Mass Shape — Lobulated
Lobulated is a mass shape descriptor indicating one or more indentations resulting in an undulating contour.
Definition
A mass that displays one or more indentations resulting in an undulating contour.
v2025 Change (Critical)
Board Pearl
“Lobulated” was reintroduced as a separate shape descriptor in v2025. In the prior 5th Edition Atlas (2013), a mass with a few gentle lobulations was included within the oval shape category. In v2025, lobulated is its own category — distinguishing from oval (no undulations), round (spherical), and irregular (acute-angle protrusions).
Imaging Appearance
- Mass contour shows smooth undulations (rounded protrusions or indentations)
- The undulating contour distinguishes lobulated from oval (smooth) and irregular (angular)
- May have circumscribed or non-circumscribed (indistinct) margins
Example Pathologies
| Pathology | Common Features |
|---|---|
| Fibroadenoma | Lobulated, circumscribed, heterogeneous — classic appearance |
| Phyllodes tumor | May be lobulated, larger |
| Invasive ductal carcinoma | Lobulated + indistinct → suspicious combination |
Differential by Margin
- Lobulated + circumscribed: Likely fibroadenoma; can be benign or malignant
- Lobulated + indistinct: More suspicious; consider IDC
Pitfalls
- Lobulated shape with circumscribed margin is benign-favoring but NOT equivalent to ≤ 2% cancer risk
- The ≤ 2% cancer risk rule requires oval (not lobulated) shape + circumscribed + T2 hyperintense + homogeneous/dark septations
- Malignancies can present as lobulated masses (e.g., IDC)