Ductal Architecture: Corrosion Casting of Canine Mammary Glands Using an Intraductal Approach

SIMPLE SUMMARY: Milk is a natural and essential nutrient for new-born mammals. Dogs were one of the first domesticated species to coexist with humans, and yet scientists lack some crucial information related to the anatomy and morphology of the canine mammary gland, the organ after which all mammals are named. This study investigated mammary glands’ inner structures using intraductal corrosion casting. We intended to provide visualisation of the glandular and ductal structures and their branching presented as a three-dimensional image. The aim was to expand current knowledge in the anatomy field by describing the in situ position (i.e., the undisturbed shape and natural position) of glandular tissue and its ductal branching pattern. No obvious teat cistern was present. Glandular branch intertwining of different gland lobes without intercommunication was observed. Ascendant teat canals could drain single or multiple gland lobes or could end blind. Although it had a small sample size, this study confirmed that the intraductal cannulation of healthy canine mammary glands is possible through functional and developed orifices. New knowledge in this field could contribute to the better management and understanding of neoplastic and non-neoplastic conditions that veterinary clinicians and surgeons often encounter. ABSTRACT: Detailed knowledge related to the morphology, anatomy, physiology, and pathology of the canine mammary gland is scarce. Mammary tissue undergoes massive changes instructed by hormones multiple times within the lifespan of every bitch, affecting its appearance. To address the ductal system’s appearance and to present how different our findings regarding the canine mammary gland are in comparison with the available literature, we obtained cadaveric specimens after euthanasia and mastectomy. All bitches were euthanised due to poor prognosis for their recovery from maladies unrelated to mammae. Using intraductal cannulation ex vivo, milk- or fluid-yielding ducts were perfused using VasQtec (polyurethane resin), which revealed casts, i.e., imprints of ducts and glandular structures in situ. We observed primary, vertically positioned ducts that ascended throughout the teat and continued branching to secondary, tertiary, etc., horizontally positioned ducts, which drained mammary gland lobes under the skin located close to the abdominal wall. The ascendant teat canal could be split into two and could be connected to gland alveoli or end blind. Alveolar formations were located along ducts and ductules in bigger and/or smaller clusters. This study is the first to generate a 3D image of canine ducts and glandular tissue using an intraductal approach.