Canal of Nuck cyst masquerading as a testicle in a neonate : A case report and review of the literature

Canal of Nuck cysts/hydroceles are rare occurrences in females of all age groups. We describe a case of a female neonate presenting with a labial mass which sonographically resembled a testicle. Upon surgical exploration, it was found to be a hydrocele of the canal of Nuck. We also review the literature on canal of Nuck cysts/hydroceles in the pediatric age group.


Introduction
The canal of Nuck, also known by its Latin name processus vaginalis peritonea femininus, was first described by the 17 th century anatomist Anton Nuck in 1691.It consists of an abnormal patency of an outpouching of parietal peritoneum that follows the round ligament, as guided through the inguinal canal by the gubernaculum, to the labia majora.
Cysts/hydroceles of this canal, also known as a female hydrocele (hydrocele muliebris), should not occur if complete obliteration of the canal is achieved.When the canal remains patent, these cysts/hydroceles can be a rare cause of inguinal or vulvar swelling in females, as well as being the source of indirect hernias [1][2][3][4][5].This rare entity has been described in females of all ages, but rarely in girls under 2 years of age.We     The patient underwent a diagnostic of a female neonate presenting with a right-sided labial mass which sonographically resembled a testicle which was found to be a canal of Nuck cyst upon surgical exploration.Case Report A full term healthy baby girl was born via repeat cesarean section to a G4P3013 mother whose pregnancy and past medical history were unremarkable.On physical exam, the only abnormality noted was asymmetric swelling of the right labia majora.Upon palpation a firm, rubbery, noncompressible mass approximately 2cm in length, 1cm in width, and 1cm in thickness was appreciated.Her external genitalia were otherwise normal.A soft tissue ultrasound of the right labia revealed a homogeneously solid structure compatible with a normal appearing testicle measuring 1.7 cm by 0.9 cm accompanied by a normal appearing epididymis [Fig.1-3].

Fig. 1 .
Fig. 1.Transverse sonographic image through the midline at the level of the labia demonstrates

Fig. 2 .
Fig. 2. Longitudinal sonographic image of the structure in the right labia again demonstrates homogeneous internal echoes with an appearance and shape typical of a testicle.Through transmission, which would be typical of a cyst, is not present.

Fig. 3 .
Fig. 3. Spectral Doppler waveform image appears to reveal a faint arterial waveform within the lesion.

laparoscopy and right groin exploration on day 3
of life.During laparoscopy a normal uterus and left ovary were visualized.The right ovary was not easily visualized, and there was tissue appearing to migrate towards the closed right internal inguinal ring from the normal location of the right ovary, consistent with an inguinal hernia.At open exploration, a cystic structure was identified in the proximal part of the inguinal canal after opening the external oblique aponeurosis.Five to ten milliliters of what proved to be sterile fluid was aspirated from this cyst, and its walls were sent for pathologic analysis, yielding a diagnosis of an epithelial inclusion cyst consisting of benign fibrous connective tissue covered by non-keratinizing squamous mucosa.DiscussionWhile hundreds of cases of canal of Nuck cysts/hydroceles exist in the literature, this rare entity only comprises 5-12% of the etiologies of all vulvar swellings in females of all ages[1,2].Few have been reported in pediatric patients, and none to date have been reported in neonates[1,3,4,5].In addition to its sonographic appearance, the nature and location of our patient's labial mass demanded a full workup for disordered sexual differentiation, this being due to a strong association between physical findings consistent with gubernacular malfunction (including hydroceles/cysts/hernias of the canal of Nuck) and renal or mullerian structure anomalies and agenesis (in this case, most likely XX male syndrome)[6,7].Independent of our patient's sonographic finding, surgical exploration of the patient's labial mass was indicated since in 15-20% of patients with a hernia of the canal of Nuck contain an ovary and are at risk for ovarian torsion or incarceration[7].Most importantly, given the questions raised by the labial sonographic findings in light of remainder of the radiologic workup, it was deemed imperative that the nature of the labial mass be defined in order to provide the parents of this infant with a definitive gender for their child.For the diagnosis of hydroceles of the canal of Nuck, ultrasound is the imaging modality of choice, with computed tomography and magnetic resonance imaging being used rarely.Sonographic features characteristic of a canal of Nuck finding include a welldefined, hypoechoic or anechoic mass, ranging in morphology from a "commashaped" lesion with its tail directed toward the inguinal canal, to a "cyst-in-cyst" appearance, or a multiseptated lesion within the labia majora or inguinal region [3,5,8,9,10].None of these were noted in our patient.Our patient's sonographic findings, both morphologically and in terms of blood flow pattern, were consistent with both testicular and epididymal tissue.Retrospectively, the dense proteinaceous contents of the cyst in combination with motion artifact and/or an arterial waveform detected immediately adjacent to the cyst probably contributed to the misinterpretation of the cyst as a testicle.It was only upon surgical exploration and excision did the true nature of this lesion become clear, with its histologic findings being consistent with canal of Nuck's peritoneal origin, consisting of linings of cuboidal or flattened mesothelial cells and being filled with fluid.Complications of a cyst/hydrocele of the canal of Nuck include infection, hemorrhage, or retroperitoneal extension of a large cyst.Curative treatment requires surgical excision since aspiration of the cyst has a risk of recurrence.The most common differential diagnosis for cysts/hydroceles of the canal of Nuck is the inguinal hernia, with one third of cases being associated with indirect inguinal hernias [9].One percent of cases suspected of being inguinal hernias in children were found to be hydroceles of the canal of Nuck [9].The use of Valsalva maneuvers with ultrasound can be used to aid in the differentiation of canal of Nuck cysts from inguinal hernias [6].Groin masses have a broad differential diagnosis in adults and children, including inflammatory lesions, hematomas, benign and malignant tumors, and most commonly, hernias with or without bowel or fat contents, with or without communication with the peritoneal cavity [10].In neonates, however, the differential diagnosis includes disorders of sexual differentiation as well.This case brings to light the fact that in the process of diagnosis of groin masses in neonates, the physical exam, laboratory tests, and radiologic workup are fraught with ambiguity: only surgical diagnosis is definitive.