The leading component of a coronal mass ejection (CME), its observed frontal structure (FS), has been detected close to the solar surface in a few near-the-limb events only. Thus far, no manifestations of such a frontal structure have been reported in reasonable proximity to a preeruptive filament located away from the solar limb. Thus the identification of the FS with preevent coronal structures remains unclear. We propose a method to estimate the parameters of the initial volume of a CME, using comparative measurements of the spatial locations of the erupting filament and FS with a self-similar solution of the magnetohydrodynamic equations describing the expansion of the CME. We develop this method by analyzing observations of a large eruptive filament on the solar disk on 4 September 2000, using data acquired with the Solar Heliospheric Observatory (SOHO), Large-Angle Spectroscopic Coronagraph (LASCO), and EUV Imaging Telescope (EIT) instruments and the Siberian Solar Radio Telescope. We show that if a magnetic structure corresponding to the FS prior to the filament eruption does exist, then it is localized at a relatively low height (here, about 100--150 Mm above the filament). At the initial stage of the motion, the shape of the hot FS approximately reproduces the configuration of the cool eruptive filament. In addition, we conclude that the coronal dimming observed in this event could be also due to CME-caused suppression of the heating and/or mass supply of the dimmed structures rather than due to their opening only. We also obtain in a simple way an exact self-similar solution of MHD equations in a form suitable for analyses of experimental data.