What is the appropriate management for a complex or oil‑filled cyst identified on mammography that is assigned BI‑RADS III (Breast Imaging Reporting and Data System category III)?

Management of Complex/Oil Cyst on Mammogram with BI-RADS III

When mammography identifies a definite benign oil cyst that unequivocally correlates with any clinical finding, clinical follow-up alone is appropriate and no short-interval imaging follow-up is necessary. 1

Understanding Oil Cysts vs Complex Cysts

Oil cysts are definitively benign lesions (BI-RADS 2) that result from fat necrosis and contain liquid fat. 1 These should not be confused with complex cysts, which have solid components and carry a higher malignancy risk. 1

• Oil cysts appear as well-circumscribed lucent masses on mammography, often with a thin calcified rim (eggshell calcification), and are classified as BI-RADS 2 (benign). 1
• Complex cysts contain discrete solid components (thick walls, thick septa, or intracystic masses) and require different management. 1

Critical Distinction: True BI-RADS Classification

If your lesion is truly an oil cyst, it should be classified as BI-RADS 2 (benign), not BI-RADS 3. 1 The assignment of BI-RADS 3 suggests diagnostic uncertainty that is inconsistent with a definitive oil cyst diagnosis.

When Ultrasound Is Indicated

Ultrasound is NOT necessary if mammography shows a definite benign oil cyst that clearly correlates with any palpable finding. 1 However, ultrasound should be performed if:

• Correlation between the mammographic finding and any palpable lesion is uncertain. 1
• The lesion does not have classic oil cyst features on mammography. 1
• Dense breast tissue obscures complete evaluation. 1

Management Algorithm

For Confirmed Oil Cyst (Should be BI-RADS 2):

• No imaging follow-up required. 1
• Return to routine age-appropriate screening. 1
• Clinical follow-up only if there was an associated palpable finding. 1

For Lesions Assigned BI-RADS 3 (Probably Benign):

If the lesion is truly BI-RADS 3 and not a definitive oil cyst, management differs:

• Short-interval follow-up imaging at 6 months is the standard approach. 1, 2
• Continue surveillance every 6-12 months for 1-2 years to assess stability. 1
• If stable throughout surveillance, return to routine screening. 1

Exceptions Warranting Immediate Biopsy Despite BI-RADS 3:

Core needle biopsy should be performed instead of surveillance in these specific circumstances: 1

• High-risk patients (strong family history, genetic predisposition). 1
• Patients awaiting organ transplantation. 1
• Patients with known synchronous cancers elsewhere. 1
• Patients planning pregnancy. 1
• Severe patient anxiety that cannot be alleviated through counseling. 1

Common Pitfalls to Avoid

Do not assign BI-RADS 3 to a lesion with definitive benign features. 1 Oil cysts meeting all criteria for benign findings should be classified as BI-RADS 2. 1 Inappropriate use of BI-RADS 3 leads to unnecessary follow-up imaging, increased costs, and patient anxiety. 3, 4

Do not perform ultrasound on every BI-RADS 2 lesion. 1 If mammography clearly demonstrates an oil cyst with typical features, additional imaging adds no value. 1

Ensure you are not misclassifying a complex cyst as an oil cyst. 1 Complex cysts have solid components and carry up to 2% malignancy risk, requiring different management including possible aspiration or biopsy. 1

When Growth Occurs on Follow-up

If a BI-RADS 3 lesion shows growth (≥20% enlargement) on follow-up: 5

• Biopsy is indicated if there are sonographic morphological changes or suspicious mammographic features. 5
• Growth alone without morphological changes carries only 1.9% malignancy risk and may continue BI-RADS 3 surveillance. 5
• Morphological changes increase malignancy risk significantly (OR 7.7). 5