In a 76-year-old woman with a remote history of ovarian and breast cancer, an MRI reveals a rim-enhancing lesion in the right pubic symphysis and bone scintigraphy shows focal uptake in the right pubic symphysis and distal sternum; what is the most likely diagnosis?

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Most Likely Diagnosis: Osteomyelitis of the Pubic Symphysis

Given the rim-enhancing lesion on MRI at the pubic symphysis with corresponding focal uptake on bone scan, combined with the patient's age and remote cancer history with no current evidence of disease, osteomyelitis of the pubic symphysis is the most likely diagnosis.

Diagnostic Reasoning

Key Imaging Features Pointing to Infection

The rim-enhancing pattern on MRI is highly characteristic of osteomyelitis rather than metastatic disease. MRI findings of pubic symphysis osteomyelitis include high T2 signal and low T1 signal in the involved pubic rami, with rim enhancement representing inflammatory tissue and potential abscess formation 1. The combination of:

  • Rim enhancement (suggests fluid collection/abscess)
  • Focal uptake on bone scan at the pubic symphysis
  • Additional sternal uptake (could represent concurrent inflammatory process)

These findings align more closely with infectious/inflammatory pathology than metastatic disease.

Why Not Metastatic Disease?

Several factors argue against bone metastases:

  • Remote cancer history with current no evidence of disease: The patient has been cancer-free with regular surveillance mammograms showing no recurrence
  • Rim enhancement pattern: Metastases typically show solid enhancement rather than rim enhancement
  • Pubic symphysis location: While metastases can occur here, osteomyelitis at this site is well-documented in the literature 2, 1, 3
  • The sternal uptake could represent SAPHO syndrome or concurrent inflammatory process rather than multifocal metastases 4

Why Not SAPHO Syndrome?

While SAPHO syndrome (Synovitis, Acne, Pustulosis, Hyperostosis, Osteomyelitis) can present with sternal and pelvic lesions 4, the rim-enhancing pubic lesion is more consistent with infectious osteomyelitis. SAPHO typically shows:

  • Bilateral sternoclavicular involvement ("bull horn" sign)
  • History of skin manifestations (palmoplantar pustulosis, acne)
  • More symmetric distribution

The patient's presentation lacks these classic features.

Recommended Next Steps

Obtain blood cultures and inflammatory markers (CRP, ESR) immediately, followed by CT-guided or ultrasound-guided aspiration/biopsy of the pubic symphysis lesion for culture and histopathology 3. This will:

  1. Confirm the diagnosis by identifying the causative organism (most commonly Staphylococcus aureus or Pseudomonas aeruginosa) 2, 3
  2. Rule out malignancy definitively through histopathology
  3. Guide targeted antibiotic therapy

Critical Pitfall to Avoid

Do not assume bone metastases based on imaging alone in a patient with remote cancer history and current no evidence of disease 4. Conventional radiography is insensitive (63% showed no evidence in proven osteomyelitis cases), making MRI the definitive diagnostic modality 1. However, biopsy remains essential when bone-only disease with few or equivocal lesions is present 5.

If Osteomyelitis is Confirmed

Treatment consists of prolonged antibiotic therapy (typically 6-8 weeks) based on culture sensitivities, with good clinical outcomes when started early 2, 3. Surgical debridement is rarely needed if antibiotics are initiated promptly.

References

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This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.