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New Advances in Ambiguous Genitalia

Starting with chromosomal sex, since that’s the thing we often think about first when we see a baby who has ambiguous genitalia. Let me tell you, the chromosomes won’t tell you everything. They aren’t always perfect predictors of what the sex of the child is. I think one obvious example is that a karyotype only sees big changes. You might not see the missing piece that will turn an XY person into a perfectly normal looking female. You may not see extra pieces that will turn an XX person into a very normal looking male. What about the concept that if some of the cells are one type - say 45 X - and the other types are 46 XY, what actually happens. And that’s an important concept of mosaicism. I’m not sure they will ask you this on the Boards but in real life you have to remember that you can get mixes of chromosomes.

Now the third thing - and I think this is very important for diagnostic purposes - are the internal genital ducts, the tubing as you would have it. I don’t know, maybe you have your mnemonic. I just remember that M stands for mother and W stands for wolf-whistle, to remember which ones are the "female" and which ones are the "male" structures.

Now the thing that we see in the delivery room, the thing that I think really leads to a lot of the distress, is the external genitalia, the ambiguity of the external genitalia. The rule is - and this is what an examiner might try to ask a question, to see if you understand - is that for every female genital structure there is a male equivalent, and vice-versa.

There is an important concept medically, that there is a critical period for external genitalia development and this is week 8-12. After the second month. Before that the male and female genitalia in the fetus look exactly alike. Between 8 and 12 weeks any androgen - whether it’s something the mother took, whether it’s a tumor the mother has.

You need to know what are some of the signs of virilization. Clitoromegaly is one. But I will tell you that there are standards, but it’s very hard to measure a clitoris and it’s sort of like the Supreme Court definition of pornography, "you know when you see it." Now I want to warn you that the clitoris of a premature infant can look very prominent because there isn’t a lot of labial fat on the sides, so it looks like the clitoris is sticking out there.

Another thing that is important is that if you see a migration of the urethral opening to the shaft of what would be the clitoris - and the urethral opening in a male should be at the tip of the corona, and in a female is down at the base of the phallic structure, but it could be anywhere in between depending on how much androgen the person has. Another very important feature for virilization is any kind of posterior fusion at the labia.

You have to know the converse too. What does an under-virilized male look like? Obviously a small penis is one thing, and you can remember the one inch rule as a rule of thumb for a term newborn. A penis that is less than one inch in length is more than 2 ½ standard deviations below the mean. That should be easy to remember, hopefully.

Here is an example … this is a bifid scrotum where you actually have some fusion in the midline right here, and that can be a sign of under-virilization as well.

Now any exposure to excess androgens during that critical 8-12 week period will lead to virilization and the most common thing that you will run into, and have a very good chance of