Verificare esistenza directory ftp

Private Function List(ByVal sCartella As String) As ListBox
        Dim sr As IO.StreamReader
        Dim lst As New ListBox
        Dim ftpRequest As Net.FtpWebRequest
        Dim ftpResponse As Net.FtpWebResponse
        sr = Nothing
        Try
            ftpRequest = Net.FtpWebRequest.Create(sCartella)
            ftpRequest.Credentials = New NetworkCredential(sUserFTP, sPasswordFTP)
            ftpRequest.KeepAlive = False
            ftpRequest.UseBinary = True
            ftpRequest.Method = WebRequestMethods.Ftp.ListDirectory
            ftpResponse = ftpRequest.GetResponse
            sr = New IO.StreamReader(ftpResponse.GetResponseStream(), System.Text.Encoding.ASCII)
            lst.Items.Clear()
            While Not sr.EndOfStream
                lst.Items.Add(sr.ReadLine)
            End While
            List = lst
        Catch ex As Exception
            List = Nothing
        Finally
            ftpRequest = Nothing
            ftpResponse = Nothing
            sr.Close()
        End Try
End Function

Private Sub Main()
        Dim lstFile As ListBox
        lstFile = List(sPathSuperiore) //il path della cartella superiore a quella da creare
        If lstFile.Items.IndexOf("nomecartella") <0 Then
                  //codice per creare la cartella
        End If
End sub