Hydrocele of the Canal of Nuck: A Rare Etiology of Inguino-Labial Swelling in a Young Female: A Case Report.

A healthy 6-year-old girl with no prior medical history presented to the pediatric surgical clinic with a right-sided inguinal swelling. The mother first noticed a painless, peanut-sized lump in the right groin 6 months ago, which gradually increased in size over the last 2 months. The patient reported no abdominal pain, vomiting, fever, trauma, or changes in bowel or bladder habits. On examination, the patient was well-appearing with stable vital signs and normal growth parameters. Cardiovascular and chest exams were unremarkable. Abdominal assessment showed a soft, non-tender, and non-distended abdomen with normal bowel sounds and no palpable organomegaly. Genitourinary examination revealed a well-defined, firm, non-tender, cystic mass measuring 3 × 3 cm in the right inguinolabial region. The swelling was irreducible, with normal overlying skin, did not change with the Valsalva maneuver, and had no thrill or bruit. The rest of the systemic examination was unremarkable. Based on the clinical presentation, an inguinal cyst was initially suspected. Consequently, the primary physician ordered a Fine Needle Aspiration Cytology (FNAC) of the groin mass. The pathologist aspirated 4 mL of straw-colored fluid from a 3 × 3 cm cystic swelling over the right mons pubis/labia majora. Microscopic examination of the smear revealed scattered cyst macrophages and lymphocytes in a fluid background, consistent with a benign cyst. Given the impression of an inguinal cyst, the patient was referred to the Pediatric Surgical Referral Clinic (PSRC) for further evaluation. A pelvic ultrasound was subsequently performed, revealing a 4 × 3 cm hypoechoic, oval-shaped, unilocular cystic lesion extending from the right inguinal canal to the labia majora. The cyst showed no internal bowel loops or omental fat components, and no peristaltic movement was observed. Additionally, there was no visible connection to the peritoneal cavity. Color Doppler imaging confirmed an avascular cystic structure, leading to a final diagnostic impression of a possible cyst of the canal of Nuck (Type 1 unilocular encysted hydrocele). Other routine laboratory investigations, including a complete blood count and urinalysis, were within normal limits. Based on the diagnostic findings, the patient was scheduled for follow-up and subsequently admitted for elective surgical excision. During surgery, the cyst was found to extend into the right labia majora and was confirmed to be an encysted hydrocele of the canal of Nuck, with no evidence of an associated inguinal hernia. The cyst was meticulously separated from the round ligament, and the canal of Nuck was ligated at its proximal end near the deep inguinal ring. Complete excision of the lesion was achieved, followed by layered wound closure. Upon incision, the cyst was noted to contain clear, mucinous, light-colored fluid. The patient had an uneventful postoperative recovery, and there were no signs of recurrence at the 3-month follow-up visit.

The embryological development of the inguinal canal involves 2 crucial structures: the gubernaculum and the processus vaginalis. In males, the gubernaculum elongates under the influence of androgens, guiding the descent of the testes into the scrotum. 1 , 2 In females, however, the absence of significant androgen influence leads to arrested gubernacular growth, causing the ovaries to remain in the pelvic cavity. 1 , 3 The gubernaculum in females subsequently develops into the round ligament of the uterus, which passes through the inguinal canal and ends in the labia majora. 4 The processus vaginalis is a peritoneal diverticulum that develops anterior to the gubernaculum. In females, its homologous structure is referred to as the canal of Nuck, first described by Dutch anatomist Anton Nuck in 1691. 5 - 9 This canal usually undergoes physiologic obliteration in a craniocaudal manner beginning at birth and is typically fully closed within the first year of life. Failure of this closure creates a potential space for fluid accumulation or organ herniation. 4 Complete failure of obliteration results in a patent canal of Nuck, which may lead to a communicating hydrocele or an inguinal hernia, whereas partial closure, with only the distal portion remaining open, can form a non-communicating hydrocele. 1 , 5 , 9 In such cases, mesothelial cells lining the persistent portion secrete fluid that accumulates to form a hydrocele of the canal of Nuck, also referred to as a female hydrocele. In these cases, the mesothelial lining of the remnant segment may continue to secrete fluid, resulting in the formation of a cystic lesion or hydrocele of the canal of Nuck, also referred to as female hydrocele. The hydrocele often presents as an elongated, sausage-shaped mass that follows the narrow anatomy of the inguinal canal. When fluid production exceeds absorption, it may assume a more rounded shape 1 , 10 ( Figure 1 ). Embryology during the fourth month of gestation. 1 Hydrocele of the canal of Nuck is considered the female equivalent of a spermatic cord hydrocele in males. Despite being benign, it is a rare and underrecognized entity that usually presents as a painless inguinal or labial swelling in young females. 11 - 14 Due to its rarity and limited representation in standard medical textbooks, it is often misdiagnosed. The differential diagnosis includes inguinal hernia, lymphadenopathy, cysts, abscesses, ectopic gonads, endometriosis, benign neoplasms, and malignancies. 4 Accurate diagnosis relies on a high index of suspicion, supported by appropriate imaging modalities such as ultrasonography or MRI. 7 , 11 In this report, we present the case of a 6-year-old girl with a hydrocele of the canal of Nuck (Type 1 unilocular encysted hydrocele), which was initially misdiagnosed as a benign right inguinal cyst based on cytology. The diagnosis was later confirmed intraoperatively and treated successfully through elective surgical excision.

The hydrocele of the canal of Nuck is classified into 3 distinct types, each characterized by specific anatomical features and clinical presentations 2 , 11 - 14 ( Figure 2 ). Type 1: This is the most common form of hydrocele of the canal of Nuck and results from partial closure of the canal, specifically with obliteration limited to the proximal portion. As there is no communication with the peritoneal cavity, it presents as an isolated cyst. Clinically, it typically appears as a painless, non-reducible swelling in the inguinal or labial region, with no change in size during the Valsalva maneuver. Rapid enlargement of the cyst may occur if there is an imbalance between fluid production and absorption, often triggered by factors such as trauma, inflammation, or impaired lymphatic drainage. Type 2: In this type, the proximal portion of the canal of Nuck fails to close, leaving a persistent connection between the hydrocele sac and the peritoneal cavity. This condition arises due to a fully patent canal of Nuck. Clinically, it presents as a soft, non-tender, and reducible mass. The size of the swelling may fluctuate depending on the patient’s posture or activity level. Diagnostic maneuvers such as the Valsalva maneuver or having the patient change from lying down to standing can help reveal the communication and confirm the diagnosis. Type 3: A combined type, a bilocular hydrocele (also called an “hourglass hydrocele”). This represents the least common form of hydrocele in the canal of Nuck. In this variant, constriction occurs at the deep inguinal ring, creating a formation resembling an hourglass. Schematic representation of canal of Nuck cyst types as classified by Counseller and Black. 11 Recognizing the different types of hydroceles of the canal of Nuck is essential, as each variant requires specific diagnostic and therapeutic strategies. 2 In our case, it was a type 1 unilocular encysted hydrocele without communication with the peritoneal cavity. Clinical examination of the hydrocele of the canal of Nuck poses challenges due to the limited literature and the clinician’s knowledge. The existing relevant literature mainly consists of case reports or small case studies. In general, Nuck’s hydrocele is 8 times rarer than the communicating hydrocele in males. It is characterized by painless and non-reducible swelling, usually mobile, with well-defined boundaries, located in the inguinal region that can expand to the ipsilateral major labium of the vagina. Swelling can range from 2.3 to 5.6 cm. 5 , 12 The differential diagnosis of inguinolabial swellings in females includes a broad spectrum of conditions. These range from common entities such as inguinal and femoral hernias, lipomas, and inguinal lymphadenopathy, to less frequent causes like vascular aneurysms, nerve sheath tumors (eg, neurofibromas of the ilioinguinal nerve), leiomyomas, round ligament endometriosis, epidermoid cysts, Bartholin’s gland cysts, and post-traumatic hematomas. 1 , 2 , 6 , 10 , 14 - 17 It is important to differentiate a canal of Nuck cyst from an inguinal hernia sac, as the former contains fluid, while a hernia sacs typically house adipose tissue or bowel loops. 4 The presence of bowel sounds over the swelling is highly indicative of a hernia. In older children, maneuvers such as the Valsalva test should be performed to help exclude a hernia. A mass that becomes apparent when standing and reduces upon lying down further supports the diagnosis of an inguinal hernia. 9 Establishing a definitive diagnosis of a hydrocele of the canal of Nuck based solely on clinical history and physical examination is often difficult, particularly due to the nonspecific nature of the presenting symptoms. Although imaging modalities can assist in the preoperative evaluation, most cases are only conclusively diagnosed during surgical exploration. Ultrasonography is typically the first-line imaging tool. Characteristic findings include a well-defined, anechoic or hypoechoic, sausage- or comma-shaped cystic lesion, located superficially in the groin, medial to the pubic bone, and adjacent to the superficial inguinal ring. These lesions usually appear avascular on color Doppler imaging. 1 , 2 , 5 , 6 , 14 , 16 , 17 However, ultrasound may not reliably determine whether the cyst communicates with the peritoneal cavity, which is a key diagnostic distinction between communicating and non-communicating hydroceles. Magnetic Resonance Imaging (MRI) offers enhanced soft tissue contrast and provides more detailed anatomical information. It can demonstrate internal septations, confirm or exclude communication with the peritoneal cavity, and more precisely define the cyst’s relationship to surrounding structures. 1 , 9 , 16 In the present case, the lesion was initially misdiagnosed as a benign inguinal cyst and was sent for cytological assessment via fine-needle aspiration (FNAC). Subsequent ultrasound imaging revealed a unilocular cystic lesion consistent with a hydrocele of the canal of Nuck, which was later confirmed intraoperatively. Surgical excision remains the treatment of choice for hydroceles of the canal of Nuck due to the potential for complications such as infection, hemorrhage, rupture, and strangulation, particularly when an associated inguinal hernia is present. The standard surgical approach involves open resection of the cyst, ligation of the processus vaginalis at the neck, and hernia repair if applicable, typically performed through an inguinal skin crease incision. 1 , 5 , 6 , 10 , 12 , 14 , 17 In our case, open surgical removal of the cyst along with ligation of the processus vaginalis was successfully performed, and the patient had an uneventful postoperative recovery. Beyond treatment, surgery also provides histopathological confirmation. On microscopic examination, the inner lining of the cyst is often composed of mesothelial cells, and the cyst wall is made up of fibrous connective tissue. The cyst usually contains clear, amber-colored fluid, with no evidence of cellular content or microbial organisms. 2 , 12 , 16 , 18

Hydrocele of the canal of Nuck is a rare and often underrecognized condition with limited coverage in surgical and gynecological literature. A lack of awareness, particularly among non-surgical clinicians, can result in unnecessary diagnostic tests, invasive procedures, or delays in appropriate surgical referral. Early recognition is therefore essential for accurate diagnosis and timely management. Ultrasonography offers a reliable, non-invasive modality for distinguishing this entity from other inguino-labial masses, while surgical excision remains the treatment of choice, providing excellent outcomes and minimizing complications. This case emphasizes the importance of considering hydrocele of the canal of Nuck in the differential diagnosis of inguino-labial swellings in young females.