A Rare Coexistence: Uterine Leiomyoma Arising in a Mature Cystic Teratoma and a Pedunculated Endometriotic Cyst Mimicking Leiomyoma-Two Case Reports

A woman in her late 40s presented to the emergency department with heavy vaginal bleeding and clots, ongoing for approximately 18 months and worsening in recent months. She had recently commenced tranexamic acid and norethisterone prescribed by her general practitioner, with minimal relief. Her gynecological history included increasingly irregular periods over the past two years, consistent with perimenopausal transition. A Mirena intrauterine system had been inserted several months earlier without improvement in symptoms. Obstetric history included spontaneous vaginal deliveries, though parity was unclear. Past medical history included anxiety, eczema, folic acid deficiency, and migraines. She was allergic to penicillin and a social smoker. Notably, she had undergone hysteroscopy with endometrial polypectomy and laparoscopy several months earlier. On speculum examination, Mirena threads were not visible. A smooth 5–6 cm mass was observed obstructing the cervix. Vaginal examination confirmed a mass of similar dimensions protruding through the cervix. She was scheduled for urgent transvaginal ultrasound (TVUS) and hysteroscopy. Laboratory: Mild anemia consistent with chronic blood loss; iron studies confirmed iron deficiency. Inflammatory markers were normal. Microbiology: Genital swabs (high vaginal, endocervical, chlamydia/gonorrhea NAAT) were negative. Previous STI screening was normal. Imaging: Patient reported TVUS showed a normally positioned Mirena coil and no uterine abnormalities; formal report unavailable. Hormonal assessment: Elevated FSH and LH with fluctuating estradiol levels, consistent with perimenopausal transition. Laboratory: Mild anemia consistent with chronic blood loss; iron studies confirmed iron deficiency. Inflammatory markers were normal. Microbiology: Genital swabs (high vaginal, endocervical, chlamydia/gonorrhea NAAT) were negative. Previous STI screening was normal. Imaging: Patient reported TVUS showed a normally positioned Mirena coil and no uterine abnormalities; formal report unavailable. Hormonal assessment: Elevated FSH and LH with fluctuating estradiol levels, consistent with perimenopausal transition. Primary considerations included: Pedunculated submucosal leiomyoma—leading preoperative diagnosis based on clinical presentation and mass characteristics. Endometrial polyp—recurrence possible given prior history, though mass size/consistency suggested otherwise. Adenomyomatous polyp—benign lesion with similar presentation. Endometrial hyperplasia/carcinoma—considered due to age, chronic bleeding, and failed hormonal therapy. Cervical pathology—less likely given apparent uterine origin. Endometriotic lesion—not initially suspected but a possible atypical presentation. Inflammatory conditions—considered unlikely. Pedunculated submucosal leiomyoma—leading preoperative diagnosis based on clinical presentation and mass characteristics. Endometrial polyp—recurrence possible given prior history, though mass size/consistency suggested otherwise. Adenomyomatous polyp—benign lesion with similar presentation. Endometrial hyperplasia/carcinoma—considered due to age, chronic bleeding, and failed hormonal therapy. Cervical pathology—less likely given apparent uterine origin. Endometriotic lesion—not initially suspected but a possible atypical presentation. Inflammatory conditions—considered unlikely. Post histology: Diagnosis of endometriotic cyst was unexpected, underscoring the importance of tissue sampling and histopathological confirmation in abnormal uterine bleeding. Hysteroscopy and polypectomy under general anesthesia revealed a 5 × 5 cm pedunculated mass with a narrow stalk protruding through the cervix. The mass was resected, and the distorted Mirena coil was removed. Estimated blood loss was < 50 mL. Postoperatively, contraceptive counseling and follow up were arranged. Five days post procedure, the patient presented with abdominal pain, dysuria, and persistent bleeding. Clinical assessment excluded endometritis; she was discharged with reassurance, safety netting advice, and instructions to restart hormonal therapy if bleeding persisted beyond six weeks. Endometrial specimen: inactive glands, pseudodecidualized stroma, scattered acute inflammatory cells; no hyperplasia, atypia, or malignancy. Resected mass: cyst wall lined by cuboidal epithelium, hemosiderin laden macrophages, occasional glands; consistent with endometriotic cyst. No features of leiomyoma or malignancy identified. Endometrial specimen: inactive glands, pseudodecidualized stroma, scattered acute inflammatory cells; no hyperplasia, atypia, or malignancy. Resected mass: cyst wall lined by cuboidal epithelium, hemosiderin laden macrophages, occasional glands; consistent with endometriotic cyst. No features of leiomyoma or malignancy identified. The patient presented to the emergency department five days post‐hysteroscopy with abdominal pain, dysuria, and persistent vaginal bleeding, raising concern for possible endometritis. However, after clinical assessment, she was reassured and discharged home without antibiotics, with safety‐netting advice to restart hormonal treatment if bleeding persisted beyond six weeks and to seek gynecological review if symptoms continued. Histopathological examination of the endometrial specimen showed features suggestive of exogenous progestational effect, with inactive endometrial glands, pseudodecidualization of the stroma, and scattered acute inflammatory cells. No evidence of hyperplasia, atypia, or malignancy was identified (Figure  2 ). Photomicrographs of the lesion, case 2. (a) Section of cyst wall showing epithelium with underlying fibrous stroma, (b) Endometrioid glands within the cyst wall, (c) Haemosiderin laden macrophages, (d) Higher power view showing cuboidal lining epithelium. The resected mass showed sections of cyst wall lined by a single layer of cuboidal epithelium with scattered inflammatory cells. Hemosiderin‐laden macrophages were present throughout the specimen, and occasional glands were noted within the cyst wall. These features were consistent with an endometriotic cyst rather than a typical leiomyoma. Notably, no definitive features of leiomyoma were identified in the specimen, and there was no evidence of malignancy.

Mena Abdalla: conceptualization, formal analysis, investigation, methodology, supervision, writing – original draft. Victoria Barker: conceptualization, investigation, visualization, writing – original draft. Anitha Nayar: investigation, visualization, writing – original draft. Sahathevan Sathiyathasan: methodology, supervision, writing – original draft. Adjoa Appiah: data curation, supervision, validation, writing – original draft. Ibrahim ElHag: resources, visualization, writing – original draft. Alexander Steshenko: investigation, methodology, writing – review and editing. Saira Khan: investigation, methodology, writing – original draft. Arjun Anilkumar: data curation, investigation, visualization. Aisha Hameed: conceptualization, data curation, formal analysis, methodology, supervision.

The authors have nothing to report.

Pedunculated uterine masses can harbor unexpected and extremely rare pathological findings, including the first reported case of leiomyoma arising within a uterine mature cystic teratoma. Endometriotic cysts can clinically mimic pedunculated leiomyomas, emphasizing the importance of histopathological examination for accurate diagnosis. Comprehensive histopathological evaluation is essential for all resected uterine specimens, as complex pathology may not be apparent from clinical presentation or imaging findings. Conservative surgical management can be effective for complex uterine pathology while preserving reproductive function. Clinicians should maintain awareness of rare pathological entities and the potential for diagnostic surprises in common clinical presentations. Pedunculated uterine masses can harbor unexpected and extremely rare pathological findings, including the first reported case of leiomyoma arising within a uterine mature cystic teratoma. Endometriotic cysts can clinically mimic pedunculated leiomyomas, emphasizing the importance of histopathological examination for accurate diagnosis. Comprehensive histopathological evaluation is essential for all resected uterine specimens, as complex pathology may not be apparent from clinical presentation or imaging findings. Conservative surgical management can be effective for complex uterine pathology while preserving reproductive function. Clinicians should maintain awareness of rare pathological entities and the potential for diagnostic surprises in common clinical presentations.

Uterine leiomyomas are the most common tumors in women worldwide and affect more than 70% of women over their lifetime [ 1 ]. When submucosal and pedunculated, they may prolapse through the cervix and present with heavy vaginal bleeding, pain, or a visible vaginal mass, often prompting urgent surgical management [ 2 ]. Primary uterine teratomas are exceptionally rare, with only a small number of uterine corpus cases reported in the literature [ 3 ]. Although transformation within mature cystic teratomas is recognized, secondary neoplasms are uncommon and are more often malignant than benign [ 4 ]. Endometriosis may also present as a mass‐forming lesion and, in its polypoid forms, can mimic other gynecological tumors or even malignancy [ 5 ]. Against this background, the two cases presented here demonstrate how seemingly typical prolapsing uterine masses may conceal unexpected pathology and why histopathological confirmation remains essential.

These two cases illustrate the diagnostic complexity that can arise in seemingly straightforward presentations of pedunculated uterine masses. Both patients presented with heavy vaginal bleeding and prolapsed cervical lesions, yet histopathological analysis revealed entirely different and unexpected pathological entities. The identification of a leiomyoma arising within a mature cystic teratoma of the uterus represents an unprecedented finding. Somatic transformation of mature cystic teratomas is recognized, most commonly involving malignant change—particularly squamous cell carcinoma in approximately 1%–2% of cases [ 6 ]. Benign secondary neoplasms within teratomas are exceptionally rare, with only a handful of reports, predominantly in ovarian teratomas [ 7 ]. The pathogenesis of this rare combination remains uncertain. The leiomyoma may have arisen from smooth muscle elements within the teratoma, representing somatic overgrowth rather than true neoplastic transformation. Alternatively, this could represent a collision tumor, with two distinct pathological processes occurring concurrently. Positive desmin staining confirmed the smooth muscle origin of the leiomyomatous component, while diverse tissue elements established the teratomatous nature of the lesion. This case underscores three key points: (1) common clinical presentations can conceal rare pathological entities; (2) comprehensive histopathological examination of all resected specimens is essential; and (3) benign secondary neoplasms can expand our understanding of uterine teratoma biology. The second case demonstrates how endometriotic cysts can clinically and macroscopically mimic pedunculated leiomyomas. Histopathology revealed hemosiderin laden macrophages and characteristic cyst wall architecture, confirming endometriotic origin. This highlights the importance of considering endometriosis in the differential diagnosis of pedunculated uterine masses, particularly in perimenopausal women with chronic pelvic symptoms. The patient's prior gynecological procedures and Mirena coil may have contributed to lesion development, though the exact pathogenesis remains unclear. This case emphasizes the potential for diagnostic confusion when relying solely on clinical and imaging findings, reinforcing the necessity of histopathological confirmation. Together, these cases highlight several important principles: Even routine gynecological presentations may conceal rare or unexpected pathology. Preoperative imaging has limitations in characterizing complex uterine lesions. Histopathological examination remains the gold standard for definitive diagnosis. Conservative surgical approaches can effectively manage complex pathology while preserving fertility and uterine function. Even routine gynecological presentations may conceal rare or unexpected pathology. Preoperative imaging has limitations in characterizing complex uterine lesions. Histopathological examination remains the gold standard for definitive diagnosis. Conservative surgical approaches can effectively manage complex pathology while preserving fertility and uterine function. These cases expand the spectrum of uterine pathology and reinforce the importance of vigilance, thorough investigation, and reliance on histology in gynecological practice.

Written informed consent was obtained from the patients for publication of this case report and any accompanying images. A copy of the written consent is available for review by the Editor‐in‐Chief of this journal.

The authors declare no conflicts of interest.