| Back ground In 1929, professor Walter Dandy first pointed out the importance of the petrosal vein in connection with surgery for trigeminal neuralgia. His illustration showed a vein that coursed in the cerebellopontine angle rostral to the trigeminal nerve to drain into the superior petrosal sinus. Later, this common stem came to be identified as the petrosal vein. Petrosal vein is an important and relatively constant anatomical landmark. It also plays an important role in surgery for tentorial and cerebellopontine angle tumours.Professor Yuan Xianrui reviewed 33 cases of acoustic neuroma surgery carried since June 2004 to October 2007, including 2 cases(coagulated petrosal vein) and 31 cases (well protected petrosal vein). Four patients that petrosal vein was coagulated developed cerebellar hemorrhagic infarction. One patient died,1 patient was carried posterior fossa decompression and recovered. Thus, Professor Yuan Xianrui pointed out that petrosal vein should be protected during surgery. His view has been supported by many scholars; however, some scholars don't think that sacrifice of the petrosal vein has effect on the results of operation. There are no exact animal experiments about the consequences after mutilation of petrosal vein at present.Objective To establish unilateral petrosal vein mutilation (coagulation by bipolar, cut by micro scissor) model of rabbit. To observe the brain water content, sodium and potassium content, SOD activity, MDA content, AQP-4 transcription and expression and pathological changes of brain tissue after mutilation of petrosal vein.Methods 1) 10 rabbits (either sex), separate the carotid artery and jugular vein, perfuse fresh rabbit cadaver by silicone. Observe rabbit cadaveric head specimens, compare it's petrosal vein with human's.2) 144 healthy adult rabbits were randomly divided into two groups, namely sham operation group and petrosal vein mutilation group. Rabbits were killed at 4h,8h,12h,24h,48h,72h after operation. Groups were divided into six sub-groups according to the time points (n=12 in each sub-group). Six of each sub-group were taken to measure water content by the wet and dry weight method; the content of sodium and potassium by flame photometer, SOD activity by xanthine oxidase assay, MDA content by thiobarbituric acid (TBA) assay, AQP-4mRNA transcription by RT-PCR. The other six of each sub-group were taken to observe the brain tissue pathological changes by HE staining, Nissl staining and electron microscopy structure, AQP-4 protein expression by immunohistochemistry.Results1 Color of perfused vessels was bright, small blood vessels were clear, anatomical structures were remained well, the petrosal vein was similar to human's. 2 Water content, sodium and potassium ion content:A) cerebellar tissues:brain water content, sodium and potassium ion content had no statistic difference in sham operation groups (p>0.05); water content and sodium content of 4h,8h,12h,24h sub-groups of petrosal vein mutilation group was higher than sham operation groups (p<0.05), potassium content of 4h,8h,12h,24h sub-groups of petrosal vein mutilation group were lower than the sham operation groups (p<0.05);4 hours after the mutilation of petrosal vein, water content and sodium content increased, they reached maximum 8-12 hours later, continued to 24 hours (p<0.05). Potassium ions content decreased to minimum 8-12 hours later (p<0.05). B) brain stem:water content, sodium and potassium ion content in sub-groups of sham operation group had no significant difference (p>0.05); 4 hours after mutilation of petrosal vein, brain water content, sodium content was higher than sham operation group (p<0.05), potassium content was lower than the sham operation group (p<0.05).3 Cerebellar pathological structural changes:structure of nerve cells of cerebellum were normal in sham operation groups; in 4h,8h,12h,24h sub-groups of petrosal vein mutilation group, the tissues appeared edema, manifested as cell swelling, disappearance of Nissl bodies, cell degeneration and necrosis. Pathological changes in the brain stem structure:4h sub-group of mutilation group show edema, pathological structures of the sham operation groups and other sub-groups of petrosal vein mutilation group were normal.4 SOD activity detection:A) cerebellum:SOD activity in the sham groups had no significant difference (p>0.05); SOD activity in 4h,8h, 12h,24h sub-groups of petrosal vein mutilation group were lower than in the sham operation groups (p<0.05); SOD activity decreased 4hours later,8-12 hours reached minimum, continued to 24 hours (p<0.05). B) brain stem:SOD activity had no significant difference in sham operation groups (p>0.05); SOD activity in 4h sub-group of petrosal vein mutilation group is lower than in sham operation group (p<0.05).5 MDA content detection:MDA content in the sham groups had no significant difference (p>0.05); MDA content in 4h,8h,12h,24h sub-groups of petrosal vein mutilation group were higher than in the sham operation groups (p<0.05); MDA content increased 4hours later, 8-12 hours reached maximum, continued to 24 hours (p<0.05). B) brain stem:MDA detection had no significant difference in sham operation groups(p>0.05); MDA content in 4h sub-group of petrosal vein mutilation group is higher than in sham operation group (p<0.05).6 AQP-4 transcription and expression:AQP-4 transcription and expression in the sham groups had no significant difference (p>0.05); AQP-4 transcription and expression in 4h,8h,12h,24h sub-groups of petrosal vein mutilation group were higher than in the sham operation groups (p<0.05); AQP-4 transcription and expression increased 4hours later,8-12 hours reached maximum, continued to 24 hours (p<0.05). B) brain stem:AQP-4 transcription and expression had no significant difference in sham operation groups(p>0.05); AQP-4 transcription and expression in 4h sub-group of petrosal vein mutilation group is higher than in sham operation group (p<0.05).Conclusions1 The structure and drainage of petrosal vein of rabbit was similar with human's, rabbits can be used to establish petrosal vein mutilation animal model.2 Compared with sham control group, cerebellar water content and sodium ion content increased in petrosal vein mutilation group, potassium content decreased. Mutilation of petrosal vein caused dysfunction of Na-K ATPase, resulted in cerebellar edema.3 Mutilation of petrosal vein can lead to pathological structural changes of rabbit brain tissues, the structural change is reversible.4 Compared with sham control group, MDA content increased in petrosal vein mutilation group, SOD activity decreased. Metabolism and function of neuron were damaged, the ability to eliminate oxygen free radicals decreased. Reduction of oxygen free radicals may contribute to brain function.5 Compared with sham control group, AQP-4 transcription and expression increased in petrosal vein mutilation group, indicating AQP-4 involved in the formation and development of cerebral edema. It suggested that inhibition of the expression of AQP-4 may be able to reduce brain edema.
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