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Terminal duct–lobular unit (TDLU) is the functional and histologic unit of the breast and is the origin site for the vast majority of benign and malignant breast lesions, including ductal and lobular carcinomas.
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| Component | Description |
|---|---|
| Lobule | Cluster of small acini (glandular structures) that produce milk |
| Terminal duct | Connects acini to the larger ductal system; lined by luminal epithelium and myoepithelium |
| Intralobular stroma | Surrounds the TDLU; composed of fibrous and adipose tissue |
| Extralobular duct | Larger ducts draining toward the nipple |
The TDLU includes both the terminal duct and its associated lobule and resides in the fibroglandular tissue of the breast.
| Modality | Imaging features |
|---|---|
| US | • Not typically visualized unless pathologically altered |
| • Lesions like fibroadenomas or duct ectasia may arise in or near TDLUs | |
| MR | • Background parenchymal enhancement (BPE) reflects hormonal activity in TDLUs |
| • Non-mass enhancement often represents DCIS or lobular neoplasia arising in TDLUs | |
| Mammography | • TDLU involution with age → replacement by fat |
| • Microcalcifications in TDLUs may be associated with DCIS or benign changes (e.g., sclerosing adenosis) |
Pathological relevance:
| Pathology | Involvement of TDLU |
|---|---|
| ‣ | Arises in terminal ducts |
| ‣ | Originates in terminal ducts; invades stroma |
| ‣ | Proliferation within lobular acini of TDLU |
| ‣ | Arises from TDLU, infiltrates in linear pattern |
| ‣ | Benign stromal and epithelial proliferation from TDLU |
| Sclerosing adenosis | Benign TDLU proliferation with dense fibrosis and distorted acini |
| Columnar cell change / atypia | Premalignant changes within TDLU epithelium |
TDLU involution: