Hydrocele of the canal of Nuck

Hydrocoele 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 majora². Incomplete obliteration of this canal (patent processus vaginalis) can result in either an inguinal hernia or a hydrocoele ^1,3.

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

Epidemiology

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

Clinical presentation

Hydrocoele 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. Hydrocoeles can be painful and cause a red swelling extending to the labium majus in case of infection.

Pathophysiology

During fetal male development, the testicle descends along the gubernaculum through the inguinal canal and into the scrotum. The testicle is enveloped in a sac-like extension of the peritoneum, known as processus vaginalis (PV). When the testis has come to rest in the scrotal sac the PV 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 PV within the inguinal canal in women is called the ‘canal of Nuck’. If the PV does not close, it is referred to as a patent processus vaginalis (PPV). If the PPV is small and only allows fluid to pass, the condition will lead to peritoneal fluid accumulation or a (communicating) hydrocele. If the PPV is larger and allows abdominal organs to protrude, the condition is referred to as hernia ⁴.

Radiographic features

Ultrasound

• 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 hydrocoele ^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

CT

Reports CT-findings of a hydrocoele of the canal of Nuck are extremely scarce. On the internet one case report is describing the CT findings of hydrocoele as follows:

• homogeneous fluid-filled uni-locular cyst, extending to the labia
• the inguinal canal may communication may not be identified on CT

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

MRI

• in the literature only one report could be found describing the MR findings of a hydrocoele of the canal of Nuck; in this case MR showed a thin-walled tense cystic mass in inguinal area ¹
• in most cases hydrocoeles are described to have a thin wall. In our example (Case 1 ) the hydrocoele has a thick-walled cystic appearance due to infection; the proximal part of the lesion is extending in the peritoneal cavity along the route of the round ligamen; the distal part is blunt and extending towards the labium majus
• the wall of the hydrocoele may show mild contrast enhancement, especially when infected

Treatment

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

History and etymology

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

Differential diagnosis

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)
• cyst
• abscess
• lymphadenopathy