Novel Use of Robotic Surgery in a Rare Case of Canal of Nuck Cyst: A Case Report and Literature Review

Introduction

The canal of Nuck is an anomalous extension of parietal peritoneum in females that protrudes through the inguinal ring into the inguinal canal. Embryologically, this canal is equivalent to a patent processus vaginalis in males. When this peritoneal extension fails to close, it creates a potential space for the development of subsequent hernias, hydroceles, and endometriosis.

A cyst within the canal of Nuck develops from failure of obliteration of the canal, leading to the formation of a distal fluid-filled sac [1]. This cyst is rarely found in pediatric patients, with prevalence rates as low as 0.74% to 1% [2]. In adults, these cysts appear so infrequently that they have been described only in case reports. Since the size of the cyst widens the internal ring, a concomitant inguinal hernia appears up to 40% of the time, which can lead to misdiagnosis [2–4]. Due to the concurrent inguinal hernia in many cases, these cysts are typically managed with an open cystectomy and inguinal hernia repair, with mesh. Since the first laparoscopic excision in 2014, there have been a few reports of laparoscopic totally extraperitoneal (TEP) and transabdominal preperitoneal (TAPP) approaches [1]. In this article, we present a case of a canal of Nuck cyst in an adult female patient that was managed via robot-assisted laparoscopic TAPP, which to the best of our knowledge, is the first report of the utilization of the DaVinci robot in the excision of this rare cyst.

Case Report

Our patient was a 42-year-old woman with no significant past medical history and surgical history notable for Cesarean delivery who presented to the surgery clinic for a bulging mass in the left inguinal area that had been present for 6 months. The patient reported that the mass fluctuated in size with her menstrual cycle but she did not report any pain or skin changes. On physical examination, there were no palpable masses, hernias with Valsalva, or focal areas of tenderness. She underwent preoperative imaging to evaluate for endometrial implants, starting with an ultrasound, which was nondiagnostic. Magnetic resonance imaging (MRI) was recommended to rule out endometriosis at the Pfannenstiel incision. She then underwent MRI, which revealed a fluid collection measuring 4.7×1.7×2.4 cm within the left inguinal canal, consistent with a canal of Nuck hydrocele (Figures 1, 2). After thorough discussion and pre-operative optimization, the patient underwent robot-assisted laparoscopic excision of the cyst and inguinal hernia repair, with mesh placement. Upon entry into the abdomen, a fluid-filled clear cyst was encountered over the internal inguinal ring (Figures 3, 4). The cyst was reduced into the peritoneal cavity and excised in its entirety. Care was taken to remove the cyst intact. After removal of the cyst, we proceeded with a standard inguinal hernia repair, with mesh placement. Surgical pathologic review of the specimen showed a benign cyst lined by reactive mesothelial cells, confirming the diagnosis of a cyst of the canal of Nuck. The patient had an unremarkable postoperative course and was discharged from the Postanesthesia Care Unit on the same day. The patient had an uncomplicated postoperative recovery and was discharged from the surgical clinic following a routine 2-week follow-up visit.

Discussion

A cyst of the canal of Nuck is an uncommon diagnosis associated with a patent processus vaginalis in female patients. These cysts are more commonly found in the pediatric population than in adults, although the pediatric prevalence itself is very low, at 0.74% to 1% [2]. As many as 40% of these cysts appear concomitantly with inguinal hernias, which can lead to misdiagnosis [2–4].

In adult female patients, most canal of Nuck cysts present as a vague discomfort and swelling in the groin that has been present for months. Due to the nonspecificity of these symptoms, the differential diagnosis is broad and can include inguinal hernias, Bartholin cysts, endometriosis, and lymphadenopathy [2]. Endometriosis should be suspected if the symptoms fluctuate with menses. Inguinal hernias can be further evaluated by conducting valsalva maneuvers at bedside or with diet intolerance and/or constipation. Bartholin cysts and lymphadenopathy can be suspected based on the position of the mass in relation to expected anatomic positions. Lymphadenopathy becomes more suspect if the patient additionally reports B symptoms, including unintentional weight loss, night sweats, and fevers. In lymphadenopathy, patients can also present with palpable masses in the neck, axillae, and contralateral groin.

When an unclear clinical presentation and examination is encountered, ultrasound is a useful noninvasive tool to further delineate the anatomy. On sonogram, this cyst appears as a homogeneous hypoechoic cyst [2]. In contrast, hernias can show entrapped hyperechoic fat or bowel structures, and endometrial implants can appear as heterogeneous hypoechoic lesions with ill-defined borders. Further imaging studies can be obtained if diagnosis is unclear with ultrasound. On MRI and computed tomography, this lesion appears as a thin-walled sac that does not enhance with contrast.

In 2020, Prodromidou et al published a systematic review of the 16 case reports on canal of Nuck cysts that had been published at the time of their review [5]. Similarly, we conducted a review of case reports published in the last 10 years [1,6–17] (Table 1). In our review, canal of Nuck cysts are predominantly right-sided, at a rate of 64.5% (31/48 cases), and the mean age of adult female patients is 38.4 years. These cysts have variable sizes on presentation, ranging as small as 1 cm to 13.5 cm, averaging 5.2 cm in the largest dimension in adult females.

There are 3 types of canal of Nuck cysts. Type I is a cyst separate from the peritoneal cavity. Type II communicates with the peritoneal cavity, and type III has a classic “hourglass shape” due to the compression of the portion of the cyst within the inguinal canal. The most common cyst is type I, which appeared at a rate of 69.4% (34/49) in our review. Type II cysts appeared at 21.6% (11/49), and type III cysts appeared most rarely, at 10.2% (5/49). Histopathologically, canal of Nuck cysts are most often hydroceles containing clear peritoneal fluid with a thin mesothelial border, as consistent with their pathophysiology. On occasion, however, these cysts can present with endometriomas (18.4%, 9/49).

Canal of Nuck cysts are best managed with surgical excision for resolution of symptoms and have been excised with open and laparoscopic approaches. In the last 10 years, there have been over 50 case reports describing various approaches to excise these cysts, with the open anterior approach as the most commonly used approach [1,6].

The rate of laparoscopy has increased significantly since the first cases were performed in 2014, reaching 38.2%, compared with just 3 of 16 cases (18.8%) reported in the review by Prodromidou et al [5]. Most of these laparoscopic cases are via the TAPP approach with mesh repair. Of note, the decision to place mesh is individualized on a case-by-case basis, depending on whether the patient has a concomitant inguinal hernia, or whether the internal ring was enlarged by the canal of Nuck cyst. In our review, the rate of mesh placement was 50% and occurred most often when the structural integrity of the deep inguinal ring was compromised. In the laparoscopic cases, the rate of mesh placement was estimated at 83% (15/18).

In our patient, the cyst was located in the proximal aspect of the inguinal canal near the internal inguinal ring. This intraperitoneal positioning made a TAPP approach ideal, allowing for complete, intact reduction of the cyst into the peritoneum and evaluation of concomitant inguinal hernia. As noted by Chihara et al, the open approach limits visualization of the center of the cyst, whereas a traditional laparoscopic approach limits peripheral visualization of the cyst [7]. The additional angles of motion and visualization allowed by robotic laparoscopy allow for full visualization of the cyst, allowing for careful dissection, thereby reducing the risk of accidental disruption of the cyst capsule.

In addition to positioning near the internal inguinal ring, these cysts are sometimes found in the subcutaneous tissue or entirely within the inguinal canal [8]. A subcutaneous cyst is best managed with an open anterior approach. In contrast, a cyst entirely within the canal can still be attempted to be reduced laparoscopically, especially with the additional range of motion provided with robot-assistance.

Other operative considerations to a surgical approach are the well-documented benefits of minimally invasive approaches. A retrospective analysis of 20 cases comparing open and traditional laparoscopic approaches showed that patients with laparoscopy had longer operative times but shorter return to work times and less postoperative pain [4]. Overall, the surgical approach should be determined by the location of the cyst and surgeon preference.

Conclusions

A canal of Nuck cyst is a rare but important differential diagnosis for an inguinal mass in a female patient. These cysts present as a nonspecific groin mass, which can be difficult to diagnose on physical examination. Further imaging workup can be obtained to define the anatomy and narrow the diagnosis. The presence of these cysts in the inguinal canal can result in enlargement and thereby compromise the integrity of the deep inguinal ring; therefore, these cysts present concomitantly with inguinal hernias up to 40% of the time. Preoperative imaging should be used for operative planning, as the surgical approach can vary depending on the size and position of the cyst. Subcutaneous cysts should be excised via the open anterior approach, whereas cysts within the inguinal canal can be managed with a minimally invasive approach. Previous case reports have described open and laparoscopic approaches to excision. In our experience, a robot-assisted approach should also be considered for better visualization of the cyst and to facilitate dissection, reduction, and removal.