Escaping from Flatland: clinical and biological aspects of human mammary duct anatomy in three dimensions

Accurate knowledge of breast duct anatomy in three dimensions is needed to understand normal breast development, how intraepithelial neoplasia may spread through a breast, and the potential for diagnostic and therapeutic access to breast parenchyma via the nipple. This paper reports three related exploratory studies. In study 1, the median number of milk‐collecting ducts in the nipple was determined in 72 breasts excised for cancer; in study 2, the volumes of all 20 complete duct systems (‘lobes’) in an autopsy breast were measured from 2 mm serial ‘subgross’ sections; and in study 3, a 3D digital model of all collecting ducts in a mastectomy nipple was made from 68 100 µm serial sections. The mastectomy nipples contained 11–48 central ducts (median 27, inter‐quartile range 21–30). In the autopsy breast, the largest ‘lobe’ drained 23% of breast volume; half of the breast was drained by three ducts and 75% by the largest six. Conversely, eight small duct systems together accounted for only 1.6% of breast volume. The 3D model of the nipple revealed three distinct nipple duct populations. Seven ducts maintained a wide lumen up to the skin surface (population A); 20 ducts tapered to a minute lumen at their origin in the vicinity of skin appendages (population B) on the apex of the nipple; and a minor duct population (C) arose around the base of the papilla. Major variations in duct morphology and extent define highly variable territories in which intraepithelial neoplasia could grow. While population A ducts appear accessible to duct endoscopy or lavage, population B and population C ducts may be less accessible. Copyright © 2004 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.