Round ligament fibroid: A case report and literature review.

A 66-year-old postmenopausal female patient presented to the emergency department with rectal bleeding. She had a CT angiogram where a 3.5 cm heterogeneously enhancing mass with central hypodensity was detected in the right side of the pelvis ( Fig. 1 ). She followed up with a gynecologist who ordered tumor markers and recommended an MRI pelvis for further evaluation of the lesion. Tumor markers were within normal limits. Multiplanar and multisequence MRI imaging of the pelvis were acquired with and without IV contrast. A right adnexal focus, along the proximal aspect of the right inguinal canal, measuring approximately 3.5 cm in the largest dimension was reported ( Fig. 2 ). Images identified the normal round ligament on the left side as a linear T2 hypointense focus, with a similar linear focus on the right side, where the lesion was attached to the right round ligament. The lesion showed peripheral low T2 signal, and peripheral enhancement with no restricted diffusion. These findings are consistent with the diagnosis of round ligament fibroid. Fig. 1 Axial (A), Coronal (B), and sagittal (C) images from CT angiogram of the abdomen and pelvis. A 3.5 cm heterogeneously enhancing mass is seen on the right side of the pelvis (white arrows), with central hypodensity. Communication with the right sided round ligament is best seen on the coronal image (broken white arrow in B). Fig 1: Fig. 2 Images from the MRI pelvis with and without contrast. The sagittal, axial, and coronal T2 weighted images (A-C) show a well-defined lesion on the right side of the pelvis that displays T2 hypointensity with an internal focus of T2 hyperintensity (white arrows). The axial contrast-enhanced MR image (D) shows heterogenous enhancement of the lesion (arrow). Axial T2 weighted images (E and F) show the linear T2 hypointense structure that represents the round ligament on the left side (white arrows in E) and a similar structure is seen on the right side, attached to the fibroid (arrow in F). Fig 2: Axial (A), Coronal (B), and sagittal (C) images from CT angiogram of the abdomen and pelvis. A 3.5 cm heterogeneously enhancing mass is seen on the right side of the pelvis (white arrows), with central hypodensity. Communication with the right sided round ligament is best seen on the coronal image (broken white arrow in B). Images from the MRI pelvis with and without contrast. The sagittal, axial, and coronal T2 weighted images (A-C) show a well-defined lesion on the right side of the pelvis that displays T2 hypointensity with an internal focus of T2 hyperintensity (white arrows). The axial contrast-enhanced MR image (D) shows heterogenous enhancement of the lesion (arrow). Axial T2 weighted images (E and F) show the linear T2 hypointense structure that represents the round ligament on the left side (white arrows in E) and a similar structure is seen on the right side, attached to the fibroid (arrow in F). The patient became menopausal at the age of 52 and was started on oral hormone replacement therapy (HRT). She was then switched to a transdermal estrogen patch and oral progesterone therapy but has paused it after recent imaging findings. Percutaneous biopsy at an outside institution showed histopathology findings consistent with a fibroid and a surgical resection was deferred as the patient was asymptomatic. Fig. 3 Graphic showing the anatomy of the round ligament, extending from the uterus to the labia, through the inguinal canal. The other structures in the female inguinal canal include the ilioinguinal nerve, the genital branch of the genitofemoral nerve, lymphatic vessels , and blood vessels. A round ligament fibroid is shown on the right side (black asterisk), where they are more common, for unknown reasons. Fig 3: Graphic showing the anatomy of the round ligament, extending from the uterus to the labia, through the inguinal canal. The other structures in the female inguinal canal include the ilioinguinal nerve, the genital branch of the genitofemoral nerve, lymphatic vessels , and blood vessels. A round ligament fibroid is shown on the right side (black asterisk), where they are more common, for unknown reasons.

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This project did not involve any research and no ethical clearance was required.

A written informed consent was obtained from the patient for the publication of this case report.

This case report highlights the rare entity of round ligament fibroid, in a postmenopausal woman, and underscores the pivotal role of MRI in diagnosis. It illustrates the challenges of differentiating these uncommon tumors from other pelvic masses. MRI proved essential in characterizing the lesion and guiding management. While round ligament leiomyomas are infrequent, their potential to present with atypical symptoms or be discovered incidentally reinforces the necessity of thorough imaging and broad differential diagnosis in managing pelvic masses.

The round ligament, derived from the embryologic gubernaculum, extends from the uterus through the inguinal canal to the mons pubis and labia majora. Composed mainly of smooth muscle and connective tissue, it can develop pathologies during reproductive years, including endometriosis and round ligament varices—tortuous veins that may arise during pregnancy [ 7 ]. Tumors in the round ligament are rare, with approximately 300 cases reported, predominantly leiomyomas, followed by endometriomas and mesothelial cysts [ 8 ]. Leiomyomas, the most common benign gynecologic tumors, affect 20%-30% of women over age 35 [ 1 , 9 ]. Originating from smooth muscle cells, they contain varying amounts of fibrous tissue and fat [ 3 , 10 ]. Their etiology remains unclear but may involve somatic mutations, local growth factors, and sex steroids like estrogen and progesterone [ 2 , 11 , 12 ]. Risk factors include Black race, early menarche, nulliparity, obesity, and hormone replacement therapy (HRT) [ 1 ]. While most arise from the uterine myometrium, leiomyomas can develop in various pelvic locations. The round ligament is the most common extrauterine site, with other locations including the vulva, ovaries, urethra, urinary bladder, and parasitic fibroids adherent to structures like the broad ligament or retroperitoneum [ 1 , 3 , 6 , 9 ]. Leiomyomas of the round ligament typically occur in middle-aged, premenopausal women and are primarily solitary, unilateral, and more frequently found on the right side ( Fig. 3 ), as in our patient [ 3 , 8 , 13 , 14 ]. The round ligament has been shown to express estrogen and progesterone receptors, suggesting that HRT may stimulate hormone-responsive myofibrous structures even in postmenopausal women [ 11 , 15 ]. About half of round ligament leiomyomas coexist with uterine fibroids; however, our patient had no such history but did use HRT [ 16 ]. These tumors are often asymptomatic, with clinical manifestations varying by size, location, and growth rate [ 8 ]. They can occur anywhere along the ligament, from the uterus to the labia majora [ 13 , 17 ]. About two-thirds are extra-abdominal, while one-third are intra-abdominal. The latter often go undetected until found incidentally during imaging or surgery for unrelated conditions, as with our patient, whose lesion was discovered during evaluation for rectal bleeding [ 8 , 14 , 17 ]. Extra-abdominal leiomyomas, particularly in the inguinal canal or vulva, are more likely to cause symptoms such as a palpable mass, pelvic or abdominal pain, painless swelling, dyspareunia, inguinal adenopathy, or may mimic an incarcerated hernia [ 1 , 3 , 13 , 15 , 17 ]. Diagnosis is challenging due to nonspecific presentation and overlap with other pelvic masses. Intra-abdominal tumors are often incidental, while inguinal or labial swellings may mimic hernia, lymphadenopathy, lipoma, cysts, abscesses, or canal of Nuck hydrocele [ 3 , 13 , 18 ]. Imaging is essential to refine the differential diagnosis, with ultrasound, CT, and MRI being complementary [ 3 , 13 ]. Ultrasound is the initial imaging modality used to diagnose and monitor the growth of leiomyomas, typically revealing a well-circumscribed, hypoechoic solid mass [ 1 , 10 ]. Doppler imaging may reveal circumferential vascularity, aiding distinction from adenomyosis and assessing surgical risk or treatment response [ 10 , 19 ]. CT usually shows a circumscribed, heterogenous, dense mass that may contain streaked or mottled calcifications. On contrast-enhanced scans, peripheral enhancement without central enhancement can suggest torsion due to the peripherally obstructed veins or degenerative change [ 10 , 16 , 20 , 21 ]. Although CT aids in initial detection, MRI remains the most accurate modality due to its superior soft tissue resolution and ability to characterize mass composition, vascularity, and anatomical continuity [ 22 ]. Leiomyomas generally demonstrate low to intermediate signal intensity compared to myometrium on T1-weighted images and low signal intensity on T2-weighted images, with signal variation depending on degeneration [ 10 ]. Low signal on diffusion-weighted imaging (DWI) reflects low cellularity, helping distinguish benign fibroids from malignancies like sarcomas [ 23 ]. The FIGO classification system aids in standardizing fibroid descriptions and guides management; type 8 fibroids are extra-myometrial, including those in the round ligament, cervix, or broad ligament [ 24 ]. Beyond its established role in characterizing leiomyomas, MRI further aids in distinguishing leiomyomas from other CT-enhancing pelvic masses of gynecologic or nongynecologic origin [ 22 , [25] , [26] , [27] ]. For instance, uterine fibroids typically appear as well-circumscribed masses with low T2 signal intensity and variable postcontrast enhancement, whereas endometriomas exhibit high T1 and low T2 signal intensity due to blood products, often with internal “shading” [ 23 , 27 , 28 ]. Round ligament leiomyomas, although rare, often mimic adnexal masses due to their proximity to the ovaries and solid appearance. MRI provides superior diagnostic accuracy in distinguishing round ligament fibroids from ovarian tumors, particularly benign fibromas, which can be clinically and radiologically similar. On MRI, they appear as well-defined, solid masses with low signal on both T1 and T2, reflecting dense smooth muscle [ 29 , 30 ]. In contrast, ovarian fibromas, while also low in T2 signal, usually arise from the ovarian stroma and may display associated signs such as absence of a normal ipsilateral ovary, presence of a gonadal vascular pedicle, or distortion of ovarian architecture, features aiding differential diagnosis [ [26] , [27] , [28] , [29] , [30] ]. MRI is particularly valuable in mapping mass relationships to adjacent structures and tracking the ligament’s course, confirming origin. For masses arising near the uterine cornu, the “bridging vessel sign”, which represents vascular connections between the uterus and the mass, supports a uterine or round ligament origin rather than an adnexal one [ 22 , 26 ]. DWI and dynamic contrast-enhanced MRI (DCE-MRI) also aid in tissue characterization. Round ligament fibroids show low signal on high b-value DWI and high ADC values (low cellularity), distinguishing them from malignancies [ 22 ]. Gradual, homogeneous enhancement on DCE-MRI supports leiomyoma diagnosis, while ovarian tumors often enhance heterogeneously or show necrosis especially when malignant [ 22 , 27 ]. By integrating anatomic location, vascular patterns, and tissue features, MRI offers comprehensive evaluation, reliably distinguishing round ligament fibroids from ovarian tumors and guiding surgical planning. Surgical excision remains the preferred treatment for symptomatic round ligament leiomyomas and allows histopathologic analysis for a definitive diagnosis [ 8 , 13 , 14 ]. Grossly, leiomyomas are typically well-circumscribed but not encapsulated. Histologically they are formed from monotonous spindle cells with indistinct borders arranged in intersecting fascicles with multiple subtypes according to the nuclei characteristics, cellular composition, and mixed additional tissue. They are commonly positive for Desmin, h-caldesmon, and smooth muscle actin [ 31 ].

Fibroids, or leiomyomas, are the most common benign gynecologic tumors [ 1 ]. They originate from smooth muscle cells, usually from the uterine myometrium, and are typically located within the myometrium, submucosal, or subserosal layers of the uterine wall [ 2 ]. Extrauterine fibroids can be found anywhere in the abdomen or pelvis, with the round ligament as the most common extrauterine location [ 1 , 3 ]. Similar to intrauterine leiomyomas, round ligament leiomyomas typically occur in middle-aged, premenopausal women [ 4 ]. Accurate diagnosis relies heavily on imaging—ultrasound, computed tomography (CT), and especially magnetic resonance imaging (MRI), which provides superior soft tissue resolution and precise anatomical localization [ [4] , [5] , [6] ]. We present the case of an asymptomatic, incidentally discovered right-sided round ligament fibroid in a postmenopausal woman, highlighting an exceptionally rare presentation of a round ligament fibroid in a postmenopausal woman without history of uterine fibroids. In addition, we included a review of current literature, which includes the pathogenesis, diagnosis, management, and outcomes of this disease entity. Most round ligament leiomyomas are identified in reproductive-aged women; thus, postmenopausal occurrence, particularly in the context of hormone replacement therapy (HRT), remains poorly understood and underreported. This case underscores the potential hormonal responsiveness of round ligament tissue even after menopause and illustrates the critical role of MRI in differentiating these lesions from other pelvic or adnexal masses. Given its rarity and diagnostic implications, this report adds valuable insight to the limited literature and may inform clinical evaluation and management of similar presentations.