Abstract: Objective To observe the pathologic changes of ganglion cell and nerve plexus in internal anus sphincter of rats with congenital anorectal malformations (ARM).Methods Healthy and pregnant Wistar-Imammichi rats were induced to ARM by ethylene thiourea (ETU). There were 67 rats with ARM at all. The pelvis was continuously cut from the exactly midsagittal plane. The HE staining was performed, and the numbers of the ganglion cell and nerve plexus in the internal anus sphincter were observed under the microscope.Results The average numbers of the ganglion cell and nerve pluxes in the ARM embryos were (1.206±0.012) and (0.308±0.051). Those of the normal control embryos were (3.710±0.043) and (1.227±0.072) respectively. There was a significant difference between two groups ( P<0.05～0.01). While, those of the embryos without ARM which dealt with ETU were (3.012±0.032) and (1.187±0.004) respectively, didn't differ from the normal control embryos.Conclusion The decrease of the ganglion cell and the nerve plexus in internal anus sphincter is an important pathologic change of ARM.

Key words: internal anus sphincter, anorectal malformations, ganglion cell, ethylene thiourea