What is the recommended next step for a patient with a cluster on their iliac crest, initially identified on a computed tomography (CT) scan and further evaluated with a bone scan 5 years ago, which was inconclusive in differentiating between bony islands and malignant lesions, and was never followed up on?

Management of Incidental Iliac Crest Lesions After 5-Year Interval

No Further Imaging or Workup Required for the Original Finding

After 5 years without clinical progression, new symptoms, or need for medical attention, the original indeterminate iliac crest lesions are effectively ruled out as concerning pathology and require no further evaluation. 1

The American College of Radiology explicitly states that if a malignancy had been present 5 years ago, the patient would have developed progressive symptoms, metastatic disease, or died by now. 1 This 5-year interval without any clinical manifestation provides definitive reassurance that the original bone scan findings represent benign entities, most likely bone islands (enostoses). 1

Understanding Bone Islands

• Bone islands are benign sclerotic lesions that are extremely common incidental findings with no malignant potential. 1
• These lesions can remain stable or even grow over time while remaining completely benign, as documented in cases with up to 31 years of follow-up. 2
• Bone islands typically appear as small round to oval sclerotic areas with irregular, radiating spicules peripherally on imaging. 3
• They are most commonly found in the axial skeleton including the pelvis, spine, and ribs. 3

Critical Management Principle

Do not order repeat bone scan, PET/CT, or any advanced imaging for the old finding. 1 These studies will not provide useful information and may generate false-positive results that lead to unnecessary anxiety and interventions. 1

If New Hip or Pelvic Symptoms Develop

Should the patient develop new bone or joint pain in the hip or pelvis region, the evaluation pathway is entirely separate from the old finding:

First-Line Evaluation

• Obtain plain radiographs of the hip in two orthogonal planes as the mandatory first investigation. 1, 4
• Radiographs provide critical information about bone architecture, joint space, periosteal reaction, cortical integrity, and any aggressive features that would suggest malignancy. 1

Red Flags Requiring Urgent Referral

• Immediate referral to an orthopedic oncologist or bone sarcoma center is required if radiographs show an aggressive-appearing lesion, before any biopsy. 1, 4
• Aggressive features include: poorly marginated or ill-defined margins, permeative or moth-eaten pattern of bone destruction, aggressive periosteal reaction, or cortical destruction with soft tissue extension. 5
• Persistent non-mechanical pain, especially night pain that wakes the patient from sleep, is highly concerning for malignancy and requires urgent referral. 1

If Radiographs Are Normal But Pain Persists

• MRI of the hip without and with IV contrast would be appropriate to evaluate for avascular necrosis, occult fracture, soft tissue pathology, or marrow abnormalities. 1, 4

Key Pitfall to Avoid

Never arrange biopsy of any lesion without first obtaining plain radiographs and, if concerning, referring to a specialized bone sarcoma center. 1 Improper biopsy technique can compromise limb-salvage surgery if a malignancy is ultimately diagnosed. 5

Clinical Context

In cancer patients with suspicious bone lesions, 21% prove to be benign, 66% are metastases from known malignancy, and only 3% represent a second primary malignancy. 6 However, this patient has no known malignancy and has been asymptomatic for 5 years, making the probability of malignancy essentially zero. 1

When bone scans show one or two new abnormalities and correlative radiographs demonstrate a benign abnormality, this is highly reliable for excluding malignancy. 7 In this case, the 5-year asymptomatic interval provides even stronger evidence of benignity than radiographic correlation alone. 1