OBJECTIVETo introduce a new animal model of graded mechanical primary brainstem injury (BSI).

METHODSAltogether 45 rabbits were subjected to BSI by type II biological impact machine designed by the Third Military Medical University. The animals were divided into 4 experimental groups (n equal to 10) and 1 control group (n equal to 5) according to different magnitudes of impact pressure imposed on the occipital nodule: Group 1, 500-520 kPa; Group 2, 520-540 kPa; Group 3, 540-560 kPa; Group 4, 560-580 kPa and Group 5, 0 kPa with 20 kPa increase in each grade. The impact depth was a constant 0.5 cm. After injury, the clinical symptoms and signs as well as pathological changes were observed.

RESULTSRabbits in Group 1 revealed mild physiological reaction of BSI. They had localized cerebral contusion with punctate hemorrhage and subarachnoid hemorrhage (SAH) was limited to the peripheral tissues at the impact area. In Group 2, obvious physiological reaction was observed. Local pathological lesions reached the superficial layer of brainstem tissues; focal hemorrhage and girdle-shaped SAH in basilar pon were observed under microscope. In Group 3, BSI was more severe with a long respiratory depression. Pathological lesions reached the inner portion of brainstem with massive hemorrhage and the whole brainstem was wrapped by subarachnoid hematoma. In Group 4, most rabbits died due to severe BSI. Pathological lesions deepened to the central brainstem with wide pathological change, rapture of the medulla oblongata central canal. Group 5 was the control group, with normal brainstem structure and no lesion observed.

CONCLUSIONThis model successfully simulates different levels of brainstem mechanical injury and clearly shows the subsequent pathological changes following injury. It takes two external parameters (impact pressure and depth) and has a similar injury mechanism to clinical accelerating BSI. Moreover it is reproducible and stable, thus being be- neficial for exploring pathophysiological mechanism, diagnosis and forensic identification of various degrees of BSI.