Hydrocele of the canal of Nuck

Last revised by Arlene Campos on 23 Jan 2024

Hydrocele of the canal of Nuck is a rare condition in female children caused by a failure of complete obliteration of the canal of Nuck 1. The canal of Nuck is an abnormal patent pouch of peritoneum extending anterior to the round ligament of the uterus into the labia majora 2. Incomplete obliteration of this canal (patent processus vaginalis) can result in either an inguinal hernia or a hydrocele 1,3.

It is homologous to a patent processus vaginalis in males which also predispose to indirect inguinal hernias and hydroceles and cysts of the spermatic cord.

The incidence of a patent processus vaginalis decreases with age. In newborns, 80-94% have a patent processus vaginalis. As many as 30% of adults are discovered to have a patent processus vaginalis at autopsy. Why all patients with patent processus vaginalis do not develop into a hernia or hydrocele is not understood 3.

Hydrocele of the canal of Nuck predominantly occurs in adult females and less frequently in infants and post-pubertal girls 1,3,4. Case reports have described congenital herniation of the ovary and fallopian tube into the canal of Nuck 2.

Hydrocele of the canal of Nuck typically presents as a painless swelling in the inguinolabial region. If the bulge is apparent in standing position and disappears while supine, a hernia is more plausible 4. Hydroceles can be painful and cause a red swelling extending to the labia major in case of infection.

During fetal male development, the testis descends along the gubernaculum through the inguinal canal and into the scrotum. The testis is enveloped in a sac-like extension of the peritoneum, known as the processus vaginalis. When the testis has come to rest in the scrotal sac the processus vaginalis closes.

The same evagination of the parietal peritoneum occurs in the female along the round ligament, through the inguinal ring, and into the inguinal canal. The portion of processus vaginalis within the inguinal canal in women is called the ‘canal of Nuck’. If the processus vaginalis does not close, it is referred to as a patent processus vaginalis. If the patent processus vaginalis is small and only allows fluid to pass, the condition will lead to peritoneal fluid accumulation or a (communicating) hydrocele. If the patent processus vaginalis is larger and allows abdominal organs to protrude, the condition is referred to as hernia 4.

  • typically presents as a cystic mass lying superficially and medially to the pubic bone at the level of the superficial inguinal ring 4,5

  • no communication with the peritoneum should be visible in case of a hydrocele 4,5

  • there should be no change with the Valsalva maneuver 5

  • ultrasound is particularly useful because of its “real-time” nature and ability to precisely depict superficial structures 5

  • ultrasound is an excellent technique to help exclude the presence of bowel in the swelling as seen in an inguinal hernia

Literature on CT findings for this condition is scarce. One case report describes the CT findings of hydrocele as follows:

  • homogeneous fluid-filled unilocular cyst, extending to the labia

  • the inguinal canal communication may not be identified on CT

The morphologic and anatomic findings should be similar to those described with MRI (see below). MRI should be the technique of choice, especially in children.

  • in the literature only one report could be found describing the MR findings of a hydrocele of the canal of Nuck; in this case, MR showed a thin-walled tense cystic mass in the inguinal area 1

  • in most, cases hydroceles are described to have a thin wall. In our example (Case 1) the hydrocele has a thick-walled cystic appearance due to infection; the proximal part of the lesion is extending into the peritoneal cavity along the route of the round ligament; the distal part is blunt and extending towards the labium majus

  • the wall of the hydrocele may show mild contrast enhancement, especially when infected

Hydroceles can be treated surgically, however, some surgeons prefer conservative treatment (see case 1). In case of infection antibiotic treatment should be started.

Persistence of the processus vaginalis peritonei (i.e. the canal of Nuck) was first described by Anton Nuck (1650-1692), Dutch anatomist, in 1691 2.

Swelling of the inguinal region in a female may also result from a number of other conditions such as 4:

  • inguinal hernia (usually hernial sac with bowel content instead of fluid)

  • tumor (lipoma, leiomyoma, sarcoma)

  • round ligament varicosities 6

  • cyst

  • abscess

  • lymphadenopathy

  • spermatic cord hydrocele - males

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