Cyst of the canal of Nuck with abdominal extension: Ultrasound findings

Clinical History

The patient presented with a painless swelling in the left groin, which had gradually increased in size during the last month. Clinical examination revealed a tense and painless mass with no evidence of inflammation.

Imaging Findings

The patient underwent an ultrasound examination of the left inguinal region with a 6-9 MHz linear array transducer, which revealed a structure with cystic characteristics. (Fig. 1) Namely, the structure was anechoic, had thin walls, showed increased through-transmission, had an hourglass configuration and its dimensions were 4x2 cm. (Fig. 2) This structure was located in the inguinal canal but also extended inside the abdominal cavity. (Fig. 3) Colour Doppler examination revealed no vascularity inside this structure. Transabdominal ultrasound was then performed with a 4.6 – 6.6 MHz linear array transducer and proved that the structure extended intra-abdominally, between the left lateral wall of the urinary bladder and the left ovary.

Discussion

By the 6th month of development, the parietal peritoneum evaginates along the round ligament of the uterus through the inner inguinal ring and into the inguinal canal, forming the canal of Nuck (CN), the female equivalent of processus vaginalis in males. The hydrocele of the canal of Nuck (HCN) or cysts of the canal of Nuck (CCN) result from the partial patency of a canal of Nuck that was not obliterated as normally expected by the first year of life. Indirect inguinal hernia can be caused by the same mechanism. The fluid collection of a HCN results from hypersecretion of the lining epithelial cells covering the canal. Factors contributing to its formation include trauma, inflammation, endometriosis or incomplete lymphatic drainage. HCN affects mainly children and rarely adults. The HCN is classified in different types depending on whether it completely or partly communicates with the peritoneal cavity or not.[1, 2, 3]
CCN present as a painless, fluctuating and nonreducible inguinal lump which may extend to the labium majus, although it has been reported to account for only 0.76% of inguinal lumps. [4] The HCN normally measures about 3 cm in length and 0.3-0.5 cm in diameter and may occasionally cause a dull pain. There are rare reports about herniation of the urinary bladder, the ovary and fallopian tubes into the canal of Nuck. [1, 5, 6] The Valsalva manoeuvre can be used to differentiate a HCN from an inguinal hernia as it is positive only in the latter case. [7]
Ultrasonography is the primary imaging modality for diagnosing HCN, establishing the diagnosis in 100% of cases. [4] HCN is seen as a well-defined, hypo- or anechoic, thin-walled cystic formation, occasionally containing septa, whose shape can be tubular, hourglass, sausage or comma-like with its tail connected to the inguinal canal. Cysts may be found inside a HCN giving a “cyst within a cyst” appearance. Colour Doppler ultrasonography shows no blood flow inside the HCN. MRI findings of HCN involve low signal on T1-weighted images and high signal on T-2 weighted images, although MRI is rarely used due to its cost. [1, 2, 5]
Infection of a HCN is a rare complication, causing the formation of an abscess or adenopathy and manifesting with enhancement of its wall on contrast-enhanced MRI.
Surgical excision of the HCN and ligation of the neck of the CN is the treatment of choice with aspiration being used in patients refusing surgery. [1, 3, 5]

Differential Diagnosis List

Final Diagnosis

Surgery revealed a large cyst of the canal of Nuck.

URL:	https://eurorad.org/case/11544
DOI:	10.1594/EURORAD/CASE.11544
ISSN:	1563-4086