Abstract
Background:
Intrathoracic ectopic liver (IEL) is a rare hepatic anomaly in dogs and can be confused with caval foramen hernia or other caudal thoracic mass-like lesions. Objective preoperative assessment of hepatic continuity, lobar segmentation, diaphragmatic relationships, and venous drainage may help distinguish these entities and guide surgery.

Aim:
To describe computed tomographic angiography (CTA) findings, venous mapping, intraoperative anatomy, and outcomes in dogs interpreted as having IEL, with emphasis on features supporting a developmental right medial lobe (RML) segmentation anomaly.

Methods:
Medical records and CTA studies from five client-owned dogs were retrospectively reviewed. Signalment, clinical and clinicopathological findings, thoracic radiographs, CTA findings, intraoperative observations, surgical treatment, histopathology when available, and short-term and long-term outcomes were recorded.

Results:
CTA demonstrated hepatic tissue within the caudal thorax that remained continuous with the abdominal liver across the diaphragm. The intrathoracic component involved the RML alone in four dogs and the RML with the left medial and quadrate lobes and gallbladder in one dog. Venous mapping demonstrated a diaphragm-spanning RML segmentation anomaly; venous drainage entered the accessory central hepatic vein in four dogs and the main central hepatic vein in one dog. The median proportion of IEL volume relative to total liver volume was 20.0% (range, 5.1%-44.1%). No caudal vena cava compression was identified. Intraoperatively, the visible diaphragmatic defect was smaller than the diameter of the intrathoracic hepatic component, and the pericardium and mediastinum were intact throughout the series. Four dogs underwent reduction into the abdomen, and one underwent partial hepatic lobectomy. Outcomes during the available follow-up period were favorable in all dogs, with long-term follow-up available in four dogs.

Conclusion:
The shared findings in these five dogs suggest that IEL is associated with a developmental RML segmentation anomaly rather than simple postnatal herniation through a caval foramen defect. However, because validated veterinary diagnostic criteria are lacking and only five dogs were included, these findings should be interpreted cautiously. CTA with venous mapping may aid preoperative diagnosis, anatomical characterization, and surgical planning.

Key words: Caval foramen hernia; Computed tomography angiography; Dog; Ectopic liver; Venous mapping.