Canal of Nuck cyst (hydrocele)
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Right inguinal swelling
CT images in sagittal and axial planes show an hourglass-shaped cyst (C). It has a deep intrapelvic component (which is separable from the opacified bowel loops and the urinary bladder (UB)) and another component within the canal of Nuck. It has a thin wall and no internal septa denoting its simple non-complicated internal characteristics.
Canal of Nuck cyst: unilocular, thin wall, no internal septa or solid components.
Components of the cystic lesion on an annotated sagittal image.
- green arrow: intrapelvic component
- orange arrow: canal of Nuck component
The canal of Nuck in females corresponds to the processus vaginalis in males. It results from developmental protrusion of the parietal peritoneum through the inguinal ring down into the inguinal canal together with the round ligament of the uterus. Failure of complete obliteration of the canal of Nuck may result in a hernia or hydrocele 1,2.
Canal of Nuck hydrocele is a cystic collection which results from the imbalance between fluid production and absorption by the peritoneum 3. It is a disorder of female infants and childhood, however may present in adults 4.
On clinical examination, a swelling at the inguinal region/labia is noted. Being irreducible differentiates it from an inguinal hernia. Also a Valsalva maneuver is done to help to differentiate, whereby a hernia will enlarge, while a hydrocele will not 3,4.
Imaging is primarily done using ultrasound. It is simple, non-invasive, and radiation-free. It identifies the contents of the swelling with real time imaging to help differentiate it from herniating bowel or pelvic organs. Canal of Nuck hydrocele appears as an anechoic thin walled cyst connected to the inguinal canal 3,4.
Cross-sectional imaging: preferably MRI to help evaluate the deeper intrapelvic component, and to accurately identify the components of the swelling and signs of complications in cases of inflammation/infection 3. CT is second-line to avoid ionizing radiation, especially when imaging infants.
In the presented case, CT images were unfortunately the only available images. However, it is recommended to do MRI if the diagnosis is still doubtful on US. In this case, the cyst was surgically removed.