A rare case of canal of Nuck cyst in a nulliparous woman of reproductive age: A case report and literature review.

A 33-year-old nulliparous woman presented with a progressively enlarging left groin swelling of approximately 18 months' duration. The swelling was associated with recurrent episodes of mild discomfort. She also reported heavy, painful and irregular menstrual cycles. She had no history of previous abdominal or pelvic surgery, medical illness, or gynaecological procedures. On physical examination, a palpable left inguinal swelling was noted with a tender 16 cm mass arising from the pelvis. The inguinal mass was associated with intermittent discomfort but no features of bowel obstruction or incarceration. Pelvic ultrasonography demonstrated bilateral complex ovarian masses, with an 11.6 cm × 5.64 cm complex cystic-solid lesion within the right ovary exhibiting internal vascularity and a 5.21 cm × 4.79 cm left ovarian cyst containing calcifications suggestive of a dermoid cyst. A left hydrosalpinx and moderate pelvic free fluid were also identified. Tumour markers revealed markedly elevated CA-125 level, reported initially at approximately 1500 U/ml and subsequently decreasing to 800 U/ml. Further evaluation with abdominopelvic magnetic resonance imaging (MRI) demonstrated a type II ccanal of Nuck cyst containing fluid ( Fig. 1 ). It also revealed bilateral enlarged multicystic ovarian masses with the appearance of “kissing ovaries” suggestive of endometriosis. The largest right ovarian cyst measured 8.4 cm and contained an enhancing papillary soft-tissue component measuring 5.8 cm × 7.0 cm, raising concern for neoplastic potential. A left ovarian endometrioma was also identified. Fig. 1 Fat-Saturated Coronal image showing a direct communication of the peritoneal cavity with the canal of Nuck cyst, indicative of a type II cyst (red arrows). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) Fig. 1 Fat-Saturated Coronal image showing a direct communication of the peritoneal cavity with the canal of Nuck cyst, indicative of a type II cyst (red arrows). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) The patient underwent exploratory laparotomy with bilateral ovarian cystectomy, myomectomy, adhesiolysis, peritoneal washings, excision of the canal of Nuck cyst, and repair of the associated left inguinal ring defect. Intraoperative findings included bilateral ovarian cysts, multiple uterine fibroids, a right hydrosalpinx, extensive pelvic adhesions, suspected endometriosis, approximately 500 ml of free straw-colored peritoneal fluid and a cystic lesion within the left inguinal canal. The left round ligament was identified where a canal of Nuck cyst was noted ( Fig. 2 A). The cystic sac was excised, and the associated inguinal ring defect was repaired with sutures ( Fig. 2 B). No herniated intra-abdominal contents were identified. Fertility-sparing surgery was performed with the preservation of residual ovarian tissue. Peritoneal cytology did not reveal any malignant cells. Histopathological examination of ovarian cysts confirmed a stage 1C1 serous borderline tumour of the right ovary. The patient's postoperative course was uneventful, and she was discharged on day 1 postoperatively. Fig. 2 Intraoperative view demonstrating (A) the canal of Nuck cyst at the point of insertion of the round ligament into the inguinal canal; (B) canal of Nuck defect repaired with absorbable sutures. Fig. 2 Intraoperative view demonstrating (A) the canal of Nuck cyst at the point of insertion of the round ligament into the inguinal canal; (B) canal of Nuck defect repaired with absorbable sutures.

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Written informed consent was obtained from the patient for the publication of the case report and accompanying images.

Cysts of the canal of Nuck are uncommon developmental abnormalities resulting from incomplete obliteration of the processus vaginalis in females [5] . Although well recognized in the pediatric population, they remain exceedingly rare in adult women and are frequently overlooked in the differential diagnoses of female groin masses [2] . The true incidence in adults is unknown, largely due to under-recognition and the limited number of reported cases in the literature [6] . A systematic review by Prodromidou et al. reported a mean age of 35 years and that the majority of patients were of reproductive age and that there was a predilection for right inguinal involvement [7] . While most cases are idiopathic, several predisposing factors have been identified, including prior pelvic surgery, trauma or a known connective-tissue disorder [7] . Embryologically, the canal of Nuck represents the female analogue of the processus vaginalis in males [5] . During fetal development, a peritoneal evagination accompanies the round ligament through the inguinal canal toward the labia majora [5] . Physiological obliteration of this peritoneal fold normally occurs during infancy, typically completing within the first year of life [5] . Failure of complete closure may result in persistent communication with the peritoneal cavity, predisposing to hydrocele formation or indirect inguinal herniation. Accumulation of serous fluid secreted by the mesothelial lining within a partially obliterated canal leads to the formation of a canal of Nuck cyst [4] . The precise mechanisms governing the failure of obliteration remain incompletely understood. However, defects in the secretory and absorptive equilibrium of the mesothelial lining of the processus vaginalis have been implicated in fluid accumulation, and it is proposed that hormonal influences during reproductive life may sustain or promote this process in adult patients [4] . The classification system described by Counsellor and Black in 1941 remains the most widely accepted framework for categorizing canal of Nuck cysts [ [1] , [8] ]. Three morphological subtypes are recognized: the type I encysted hydrocele, which does not communicate with the peritoneal cavity and represents the most common variant; the type II communicating hydrocele, which maintains an open connection to the peritoneal cavity and carries the potential for herniation; and the type III bilocular hydrocele, which assumes an hourglass configuration due to constriction at the level of the deep inguinal ring [ [1] , [8] ]. The differential diagnosis of an inguinal mass in women is broad and includes indirect inguinal hernia, femoral hernia, lymphadenopathy, lipoma, Bartholin gland pathology, abscess formation, round ligament leiomyoma, and endometriosis of the round ligament [4] . Canal of Nuck cysts are particularly challenging to diagnose preoperatively because they frequently mimic inguinal hernias or other groin lesions on clinical examination, and the definitive diagnosis is established only on surgical exploration and histopathological assessment [4] . Imaging plays a pivotal role in narrowing the differential diagnoses. Ultrasonography is generally used as the first-line modality and demonstrates a well-circumscribed, thin-walled, anechoic cystic lesion within the inguinal canal with no demonstrable internal vascularity on colour Doppler assessment [9] . MRI provides superior soft-tissue characterization. It is particularly valuable in atypical or complex presentations, demonstrating a lesion that is hypointense on T1-weighted imaging and hyperintense on T2-weighted imaging, with a well-defined wall and no evidence of internal septation or solid component in uncomplicated cases [9] . In the present case, MRI of the pelvis proved indispensable, delineating within a single examination the canal of Nuck cyst, the ovarian masses with their internal architecture and uterine fibroids. The coexistence of a complex adnexal mass and a palpable inguinal swelling created a significant diagnostic challenge that necessitated careful radiological and intraoperative assessment to distinguish between independent pathologies. This case highlights that in adult women of reproductive age presenting with an inguinal swelling, pelvic MRI should be considered early in the diagnostic workup, particularly where concurrent pelvic pathology is identified or suspected on clinical examination. Surgical excision remains the gold standard for both diagnosis and treatment of canal of Nuck cysts [10] . Complete cyst excision with high ligation of the patent processus vaginalis and repair of any associated inguinal defect provides excellent outcomes with minimal recurrence [10] . Both open and laparoscopic approaches have been described, although most reported cases have been managed through an open inguinal approach, which affords direct visualization and precise removal of the cyst [6] . The choice of technique is principally informed by the cyst type and the presence of a concomitant hernia, with open surgery generally favoured for type 1 lesions given their external location and absence of intraperitoneal extension, whilst a laparoscopic approach is more readily applicable to type II lesions with peritoneal communication [10] . Repair of associated inguinal ring defects may be performed with or without prosthetic mesh, depending on the size of the defect and the surgeon's preference [11] . In the present case, primary repair without mesh was undertaken, supported by the absence of a frank hernia and the patient's nulliparous status, with the aim of minimizing mesh-related complications. Moreover, the uneventful completion of concurrent procedures in this case, comprising bilateral cystectomy, myomectomy and excision of endometriotic deposits, within a single anaesthetic course demonstrates that comprehensive single-stage surgical management is both safe and feasible in appropriately selected patients, provided that thorough preoperative planning and surgical expertise are available. In conclusion, canal of Nuck cysts are rare developmental abnormalities that may present as inguinal swellings in adult women and frequently mimic more common groin pathologies. The present case is seemingly unique in the cyst's association with a serous borderline ovarian tumour, a contralateral ovarian cyst, bladder peritoneal endometriosis, and a uterine leiomyoma, requiring comprehensive surgical management within a single operative setting. Awareness of this uncommon entity and the importance of radiological findings interpreted within the broader gynaecological context are hallmarks of this case. Expanded case series and prospective data collection will be necessary to further characterize the epidemiology and any pathophysiological relationships between canal of Nuck cysts and concurrent pelvic disease in this patient population.

This article was not commissioned and was peer reviewed. Vishal Bahall, an editorial board member for Case Reports in Women's Health , was not involved in editorial consideration of the manuscript and was blinded to the process.

Vishal Bahall contributed to patient care, drafting the manuscript and revising the article critically for important intellectual content. Lance De Barry contributed to patient care, drafting the manuscript, undertaking the literature review and revising the article critically for important intellectual content. Nadia Nidhan contributed to patient care, drafting the manuscript, undertaking the literature review and revising the article critically for important intellectual content. Steven Sankar contributed to patient care and revising the article critically for important intellectual content. All authors approved the final submitted manuscript.

The canal of Nuck is the female anatomical analogue of the processus vaginalis in males, representing a peritoneal evagination that traverses the inguinal canal in close association with the round ligament of the uterus, extending to the labia majora [1] . Under normal embryological development, this peritoneal fold undergoes progressive obliteration, typically completing within the first year of life, and in most cases before the fifth year [1] . Failure of obliteration, either partially or completely, results in a patent canal that may accumulate peritoneal fluid, giving rise to a hydrocele or cyst of the canal of Nuck [2] . This condition, first described by the Dutch anatomist Anton Nuck in 1691, is considered a rare disorder in adult females, and the literature pertaining to its occurrence in this demographic is limited to case reports and small case series [3] . Canal of Nuck cysts typically present as a painless or mildly uncomfortable inguinal or inguinolabial swelling, most commonly on the right side [3] . The differential diagnosis of inguinal swellings in adult females is broad and includes direct inguinal hernia, lymphadenopathy, lipoma, leiomyoma, Bartholin cyst, endometriosis of the round ligament and soft-tissue neoplasms [4] . Given this diagnostic breadth, the canal of Nuck cyst is frequently misdiagnosed preoperatively, most often as an inguinal hernia, with the definitive diagnosis established only intraoperatively or following histopathological assessment [4] . Surgical excision remains the definitive treatment, with the choice between open and laparoscopic approaches guided by the nature of the defect, the presence of concomitant hernia and surgical expertise [5] . The concurrent identification of a canal of Nuck cyst alongside multiple significant pelvic pathologies in a single patient of reproductive age has not been previously described. This report describes the case of a 33-year-old nulliparous woman in whom a left canal of Nuck cyst was identified, along with a serous borderline ovarian tumour, contralateral ovarian cyst, endometriotic deposits on the bladder peritoneum and a uterine fibroid, all managed in a single operative setting with fertility-sparing intent. This case represents a uniquely complex presentation of canal of Nuck cyst in the published literature and highlights the importance of comprehensive pelvic evaluation and multidisciplinary planning in the management of inguinal pathology in women of reproductive age.

The authors declare that they have no competing interest regarding the publication of this case report.