Introduction

Umbilical endometriosis (UE), also known as Villar's nodule, was first described by Villar in 1886 and represents a rare form of extrapelvic endometriosis characterized by the presence of functional endometrial glands and stroma within the umbilical region. UE is classified as either primary, occurring in the absence of previous abdominal or pelvic surgery, or secondary, developing after surgical procedures such as cesarean section, laparoscopy, or laparotomy as a result of iatrogenic implantation of endometrial tissue. Although secondary UE may present several years after the inciting surgery, delayed presentation has been well documented in the literature [1, 2].

Secondary umbilical endometriosis is an uncommon manifestation of extragenital endometriosis and is most frequently associated with prior abdominal surgery, particularly cesarean section, supporting the theory of iatrogenic implantation of endometrial tissue. Although it represents a small proportion of extragenital endometriosis cases, it remains clinically important due to its diagnostic difficulty and potential for misdiagnosis as other umbilical conditions [3]. Recent case reports continue to highlight these diagnostic challenges, especially when the lesion mimics more common surgical entities such as umbilical hernia [4].

Clinically, UE most commonly presents as an umbilical mass associated with cyclical pain, swelling, and occasionally bleeding or discharge that correlates with the menstrual cycle. However, due to its rarity and nonspecific presentation, diagnosis is often delayed or missed, and patients may initially be evaluated for more common conditions affecting the umbilicus [2].

Preoperative imaging, particularly ultrasonography, may assist in assessing lesion size, depth, and relationship with surrounding structures; however, it is not definitive for diagnosis. Therefore, histopathological examination following surgical excision remains the gold standard for confirmation of UE [5, 6]. Fine‐needle aspiration cytology has limited diagnostic value and may yield inconclusive results in a significant proportion of cases [2].

Management is primarily surgical, with complete excision recommended to achieve definitive diagnosis, symptom relief, and reduction of recurrence risk. Medical therapy may provide temporary symptom control but is generally not curative [7, 8]. Given the potential association with pelvic endometriosis in a subset of patients, further evaluation may be considered in selected cases based on clinical suspicion.

In this report, we present a rare case of large secondary umbilical endometriosis initially misdiagnosed as an irreducible umbilical hernia, highlighting the diagnostic pitfalls, surgical considerations, and importance of considering UE in the differential diagnosis of umbilical masses.