH, Philip D, Verma S. Brodie's Abscess: A Diagnostic Conundrum. Cureus. 2021 Jul 16;13(7):e16426. doi: 10.7759/cureus.16426. PMID: 34422465; PMCID: PMC8369975.

van der Naald N, Smeeing DPJ, Houwert RM, Hietbrink F, Govaert GAM, van der Velde D. Brodie's Abscess: A Systematic Review of Reported Cases. J Bone Jt Infect. 2019 Jan 24;4(1):33-39. doi: 10.7150/jbji.31843. PMID: 30755846; PMCID: PMC6367194.

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