Follicular occlusion due to hyperkeratosis: A new hypothesis on the pathogenesis of mammillary fistula

Summary

Mammary fistula (MF) is a disease characterised by recurrent draining abscesses around the areola. The aetiology of MF remains unclear. The most common cause is duct obstruction by squamous metaplasia. The clinical aspects and histological findings of MF are very similar to those observed in hidradenitis suppurativa (HS). We propose a new hypothesis on the pathogenesis of MF and suggest that occlusion of hair follicles by keratinous plugging may relevantly contribute to the development of MF.

Introduction

Mammillary fistula (MF), or Zuska’s disease, is a recurrent condition characterised by draining abscesses around the areola and is usually associated with a non-lactating subareolar abscess, periductal mastitis or previous surgery [1], [2], [3], [4], [5], [6]. A variety of different terms have been used for this condition and these probably reflect different stages in a single disease process. It appears to be responsible for 1–2% of all symptomatic breast conditions [7]. Clinically a history of either drainage of a subareolar abscess or spontaneous rupture of an inflammatory mass preceded the development of mammillary fistula in the majority of patients. Cutaneous signs and symptoms in subareolar abscesses of the breast or MF are common and frequent, which typically drain at the margin of the areola [8]. It is a condition with a prolonged morbidity and is frequently difficult to manage [9], having a profound impact on the quality of life.

The aetiology of MF is still unclear. Several authors [10], [11], [12], [13] incline towards the obstruction of a distal lactiferous duct by squamous metaplasia with keratinisation and/or epidermisation of the duct as the cause of MF. The epithelial squamous metaplasia causes plugging and obstruction of the ducts is a pathogenetic event.