What is the management approach for an asymptomatic patient with an incidental finding of bilateral iliac crest aneurysmal bone cysts?

Management of Asymptomatic Bilateral Iliac Crest Aneurysmal Bone Cysts

For asymptomatic aneurysmal bone cysts (ABCs) discovered incidentally, observation with periodic imaging surveillance is the appropriate initial approach, as intervention is typically reserved for symptomatic lesions or those at high risk for pathological fracture. 1

Initial Imaging Evaluation

When ABCs are discovered incidentally on non-musculoskeletal imaging (such as CT or MRI performed for other indications), the next step is obtaining dedicated radiographs of the affected area to establish baseline characteristics and assess fracture risk 1. Radiographs provide critical information about:

• Lesion margins and periosteal reaction (indicators of biological activity) 1
• Cortical thinning or destruction (fracture risk assessment) 1
• Size and extent of bone involvement 1
• Baseline measurements for future comparison 1

If radiographs show a definitively benign appearance without features suggesting high fracture risk, no additional advanced imaging is routinely indicated for asymptomatic lesions 1.

Risk Stratification for Pathological Fracture

The primary concern with asymptomatic ABCs is the risk of pathological fracture, which depends on:

• Size of the lesion: Large ABCs carry higher fracture risk 1
• Location: Pelvic/iliac crest lesions are weight-bearing adjacent structures 1
• Degree of cortical thinning: Extensive cortical destruction increases fracture risk 1
• Patient activity level: Higher mechanical stress increases fracture probability 2

ABCs at significant risk for pathological fracture warrant intervention even when asymptomatic 1. For bilateral iliac crest lesions, assess whether the cortical bone is sufficiently compromised to pose fracture risk with normal activities.

Observation Protocol for Low-Risk Asymptomatic Lesions

For asymptomatic ABCs without high fracture risk, implement surveillance imaging:

• Baseline radiographs establish initial size and characteristics 1
• Follow-up radiographs at 3-6 month intervals initially to document stability or growth 1
• If stable after 1-2 years, extend intervals to annual imaging 1
• MRI may be added if radiographs show concerning changes (expansion, new cortical destruction) 1

Patients should be counseled to report new symptoms immediately, particularly pain, which may indicate lesion expansion or impending fracture 1, 3.

Indications for Intervention in Asymptomatic Lesions

Intervention becomes necessary when asymptomatic ABCs demonstrate:

• Progressive enlargement on serial imaging (even without symptoms) 1, 3
• Significant cortical thinning creating fracture risk 1
• Large size (generally >5 cm in long bones, though pelvic criteria less defined) 1, 3
• Location in critical weight-bearing areas with structural compromise 1

Treatment Options When Intervention Is Required

When asymptomatic ABCs require treatment due to fracture risk or growth:

Percutaneous Sclerotherapy

Percutaneous sclerotherapy with polidocanol has emerged as a safe, minimally invasive first-line option with 96% healing or stable disease rates in recent series 3. This approach involves:

• Fluoroscopic-guided percutaneous injection of 4mg polidocanol/kg body weight 3
• Median of 4 treatments (range 1-8) to achieve healing 3
• General anesthesia required for each injection 3
• 70% complete healing rate, 26% partial healing with stable disease 3

Percutaneous Cryoablation

MRI-guided cryoablation is an alternative minimally invasive option, particularly useful for:

• Recurrent or residual lesions after other treatments 4
• Young children where CT guidance is challenging due to immature skeleton 4
• Smaller lesions requiring precise targeting 4
• Avoidance of ionizing radiation exposure 4

Surgical Curettage

Traditional open surgical curettage with bone grafting remains an option but is typically reserved for:

• Failed minimally invasive treatments 3
• Lesions with impending or actual pathological fracture 1
• Anatomically unsuitable lesions for percutaneous approaches 3

Common Pitfalls and Caveats

Do not assume all incidental lytic pelvic lesions are benign ABCs—approximately one-third of ABCs arise secondary to other lesions including giant cell tumor (19-39% of secondary cases), osteoblastoma, chondroblastoma, or rarely osteosarcoma 2. Radiographic features suggesting aggressive behavior (permeative margins, cortical destruction without expansion) warrant biopsy before assuming benign ABC 1, 2.

Bilateral presentation is exceedingly rare for primary ABCs 5. Multiple synchronous lesions should prompt consideration of secondary ABC arising from an underlying systemic process or other primary bone pathology 5.

ABCs in skeletally immature patients (<20 years old) account for 80% of cases 2. In older adults, alternative diagnoses should be carefully excluded 2.

Pain is the most common presenting symptom when ABCs become symptomatic (present in most cases), typically developing over less than 6 months 2, 6. New onset of pain during observation mandates immediate re-evaluation with advanced imaging 1, 3.