Inguinal endometriosis mimicking an inguinal hernia: A case report and literature review

A 38-year-old female patient, gravida 2 para 2 (G2P2), who had both deliveries by vaginal route and had not undergone any prior abdominal or pelvic surgery, presented with a several-month history of intermittent right inguinal pain. Her gynecological history was notable for dysmenorrhea of variable intensity; she reported no infertility and no previously diagnosed pelvic endometriosis, and had previously used combined estrogen-progestin hormonal contraception for three years. On physical examination, a firm, fairly hard, poorly mobile, non-reducible swelling approximately 1.5 cm in diameter was found at the level of the right external inguinal ring, with mild tenderness and no impulse or increase in size on Valsalva maneuver. No laboratory investigations, including tumor markers such as CA-125 or inflammatory markers, were performed. In view of the clinical suspicion of an inguinal hernia, the very first step was to carry out ultrasound of the right groin. Ultrasonography revealed a well-defined, heterogeneous, nodular soft-tissue lesion with internal vascularity on color Doppler imaging, measuring 9 × 21 × 22 mm (AP × T × H), lying along the course of the right round ligament within the inguinal canal ( Fig. 1 ). It was not possible to establish a connection between the lesion and the peritoneal cavity. Also, features of hernia sac like peristaltic bowel content and omental echotexture were not identified. Fig. 1 Grayscale and color Doppler ultrasound of the right inguinal region showing a well-defined, heterogeneous, hypervascular nodular lesion measuring 9 × 21 × 22 mm (AP × T × H), consistent with an inguinal endometriotic nodule. Fig 1 – dummy alt text Grayscale and color Doppler ultrasound of the right inguinal region showing a well-defined, heterogeneous, hypervascular nodular lesion measuring 9 × 21 × 22 mm (AP × T × H), consistent with an inguinal endometriotic nodule. For additional evaluation, pelvic MRI was performed on a 1.5 Tesla scanner, including axial T1-weighted sequences, coronal and sagittal T2-weighted Dixon sequences, and diffusion-weighted imaging (DWI, b = 1000 s/mm²) with apparent diffusion coefficient (ADC) mapping. It revealed in the right inguinal canal a nodular lesion near the round ligament, with spiculated, stellate margins, isointense to muscle on T1-weighted images and markedly hypointense on T2-weighted images, a signal pattern consistent with a fibrotic endometriotic nodule rather than a hemorrhagic cystic lesion ( Fig. 2 ). No significant diffusion restriction was noted within the lesion, with an ADC value of 1.21 × 10⁻³ mm²/s ( Fig. 3 ). Sequential axial images further demonstrated continuity of the lesion with the right round ligament as it coursed through the inguinal canal toward its normal peritoneal insertion, without an associated hernia sac ( Fig. 4 ). There was no evidence of a hernia defect or communication with the intra-abdominal structures. It was felt at imaging that it was inguinal endometriosis rather than a simple inguinal hernia, especially since the clinical presentation was that of fluctuating symptoms. The imaging findings were discussed collegially among radiologists within our department prior to the final interpretation. Fig. 2 Axial T1-weighted (A), T2-weighted (B), and post-contrast (C) pelvic MRI showing a nodular mass with spiculated margins in the right inguinal region, isointense on T1-weighted images, hypointense on T2-weighted images, and demonstrating enhancement following contrast injection (Orange arrow). Fig 2 – dummy alt text Fig. 3 Axial diffusion-weighted imaging (DWI, b = 1000 s/mm²) (Yellow arrow) (A) and corresponding apparent diffusion coefficient (ADC) map (B) showing no significant diffusion restriction within the inguinal nodule (ADC = 1.21 × 10⁻³ mm²/s). Coronal (C) and sagittal (D) T2-weighted Dixon images confirm the nodular lesion along the course of the right round ligament within the inguinal canal (Yellow arrow). Fig 3 – dummy alt text Fig. 4 Sequential axial T1-weighted MRI images from lateral (A) to medial (B, C), demonstrating continuity of the endometriotic nodule with the right round ligament as it courses through the inguinal canal (A, B) toward the deep inguinal ring and its normal peritoneal insertion (C), confirming its intraligamentous, extrapelvic location without an associated hernia sac (Green arrows). Fig 4 – dummy alt text Axial T1-weighted (A), T2-weighted (B), and post-contrast (C) pelvic MRI showing a nodular mass with spiculated margins in the right inguinal region, isointense on T1-weighted images, hypointense on T2-weighted images, and demonstrating enhancement following contrast injection (Orange arrow). Axial diffusion-weighted imaging (DWI, b = 1000 s/mm²) (Yellow arrow) (A) and corresponding apparent diffusion coefficient (ADC) map (B) showing no significant diffusion restriction within the inguinal nodule (ADC = 1.21 × 10⁻³ mm²/s). Coronal (C) and sagittal (D) T2-weighted Dixon images confirm the nodular lesion along the course of the right round ligament within the inguinal canal (Yellow arrow). Sequential axial T1-weighted MRI images from lateral (A) to medial (B, C), demonstrating continuity of the endometriotic nodule with the right round ligament as it courses through the inguinal canal (A, B) toward the deep inguinal ring and its normal peritoneal insertion (C), confirming its intraligamentous, extrapelvic location without an associated hernia sac (Green arrows). The patient was given a gynecological and surgical consult to discuss the possibility of removing the lesion by surgery along with the segment of the round ligament involved. The patient subsequently underwent laparoscopic excision of the inguinal lesion together with the involved segment of the round ligament; no true hernia defect was identified intraoperatively. Histopathological examination of the surgical specimen confirmed the diagnosis of endometriosis, demonstrating endometrial-type glandular epithelium and cytogenic stroma embedded within fibromuscular round ligament tissue, with adjacent foci of hemosiderin-laden pigment consistent with prior cyclical hemorrhage ( Fig. 5 ). Fig. 5 Photomicrographs (hematoxylin and eosin stain) of the excised round ligament specimen. (A, C) Low-power views showing endometrial-type glands and stroma embedded within fibromuscular round ligament tissue, with an adjacent hemorrhagic, hemosiderin-laden cystic space. (B) Higher-power view of an endometrial-type gland lined by columnar epithelium surrounded by cytogenic stroma. (D) Endometriotic focus set within smooth-muscle bundles of the round ligament, confirming the extrapelvic, intraligamentous location of the lesion. Fig 5 – dummy alt text Photomicrographs (hematoxylin and eosin stain) of the excised round ligament specimen. (A, C) Low-power views showing endometrial-type glands and stroma embedded within fibromuscular round ligament tissue, with an adjacent hemorrhagic, hemosiderin-laden cystic space. (B) Higher-power view of an endometrial-type gland lined by columnar epithelium surrounded by cytogenic stroma. (D) Endometriotic focus set within smooth-muscle bundles of the round ligament, confirming the extrapelvic, intraligamentous location of the lesion.

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Inguinal endometriosis might be considered as a differential diagnosis of a fluctuating right inguinal mass or pain in women of fertile age, even if there is no prior history of gynecological surgery. Ultrasound remains the first-line investigation, while MRI serves as a complementary technique that further characterises the lesion and helps resolve diagnostic uncertainty, particularly for preoperative planning. Recognising this entity on imaging before surgery allows for appropriate surgical planning, distinct from standard hernia repair, and helps avoid diagnostic delay or incomplete treatment.

Inguinal endometriosis is a rare, but very important clinical condition that should be differentiated from inguinal hernia as these two can be mistaken for each other. Only a good preoperative diagnosis that is done correctly can lead to suitable surgical intervention. Most cases reported in the literature describe painful right inguinal masses in which the size and intensity of the pain vary with the menstrual cycle, reflecting the hormone-dependent nature of endometrial tissue at this ectopic site within the round ligament [ 3 , 4 ]. While inguinal endometriosis was in the past thought to be most frequently associated with surgery of the gynecological or obstetric type, a review of the literature in recent times found that as many as 75% of cases reported were in patients with no record of surgery of this type, and such patients were also frequently multiparous [ 2 , 6 ]. Our case, presenting with multiparity, two uncomplicated vaginal deliveries, and no prior abdominal or pelvic surgery, is in fact very much in line with this latest understanding of the disease and should not be regarded as an unusual finding. Ultrasound is the preferred initial imaging technique for a suspected inguinal mass and it is also useful for the detection of a coexisting hernia sac if there is one. The reported sonographic manifestations of inguinal endometriosis are quite diverse, ranging from cystic lesions — related to intracystic hemorrhage at menstruation — to solid or mixed cystic-solid masses. This can cause the sonographic differentiation from hernia sac, hydrocele of the canal of Nuck, or other soft tissue masses rather challenging [ 3 , 4 ]. MRI has been shown to be better than ultrasound or CT in strictly diagnostic imaging of inguinal endometriosis, with lesions most commonly reported as one of two major types: cystic, hyperintense on T1-weighted images, or lesions with a solid component [ 4 ]. Distinguishing an endometriotic nodule from an endometrioma is essential for accurate MRI interpretation, as these two entities differ both anatomically and in signal characteristics. Endometriomas are cystic ovarian lesions containing hemorrhagic debris of varying age, typically showing homogeneous T1 hyperintensity together with a T2 “shading” sign reflecting the progressive concentration of blood products [ 7 ]. In contrast, deep infiltrating endometriotic nodules, such as the one identified along the round ligament in our patient, are solid fibromuscular lesions resulting from a reactive fibrotic response to ectopic endometrial tissue; they typically demonstrate intermediate to low T1 signal and marked T2 hypointensity, often with irregular or spiculated margins and architectural distortion of adjacent structures, with small T1- or T2-hyperintense foci occasionally corresponding to residual glandular or hemorrhagic components [ 7 , 8 ]. The imaging findings in our patient — a nodular lesion with spiculated, stellate margins, isointense on T1-weighted images and markedly hypointense on T2-weighted images — are entirely consistent with this fibrotic nodular pattern rather than a hemorrhagic cystic endometrioma, a distinction that reinforces the value of MRI in differentiating extrapelvic endometriotic nodules from other groin masses, including inguinal hernia. Beyond inguinal hernia and hydrocele of the canal of Nuck, several other solid soft-tissue lesions of the inguinal canal and round ligament should be considered in the differential diagnosis. Round ligament leiomyoma is a benign smooth-muscle tumor that, like endometriotic nodules, tends to be hypointense on T2-weighted images, but typically shows more homogeneous signal, well-circumscribed rounded margins, and marked, relatively uniform post-contrast enhancement, without the spiculated, infiltrative margins seen in endometriosis. Desmoid-type fibromatosis is another important mimicker, presenting as an infiltrative, T2-hypointense mass with variable enhancement; unlike endometriosis, it is not related to the menstrual cycle and tends to show progressive local growth over time. Inflammatory or granulomatous lesions (eg, chronic groin abscess, foreign-body reaction, or reactive lymphadenopathy) can also mimic an endometriotic nodule, usually with associated edema, adjacent fat stranding, and a more acute clinical course. Other soft-tissue tumors of the inguinal region, including nerve sheath tumors (schwannoma, neurofibroma), lipoma, and, more rarely, sarcoma, should be considered when the lesion lacks the classic cyclical symptomatology or typical MRI signal pattern of endometriosis. Correlating imaging findings with the cyclical, menstruation-related nature of the patient's symptoms is therefore essential in narrowing this differential. It is important to accurately identify inguinal endometriosis preoperatively, because the treatment differs substantially from that of a regular inguinal hernia: complete surgical excision of the extraperitoneal round ligament segment and endometriotic lesion is considered locally curative and it also provides histological confirmation of the diagnosis; however, any coincident hernia defect should be repaired at the same time [ 5 ]. If a simple hernia is misdiagnosed, then the endometriotic tissue will be incompletely removed, and the patient's symptoms will not be completely relieved, leading to disease recurrence. Table 1 summarises the present case alongside three previously reported individual cases and one larger case series of inguinal endometriosis mimicking inguinal hernia [ 1 , [4] , [5] , [6] ]; because the series by Li et al. pools findings from ten patients, its data are presented as ranges rather than compared point-for-point with the single-patient reports. Among the individual cases, the right side was consistently affected, in keeping with the well-documented right-sided predominance of the disease, also reflected in the series. Patient age at diagnosis clustered around the late thirties among the individual cases (38–39 years), and most patients, including the present one, had no prior gynecological or obstetric surgery, reinforcing the observation that inguinal endometriosis is not primarily a post-surgical phenomenon. Imaging findings were heterogeneous across reports, ranging from hypoechoic masses of variable vascularity on ultrasound to an elongated cystic lesion along the round ligament on CT, reflecting the variable sonographic and cross-sectional appearance of this entity noted above. Among the individual cases, including ours, surgical excision of the lesion together with the involved segment of the round ligament was performed, with concurrent hernia repair when a coexistent defect was identified, consistent with the standard management approach for this condition. Table 1 Comparative summary of reported cases of inguinal endometriosis mimicking inguinal hernia, including the present case. Table 1 dummy alt text Study Age Side Surgical/Obstetric History Imaging Key Findings Management Histology Confirmed Follow-up/Recurrence Mehdizadeh et al. [ 1 ] 39 Right Nulliparous, no prior surgery US Hypoechoic oval mass, minimal vascularity Laparoscopic excision Not specified in report Not specified in report Li et al. [ 4 ] Range Predom. right 5/10 prior pelvic endometriosis US (all), MRI (select.) Mostly inconclusive heterogeneous lesions on US Surgical excision (extensive resection) Presumed (surgical series) Collected across cohort; not itemised per case Almagushi et al. [ 5 ] 39 Right No prior gynecological surgery CT Elongated cystic mass along round ligament Excision + concurrent hernia repair Not explicitly stated Not reported Rokhgireh et al. [ 6 ] 39 Right No prior surgery; series often multiparous US Hypoechoic, hypervascular mass (24 × 32 × 21 mm) Laparoscopic excision Yes (endometrial glands + stroma in fibrous tissue) Uneventful short term; dienogest given to prevent recurrence; long-term recurrence not reported Present case, 2026 38 Right G2P2, vaginal deliveries, no prior surgery US + MRI Oval lesion along round ligament, 9 × 21 × 22 mm, no hernia defect Laparoscopic excision; histologically confirmed Yes ( Fig. 5 ) Referred to gynecology department for further follow-up; no recurrence to date Comparative summary of reported cases of inguinal endometriosis mimicking inguinal hernia, including the present case.

Endometriosis is defined by the ectopic presence of endometrium-like tissue, comprising both glandular and stromal components, at sites distant from the uterine cavity. Besides pelvic peritoneum, ovaries, and pouch of Douglas, extrapelvic locations of endometriosis include inguinal canal involvement, a rare but well-described entity first described by Cullen, which is estimated to affect approximately 0.3–0.6% of women with endometriosis [ 1 , 2 ]. The right side is affected in the vast majority of reported cases, accounting for approximately 90–94%, this asymmetry is put down to embryological and anatomical factors, including physiological patency of processus vaginalis and difference in peritoneal fluid flow between the two sides [ 1 ].In most cases, a painful or tender right inguinal mass which usually fluctuates in size and intensity with the menstrual cycle is the presenting clinical feature of the patient. This presentation is not only classically that of an inguinal hernia but can also be that of a hydrocele of the canal of Nuck and other groin masses [ 3 , 4 ].It is very important that preoperative diagnosis is made with the help of imaging, which also permits proper planning of the operation such as excision of the round ligament and the management of any associated hernia defect, and not just a simple hernia repair [ 5 ].