Background

Lymphatic malformations in humans are categorized by the 2025 International Society for the Study of Vascular Anomalies (ISSVA) classification into localized lymphatic malformations and systemic disorders termed complex lymphatic anomalies (CLAs), including generalized lymphatic anomaly (GLA) and central conducting lymphatic anomaly (CCLA). Veterinary reports of systemic lymphatic disorders are rare and historically described using inconsistent terminology. This case report aimed to characterize a systemic lymphatic disorder in a young cat using the ISSVA framework to facilitate comparative understanding between veterinary and human medicine.

Methods

A five-month-old intact male domestic shorthair cat presenting with progressive dyspnea was evaluated clinically, hematologically, and through imaging. Thoracocentesis and abdominocentesis confirmed chylothorax and chylous ascites via cytology and biochemical analysis. Whole-body computed tomography (CT), including CT lymphangiography following intraplantar contrast injection, was performed to identify lymphatic leakage sites. Surgical exploration of the thoracic duct region was undertaken, and subcutaneous punch biopsies were obtained for histopathology. Postmortem examination included histopathologic evaluation of affected tissues.

Results

CT lymphangiography demonstrated contrast leakage from the thoracic duct at two sites: the aortic hiatus and cranial thoracic region, alongside diffuse subcutaneous edema. No mass lesions or thrombi were identified. Histopathology of subcutaneous tissues revealed proliferative, anastomosing lymphatic channels consistent with GLA. Imaging findings indicating thoracic duct dysfunction supported concurrent CCLA, suggesting an overlapping CLA phenotype. Despite medical therapy (rutin, low-fat diet, prednisolone) and surgical intervention aimed at controlling lymphatic leakage, the cat developed progressive generalized edema, hemorrhagic pleural effusion, and died on day 51. Postmortem findings confirmed extensive lymphatic proliferation with areas of endothelial atypia consistent with partial malignant transformation.

Limitations

This report describes a single case, limiting generalizability. Genetic analysis was not performed, precluding molecular characterization. Advanced lymphatic imaging modalities such as MR lymphangiography and lymphoscintigraphy were not available. Coagulation testing was not conducted despite development of hemorrhagic effusion.

Conclusions

This case represents the first reported feline complex lymphatic anomaly exhibiting overlapping features of GLA and CCLA as defined by the human ISSVA classification. CT lymphangiography proved valuable for identifying multifocal lymphatic leakage and systemic involvement. The findings demonstrate that cats can develop systemic lymphatic disorders analogous to human CLAs and highlight the applicability of the ISSVA framework in veterinary medicine. Comparative insights from human molecular research may inform future diagnostic and therapeutic strategies for veterinary lymphatic diseases.

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