Pleural effusion secondary to thoracic metastatic mammary adenocarcinoma in a mare.

The study involves a 17-year-old Quarter Horse mare afflicted with a significant health issue, specifically thoracic metastatic mammary adenocarcinoma, which resulted in a pleural effusion. This condition was observed approximately three years after the mare underwent surgery for an initial adenocarcinoma, indicating potential postoperative complications or recurrence of the disease.

Background of the Study

• The mare was initially treated for a papillary mammary gland adenocarcinoma through excision and cryotherapy. After treatment, the mare was engaged in regular pleasure riding.
• However, over time, the mare started showing signs of progressive dyspnea, indicative of potential health concerns.

Clinical Assessment and Findings

• The mare showed clinical signs of pleural effusion, a condition where there is an excess buildup of fluid between the tissues that line the lungs and the chest cavity.
• Unfortunately, the mare died before any further examination or treatment could be applied.
• Post-mortem, an autopsy revealed the presence of deep mammary masses and similar nodules in multiple areas including the deep inguinal, renal, and mediastinal lymph nodes, as well as in the lungs, pericardium, visceral and parietal pleurae, and left ovary.

Pathology and Analysis

• The masses were clinically identified as papillary mammary gland adenocarcinoma, the same condition the mare was previously treated for, suggesting a recurrence or spread of the disease.
• Large amounts of free pleural and peritoneal fluid were detected, confirming the suspicion of pleural effusion.
• The same neoplastic cells were found in the pleural fluid. These could potentially have been identified via exfoliative cytologic examination had the mare survived long enough for this procedure to be carried out.

Conclusion

• This study indicates the potential severity and progression path of papillary mammary gland adenocarcinoma in mares, with metastatic spread leading to fatal complications such as pleural effusion.
• The detection of similar neoplastic cells in the pleural fluid suggests that cytologic examination can be a viable diagnostic procedure for such scenarios in the future.