mesonephric duct

Second, define the gonads.

Third, define Mullerian and Wolffian anatomy.

Fourth, reconstruct Sertoli and Leydig function.

Fifth, Evaluate androgen synthesis, metabolism, and action.

Because functioning Sertoli cells produce AMH, Mullerian structures are usually absent.

Because Leydig cells produce testosterone, Wolffian structures and male external differentiation may develop.

But phenotype depends on how completely the testicular program formed.

Some individuals have typical male external genitalia.

Müllerian structures depend on fetal AMH exposure.

Wolffian structures depend on fetal testosterone.

An ovotestis may produce both, but not uniformly.

So a uterus may be present, partially developed or absent.

What should the pediatric urologist do when an unexpected ovotestis is encountered? Do not improvise irreversible surgery.

Document the anatomy.

Define Müllerian and Wolffian structures.

Preserve blood supply.

It is a historical record of inadequate local Sertoli cell function.

The Wolffian structures tell the complementary story.

If fetal Leydig cells produced enough testosterone on the better developed side, an epididymis or vas may form.

If androgen production was inadequate on the other side, Wolffian structures may regress.

One patient can therefore carry two different internal developmental histories.

This is why mixed gonadal dysgenesis should be approached side by side.

Map both sides.

Identify gonadal position.

The external genitalia therefore develop along a female typical pathway.

And because androgen signaling is also required for Wolffian duct stabilization, internal male duct structures are often absent or poorly developed.

This separates complete androgen insensitivity from several disorders we have already discussed.

In Leydig cell hypoplasia, the Leydig compartment does not respond adequately to HCG or LH.

They do not prove normal androgen synthesis.

Preserved Wolffian structures suggest meaningful testosterone effect.

Incomplete external virilization tells you that the genital target did not receive sufficient effective androgen signaling.

The combination is a pathway map.

Start with fetal anatomy.

Testosterone from Leydig cells stabilizes the Wolffian ducts.

That supports development of the epididymis, vas deferens, and seminal vesicles.

Sertoli cells independently produce AMH, so Müllerian structures regress.

Another amplifies testosterone into DHT before the receptor sees the final signal.

That is why SRD5A2 deficiency can produce micropenis, severe hypospadias, incomplete labioscrotal fusion, cryptorchidism, or predominantly female external genitalia.

The prostate is often small, yet Wolffian structures may be preserved.

The anatomy maps where DHT mattered.

Mullerian regression tells you that Sertoli cells produced effective AMH early enough.

A developed epididymis and vas deferens tell you that fetal testosterone stabilized the Wolffian duct.

Male typical external genitalia tell you that androgen production and peripheral androgen action occurred during the critical virilization window.

If all three footprints are present but the gonad is gone, testicular development cannot have failed from the beginning.

A missing gonad may tell you more about fetal testicular function than a poorly characterized gonad that is still present.

Read the uterus.

Read the Wolffian structures.

Read the genital phenotype.

That creates a continuum.

There may be partial Müllerian regression, partial Wolffian development, incomplete external virilization, and asymmetric gonads.

This gives us a useful diagnostic distinction.

In an androgen synthesis defect, the testis may be structurally well-differentiated, but unable to make the right steroid.