Cyst of the canal of Nuck: ultrasound and MRI appearances

Clinical History

Female patient, 45 years old, reported a moderately painful swelling in the right groin for about 1 month. No other symptoms. Physical examination revealed a soft irreducible swelling, with no signs of inflammation.

Imaging Findings

Ultrasound examination of the right groin (using a linear transducer) revealed, in the subcutaneous adipose tissue, a cystic structure measuring 2.5x1.4x4.1 cm of largest diameters with moderately thickened walls but with no colour Doppler vascular signal. The cystic structure continues in the inguinal canal, but no bowel loop or omental fat was observed in or around the cyst when the patient coughed (Fig. 1).
MRI showed a pear-shaped cyst with a superior pedicle continuing in the inguinal canal, along the course of the round ligament of the uterus. The cyst contains some thin septa (hypointense on T2-weighted images) that give it an aspect of crown of the rosary at the inguinal orifice (Fig. 2).

Discussion

The cyst of the canal of Nuck, also named female hydrocele, is a rare developmental disorder (only about 400 reported cases), first described by the 17th-century Dutch anatomist Anton Nuck van Leiden [1, 2].
The canal of Nuck originates from a small evagination of the parietal peritoneum that descends into the inguinal canal, accompanying the round ligament of the uterus to the upper part of labium majus (corresponding to the processus vaginalis in males). Normally, the canal of Nuck undergoes obliteration around the sixth month of intrauterine life and the peritoneum stops at the internal inguinal orifice within the first year of life [3].
The pathological persistence, total or partial, may promote the occurrence of a congenital inguinal hernia or cystic collections, which may arise also in adulthood (comparable to scrotal hydrocele). An imbalance between secretion and absorption of liquid by the peritoneal secretory membrane can favour the development of a cyst. This imbalance is usually idiopathic, but may be caused by a defective lymphatic drainage following a traumatic or inflammatory process [2].
Clinically the patients present a tense-elastic swelling in the groin, of 3-5 cm in size, not reducible or expandable during the Valsalva manoeuvre, painless or slightly painful. The clinical diagnosis is not so simple because in a third of cases there is also a concomitant inguinal hernia [2, 3].
Ultrasound is the imaging modality of choice. The ultrasound features described in the literature are various: anechoic, tubular or oval, sausage-shaped structure along the round ligament, a comma-shaped lesion with its tail directed toward the inguinal canal, a “cyst-within-a-cyst”, dumbbell shaped cyst with internal septum [1, 3, 4]. The Valsalva manoeuvre, or coughing, during the real time ultrasound helps to differentiate a cyst of the canal of Nuck from an inguinal hernia, especially if the latter shows intestinal or omental component [5].
MRI allows to better define the extent of the cyst, hypointense on T1-weighted images and hyperintense on T2-weighted images; if present, any septa appear hypointense on T2-weighted series [4]. The hydrocele of the canal of Nuck is treated surgically if symptomatic, especially if there is a risk of infection [3].

Differential Diagnosis List

Final Diagnosis

Surgical excision showed a cyst of the canal of Nuck.

URL:	https://www.eurorad.org/case/12482
DOI:	10.1594/EURORAD/CASE.12482
ISSN:	1563-4086