鞘膜积液(英国英语：hydrocoele)表示浆液(serous fluid)在体腔内的病变积累。

睾丸鞘膜积液是围绕睾丸的流体积累，并且是相当普遍的。它是由腹膜(peritoneum)缠绕着睾丸体的部分、称为鞘膜(tunica vaginalis)，所分泌之流体引起的。目前只要没有疝气，1岁以下小孩的鞘膜积液，通常会自行痊愈。原发性鞘膜积液可能发展在成年期、尤其是老年人，在炎热的国家尤为常见，经由浆液性液体、大概是由受损的重吸收所引起的，这似乎是最主要的鞘膜积液的解释，虽然原因还不清楚。 鞘膜积液也可是反复性地经由班氏丝虫(Wuchereria bancrofti)或马来丝虫(Brugia malayi)的慢性感染、或非洲和东南亚地区的两种蚊子传播的寄生虫等所引起的"插销性腹股沟淋巴系统"(Inguinal lymph node)的结果。因此，如果发病条件会是较弥漫性的后遗症(sequela)之一部分、通常被称为象皮病(elephantiasis)，这也影响在身体其它部分的淋巴系统。

A hydrocele (Br English: hydrocoele) denotes a pathological accumulation of serous fluid in a body cavity.

A hydrocele testis is the accumulation of fluids around a testicle, and is fairly common. It is often caused by fluid secreted from a remnant piece of peritoneum wrapped around the testicle, called the tunica vaginalis. Provided there is no hernia present, hydrocoeles below the age of 1 year usually resolve spontaneously. Primary hydrocoeles may develop in adulthood, particularly in the elderly, particularly common in hot countries, by slow accumulation of serous fluid, presumably caused by impaired reabsorption, which appears to be the explanation for most primary hydroceles although the reason remains obscure. A hydrocele can also be the result of a plugged inguinal lymphatic system caused by repeated, chronic infection of Wuchereria bancrofti or Brugia malayi, two mosquito-borne parasites of Africa and Southeast Asia, respectively. As such, the condition would be a part of more diffuse sequelae commonly referred to as elephantiasis, which also affects the lymphatic system in other parts of the body.