The establishment of an animal liver metastasis model has great significance for clinical and scientific research. In this study, a rabbit liver metastasis model was established by percutaneous splenic implantation of the VX2 tumor strain under CT guidance, and it was compared with the establishment of open splenic implantation. The results showed that CT guided percutaneous splenic implantation of the VX2 tumor strain to establish a rabbit liver metastasis model is a minimally invasive and feasible method, the success rate of this method is not lower than the method using open splenic implantation, and this method is associated with low mortality, low incidence of complications, and short operation time. At present, a similar method has not been reported.
The study showed that the biological characteristics of the rabbit liver metastasis model formed by splenic implantation are closer to the biological characteristics of human liver metastasis. Shi Bo et al. reported that the model established by spleen inoculated with the VX2 tumor strain was found to be closer to human primary liver metastasis by using the CT scan and digital subtraction angiography (DSA). Our research also confirmed this finding. But laparotomy can cause large trauma, and then can lead to higher mortality. One study has also reported the use of an image-guided percutaneous puncture target organ to establish a tumor model. But the rabbit spleen is relatively small, and it is difficult to operate under ultrasound guidance. Therefore, we established a liver metastasis model by puncturing the spleen under CT guidance.
The results of this study showed that CT-guided percutaneous splenic implantation to establish a rabbit liver metastasis model is a feasible modeling method, and its success rate is similar to that of open splenic implantation. In group A, one rabbit had no tumor growth, one had both needle track and peritoneal metastasis, and one had only peritoneal metastasis. The reason for this occurrence may be that the needle tip did not enter the spleen during the drip of VX2 tumor suspension; thus, the VX2 tumor strain was implanted in the peritoneum and puncture path. There were 3 cases of peritoneal metastasis in group B, of which 2 rabbits died. The reason for this occurrence may be that the VX2 tumor suspension leaked along the puncture path after implanting into the spleen, resulting in extensive peritoneal implantation. On the comparison of complications, two cases of wound infection occurred in group B, as the laparotomy is more traumatic. No obvious complications occurred in group A. The result indicates that the method of CT-guided percutaneous puncture is associated with less trauma and a low incidence of complications.
Attention should be paid to the following aspects in the operation of CT-guided percutaneous splenic implantation. (1) Localization scanning: because the rabbit spleen is small, thin-layer continuous scanning with a thickness of 1–2 mm is required, and the largest slice of the spleen should be selected for puncture. In addition, the spleen is crescent-shaped; thus, we should formulate an oblique puncture angle from the inside to the outside, increase the length of the needle path in the spleen, and then reduce the probability of penetrating the spleen to damage the stomach and other structures. (2) Needle selection: due to the small volume and large mobility of the rabbit spleen, a 22G coaxial puncture needle should be selected, as the needle tip is inclined and sharp, which can reduce the probability that the use of a small force cannot puncture the spleen and use of a large force completely penetrates the spleen, and it can reduce the risk of spleen rupture and bleeding. (3) Puncture technology: when the needle tip approaches the spleen, it is necessary to quickly puncture the spleen, which can effectively reduce the repeated puncture and save the puncture time. (4) After dropping the suspension, the needle path should be blocked with a gelatin sponge to prevent the leakage of tumor suspension, which can reduce the incidence of peritoneal and needle path metastases.
Meanwhile, the operation time of CT-guided percutaneous splenic implantation is significantly lower than that of open splenic implantation. After mastering the key points of CT-guided percutaneous splenic implantation, the operator can complete the operation in a short time. However, the steps of laparotomy are relatively complex and cumbersome. If the laparotomy incision is small, it is difficult to identify the spleen; and if the incision is large, the injury to the rabbit is obvious and it also increases the risk of infection. A skin suture and other operations are also required; thus, a relatively long time is needed.
MRI manifestations of the two groups of liver metastases were multiple nodular-like abnormal signal shadows in the liver, low signal on T1WI, a slightly high or equal signal on T2WI, high signal on DWI, and circular enhancement on enhanced scanning. They were typical imaging manifestations of liver metastasis, which were similar to those of human liver metastasis[9, 10]. In addition, HE stained sections from groups A and B showed that there were vigorous tumor cells in liver metastases. There was no difference in the imaging and pathological findings between the two groups. This finding is consistent with the research by Shi Bo et al.