Abdomen and pelvis

Descent of the testis

6 steps · 3 anomalies · Weeks 5 to 6 to Weeks 33 to birth

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A journey worth knowing because it explains the anatomy of an adult you will meet in a surgical outpatient clinic. The testis begins on the posterior abdominal wall and ends outside the body, and it takes its blood supply, its nerves and its lymphatic drainage with it. That is why a testicular tumour spreads to nodes beside the aorta rather than to the groin.

Weeks 5 to 6

Step 1 of 6

What happens: The testis develops from the gonadal ridge on the posterior abdominal wall, at the level of the tenth thoracic to the third lumbar segments.
What it forms: A gonad high in the abdomen, with its artery arising from the aorta at that level.
What remains in the adult: The testicular artery still arises from the abdominal aorta, and lymph still drains to the para-aortic nodes.

Nothing in this set goes wrong at this step — it is here because the story does not make sense without it.

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Senior’s 30-second takeaway

Descent of the testis — the whole bench in four lines. Read this on the way in.

If you see this: An empty scrotum in a newborn · A groin swelling reaching into the scrotum · A question about testicular lymphatic drainage
If asked to identify it: The testis descends from the posterior abdominal wall and keeps the artery, nerves and lymphatics of its original level.
If asked one more: The processus vaginalis goes ahead of it and should obliterate, leaving the tunica vaginalis.
If asked why it matters: A patent processus gives a congenital indirect inguinal hernia or a hydrocele.

Then stop. Let the examiner ask the next question.

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Senior’s 30-second takeaway

Read this first