INTRODUCTION
Female adnexal tumor of probable Wolffian origin (FATWO) is an exceedingly rare gynecologic neoplasm with low malignant potential, which is derived from mesonephric (Wolffian) duct remnants [1]. Since its initial description in 1973, fewer than 100 cases have been reported globally. The majority of lesions occur in the broad ligament or mesosalpinx, and the clinical and imaging characteristics are non-specific [2].
Preoperative diagnosis remains extremely challenging, and the majority of cases are misdiagnosed as ovarian fibroma, granulosa cell tumor, cyst, or leiomyoma. Imaging investigations, particularly ultrasound, serve as the first-line examination for adnexal masses; however, the ultrasonic features of FATWO have not been well-defined. Published reports are limited, and most concentrate on pathology or magnetic resonance imaging (MRI) rather than systematic ultrasound findings [2-4].
Therefore, this study aimed to summarize the ultrasonic features of four pathologically confirmed FATWO cases from a single institution, compare them with previously reported cases, and identify key imaging indicators to enhance preoperative recognition. The study adheres to the CARE guidelines for case series reporting.
CASE PRESENTATION
This was a retrospective case series study approved by the Ethics Committee of Women’s Hospital, School of Medicine Zhejiang University, China. Written informed consent was obtained from all patients or their legal representatives prior to study inclusion.
Study Period and Case Selection
We reviewed all gynecologic tumor patients treated at our hospital between January 2018 and June 2024. Four patients with pathologically confirmed female adnexal tumor of probable Wolffian origin (FATWO) were enrolled. These were non-consecutive, clinically encountered cases collected over the study period due to the extreme rarity of the tumor.
Ultrasound Imaging
All patients underwent transvaginal pelvic ultrasound using:
(1) Samsung WS80A ultrasound system with an intracavitary probe
(2) GE E6/E8 ultrasound system with an intracavitary probe
Ultrasound examinations were performed and interpreted by two senior attending radiologists specializing in gynecologic imaging who were blinded to the final pathological diagnosis. Evaluated features included lesion location, size, echo pattern (solid/cystic/mixed), boundary, septa, internal vascularity, and resistive index (RI).
Pathologic and Immunohistochemical Analysis
Surgical specimens were fixed in 10% neutral-buffered formalin, processed routinely, and embedded in paraffin. Sections (4 μm) were stained with hematoxylin and eosin (HE) for morphological evaluation. Immunohistochemical staining was performed using the EnVision method for the following markers: CK, inhibin, WT-1, calretinin, GATA-3, and PAX8.
All slides were reviewed by two senior gynecologic pathologists to confirm the diagnosis of FATWO.
Follow-up
Clinical follow-up was conducted via outpatient visits or telephone interviews. Follow-up data included survival status, tumor recurrence, and metastasis, with the last follow-up completed in October 2025.
Clinical Data
Case 1
A 27-year-old female presented with a pelvic mass. Ultrasound showed a 2.7×2.0×2.5 cm hypoechoic mass adjacent to the right ovary (Fig. 1a), with internal vascularity (Fig.
1b), RI 0.72. It was misdiagnosed as fibroma. Pathology confirmed FATWO.
Case 2
A 42-year-old female presented with a pelvic mass. Ultrasound showed a 2.3×2.3×1.7 cm cystic-solid mass in the left adnexa (Fig. 2a–c), misdiagnosed as corpus luteum cyst or endometrioma.
Pathology confirmed FATWO.
Case 3
A 41-year-old female presented with a pelvic mass. Ultrasound showed a 5.1×3.9×3.2 cm septated cystic-solid mass (Fig. 3a and b), misdiagnosed as granulosa cell tumor.
Pathology confirmed FATWO.
Case 4
A 53-year-old female presented with menstrual disorder. Ultrasound showed a 1.3×1.2 cm anechoic lesion adjacent to the left ovary (Fig. 4), misdiagnosed as a simple ovarian cyst.
Pathology confirmed FATWO.
Follow-up Results
Follow-up was completed in October 2025.
Case 1
Follow-up duration was 83 months (January 2018 to October 2025). No recurrence, no metastasis, no additional treatment, no reoperation.
Case 2
Follow-up duration was 75 months (July 2019 to October 2025). No recurrence, no metastasis, no additional treatment, no reoperation.
Case 3
Follow-up duration was 32 months (February 2023 to October 2025). No recurrence, no metastasis, no additional treatment, no reoperation.
Case 4
Follow-up duration was 16 months (June 2024 to October 2025). No recurrence, no metastasis, no additional treatment, no reoperation.
All patients were alive with no evidence of disease (NED) at the last follow-up. The clinical, ultrasonographic, and pathological features of the four patients are summarized in Table 1.
Imaging Findings
Case 1
Using a Samsung WS80A intracavitary probe for uterine and bilateral adnexal scanning, a 2.8×2.4×2.4 cm hypoechoic mass with well-defined borders (Fig. 1a) and internal blood flow signals was observed adjacent to the right ovary, with an RI of 0.72 (Fig. 1b).
Pelvic magnetic resonance imaging (MRI) revealed a well-defined oval solid mass in the right adnexal region. On T1-weighted axial imaging, the mass appeared isointense to skeletal muscle (Fig. 1c).
On T2-weighted fat-suppressed axial imaging, the signal was slightly higher than that of skeletal muscle (Fig. 1d). Diffusion-weighted imaging (DWI) with b = 800 s/mm2 displayed markedly increased signal intensity (Fig.
1e). After enhancement, the mass showed a slight increase (Fig. 1f).
Case 2
Using a Samsung WS80A intracavitary probe for uterine and bilateral adnexal scanning, the left ovary shows a 2.3×2.3×1.7 cm cystic echo (Fig. 2a) with 1.7×1.5×1.5 cm enhanced areas (Fig. 2b), well-defined margins, and minimal blood flow signals, RI: 0.53 (Fig.
2c). Pelvic MRI revealed an oval mass of approximately 2.3×2.1×2.0 cm in the left ovary. On T1-weighted axial imaging, the mass appeared isointense to skeletal muscle (Fig.
2d). On T2-weighted fat-suppressed axial imaging, the signal was slightly higher than that of skeletal muscle (Fig. 2e).
DWI with b = 800 s/mm2 displayed markedly increased signal intensity (Fig. 2f). After enhancement, no significant enhancement was observed in the mass (Fig.
2g).
Case 3
During a uterine and bilateral adnexal scan using a GE E6 intracavitary probe, a cystic mass measuring 5.1×3.9×3.2 cm with septa was identified on the surface of the right ovary (Fig. 3a). The presence of slightly abundant blood flow above the septa (Fig.
3a) suggests a potentially active lesion. The cystic mass contained fluid that was heterogeneous, with areas of clarity and viscosity, which is typical for ovarian cysts. Given the size of the cyst and the observed blood flow, further medical evaluation and monitoring are warranted.
Pelvic MRI revealed a cystic mass in the posterior right aspect of the uterus, with relatively well-defined margins and dimensions of approximately 5.3×3.5×4.1 cm. On T1-weighted axial imaging, the mass presented with isointense signal intensity and contained multiloculated septations (Fig. 3c).
On T2-weighted fat-suppressed axial imaging, the mass presented with a mixed signal (Fig. 3d). DWI with b = 800 s/mm2 displayed local high signal intensity (Fig.
3e). The enhancement of the scan edges showed progressive intensification (Fig. 3f).
Case 4
Utilizing a GE E8 intracavitary probe to conduct scans of the uterus and bilateral adnexa, a 1.3×1.2 cm anechoic lesion was detected adjacent to the left ovary (Fig. 4). Preoperatively, this lesion was misdiagnosed as a simple ovarian cyst.
The specimens underwent comprehensive harvesting and were subjected to HE staining, followed by sequential immunohistochemical staining. The tumor cells are arranged in a mixed structure of tubular (hollow or solid), cystic, reticular, or diffuse solid forms, partially located in a background of hyaline degenerated fibrous stroma. The lumen and reticular spaces of the nuclei often contain eosinophilic secretions.
The tumor cells are cuboidal to oval, with sparse cytoplasm, warm and atypical nuclei, indistinct nucleoli, and rare mitotic (Fig. 5). Immunohistochemical staining: CK (Fig.
6a), inhibin (Fig. 6b), WT-1 (Fig. 6c), and calretinin (Fig.
6d) were moderately to strongly positive in all 4 patients, GATA-3 (Fig. 6e) and PAX 8 (Fig. 6f) were all negative.
DISCUSSION
Female adnexal tumor of probable Wolffian origin (FATWO) is an extremely rare neoplasm originating from mesonephric (Wolffian) duct remnants. The majority of lesions develop in the broad ligament or mesosalpinx, while ovarian involvement is infrequent [1, 2]. Since its initial description in 1973, fewer than 100 cases have been reported globally [1].
Owing to the lack of specific clinical manifestations and imaging features, preoperative diagnosis remains arduous, and misdiagnosis is prevalent [2]. Definitive diagnosis depends on postoperative pathological examination. This study summarizes the ultrasound features of four pathologically confirmed FATWO cases and reviews the literature to enhance preoperative recognition.
All four patients had no recurrence during follow-up (16–83 months), supporting the generally benign behaviour of FATWO [4, 5].
In our series, all four tumours were extraovarian (Figs. 1-4), consistent with previous reports. Most lesions were well-circumscribed, solid or cystic-solid hypoechoic masses with mild to moderate internal vascularity.
These features correspond directly to the ultrasound images (Figs. 1-4). Our findings confirm previous ultrasonic features of FATWO: extraovarian origin, clear boundary, absent calcification, and mild internal vascularity [2, 6, 7].
The ultrasound features must be distinguished from sex cord-stromal tumours, fallopian tube tumours, and subserosal leiomyomas. Accurate recognition of extraovarian location (Figs. 1-4) is the most important clue [8, 9].
FATWO has a low malignant potential. The reported age range is 15–81 years, with an average onset of approximately 50 years. Tumour size varies significantly, ranging from 0.8 cm to 20 cm [2, 5].
Most patients are asymptomatic, and lesions are often incidentally discovered during routine gynecologic examinations or surgeries. Although most FATWOs are benign, malignant cases have been reported. Diagnostic criteria for malignant FATWO have been established, including tumour diameter >10 cm, hypercellularity, necrosis, capsular invasion, rupture, tumour implantation, or metastasis [4].
Approximately 10% of patients experience recurrence or metastasis, most commonly in the liver and lungs, typically within 2 years [4, 5, 10].
Pathological diagnostic criteria for FATWO include [1, 2, 8]:
There is no single specific immunohistochemical marker for FATWO. Previous studies have demonstrated consistent expression of CK, vimentin, CD10, calretinin, and inhibin, and the absence of PAX8 and GATA-3 [6, 11]. The four cases in this study displayed typical morphological features and immunohistochemical profiles consistent with previous reports, with no marked atypia, increased mitoses, or malignant features.
However, reports describing the imaging features of FATWO are still limited. By 2026, at least 18 cases with detailed MRI or CT findings have been documented in the English literature [4, 12-14].
As the first-line imaging modality for pelvic masses, ultrasound is crucial for the preoperative recognition of FATWO, yet dedicated ultrasound reports are extremely scarce. To clarify the contribution of the present study, we systematically compare our four cases with previously published ultrasound findings of FATWO [2, 8, 11].
Overlapping features consistent with previous ultrasound reports
Lesions are predominantly extraovarian, arising from the mesosalpinx or broad ligament, with identifiable normal ovarian tissue [1, 2, 8].
Masses are well-circumscribed with distinct borders [2, 8, 11].
Most lesions show internal vascularity with a resistive index (RI) ranging from 0.5 to 0.7 [1, 2].
The absence of calcification, papillary projections, and significant ascites is typical [1, 2, 8].
Confirmatory Findings Validated in the Present Study
A solid hypoechoic appearance is the most common pattern [2, 8].
Cystic-solid components and internal septations may be present [11].
Tumors are typically unilateral and encapsulated [1, 2, 6].
Novel Findings of this Study (Not Previously Emphasized)
We clarify that capsular vascularity and intratumoral vascularity can coexist, which aids in distinguishing FATWO from leiomyoma.
We provide a standardized ultrasound diagnostic approach based on a four-case cohort, including precise localization, echo characterization, and vascular analysis.
By distinguishing overlapping, confirmatory, and novel ultrasonic features, this study strengthens the ultrasonographic diagnostic criteria for FATWO. The present series represents one of the largest ultrasound cohorts of FATWO and provides more reliable features for preoperative clinical suspicion.
Since FATWO arises from mesonephric duct remnants, it occurs along the migratory path of the Wolffian duct, including the ovarian hilum, mesosalpinx, lateral uterus, and upper vagina. Most lesions are extraovarian, and careful scanning often identifies a normal ovary. Accurate localization is thus beneficial for diagnosis [1, 2, 6].
The sonographic appearance must be differentiated from:
Sex cord-stromal Tumors
Cystic-solid lesions such as granulosa cell tumors may resemble FATWO, but these almost never occur outside the ovary [6, 9].
Fallopian Tube Tumors
Hydrosalpinx appears tubular or sausage-shaped; malignant tubal tumors show irregular masses, papillary projections, and are often associated with effusion [1, 2].
Subserosal or Broad Ligament Leiomyomas
These may exhibit degenerative cystic changes, but their anatomical relationship to the uterus and vascular characteristics differ from FATWO [1, 2].
When a well-defined hypoechoic or mixed adnexal mass is detected, especially with an extraovarian location, FATWO should be included in the differential diagnosis. MRI and CT may offer complementary information, but the gold standard remains surgical pathological diagnosis [4, 8, 12-14].
Recent studies using next-generation sequencing have shown that FATWO lacks common mutations such as KRAS/NRAS, PTEN, PIK3CA, or CTNNB1 [4]. A subset of cases shows STK11 alterations [13]. Most tumors behave benignly, and treatment involves complete surgical resection with long-term follow-up.
The role of chemotherapy, radiotherapy, or hormonal therapy for malignant cases remains unclear [3, 5]. All four patients in this study were alive with no evidence of disease (NED) at the last follow-up (range: 16–83 months).
CONCLUSION
Given the nonspecific imaging features of FATWO, a preoperative diagnosis remains challenging. The present cases suggest that a well-defined extra-ovarian solid or cystic-solid adnexal mass with mild internal blood flow could raise suspicion for FATWO and warrant inclusion in the differential diagnosis.
FATWO should be included in the differential diagnosis of well-circumscribed extraovarian solid or cystic-solid adnexal masses detected by ultrasound, even when the appearance mimics common benign ovarian lesions.
AUTHOR’S CONTRIBUTIONS
The authors confirm contribution to the paper as follows: L. X., K.C., J.W.: Study conception and design; L.Y., L.X.: Data collection; K.C., L.Y., L.X.: Analysis and interpretation of results; L.Y., L.X., J.W.: Draft manuscript. All authors reviewed the results and approved the final version of the manuscript.