What is the fine-grained topic of the following text: In this book, a systematic documentation of characteristic as well as rarer alterations is presented involving 444 patients who had been operated on in Germany between 1990 and 1997 at the Bethel Epilepsy Centre in Bielefeld. Only return the topic.
Documenting alterations in epilepsy patients operated at the Bethel Epilepsy Centre in Germany from 1990-1997.