Site-specific induction of lymphatic malformations in a rat model for image-guided therapy

Background Lymphatic malformation is a common benign mass in children and adults and is representative of a derangement in lymphangiogenesis. These lesions have high recurrence rates and significant morbidity associated with surgery. Several sclerotherapy regimens have been developed clinically to treat lymphatic malformations; however, an animal model has not been developed that is adequate to test the efficacy of image-guided therapeutic interventions. Objective To develop an animal model suitable for evaluation of percutaneous treatments of lymphatic malformations. Materials and methods Male Harlan Sprague-Dawley rats (n = 9) received two US-guided injections of Incomplete Freund’s Adjuvant (IFA) over a 2-week period. All nine rats were injected twice into the peritoneum (IP); a subgroup (n = 3) received additional injections into the neck. Three animals that received IP injections of saline were used as controls. The injection sites were monitored for the development of lesions by high-resolution ultrasonography at 2-week intervals for 100 days. High-resolution (4.7 Tesla) magnetic resonance imaging was then performed on two animals noted to have developed masses. The rats were sacrificed and histologic examination of the identified lesions was performed, including immunohistochemical staining for vascular (CD31) and lymphatic (Flt-4 and Prox-1) endothelium. Results All animals injected with IFA developed cystic lesions. The three animals injected at dual sites were noted to have both microcystic and macrocystic malformations in the neck and microcystic plaque-like lesions in the peritoneum. The macrocystic malformations (≥5 mm) in the neck were detected by ultrasonography and grossly later during necropsy. Histopathologic analysis revealed the cystic spaces to be lined by lymphatic endothelium supported by a connective tissue stroma. Control animals did not exhibit detectable lesions with either ultrasonography or necropsy. Conclusion This model represents a promising tool for translational development of image-guided interventions for lymphatic malformations. It may also serve as a model for the study of lymphangiogenesis and the development of anti-lymphangiogenic therapies.