The complex anatomy and specific terminology within embryology make this subject difficult to teach.
Furthermore,
the developmental abnormalities of the urogenital system become prohibitively complex on imaging if the fundamental structural pathways are not fully understood.
Clay models are a cost effective and intuitive teaching tool for embryological development because it allows for accurate three dimensional representation of anatomy.
Additionally,
the tactile experience of creating these models serves to solidify anatomical knowledge.
The clay is easily altered to demonstrate subtle changes of each embryological component over the course of development,
and the components that contribute to embryological abnormalities.
Female Reproductive Development
Bipotential gonads develop from the urogenital ridge (intermediate mesoderm) at approximately 6-7 weeks gestation (Fig.
1) and remain undifferentiated until this point.
The urogenital ridge can become either the testes or ovaries.
The abscence of SRY (on the Y-chromosome) leads to the development of ovaries.
Because no testosterone is produced,
the Wolffian ducts regress,
and because no Anti-Mullerian hormone is produced the mullerian ducts persist.
The cloaca is the terminal aspect of the hindgust and eventually forms the bladder.
The metanephros form the kidneys and partially originate from an extension of the Wolffian duct.
Mesoderm and ectoderm surrounding the cloacal membrane produce the external genitalia in both females and males. Remnants of the Wolffian ducts form the appendices of the ovaries and Gartner's ducts.
Male Reproductive Development
Stemming from the branch point of the undifferentiated urogential ridge at approximately 6-7 weeks (Fig.
2),
the presence of SRY on the Y-chromosome leads to the development of testes,
which produce testosterone (leydig cells) supporting Wolffian ducts and anti-mullerian hormone (sertoli cells) inducing regression of the mullerian ducts.
Over the course of the development until birth there is descent of the testes.
This descent is mediated by connection of the testes to the abdominal wall by the gubernaculum,
which over time pulls the testes through the inguinal canal and out of the abdominal cavity with increasing embryo growth.
Some testosterone is also converted to dihydroxytestosterone which aids developemnt of the prostate,
scrotum,
and penis.
The prostate originates from the urogenital sinus and epididymus from the Wolffian ducts.
Mullerian Duct Abnormalities (MDAs)
MDAs occur when all or part of the mullerian tissue fails to develop completely,
incompletely develops due to fusion abnormalities,
or fails to resorb.
The reported prevalence of MDAs is extremely variably with the lowest at 0.4% in women presenting with nonobstetric US,
and highest at 8-25% in women with recurrent miscarriage on hysterosalpingography.
Diagnosis is most often made on hysterosalpingography,
ultrasound,
or MRI.
MRI yields best characterization of anatomy and is the preferred modality.
Renal tract abnormalities are associated with MDAs in approxmately one third of patients with the most prevalent being renal agenesis.
It is important to image the renal system on MR or US at the time of MDAs assessment.