What is the embryologic abnormality?
The gonads begin as the genital ridges in which germ cells appear in the 6th week. The germ cells migrate from the wall of the yolk sac along the dorsal mesentery of the hindgut to invade the genital ridges. Under the influence of the SRY gene of the Y chromosome, a gonad becomes a testis, and Leydig cells form that secrete testosterone by the 8th week. In target tissues, the 5-alpha-reductase enzyme converts testosterone to dihydrotestosterone which binds to an intracellular hormone receptor. The developing testis and mesonephros become attached to the posterior abdominal wall by the end of 8 weeks. A caudal genital ligament forms along with a portion of mesenchyme called the gubernaculum that leads to the inguinal region. An extra-abdominal portion of gubernaculum leads to the scrotum. An evagination of peritoneum called the processus vaginalis extends to the inguinal region and forms the inguinal canal into the scrotum. The testis descends along this path, carrying its vascular supply and vas deferens in connective tissue destined to be the spermatic cord. If the testis does not descend into the scrotum, but remains in the abdomen, it is called a cryptorchid testis.
Conversely, if the connection between the abdominal cavity and the scrotum remains open (it typically closes after birth), then abdominal contents, usually small bowel, can herniate downward--an inguinal hernia.
What are potential problems that can result?
If the testis does not assume its extra-abdominal position, then it will not function properly. Spermatogenesis must occur at a temperature a couple of degrees cooler than the rest of the body. A cryptorchid testis will not function to produce sperm. Unilateral cryptoorchidism leads to a decreased sperm count, but infertility is unlikely, because the other testis is functional. There is a long term risk in a cryptorchid testis for malignancy‹a seminoma. In childhood, an orchiopexy procedure can be done (recommended before the age of 2) and the testis placed in the proper position, and most of the time the testis will function. Following puberty, it is unlikely that a cryptorchid testis will have spermatogenesis function.
Is there a relationship to maternal age?
No.
Is there a karyotypic abnormality?
Unlikely. For a phenotypic male, this condition is typically sporadic.
A phenotypic female is found on physical examination to have a small vagina and no palpable uterus or adnexae. Bilateral inguinal masses are present. Her karyotype is 46, XY. What is this condition?
She has androgen insensitivity syndrome (so-called testicular femininization syndrome) in which there is either a lack of androgen receptors or receptor failure, so dihydrotestosterone has no effect in producing male differentiation in target cells. The testes remain cryptorchid and are often found in the inguinal region (palpable as masses). The risk for malignancy in the cryptorchid testes is so great that the testes are removed. Vaginal reconstruction can be done. Female hormones can be administered.
