Doctors claim to have found the first compelling evidence that the G spot exists, but say not all women appear to have one.

Ultrasound scans revealed clear anatomical differences between women who said they experienced vaginal orgasms and a group of women who did not. The scans identified a region of thicker tissue where the G spot was rumoured to be lurking, which was not visible in the women who had never had a vaginal orgasm.

Doctors at the University of L'Aquila in Italy, where the study was conducted, say the findings make it possible for women to have a rapid test to confirm whether or not they have a G spot.

The location, and even existence, of the G spot has been hotly contested in medical circles. While doctors know that female sexual anatomy varies substantially, until now there has been no solid evidence to link those differences to a woman's sexual responses.

"For the first time, it is possible to determine by a simple, rapid and inexpensive method if a woman has a G spot or not," Dr Emmanuele Jannini told New Scientist magazine.

The G spot is only thought to affect a woman's ability to have vaginal orgasms, so if women do not have one "they can still have a normal orgasm through stimulation of the clitoris," Jannini said.

The team used ultrasound to scan nine women who had experienced vaginal orgasms and 11 women who said they had not. In the first group of women, the tissue between the vagina and the urethra was found to be substantially thicker than in the other women.

Jannini, whose study appears in the Journal of Sexual Medicine, said the scans suggested that "women without any visible evidence of a G spot cannot have a vaginal orgasm".

The research supports a previous study by the team which reported differences in the chemical make-up of the G spot tissues. Women who appear to have a G spot produced specific chemicals, including an enzyme that processes nitric oxide, the substance that triggers male erections.

Other researchers welcomed the findings, but said it was unclear whether the team had identified a distinct G spot structure or an internal part of the clitoris.

"This may be related to the presence of the controversial G spot," said Tim Spector, a consultant rheumatologist at St Thomas' hospital in London. "However, many other explanations are possible, such as the actual size of the clitoris, which although not measured in this study appears highly variable."

Elisabeth Lloyd, a professor at Indiana University and author of The Case of the Female Orgasm, said scans should now be conducted on a larger group. "There's been controversy over which parts of the female anatomy might be the G spot, and what the role of it might be," she said.

Lloyd said only 20% to 25% of women had vaginal orgasms during sex. "It has never been explained why that is the case; it's a mystery. This paper doesn't totally explain it, but it might do partially, and that could help us understand what those numbers are about."