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.
