Discussion

Umbilical endometriosis (UE), also referred to as Villar's nodule, was first described by Villar in 1886 and represents a rare form of extrapelvic endometriosis characterized by the presence of endometrial glands and stroma within the umbilical region [9]. It may occur as a primary lesion in the absence of prior surgery or as secondary UE following abdominal procedures such as cesarean section, laparoscopy, or laparotomy [1, 2, 10]. Recent case reports continue to emphasize the rarity of this condition and its diagnostic challenges, particularly due to its ability to mimic other umbilical pathologies [4].

Secondary UE accounts for approximately 0.5%–1% of extragenital endometriosis cases and is strongly associated with prior abdominal surgery, supporting the theory of iatrogenic implantation of endometrial tissue [3]. In the present case, the patient had a history of two cesarean sections, which strongly supports a secondary origin. Although the patient's symptoms developed several years after her cesarean sections, delayed clinical presentation has been reported in previous studies and does not preclude classification as secondary umbilical endometriosis. UE typically affects women of reproductive age as an estrogen‐dependent condition, with a reported mean age of onset of 37.7 ± 0.98 years [6]. The patient in this report was a 43‐year‐old premenopausal woman, consistent with the expected demographic profile.

Clinically, UE most commonly presents as an umbilical mass associated with cyclical pain, swelling, and sometimes bleeding or discharge [2]. Umbilical swelling is reported in up to 90% of cases, cyclical pain in 82%, and bleeding or discharge in nearly half [2, 11]. In this case, the combination of cyclical periumbilical pain and bloody discharge represented a typical but initially unrecognized presentation, contributing to diagnostic delay.

A major diagnostic challenge in this case was the preoperative misinterpretation as an irreducible umbilical hernia. Ultrasound suggested a fascial defect with protruding mesenteric fat, leading to a provisional diagnosis of incarcerated hernia. The sonographic appearance was likely influenced by surrounding fibrosis and chronic inflammatory changes, which may have simulated protruding preperitoneal fat through a fascial defect. In retrospect, the presence of two sinus‐like openings and cyclic bloody discharge should have broadened the differential diagnosis beyond an incarcerated umbilical hernia. However, intraoperative findings revealed a firm fibrotic lesion extending into the anterior rectus fascia without a true hernia sac. This highlights the limited specificity of imaging in UE. Although ultrasound is useful for assessing lesion size and depth, it cannot reliably establish the diagnosis. Magnetic resonance imaging (MRI) provides superior soft‐tissue characterization and may improve preoperative diagnostic accuracy in selected patients with equivocal clinical or ultrasonographic findings [5, 6, 12]. Therefore, UE should always be considered in the differential diagnosis of umbilical masses in women of reproductive age, particularly when symptoms are cyclical. Although fine‐needle aspiration cytology has been described as an adjunctive diagnostic tool, it was not performed in the present case because surgical exploration was already indicated based on the presumed diagnosis of an irreducible umbilical hernia.

Another important feature of this case was the unusually large lesion size. Most reported UE nodules measure between 0.5 and 3 cm [7]. In contrast, the lesion in this patient measured approximately 6.5 × 5 × 3.1 cm and demonstrated extension into the anterior rectus fascia. This discrepancy between clinical and intraoperative findings suggests that deeper fascial involvement may lead to underestimation of lesion size preoperatively and increases surgical complexity.

Histopathological examination remains the gold standard for diagnosis [5, 6]. Typical findings include endometrial glands within a cellular and vascular stroma resembling functional endometrium. Immunohistochemical staining for CD10 and estrogen receptors further supports the diagnosis [8, 13]. In this case, both histopathological and immunohistochemical findings confirmed UE.

Surgical excision is the definitive treatment for UE, providing both diagnostic confirmation and symptom resolution while minimizing recurrence risk [7, 8]. Although conservative umbilicus‐preserving procedures have been described, total omphalectomy with en bloc excision of the involved fascia was performed in this patient due to the lesion's large size and fascial involvement. This approach ensured complete resection and reduced the likelihood of residual disease. Primary fascial closure without mesh was feasible because complete tension‐free approximation was achieved following excision of the involved fascia.

Comparison with previously published reports highlights the uniqueness of this case. The combination of a large lesion size, deep fascial involvement, and preoperative misdiagnosis as an irreducible hernia is rarely reported together. This underscores the importance of maintaining a high index of suspicion for UE in atypical umbilical masses, particularly in patients with prior abdominal surgery.

Concurrent pelvic endometriosis has been reported in approximately 13%–15% of UE cases [6, 14]. However, in the absence of pelvic symptoms, routine additional imaging is not universally recommended. In this case, the patient had no clinical features suggestive of pelvic endometriosis, and no further evaluation was performed. The patient was advised to undergo routine gynecological follow‐up, and further evaluation for pelvic endometriosis would be considered if pelvic symptoms developed.

Postoperatively, the patient was started on oral contraceptive therapy by the treating gynecologist, primarily with the aim of reducing the risk of recurrence following surgical excision. However, current evidence remains insufficient to support routine postoperative hormonal therapy for all patients after complete surgical excision, and the decision to initiate hormonal suppression should be individualized based on patient characteristics, symptoms, and clinical circumstances. In selected patients, careful clinical follow‐up without hormonal therapy may also be an appropriate management strategy. In this case, although postoperative hormonal therapy was administered, the patient continued to experience regular menstrual cycles during follow‐up; therefore, the absence of recurrent cyclical symptoms cannot be attributed solely to hormonal suppression. Furthermore, hormonal therapy may theoretically delay the recognition of recurrent cyclical symptoms, emphasizing the importance of long‐term clinical surveillance regardless of whether hormonal treatment is used. Nevertheless, the potential contribution of postoperative hormonal therapy to symptom control should be considered when interpreting short‐term postoperative outcomes.

The recurrence rate of UE after surgical excision has been reported to range from 5.4% to 27% [7, 8]. Although no recurrence was observed during the three‐month follow‐up period, longer follow‐up is necessary to assess long‐term durability. The patient reported complete resolution of symptoms and high satisfaction with both the cosmetic outcome and overall quality of life, although no standardized patient‐reported cosmetic outcome measure was used. The patient reported complete resolution of symptoms and high satisfaction with both the cosmetic outcome and quality of life. Long‐term clinical follow‐up was planned, and the patient was counseled regarding the possibility of recurrence and advised to seek medical attention if new cyclical symptoms or umbilical swelling developed.

This case has several limitations. Additional evaluation for concurrent pelvic or extra‐umbilical endometriosis was not performed; therefore, asymptomatic disease cannot be excluded. The follow‐up period was limited to 3 months, which is insufficient to assess long‐term recurrence. In addition, postoperative hormonal therapy may have influenced symptom control and should be considered when interpreting early outcomes. Future studies with longer follow‐up periods and standardized patient‐reported cosmetic outcome measures are needed to better evaluate long‐term outcomes after surgical management of secondary umbilical endometriosis.