Mature cystic teratoma at a cesarean-scar uterine isthmus: a case report and literature review.

A 41-year-old gravida 2 para 2 (G2P2) woman presented with a six-month history of irregular menstrual cycles (ranging from 20 to 60 days) and menstrual bleeding lasting 6–7 days, accompanied by 3–5 days of brownish vaginal discharge following each menses. Her obstetric history included two prior cesarean deliveries. She initially noted the postmenstrual discharge eight months before admission; the discharge was odorless and scant. An initial transvaginal ultrasound revealed a mixed echogenic mass measuring 3.8 × 2.5 × 2.4 cm within the anterior uterine isthmus extending to the cervix. The mass contained scattered anechoic areas (largest measuring 1.1 × 0.5 cm) and demonstrated no detectable blood flow on Doppler interrogation. She was advised to return for follow-up monitoring in three months, during which her symptoms persisted unchanged. Follow-up ultrasonography revealed a posteriorly positioned uterus measuring 55 × 45 mm, exhibiting a normal configuration and smooth capsular contour. The myometrial echotexture was heterogeneous. A mixed echogenicity mass, measuring 4.0 × 2.6 × 2.7 cm, was identified within the anterior isthmus extending into the cervix. This mass contained multiple anechoic regions (the largest measuring 1.0 × 0.7 cm) and demonstrated no detectable internal vascular flow. The minimal thickness of the anterior isthmic myometrium measured 1 mm. Given the extremely thin residual myometrium and the close proximity of the bladder, this finding was taken into account during surgical planning, and the subsequent therapeutic hysteroscopic procedure was performed under laparoscopic monitoring to reduce the risk of myometrial injury, uterine perforation, and bladder injury. The endometrial line was obscured, with a corresponding endometrial thickness of 0.6 cm. The left ovary appeared diminutive and hypoechoic, while the right ovary demonstrated normal morphology. Concurrently performed pelvic magnetic resonance imaging (MRI) demonstrated a retroverted, retroflexed uterus without endometrial dilation. A lobulated mass arising from the isthmic and cervical myometrium protruded into the endometrial cavity, resulting in obscuration of the local endometrium and diffuse myometrial thickening. The mass measured approximately 2.5 × 2.7 × 3.7 cm with well-defined, smooth margins. Signal characteristics included predominant hyperintensity on T1-weighted images interspersed with foci of intermediate signal intensity. Partial signal suppression was noted on fat-saturated sequences, consistent with intralesional fat content. Heterogeneous signal intensity was observed on T2-weighted images. Diffusion-weighted imaging revealed iso- to hyperintense signal with correspondingly variable apparent diffusion coefficient (ADC) values. Post-contrast sequences demonstrated mild enhancement confined to the mass wall and associated nodules, with no significant enhancement of the remaining mass components. Bilateral adnexal structures were poorly visualized, and no pelvic lymphadenopathy was identified (Fig.  1 ). Fig. 1 Pelvic MRI showing a mass in the anterior wall of the uterine isthmus at the site of a prior cesarean-section scar, protruding into the uterine cavity with unclear local endometrium. Arrows indicate the lesion. A T1-weighted (T1WI) axial image: the lesion shows slightly hyperintense signal. B T2-weighted (T2WI) axial image: the lesion exhibits heterogeneous/mixed signal intensity. C FLAIR axial image: the lesion demonstrates intermediate to hyperintense signal. D Contrast-enhanced T1-weighted (T1WI+C) axial image: the mass wall shows enhancement with enhanced mural nodules, and no obvious enhancement is observed in the remaining portion. E Diffusion-weighted imaging (DWI) axial image: the lesion shows iso- and hyperintense signal. F ADC map axial image: iso- and hypointense signal is visible Pelvic MRI showing a mass in the anterior wall of the uterine isthmus at the site of a prior cesarean-section scar, protruding into the uterine cavity with unclear local endometrium. Arrows indicate the lesion. A T1-weighted (T1WI) axial image: the lesion shows slightly hyperintense signal. B T2-weighted (T2WI) axial image: the lesion exhibits heterogeneous/mixed signal intensity. C FLAIR axial image: the lesion demonstrates intermediate to hyperintense signal. D Contrast-enhanced T1-weighted (T1WI+C) axial image: the mass wall shows enhancement with enhanced mural nodules, and no obvious enhancement is observed in the remaining portion. E Diffusion-weighted imaging (DWI) axial image: the lesion shows iso- and hyperintense signal. F ADC map axial image: iso- and hypointense signal is visible Because of an intercurrent respiratory infection, the planned admission was postponed. Repeat ultrasonography during follow-up demonstrated comparable findings (Fig.  2 ). After recovery, the patient was admitted for diagnostic hysteroscopic evaluation. Fig. 2 Serial transvaginal ultrasound images of the cesarean-scar/isthmic lesion. Arrows indicate a mixed-echogenic mass extending toward the uterine cavity and cervical canal, containing scattered anechoic areas and showing no definite internal vascularity on Doppler imaging Serial transvaginal ultrasound images of the cesarean-scar/isthmic lesion. Arrows indicate a mixed-echogenic mass extending toward the uterine cavity and cervical canal, containing scattered anechoic areas and showing no definite internal vascularity on Doppler imaging At diagnostic hysteroscopy, the endometrium was thin and uniform, and both tubal ostia were visible. The uterine cavity contained filamentous material admixed with yellowish-white caseous material (Fig.  3 ). A spherical, firm, whitish mass measuring 2.5 × 2.5 × 2.0 cm, resembling a leiomyoma, was observed protruding into the cervical canal from the anterior isthmus. Only the filamentous material was removed for histopathological examination at this stage. Fig. 3 Representative hysteroscopic intraoperative findings. a Multiple filamentous whitish hair-like structures are seen within the lesion. b Yellow-white caseous/sebaceous material is exposed during resection Representative hysteroscopic intraoperative findings. a Multiple filamentous whitish hair-like structures are seen within the lesion. b Yellow-white caseous/sebaceous material is exposed during resection Pathological analysis identified hair shafts with calcification, keratinized debris, scant fragmented endometrial tissue, and detached cervical squamous epithelium within a background of coagulated blood. Correlation of the clinical history, imaging findings, and tissue sampling strongly suggested a teratomatous lesion. Based on the hysteroscopic findings, tissue sampling results, and imaging features, the patient subsequently underwent definitive hysteroscopic resection under laparoscopic monitoring. During the definitive hysteroscopic procedure, a white, spherical, tumor-like mass measuring approximately 3.5 × 3.5 × 3.0 cm was observed protruding from the anterior uterine isthmus at the site of the prior cesarean-section scar. Yellowish-white hair-like and adipose-like material was noted adjacent to the mass (Fig.  3 ). The uterine cavity was otherwise unremarkable, the endometrial surface appeared smooth, and both tubal ostia were clearly visualized. The postoperative pathological examination identified a mass situated at the anterior isthmus scar. This mass comprised a cystic lesion measuring 3.5 × 2.0 × 1.0 cm, exhibiting a wall thickness ranging from 1 mm to 5 mm. Examination of the cut surface revealed a thickened area measuring 1.8 × 1.0 cm (Fig.  4 ). Fig. 4 Gross and histopathologic findings of the resected lesion. A Gross specimen showing yellow-white sebaceous/keratinous material. B Histologic examination demonstrates mature tissue elements, consistent with mature cystic teratoma Gross and histopathologic findings of the resected lesion. A Gross specimen showing yellow-white sebaceous/keratinous material. B Histologic examination demonstrates mature tissue elements, consistent with mature cystic teratoma The patient received a follow-up examination in April, which revealed no abnormalities. To date, no recurrence has occurred, and the patient maintains stable condition.

Teratomas represent the most common type of germ cell tumor, typically occurring in the ovaries [ 1 ]. Based on the presence or absence of immature neuroectodermal tissue within the tumor, teratomas can be classified into mature teratomas and immature teratomas. Mature teratomas (solid or cystic) are composed of tissues derived from two or three germ layers, including ectoderm, mesoderm, and endoderm [ 2 ]. Among them, mature cystic teratomas (dermoid cysts) constitute the most prevalent type. In contrast, extragonadal teratomas are exceedingly rare, particularly those arising within the uterus. Primary uterine teratomas remain exceedingly uncommon, and preoperative misdiagnosis as fibroids or endometrial/cervical polyps is frequent [ 3 – 5 ]. This report describes an extremely rare mature cystic teratoma arising in the anterior uterine isthmus at a prior cesarean-section scar and highlights the associated imaging features and postoperative surveillance considerations.

This case report describes an extremely rare mature cystic teratoma arising at a cesarean-section scar in the anterior uterine isthmus. It highlights the importance of considering rare entities such as teratoma in the differential diagnosis of atypical cesarean-scar or isthmic uterine masses, particularly in women with a history of cesarean delivery. Ultrasound remains the first-line imaging modality, whereas MRI is especially helpful for demonstrating intralesional fat and refining the differential diagnosis. Correlation among imaging, hysteroscopic findings, and histopathology is essential for accurate diagnosis. Complete hysteroscopic excision under laparoscopic monitoring was effective in this case, with no recurrence observed during follow-up.

Teratomas, constituting the most common type of germ cell tumors, occur predominantly in the gonads, such as the ovaries and testes. Extragonadal germ cell tumors are primarily located in the pineal gland, retroperitoneal space, presacral region, and mediastinum. Primary uterine teratomas are exceptionally rare. This case presentation is unusual, as to date, only a limited number of reported cases describe uterine teratomas originating within the uterine body; furthermore, the occurrence of a teratoma within a cesarean section scar represents an additional rare event [ 3 – 6 ]. Representative previously reported uterine teratoma cases are summarized in Table 1 . Table 1 Representative previously reported uterine teratoma cases relevant to lesion site, presentation, and management Study Site Presentation/ initial impression Management Relevance to current case Papadia et al. Uterus/endometrial polyp-like lesion Presented as an endometrial polyp Surgical removal Shows that uterine teratoma may mimic a polyp Wang et al. Uterine corpus Uterine mature cystic teratoma Tumor resection Important for pathogenesis discussion Maçães et al. Previous cesarean-section scar Scar-associated dermoid cyst Surgical treatment Relevant scar-related comparator Chou et al. Near cesarean scar / endometrial polyp Initially managed as presumed endometrial polyp Hysteroscopic management Relevant for hysteroscopic diagnosis and management Li and Zheng Uterine cervix Cervical teratoma Tumor excision Broadens anatomic spectrum of uterine teratoma Present case Anterior uterine isthmus at prior cesarean scar Postmenstrual brown discharge; mixed-echogenic avascular lesion; fat-containing MRI lesion Hysteroscopic excision under laparoscopic monitoring Distinct for isthmic scar location and combined minimally invasive management Representative previously reported uterine teratoma cases relevant to lesion site, presentation, and management The uterine isthmus is the narrow transitional zone between the uterine corpus and the cervix. While obstetric literature sometimes functionally groups it within the lower uterine segment in late pregnancy, standard anatomical nomenclature distinguishes the isthmus from the corpus. This distinction is critical here because the lesion originated at the anterior isthmic cesarean-section scar (isthmocele) rather than within the corpus. The histogenesis of uterine teratomas remains controversial. One proposed mechanism is implantation of pluripotent embryonic or fetal tissue during pregnancy-related events or uterine procedures [ 7 ]. In the present case, because the lesion arose precisely at a prior cesarean-section scar, implantation during previous uterine surgery is a biologically plausible site-specific hypothesis [ 6 ]. However, this mechanism cannot be proven in our patient. Alternative explanations include misplaced primordial germ cells (PGCs) or other pluripotent germ-cell precursors within the uterus, which have been supported by molecular and allelotyping studies [ 8 – 10 ]. Linder et al. demonstrated that benign ovarian teratomas may arise from parthenogenetically activated ovarian oocytes after the first meiotic division [ 11 ], but the origin of uterine teratomas may differ from that of ovarian teratomas [ 9 ]. Unfortunately, further molecular testing could not be performed in the present case. Ultrasound remains the first-line imaging modality for evaluating female pelvic masses because of its accessibility, low cost, and real-time assessment capability. In mature cystic teratoma, ultrasound may show a mixed echogenic lesion, echogenic lines or bands related to hair, calcific foci, and posterior attenuation [ 12 ]. MRI is particularly useful when ultrasound findings are indeterminate, because it can directly demonstrate intralesional fat, typically as T1 hyperintensity with signal suppression on fat-saturated sequences [ 12 ]. In our patient, the lesion showed mixed echogenicity and no definite internal vascularity on ultrasound, while MRI demonstrated intralesional fat with only limited mural enhancement, findings that strongly supported the diagnosis of mature cystic teratoma. Although this patient has been pathologically confirmed to have a mature teratoma, enhanced wall nodules can still be observed on MR imaging.Hence, long-term follow-up is required to monitor the condition. Although malignant transformation is rare, it should be considered in long-standing teratomatous lesions. Reported warning signs include older or postmenopausal age, large or enlarging masses, the presence of prominent solid or irregularly enhancing components, extrauterine spread, and markedly abnormal tumor markers. Squamous cell carcinoma is the most commonly reported malignant component. In our patient, the lesion showed only limited mural enhancement and no imaging evidence of invasion or extrauterine disease, favoring a benign process [ 13 ]. In the cesarean-scar anterior isthmus, the principal mimics include submucosal leiomyoma or lipoleiomyoma, endometrial or endocervical polyp, cesarean-scar pregnancy/retained products, isthmocele hematoma, adenomyosis or adenomyoma, scar endometriosis, uterine arteriovenous malformation (AVM), and polypoid malignancy. Distinguishing this lesion from endometriosis is particularly important because both may appear hyperintense on T1-weighted MRI. However, mature cystic teratoma typically contains macroscopic fat and therefore shows signal drop on fat-suppressed sequences, sometimes with fat–fluid level, calcification, or hair/Rokitansky protuberance [ 12 ]. By contrast, blood products in endometriosis or hematoma usually remain hyperintense on fat-suppressed T1-weighted images and may show T2 shading [ 14 ]. A vascular stalk supports a polyp [ 15 ], bridging vessels favor leiomyoma [ 16 ], and turbulent high-flow Doppler signals suggest AVM [ 17 ]. In our patient, MRI demonstrated intralesional fat with only limited mural enhancement, while hysteroscopy revealed hair-like and keratinous material, findings that strongly favored mature cystic teratoma. On surveillance, new enhancing mural nodules or progressive wall thickening should prompt reassessment for malignant transformation [ 13 ]. Serum tumor markers should be regarded as adjunctive rather than diagnostic. Mild CA19-9 elevation may occur in mature cystic teratoma [ 18 ], but its specificity is limited. Markedly abnormal tumor markers may raise concern for malignant transformation in selected cases [ 13 ]. In our case, the patient’s CA19-9 level was 19.34 U/mL, only 0.34 above the upper limit of normal (0–19 U/mL), underscoring its limited standalone diagnostic value for uterine mature cystic teratoma. Given rare reports of recurrence or malignant transformation in uterine teratomas, we recommend structured follow-up after complete resection: pelvic ultrasound or MRI at 6–12 months, then annually for 2–3 years, with tumor markers (CA19-9, CA125, CEA) as adjuncts when clinically indicated. Patients should be advised to seek earlier re-evaluation if new symptoms such as abnormal bleeding, pelvic pain, or imaging features suggestive of recurrence (e.g., enhancing mural nodules, progressive wall thickening) emerge. In this patient, no recurrence has been observed through approximately 20 months of follow-up (as of November 2025). Because uterine mature teratomas are extremely rare, no standardized management guidelines are currently available. Complete excision remains the main treatment principle. In younger patients desiring fertility preservation, conservative hysteroscopic resection may be appropriate for selected lesions protruding into the uterine cavity [ 4 ]. In our case, because the residual anterior isthmic myometrium was extremely thin, the hysteroscopic procedure was performed under laparoscopic monitoring to improve safety and reduce concern for uterine perforation and bladder injury. Laparoscopic surgery or scar repair may be considered when the lesion is deeply embedded in the cesarean-scar niche or when myometrial thinning is marked. Open abdominal surgery or hysterectomy may be appropriate when complete minimally invasive excision is not feasible, when there is extensive involvement, or when malignant transformation is suspected [ 5 , 19 ]. With complete resection and appropriate follow-up, the prognosis is generally favorable. Extragonadal teratomas are relatively rare in adults. When differentiating intrauterine masses, extragonadal teratomas should still be considered despite the lack of typical radiological features, in order to avoid misdiagnosis or missed diagnosis. In terms of treatment, tumor resection or total hysterectomy is generally employed, with the specific approach tailored to the patient’s individual condition and the nature of the tumor. Overall, with appropriate treatment, the prognosis is typically favorable, warranting proactive attention from clinicians in the management and treatment of this condition.