FEMALE HYDROCELE [CYST of the CANAL of NUCK]

Nang ống Nuck

Discussion

Female hydrocele, also named a cyst of the canal of Nuck, is an unusual diagnosis with only about 400 reported cases. Because this entity is not

mentioned even in comprehensive surgical and gynecologic textbooks, many physicians are unaware of its very existence.

In the male fetus, an evagination of the parietal peritoneum, the processus vaginalis, accompanies the testis as it descends into the scrotum.

The same gloved fingerlike processus vaginalis, named the canal of Nuck after a 17th century Dutch anatomist, follows the round ligament of the uterus as it passes through the female inguinal canal. Normally this peritoneal evagination undergoes obliteration soon after birth in both sexes. If it remains completely patent, it forms an avenue for an indirect inguinal hernia.

Partial proximal obliteration, which leaves the distal portion of the processus vaginalis open, creates the anatomic prerequisite for a hydrocele of the spermatic cord and a cyst of the canal of Nuck, respectively. An imbalance of fluid secretion and absorption by the secretory membrane lining the processus vaginalis may eventuate in the development of a cystic swelling.

Hypersecretion or underabsorption may result from inflammation, trauma, or impairment of lymphatic drainage, for instance, owing to a large hernia, but in most cases it is idiopathic. The histologic composition of a cyst of the canal of Nuck reflects its peritoneal origin: a variously thick fibrous outer wall containing blood vessels and occasionally smooth muscle fibers, lined on the inside with a single layer of mesothelial cells. The diagnosis of a female hydrocele is seldom made on the basis of clinical findings alone. In fact, most of the cases reported in the literature were diagnosed at surgery performed for suspected inguinal hernias. Patients usually have a painless or moderately painful fluctuant inguinal mass, which is irreducible and can be transilluminated if large enough. There are no acute abdominal symptoms as with an incarcerated inguinal hernia, for which it is often mistaken. Clinical diagnosis is even made more difficult by the fact that in one third of the patients, a concomitant inguinal hernia is found. There are many differential diagnoses for groin masses. Most commonly they are caused by inguinal or femoral hernias, followed by enlarged lymph nodes and soft tissue tumors (eg, lipomas, leiomyomas, and endometriosis of the round ligament). Further down the list are vascular abnormalities (eg, arterial and venous aneurysms) and some very rare entities such as ganglion cysts protruding out of the hip joint and paraspinal abscesses surfacing in the groin.  High-resolution sonography can identify the nature of groin tumors in most cases or at least can narrow down the list of differential diagnoses.

To the best of our knowledge, there has been only 1 report dealing with the sonographic appearance of hydrocele of the canal of Nuck.

Anderson et al  found a tubular anechoic mass extending along the course of the round ligament without any internal structures, thus representing a unilocular hydrocele. Miklos et al described sonographically guided placement of a hook-wire needle to facilitate surgical exposure of a multicystic hydrocele of the canal of Nuck without further detailing its sonographic features.

Multiloculated hydroceles are reported in female as well as in male patients, so internal septations are obviously not uncommon. As for the somewhat strange internal structures in our cases (cysts within cysts), we can only speculate. We assume that they represent remnants of a futile attempt by nature at obliteration.

There are few conditions that can be confused with hydrocele of the canal of Nuck on sonography. Malignant lymphomas may at first glance have the appearance of anechoic cysts but show abundant vasculature on color-coded Doppler sonography. Generally, we would suggest color Doppler interrogation of all seemingly cystic structures to rule out a vascularized structure before performing interventional measures. An incarcerated hernia contains fluid, but there is always a solid, mostly hyperechoic component protruding out of the hernial orifice into the sac, representing compressed omentum or intestine (Figure 3).

Abscesses, apart from occurring in an entirely different clinical setting, usually have an irregular hypoechoic wall and echogenic debris or gas bubbles in their contents. The peculiar sonographic morphologic features of hydrocele of the canal of Nuck, namely, a cystic mass with a fine circumferential echogenic margin, possibly with septa or cystic internal structures, make high-resolution sonography the imaging modality of choice for diagnosing this entity.

In conclusion, hydrocele of the canal of Nuck is a rare developmental disorder, but it ought to be on the differential diagnosis list of groin tumors in female patients. The ultrasound community especially should be aware of this entity because this diagnosis can readily and confidently be established on the basis of sonography. A concomitant inguinal hernia can be shown or ruled out in the same way. Although surgical excision is curative and therefore the treatment of choice, in our opinion, sonographically guided aspiration can be used to temporarily alleviate patient discomfort in this absolutely benign condition.