Development of a total colonoscopy rat model with endoscopic submucosal injection of the cecal wall

BACKGROUND

Experimental models of colorectal tumor require either laparotomy for induction or anastomosis following resection. The long murine cecum avoids the need for an anastomosis, making the cecum the preferred site for induction. This study aimed to evaluate total colonoscopy with submucosal injection of cecal wall (TCWI) in rats in terms of failure rate (FR), complication rate (CR), and reproducibility (R).

METHODS

A bolus of bowel prep was given. Anesthesia was injected intraperitoneally. A video fiberscope (5.9 mm outer diameter, 180/90 degrees up/down bending, 100/100 degrees right/left bending, 103 cm working length, 120 degrees view field, and 2.0 mm channel) allowed for irrigation and suction. Saline 1 ml was injected in the cecal wall through a 4-mm-long, 23-gauge needle placed on a 3-mm wire, resulting in a blister. FR was a failure to reach and inject the cecum. Rats were allowed to recover. CR was measured at necropsy. R was assessed by comparing TCWI time, FR, and CR for three investigators. Sample size of 120 (type I error, 0.05; power, 80%) was based on a pilot study. Data are presented as median (range).

RESULTS

A total of two of 122 rats (1.6%) died after prep or anesthesia. Bowel prep resulted in 99.1% evacuation of solid feces. A total of 120 male Sprague-Dawley retired breeders weighing 592 g (range, 349-780) underwent TCWI. Scope depth was 28 cm (range, 20-36). Irrigating fluid was 290 ml (range, 100-600). TCWI time was 7 min (range, 4-28). FR was 4%. In three failed cases, the scope reached the ascending colon. CR was 2%. There were two perforations in the ascending colon. All three operators had similar TCWI time (p = 0.673), FR (p > 0.1), and CR (p > 0.1). A total of 98.3% of rats survived to planned sacrifice. At 48-h necropsy, the injection site was macroscopically identified in 118 rats.

CONCLUSIONS

A safe and reproducible TCWI rat model has been achieved, which may provide a valuable tool in the future for studies of solid colorectal tumors.

Lung microcytoma: a multidisciplinary therapeutic approach

This report is of 26 patients diagnosed with microcytoma of the lung in stages I, II, and IIIa. All patients received surgical treatment as well as postoperative chemoradiotherapy when indicated by stage. Mean survival rates were 16 months for stage 1, 10 months for stage II and 6 months for stage IIIa disease. For many years surgery was considered contraindicated in the treatment of pulmonary microcytoma. Now a multidisciplinary approach is being used in which surgery has a crucial role. Microcytoma of the lung has a poor prognosis due to its early metastasis and rapid growth. It is crucial to have early diagnosis and accurate, consistent staging as the basis for treatment. A review of literature shows that the use of surgery, chemotherapy and radiotherapy are all important in treatment of microcytoma. Chemotherapy is successfully utilized preoperatively to improve local control, decrease neoplastic mass, induce histological regression and as postoperative adjuvant therapy. Radiotherapy has been shown to be effective preoperatively to reduce local mass and prophylactically for cerebral metastasis. Surgery is crucial to irradicate the neoplastic mass, improve staging accuracy, decrease the possible selection of neoplastic clones resistant to postoperative therapy, decrease local recurrence and allow less aggressive chemoradiotherapy. We feel the most effective protocol for pulmonary microcytoma includes preoperative chemotherapy and radiotherapy when indicated followed by surgical intervention and finally successive adjuvant therapy. The limited number of our cases does not consent a statistically significative conclusion. Our data confirm the importance of the surgical procedure in stages I and II, where according also to other authors, the best results are obtained. Surgical indication in stage IIIa is still discussed due to precocius lymphnode dissemination that significantly affects long-term survival.