Today there is insufficient awareness among the physicians about the benign breast conditions such as mammary duct ectasia and periductal mastitis, both causing nipple discharge. Not only those two entities can ring a false alarm of malignancy, they are also considered the second most common cause of benign diseases of the breast.
There has been much debate in scientific circles about the relationship between mammary duct ectasia and periductal mastitis. Even though it has often been held that these two conditions represent variants of the same pathological process (with periductal mastitis probably arising as a result of mammary duct ectasia), these two conditions are quite different.
Mammary duct ectasia is an involutional, regressive process that is a result of a normal breast change. As women age and reach menopause, the major ducts get shorter and wider. Consequently, by the age of 70, basically 40% of women have bilateral and only slightly symptomatic mammary duct ectasia.
On the other hand, periductal mastitis represents an inflammatory process, usually due to fibrous obliteration of the ducts. It can affect women of all ages (although it most often occurs in premenopausal women), and is also known under many different terms (such as mastitis obliterans or comedomastitis).
These definitions suggest that mammary duct ectasia and periductal mastitis are distinct conditions of the breast that affect different age groups, have rather different etiologies, and should be considered as separate clinical entities.
Regardless of the aforementioned differences in defining those two conditions, the pathogenesis of mammary duct ectasia and periductal mastitis can be viewed as a sequence where different processes coexist and interact, resulting in a wide spectrum of clinical presentations.
First, we have mammary duct ectasia with ducts that are full of stagnant secretions, leading to small amount of nipple discharge. The ulceration of the epithelial lining may ensue, resulting in blood-stained nipple discharge and leakage of secretions into the periductal tissue.
This kicks off an inflammatory response to secretions that contain fatty acids that act as chemical irritants. Later, the inflammation can become bacterial, especially if the dilatation extends into the subsegmental ducts that are located more peripherally in the breast.
When abscess formation occurs, simple drainage is very unlikely to be curative, and the patient can end up with a persistent or recurrent fistula. In some instances, a massive fibrotic reaction halts abscess formation and forms a mass which may eventually stimulate a cancer. When fibrous tissue contracts, a nipple retraction ensues.
Various clinical and epidemiological observations point to differences in these two conditions. For example, Dixon and his colleagues confirmed that periductal mastitis is more prevalent in young women who smoked, whereas mammary duct ectasia was more characteristic for older women who did not smoke.
The earlier suggestion of the continuum in the pathogenesis of these two conditions is contradicted in the 1996 publication (again by Dixon and his colleagues) who suggested that mammary duct ectasia and periductal mastitis should be regarded as two entirely different conditions affecting women of different age groups (due to different etiological factors).
Although lactation and multiple pregnancies (births) have been implicated in the periductal mastitis, they are not universally accepted as etiological risk factors for mammary duct ectasia. The latter condition is commonly seen in women who did not give birth.
In conclusion, despite conflicting literature reports on the pathogenesis of mammary duct ectasia and periductal mastitis (and the debate whether they are one disease process or two different entities), both of them can be seen in the same breast biopsy or histological evaluation, pointing towards a continuum of the same disease process.