Mammary duct ectasia represents a type of benign blockage of milk ducts with a varying incidence, depending on the diagnostic methods used. Albeit historically descriptions of mammary duct ectasia involved different terminologies (according to diverse symptomatic and histological characteristics), in 1951, Haagensen and his colleagues proposed a formal and unified named based on its dominant pathological feature – a clogged lactiferous duct.
The disease occurs mostly in premenopausal women, but can also occur in men and children. Microscopically the disease has been described in up to 40% of autopsies. Smoking has also been implicated as one of the etiological factors in mammary duct ectasia, most probably due to the direct toxic effects on the breast epithelium.
Mammary duct ectasia is the result of glandular involution and secretory retention in the ducts; as a result, the major ducts enlarge. With time, the secretions are able to penetrate the duct wall, resulting in a different secondary condition known as periductal mastitis.
The histological features can differ according to the stage of the condition. In the early stages, the ducts are tortuously dilated and filled with proteinaceous eosinophilic material with minimal or no inflammation. In later stages, the ducts are obliterated with cellular lipid accumulation and fibrosis. Dystrophic calcifications can also be present, which can radiologically simulate malignancy.
Instead of the proliferation of the epithelial cells, there is atrophy present in involved ducts. The epithelium can be so thinned out that it is barely observable in low power magnification, and as the mammary duct ectasia progresses, the continuity of the atrophic epithelium is broken in different places. Hence, the disease is often considered a lesion of the aging and inactive breast.
Thus far, there are no reports indicating that mammary duct ectasia is linked to the increased risk of breast cancer, most likely due to the fact that destruction instead of hyperplasia of the ductal epithelium is observed in this condition. Nevertheless, certain ducts can exhibit squamous metaplasia, predisposing affected individuals to primary squamous cell carcinoma of the breast.
In the early stages of the disease, mammary duct ectasia usually presents with nipple discharge from several ducts that can be creamy, brown, grey, or green, and sometimes also bloody. The secretions are sometimes described thick as toothpaste, with accompanying subareolar tenderness.
Four types of masses are associated with mammary duct ectasia: the evanescent mass, the recurrent mass, the persistent mass, and the chronic mass. The evanescent mass is small and slightly tender subareolar lesion which can resolve spontaneously (without any treatment).
The recurrent mass is similar to the evanescent mass, but it occurs in the subareolar region at intervals of a few months to ten years, getting more severe with each recurrence. The persistent mass is usually well-defined and firm; thus an excisional biopsy is usually warranted as cancer cannot be easily excluded.
Finally, the chronic mass is edematous, hard, and fixed to the skin with accompanying nipple retraction, showing all the specific hallmarks of cancer (most notably if associated with axillary enlargement of the lymph nodes). Therefore, a formal excision biopsy with antimicrobial coverage is advocated.