Undescended testicles

During fetal development, the testicles, which are located in the abdominal cavity, gradually descend as the baby develops, and are normally completely contained within the scrotum at birth (testicular descent phenomenon). However, when this normal testicular descent does not occur and the testicles become stuck somewhere along the way, this is called cryptorchidism. It is more common for it to occur on one side than on both sides, with the most common being in the inguinal region. It is a relatively common congenital abnormality of the testicles, occurring in one out of every several hundred people.

If the testicles do not descend naturally by the age of 5, gonadotropic hormones must be administered or surgery must be performed to lower the testicles into the scrotum. The spermatogenic ability of the testicles is easily impaired by high temperatures, and since the abdomen is about 1°C warmer than the scrotum, it is believed that there is little hope of recovery of spermatogenic ability for undescended testicles that are left undescended until the age of 10. In addition, it is believed that undescended testicles are prone to developing malignant tumors, so undescended testicles discovered after puberty should be removed. However, testicles that move freely between the scrotum and the groin can be left undescended.

[Matsushita Kazuo]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

胎生期には腹腔(ふくくう)内にあった睾丸が、成育とともに漸次下降して、出産時には陰嚢(いんのう)内に完全に収まる（睾丸下降現象）のが普通であるが、この正常な睾丸下降が行われず、下降経路のどこかで睾丸が停滞してしまった場合を停留睾丸という。両側性より片側性のほうが多く、鼠径(そけい)部の停留がもっとも多い。睾丸の先天異常としては比較的多く、数百人に1人という割合でみられる。

　5歳までに自然下降しないときには性腺(せいせん)刺激ホルモンを投与するか、手術によって睾丸を陰嚢内に引き降ろす睾丸固定術を行わなければならない。睾丸の精子形成能力は温度が高いと損なわれやすく、腹部は陰嚢内よりも1℃ほど高いので、10歳まで放置された停留睾丸に対しては、精子形成能力の回復はまず望めないと考えられている。また、停留睾丸には悪性腫瘍(しゅよう)が発生しやすいとされており、思春期以降に発見された停留睾丸は切除してしまったほうがよい。なお、陰嚢内と鼠径部の間を自由に移動する睾丸は放置しても差し支えない。

［松下一男］

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