Found while googling recently:

Excerpt from  
                 Online CME Courses 
                 Sonographic Evaluation Of The Breast 
Sandra Hagen-Ansert, B.A., RDMS, RDCS
Chair, Diagnostic Medical Sonography
Baptist College of Health Sciences
Memphis, Tennessee

"Lactiferous Ducts. The lactiferous ducts are easily seen on most scans,
especially when they are dilated. A typical breast is composed of 15-20
lobules which are drained by a network of ducts. These ducts branch into
the peripheral breast tissue and join in the subareolar region to form
approximately 15-20 ducts which drain into the nipple. THE LACTIFEROUS
DUCTS ARE USUALLY COLLAPSED IN THE NONLACTATING BREAST AND MEASURE UNDER
2mm. AT THE SINUS LEVEL IN THE SUBAREOLAR REGION THE DUCTS MAY HAVE A
POTENTIAL  DIAMETER OF 8mm. IN THE PERIPHERY OF THE BREAST, A DIAMETER OF
2-4mm IS NORMAL IN THE LACTATING BREAST. Surrounding the subareolar ducts
are varying amounts of fibrosis, which accentuate the degree of nipple
shadowing observed. The terminal ductal lobular unit is the site of
fibroadenoma, epithelial cyst, ductal and lobular carcinoma in situ,
infiltrating ductal and lobular carcinoma adenosis, epithiosis, and
apocrine metaplasia." 

(8 mm is not very big, but it appears to be evidences based reality.
Since Lactnet technically filters out stuff like bolding, italics and
underlining, please excuse the capitals which were not really to indicate
shouting, but emphasis, which of course, was mine;-)

Jean
**********************
K. Jean Cotterman RNC, IBCLC
Dayton, OH USA

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