(AP)

[This post has been updated]

Ben Carson doesn't deny using fetal tissue from aborted fetuses for medical research in the early 1990s. But the way in which the former Johns Hopkins neurosurgeon received and used the tissue is very different from how Planned Parenthood obtains and sells its fetal tissue, he claims.

News of Carson's medical research with fetal tissue came to light Wednesday night when a fellow doctor  published details of Carson's 1992 research using fetal tissue on her blog. The issue is timely, given Republicans — including Carson — have denounced Planned Parenthood after secretly records video showed officials talking about procurement of fetal tissues.

It also threatens to dog Carson's presidential ambitions — especially given his somewhat odd explanation.

Carson on Thursday rejected the comparison between his research and what Planned Parenthood has been accused of doing.

"You have to look at the intent," Carson told The Washington Post's Dave Weigel before he began a campaign swing through New Hampshire. "To willfully ignore evidence that you have for some ideological reason is wrong. If you’re killing babies and taking the tissue, that’s a very different thing than taking a dead specimen and keeping a record of it."

If you had to reread that once or twice, you're not alone. It's a very complex — and politically charged — issue.

Carson appears to be saying that the fetal tissue he used for research didn't come from fetuses aborted specifically for use in medical research. He also appears to accuse Planned Parenthood of doing just that. But that's a charge Planned Parenthood has flatly rejected and isn't proved by the videos.

First, a little background: Fetal tissue is used in experimental medical research to treat diseases. It has been linked to helping patients with Parkinson's disease and paralysis. But selling fetal tissue for profit is illegal in the United States.

Last month, several videos from anti-abortion activists showed Planned Parenthood officials talking casually about using fetal tissue from aborted fetuses for medical research. The videos implied that they were benefiting financially. Planned Parenthood officials apologized for their tone in the videos but maintain to this day they've done nothing wrong.

[How Planned Parenthood actually uses its federal funding]

That didn't stop Republicans in Congress and on the 2016 campaign trail from coming down hard on Planned Parenthood, promising to strip the organization from some $500 million in annual federal funding.

Carson was among those hitting Planned Parenthood hard, lending his considerable medical heft as a renowned neurosurgeon to the debate. He told Fox News's Megyn Kelly that fetal tissue research was basically useless and the same things could be accomplished without it.

"And if you go back over the years, and look at the research that has been done and all the things that it was supposed to deliver, very little of that has been done, and there’s nothing that can’t be done without fetal tissue," Carson said.

On Thursday, though, Carson told Weigel that the use of fetal tissue shouldn't be banned. He declined to say whether Planned Parenthood should stop providing fetal tissue for medical research. So one one hand, Carson said the use of fetal tissue doesn't produce results and is interchangeable with less morally fraught materials, and on the other he used it himself and now says it shouldn't be banned.

Carson's views on abortion appear to have long been complicated. In 1992, he appeared in an ad encouraging Maryland voters to oppose a law that would effectively keep abortions legal in the state if the Supreme Court overturned or weakened Roe v. Wade. He later appeared at a pro-abortion-rights activist press conference disavowing the ad, saying he didn't realize he was making a political statement.

Carson told Weigel that there really is no conflict between the research he did and his anti-abortion-rights views today:

"My primary responsibility in that research was when I operated on people and obtained the tissue," said Carson, who noted that he has not used fetal tissue samples since then.

Something tells us Carson hasn't issued his last comments on this.