Background The use of natural openings for abdominal surgery started at the beginning of the 21th century. A transDouglas endoscopic device has been designed to perform most of the intra-abdominal operations in women through the pouch of Douglas. The posterior vaginal vault is limited in size and could be damaged by an oversized instrument. This study investigates the optimal dimensions of the instrument by measuring the limiting factor in the passage. Methods In ten female embalmed bodies the transversal and sagittal diameter of the fornix posterior vaginalis was measured by two observers. The pouch of Douglas was filled to its maximal capacity with mouldable latex through an open abdomen. By internal vaginal examination the connective tissue borders of the fornix posterior were palpated and the impression in the cast was measured. The mean value of these two diameters was evaluated in this study. The level of agreement between the observers was calculated.Results The mean fornix posterior diameter was 2.6 cm (standard deviation, SD 0.5 cm) with a range of 2.0-3.4 cm. The mean difference between the two observers of all measurements was 0.08 cm (not significant). Both observers had an acceptable intraobserver variation. The interobserver agreement was excellent. Conclusion Instruments with dimensions within the measured limits can be used safely for intra-abdominal operations via the natural orifice of the vagina.Keywords Fornix vaginalis Á Pouch of Douglas Á Natural orifice surgery The 19th century was the era of the laparotomy. Endoscopy was developed in the 20th century. The use of the natural openings for abdominal surgery started at the beginning of the 21st century. Instruments have been designed in order to perform most of the intra-abdominal operations in women through the pouch of Douglas. In order to find the optimal dimensions of this instrument, the limiting factor in the passage through the vagina into the abdominal cavity, the fornix vaginalis, has to be measured.
AnatomyThe fornix vaginalis is formed anatomically by the vagina around the cervix uteri. It is most spacious dorsally, where