What is the appropriate diagnosis and management for lytic osseous destructive lesions of the left acetabulum?

Lytic Osseous Destructive Lesions of the Left Acetabulum

Diagnostic Approach

The initial workup for lytic acetabular lesions must include plain radiographs of the pelvis, followed by cross-sectional imaging with MRI (with or without contrast) or CT to characterize the lesion, assess soft tissue extension, and guide biopsy planning. 1, 2

Imaging Strategy

• Plain radiographs serve as the first-line modality to identify the lytic lesion and assess for pathologic fracture 1
• MRI with gadolinium contrast is the most sensitive modality for characterizing bone lesions, detecting soft tissue extension, and evaluating bone marrow involvement 1
• CT imaging provides superior detail of cortical destruction, fracture patterns, and is essential for biopsy planning 1, 2
• Whole-body imaging (PET/CT or whole-body low-dose CT) should be obtained to identify additional skeletal lesions and assess for metastatic disease 1, 2

Critical Differential Diagnosis

The differential for lytic acetabular lesions includes:

• Metastatic disease (most common in adults) - particularly from breast, lung, kidney, or thyroid primaries 2, 3
• Multiple myeloma - the classic presentation of lytic bone lesions, requires serum protein electrophoresis (SPEP), urine protein electrophoresis (UPEP), serum free light chains, and bone marrow biopsy 1, 2
• Primary bone sarcomas - including chondrosarcoma (common in pelvis) or osteosarcoma 1, 4
• Infection - tuberculosis can present as isolated lytic lesions mimicking malignancy 5
• Brown tumor from hyperparathyroidism - particularly in patients with renal failure, shows hemosiderin on MRI 6
• Rosai-Dorfman-Destombes disease - rare, typically with mixed lytic/sclerotic appearance 1

Biopsy Requirements

Biopsy must be performed at a bone sarcoma reference center by the surgeon who will perform definitive resection if malignancy is confirmed. 1, 4

• Core needle biopsy under CT or fluoroscopic guidance is preferred to obtain adequate tissue while minimizing contamination 4
• Biopsy tract must be planned along the definitive surgical approach to allow en bloc resection if needed 1
• Adequate sampling is essential as osteoid production in osteosarcoma may be focal 4

Laboratory Workup

Essential laboratory studies include:

• Complete blood count - evaluate for anemia, leukocytosis, thrombocytopenia 1
• Comprehensive metabolic panel - assess calcium, alkaline phosphatase, renal function 1, 6
• Serum protein electrophoresis (SPEP), urine protein electrophoresis (UPEP), serum immunofixation, and serum free light chains - to evaluate for multiple myeloma 1
• Parathyroid hormone (PTH) - if brown tumor suspected, particularly with renal disease 6
• Erythrocyte sedimentation rate - elevated in Rosai-Dorfman disease 1

Management Considerations

For Metastatic Disease

• Percutaneous cementoplasty (acetabuloplasty) provides pain relief and mechanical strengthening for weight-bearing acetabular lesions when surgery is not tolerated 3
• Bisphosphonates have established efficacy for lytic bone lesions from metastatic disease and multiple myeloma 2
• Radiotherapy may be appropriate for palliation 1

For Primary Bone Sarcomas

• Surgical excision with wide margins is the definitive treatment for chondrosarcoma and most bone sarcomas of the pelvis 1
• High-grade chondrosarcomas (grade II-III) and all pelvic chondrosarcomas require wide surgical margins 1
• Neoadjuvant chemotherapy may be considered for mesenchymal chondrosarcoma or dedifferentiated chondrosarcoma 1

For Multiple Myeloma

• Full skeletal survey is required to document extent of lytic lesions 1
• Presence of lytic bone lesions indicates progression from smoldering to symptomatic myeloma requiring treatment 2
• Bone marrow aspiration and biopsy with cytogenetics and FISH are mandatory 1

Critical Pitfalls to Avoid

• Never perform internal fixation of a pathologic fracture before biopsy - this contaminates tissue planes and compromises definitive oncologic resection 1
• Do not assume metastatic disease without tissue diagnosis - tuberculosis, brown tumor, and primary sarcomas can mimic metastases 6, 5
• Avoid biopsy at non-specialized centers - improper biopsy technique can compromise limb salvage options 1, 4
• Do not rely on radiographs alone - cross-sectional imaging is essential to assess soft tissue extension and guide treatment 1, 2