{"paper_id":"6fa5b5e4-02d1-469f-beae-d00a5511cc2b","body_text":"INTRODUCTION\nThe ectopic development of endometrial glands and stroma outside the uterine cavity is known as endometriosis. It is a common gynecological condition that affects roughly 6% of postmenopausal women and 15% of women of reproductive age.[,] The disorder most frequently affects the ovaries, fallopian tubes, cervix, vagina, and surrounding peritoneum in a pelvic distribution.[] On the other hand, although far less common, extrapelvic symptoms are widely described and include the intestines, urinary tract, peritoneum, omentum, lungs, chest wall, abdominal wall, surgical scars, and umbilicus.[,]\nUmbilical endometriosis constitutes approximately 40% of all extrapelvic endometriosis cases and is classified into primary (spontaneous) and secondary (scar-related) forms. Secondary umbilical endometriosis is more prevalent and typically arises as a complication of prior pelvic or abdominal surgery, including cesarean section, hysterectomy, or laparoscopy.[] First identified by Villar in 1886, primary umbilical endometriosis (PUE), also known as Villar’s nodule, is a very uncommon condition that accounts for just 0.5% to 1% of all occurrences of extragenital endometriosis and develops without any prior surgical history.[]\nThe clinical diagnosis of PUE is inherently challenging owing to its protean presentation, which closely resembles diverse benign and malignant umbilical pathologies, including hernias, granulomas, hematomas, lipomas, desmoid tumors, primary melanoma, and metastatic carcinoma (Sister Mary Joseph nodule).[] The diagnostic workup is further complicated by the limited sensitivity and specificity of conventional imaging modalities, including ultrasonography, computed tomography, and magnetic resonance imaging (MRI), none of which yield pathognomonic findings for umbilical endometriosis.[]\nIn this context, fine-needle aspiration cytology (FNAC) emerges as a pivotal, minimally invasive, and cost-effective first-line diagnostic tool that can establish a preoperative diagnosis by identifying characteristic cytomorphological features. The present report details a case of PUE in which a preoperative cytodiagnosis was established on FNAC, subsequently confirmed by histopathology, with the primary focus on elucidating the cytomorphological features and diagnostic challenges encountered in this setting. This report adheres to the CAse REport guidelines. Although several FNAC-diagnosed cases of PUE have been reported, the condition remains exceptionally rare. This report highlights the characteristic cytomorphological findings that enabled an accurate preoperative diagnosis and emphasizes the practical diagnostic role of FNAC in differentiating PUE from other umbilical lesions.\nCASE REPORT\nPatient information\nA 46-year-old multiparous woman (gravida 3, para 3) of Asian ethnicity, with no prior abdominal or pelvic surgical history, presented to the outpatient department with a progressively enlarging umbilical swelling of 7–8 months’ duration. She denied any associated discharge from the umbilicus. She reported no personal or family history of endometriosis or gynecological malignancy. Her menstrual cycles were regular.\nClinical findings\nThe patient’s primary complaint was a swelling in the umbilicus, associated with localized pain that characteristically intensified during menstruation (cyclical pain). General physical examination was unremarkable. Local examination of the umbilicus revealed a solitary, well-defined, tender nodule measuring approximately 1.5 cm × 1.0 cm × 0.7 cm, with a brown-to-black surface discoloration. No inguinal lymphadenopathy was detected. Systemic examination was otherwise within the normal limits [Figure 1].\nEvaluation for pelvic endometriosis\nImaging\nUltrasonography of the anterior abdominal wall was performed. A lobulated hypoechoic lesion measuring 12.6 mm × 11.7 mm was identified in the umbilical region. Color Doppler examination demonstrated increased internal vascularity. No umbilical sinus, tract formation, or extraperitoneal extension of the lesion was identified. The sonographic differential diagnoses offered included umbilical polyp, endometriosis, and umbilical deposit/metastasis [Figure 2].\nCytological findings (fine-needle aspiration cytology) – primary diagnostic investigation\nFNAC was selected as the primary diagnostic investigation to characterize the cellular nature of the mass before surgical intervention. The procedure was performed under aseptic conditions in the outpatient setting without anesthesia. A 23G needle attached to a 20 mL syringe was used to aspirate the nodule using the standard free-hand technique. The aspirate obtained was hemorrhagic, and multiple smears were prepared and stained with Hematoxylin and Eosin (H and E) and May-Grünwald-Giemsa stains. Cytological examination revealed moderately cellular smears composed of sheets and cohesive clusters of endometrial glandular epithelial cells showing crowded, ovoid to round nuclei with coarsely granular chromatin, and scanty ill-defined cytoplasm. Scattered fragments of endometrial-type spindle-shaped stromal cells were also identified. The background showed numerous inflammatory cells, hemorrhage, and hemosiderin-laden foamy macrophages. No cellular atypia, atypical mitotic figures, or features suggestive of malignancy were observed. The characteristic cytological triad comprising endometrial glandular epithelial cells, stromal fragments, and hemosiderin-laden macrophages supported a cytodiagnosis of umbilical endometriosis [Figure 3].\nHistopathological findings\nThe patient had a wide local surgical excision of the umbilical nodule under general anesthesia after the FNAC-based preoperative diagnosis. A 2.2 cm × 2.3 cm × 1.8 cm chunk of soft tissue coated in the skin was discovered upon gross examination of the removed material. A 1.5 cm × 1.0 cm × 1.0 cm solid nodule with a brownish cut surface and tiny cystic pockets was found after serial sectioning. Microscopic examination of H and E-stained sections [Figures 4 and 5] demonstrated ectopic endometrial glands lined by columnar epithelium surrounded by endometrial-type stroma within fibrovascular tissue. Areas of extravasated erythrocytes were also noted. The overlying skin was unremarkable and no cytological atypia or malignant features were identified. These histopathological findings confirmed the diagnosis of PUE.\nDiagnostic assessment\nA gynecological evaluation was performed, including detailed clinical history and pelvic examination, which did not reveal the symptoms or signs suggestive of pelvic endometriosis. Pelvic ultrasonography showed no evidence of ovarian endometrioma or other pelvic pathology. As the patient had no pelvic symptoms and imaging findings were unremarkable, further invasive evaluation such as diagnostic laparoscopy was not considered clinically indicated.\nTherapeutic intervention\nWide local surgical excision with adequate margins of surrounding normal tissue was performed as the definitive treatment. No adjuvant hormonal therapy was instituted in the immediate postoperative period because there was no clinical evidence suggestive of concomitant pelvic endometriosis. The patient had no pelvic symptoms on history and clinical evaluation did not reveal findings warranting further invasive investigation.\nFollow-up and outcomes\nThe patient was followed up at 6 months postoperatively. She reported complete resolution of cyclical umbilical pain and no evidence of local recurrence at the time of last follow-up. She was counseled regarding the possibility of recurrence and the importance of continued gynecological surveillance.\nPatient perspective\nThe patient expressed significant relief following the resolution of chronic, cyclically debilitating pain. She reported that the recurrent nature of her symptoms before the diagnosis had substantially impacted her quality of life and daily activities.\nDISCUSSION\nOverview of primary umbilical endometriosis\nPUE (Villar’s nodule) is an exceptionally rare extragenital manifestation of endometriosis. The condition disproportionately affects the women of reproductive age, typically presenting in the third to fifth decades of life, consistent with the demographics of our patient.[,,,] The pathognomonic clinical triad consists of (i) a pigmented or discolored umbilical nodule; (ii) cyclical pain synchronized with menstruation; and (iii) absence of prior abdominal surgery.[] Our patient exhibited all three components, which should immediately raise the clinical suspicion.\nPathogenesis\nThe pathogenesis of PUE remains debated. Two principal theories are invoked: (i) the metastatic (implantation) theory, which proposes the transport of viable endometrial cells to the umbilicus via lymphatic dissemination, hematogenous spread, or direct peritoneal seeding through the abdominal cavity; and (ii) the metaplastic (coelomic metaplasia) theory, which posits that primitive pluripotential mesenchymal cells resident in the umbilical region undergo differentiation into functional endometrial tissue under appropriate hormonal stimulation.[] An additional hypothesis invokes the persistence of embryonic umbilical structures – specifically the urachus and umbilical vessels – as conduits for endometrial cell dissemination.[,] In the absence of a surgical history, the metaplastic or lymphohematogenous metastatic routes are considered most plausible.\nThe central role of fine-needle aspiration cytology in diagnosis\nThe diagnostic challenge posed by PUE is substantial: its clinical and morphological overlap with diverse benign and malignant umbilical lesions frequently results in misdiagnosis or delayed diagnosis. Imaging modalities, including ultrasonography, computed tomography, and MRI, lack specificity and sensitivity for PUE, offering no pathognomonic findings.[] FNAC therefore assumes paramount diagnostic importance as a minimally invasive, office-based, rapid, and cost-effective first-line modality.\nThe cytological diagnosis of endometriosis rests on the identification of any two of the following three characteristic features: (i) endometrial glandular epithelial cells, (ii) endometrial stromal cells, and (iii) hemosiderin-laden macrophages.[,] This diagnostic triad was identifiable in the present case, enabling a confident preoperative cytodiagnosis. Patient summary and clinical timeline are mentioned in Table 1. Furthermore, the cytomorphological features and their diagnostic significance are mentioned in Table 2. Although concerns regarding needle-track implantation of endometrial tissue following FNAC have been theoretically proposed, documented evidence remains exceedingly rare, and the diagnostic benefits of FNAC generally outweigh this potential risk.\nCytological diagnostic pitfalls\nDespite its utility, FNAC-based diagnosis of umbilical endometriosis is technically demanding. Several factors may confound accurate cytological interpretation:\nHormonal phase-dependent variability: During the proliferative phase, glandular epithelial cells appear as tightly packed clusters of small, monomorphic cells with minimal cytoplasm and bland chromatin. In the secretory phase, hyperplasia and predecidualization of stromal cells impart an epithelioid appearance to the smear, substantially increasing cellularity and potentially mimicking a mesenchymal or even malignant process. This heightened cellularity, compounded by a prominent capillary network, can lead to an erroneous diagnosis of aggressive mesenchymal neoplasm or malignancy.[]\nHemorrhage-dominated smears: When the aspirate is predominantly hemorrhagic, only sparse macrophages and inflammatory cells may be retrieved, rendering the complete cytological triad unrecognizable and endometriosis liable to be missed.[]\nStromal paucity: Stromal fragments are often scant and may be overlooked, particularly by less experienced cytopathologists unfamiliar with this rare entity.\nDifferential diagnostic considerations: From a cytological standpoint, the principal differentials on FNA include smears dominated by foamy macrophages (fat necrosis), benign spindle-cell proliferations (fibrosis and desmoid tumor), granulomatous inflammation (suture granuloma and mycobacterial infection), and hypercellular smears with malignant cells (melanoma and metastatic carcinoma). A detailed cytological differential diagnosis with distinguishing features is provided in Table 3. Awareness of these pitfalls, combined with correlation with clinical history and hormonal status, is indispensable for diagnostic accuracy.[]\nDifferential diagnosis\nTable 3 summarizes the broad differential diagnosis of umbilical masses with their distinctive clinical and imaging characteristics as well as their unique cytological findings. Given the clinical urgency and unique treatment approach of metastatic cancer (Sister Mary Joseph nodule), it is very crucial to rule it out. In the present case, metastatic carcinoma (Sister Mary Joseph nodule) was considered unlikely because the patient had no history or clinical evidence of an underlying visceral malignancy, the lesion demonstrated cyclical pain associated with menstruation, and FNAC revealed benign endometrial glandular cells, stromal fragments, and hemosiderin-laden macrophages without malignant cytological features. Melanoma was excluded based on the absence of significant cytological atypia, prominent nucleoli, intranuclear inclusions, or melanin-containing malignant cells. Histopathological examination further excluded both entities.\nHistopathological confirmation\nWhile FNAC provides a reliable preoperative diagnosis, histopathological examination of the excised specimen remains the gold standard for definitive confirmation of umbilical endometriosis. The pathological criteria require the simultaneous presence of both endometrial glands and stroma.[] In the present case, histopathology unequivocally demonstrated ectopic endometrial glands lined by columnar epithelium with surrounding endometrial-type stroma and extravasated red blood cells, confirming the cytodiagnosis. In diagnostically challenging cases, ancillary immunohistochemical markers may be useful. Endometrial stromal cells typically demonstrate CD10 positivity, while endometrial glands commonly express estrogen receptor, progesterone receptor, and cytokeratin markers, assisting in confirmation and exclusion of mimics.\nManagement\nThe final treatment for PUE is wide local surgical excision with sufficient tumor-free margins.[] According to Victory et al., over 70% of PUE patients needed surgery.[] The surgical strategy may entail targeted excision of the endometriotic nodule or complete umbilical resection with or without fascial reconstruction. To reduce the chance of a local recurrence, it is crucial to have clear resection margins. Patients with contemporaneous pelvic endometriosis or persisting symptoms after surgical excision may be candidates for adjuvant hormonal therapy, which includes combined oral contraceptives, progestins, gonadotropin-releasing hormone agonists, or danazol.[,] A limitation of the present report is the relatively short follow-up duration of 6 months. Although no recurrence was observed, longer surveillance is necessary because delayed recurrence has been reported in some cases of cutaneous endometriosis.\nThe comparison of the present case with selected published cases of PUE diagnosed by FNAC is illustrated in Table 4.\nCONCLUSION\nPUE is a rare but important differential diagnosis of umbilical nodules in women presenting with cyclical symptoms. This case demonstrates that FNAC can serve as a reliable preoperative diagnostic tool when interpreted alongside clinical and radiological findings, facilitating appropriate surgical management. Histopathological examination remains the gold standard for definitive diagnosis.\nEthics approval\nEthical clearance for this case report was obtained from the Institutional Independent Ethics Committee, Acharya Shri Chander College of Medical Sciences and Hospital, Jammu (Approval No.: ASCOMS/IEC/CRP and T/2026/127). Written informed consent was obtained from the patient, and anonymity has been maintained throughout the study.\nAuthors contribution\nSFRZ contributed to conceptualization, data collection, cytological evaluation, literature review, manuscript drafting, and preparation of the final manuscript. AS contributed to study conception, supervision, interpretation of findings, critical revision of the manuscript, and final approval. AS contributed to cytopathological diagnosis, supervision, critical review, and manuscript editing. PK contributed to data interpretation, manuscript review and editing, and final approval of the manuscript. All authors read and approved the final manuscript.\nData availability statement\nThe data supporting the findings of this case report are available within the article. Additional information is available from the corresponding author upon reasonable request, subject to patient confidentiality and institutional policies.\nDeclaration of patient consent\nThe authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given her consent for her images and other clinical information to be reported in the journal. The patient understands that name and initials will not be published and due efforts will be made to conceal identity, but anonymity cannot be guaranteed.\nFinancial support and sponsorship\nNil.\nConflicts of interest\nThere are no conflicts of interest.\nREFERENCES\n1.\nGilks B. Uterus: Corpus. In: Goldblum JR, Lamps LW, McKenney J, Myers JL, editors. Rosai and Ackerman’s Surgical Pathology. 11th ed. 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