How could i check if the extract file from .gz is already in

This Code should decomprees the .gz extention files and it does . but i want to check if the file is already extracted 
or the file is already exsosts .
How can I do that or check ? 
public static void Decomprees (FileInfo fileToDecompress)  
{  
 using (FileStream originalFileStream = fileToDecompress.OpenRead())  
{  
 string currentFileName = fileToDecompress.FullName;  
 string newFileName = currentFileName.Remove(currentFileName.Length - fileToDecompress.Extension.Length);  
 using (FileStream decompressedFileStream = File.Create(newFileName))  
   {  
    using (GZipStream decompressionStream = new GZipStream(originalFileStream, CompressionMode.Decompress))  
    {  
   decompressionStream.CopyTo(decompressedFileStream);  
 }  
 }  
 }  
  }