Contrast-enhanced ultrasonography of the rabbit VX2 tumor model: Analysis of vascular pathology

The accuracy of diagnosing tumors may be improved significantly by detecting the microvascular distribution. Indeed, contrast-enhanced ultrasonography (CEUS) has shown a distinct advantage in detecting microvasculature. This study aimed to determine the angiogenic characteristics of VX2 tumors in rabbits using CEUS. A total of 17 rabbits were injected with 0.5 ml VX2 cell suspension into the muscles of both hind legs to prepare the VX2 tumor models. At 14, 21, 28 and 35 days after tumor inoculation, CEUS was performed on the rabbits with 0.3 ml SonoVue following a local anesthesia. The pathological findings of the tumors were compared. A total of 12 rabbits survived after being inoculated with the tumor cells and developed a total of 38 tumors. The size of the tumors ranged from 1.12 to 10.85 cm. Using CEUS, all tumors demonstrated rim enhancement with some unenhanced regions. Enhancement began from the peripheral region and quickly showed internal reticular vessels. Regardless of the tumor size or the presence of necrosis, no complete enhancement of the tumors was observed. On microscopic examination, VX2 tumor cells were detected in striated muscles, immature blood capillaries and fibrosis tissues scattered in tumor nests. Immunohistochemical examination revealed that CD34+ cells appeared mainly in the muscles adjacent to vessels. In conclusion, CEUS may be an efficient method to evaluate angiogenesis and blood perfusion in VX2 tumors.