An Unusual Site of Mature Cystic Teratoma in the Fallopian Tube: A Rare Case Report

A 34-year-old, nulligravida (P0A0, married for 6 months) was referred from a regional hospital with a diagnosis of left ovarian endometrioma and right ovarian cystoma. She presented with intermittent left lower abdominal pain for one month, markedly exacerbated during menstruation, particularly on days 3 to 4, and was severe enough to cause diaphoresis and functional limitation. She also reported a progressively enlarging lower abdominal mass over the preceding six months. There was no history of weight loss, abnormal vaginal bleeding, urinary or bowel symptoms, or previous surgery. Menstrual cycles were regular, and the patient desired future fertility. Family history was notable for a maternal ovarian cyst requiring surgery without malignancy. Preoperative transvaginal ultrasonography ( Figure 1 ) demonstrated. A cystic mass with a dermoid plug (echogenic mural nodule) measuring approximately 2.46×2.17 × 2.20 cm. The right ovary demonstrated a large tubular anechoic mass with incomplete septations and a positive waist sign, measuring approximately 15.61×6.83 × 8.58 cm, suggestive of hydrosalpinx. Additionally, a cystic lesion with ground-glass appearance measuring 4.98×4.26 × 4.17 cm was noted, adherent to the posterior uterus, consistent with an endometriotic cyst. The left ovary showed a cystic lesion with ground-glass appearance measuring 2.47×2.04 × 2.18 cm. The sliding sign was negative, suggesting pelvic adhesions. Figure 1 Ultrasound findings. Uterus with normal size and density ( A ), Dermoid cyst ( B ), bilateral endometriomas ( C and D ) and suggestive of hydrosalpinx ( E ). ## Critique of the available answer - The image is not a single ultrasound; it is a composite containing five numbered sub-images, so the response fails to enumerate and describe each sub-image separately. - The response uses prohibited first-person style and capability language (for example, “too small to read,” “preventing accurate transcription”). - The response does not describe the actual observable structures, overlays, calipers, labels, or layout. - The response does not follow the required sub-image labeling format (A), B), C), D), E)). - The response omits multiple clearly readable on-image text labels (for example, “RIGHT DERMOID CYT,” “LEFT ENDOMETRIOMA,” “RIGHT HYDROSALPINX”). ## Long description (compliant) A) The image A showing a grayscale ultrasound frame pair placed side-by-side within the sub-image labeled “1” at the top-left. Multiple yellow caliper markers and dotted measurement lines overlay the anatomy. A small yellow measurement table with multiple rows is located at the lower-right corner of this sub-image. White system text is present near the upper-right corner of the ultrasound frame area. B) The image B showing a grayscale ultrasound frame pair placed side-by-side within the sub-image labeled “2” at the top-center. Yellow caliper markers and dotted measurement lines are placed across a rounded internal region. Yellow text near the lower middle reads “RIGHT DERMOID CYT.” A small yellow measurement table with multiple rows is located at the lower-right corner of this sub-image. White system text is present near the upper-right corner of the ultrasound frame area. C) The image C showing a grayscale ultrasound frame pair placed side-by-side within the sub-image labeled “3” at the top-right. Yellow caliper markers and dotted measurement lines overlay a rounded region. Yellow text near the lower middle reads “LEFT ENDOMETRIOMA.” A small yellow measurement table with multiple rows is located at the lower-right corner of this sub-image. White system text is present near the upper-right corner of the ultrasound frame area. D) The image D showing a grayscale ultrasound frame pair placed side-by-side within the sub-image labeled “4” at the bottom-left. A large rounded structure occupies most of each frame, with yellow caliper markers placed at multiple boundary points and dotted measurement lines spanning the structure. A small yellow measurement table with multiple rows is located at the lower-right corner of this sub-image. White system text is present near the upper-right corner of the ultrasound frame area. E) The image E showing a grayscale ultrasound frame pair placed side-by-side within the sub-image labeled “5” at the bottom-right. A large dark fluid-filled region occupies much of each frame, with yellow caliper markers and dotted measurement lines spanning the dark region. Yellow text near the lower middle reads “RIGHT HYDROSALPINX.” A small yellow measurement table with multiple rows is located at the lower-right corner of this sub-image. White system text is present near the upper-right corner of the ultrasound frame area. Grayscale ultrasound with 5 sub-images, caliper measurements, annotations and tables on black background. Ultrasound findings. Uterus with normal size and density ( A ), Dermoid cyst ( B ), bilateral endometriomas ( C and D ) and suggestive of hydrosalpinx ( E ). Laboratory evaluation, such as routine hematology panels and and normal coagulation factor, showed within normal limits. The other reproductive hormones, including Anti-Müllerian Hormone (AMH) (2.39 ng/mL), were within normal reference limits. Hysterosalpingography examination was performed with the conclusion: the right fallopian tube was associated with hydrosalpinx. The left fallopian tube was non-patent (tubal occlusion). Based on the clinical and imaging findings, the patient underwent laparoscopic exploration. Intraoperatively ( Figure 2 ), laparoscopic evaluation of the pelvic cavity revealed bilateral endometriomas. Chromotubation (tubal patency test) demonstrated bilateral tubal spill, indicating tubal patency, which differed from the previous hysterosalpingography interpretation. A large cystic mass was identified in the left adnexal region. In the Trendelenburg position, the mass was displaced superiorly, revealing a 15×15 cm cystic lesion suspected to originate from the left paratubal area. Initial laparoscopic access was achieved using a 10-mm trocar inserted in the left hypogastrium, penetrating the cyst and allowing drainage of serous fluid. Figure 2 Intraoperative findings: laparoscopic view of the pelvic cavity showed bilateral endometriomas ( A ), (L: left ovary, and R: right ovary), bilateral tubal spill (patency test) ( B ). After further identification and reposition, a large cystic mass originating from the left adnexal region ( C ), (with asterisk, *), with a component of hair identified within the mass, suggestive of a dermoid cyst ( D ). Panel A shows bilateral endometriomas involving the ovaries, labeled “L” for left ovary and “R” for right ovary. Surgical instruments are positioned near the ovarian structures. Panel B shows bilateral tubal spill during a tubal patency test, with an arrow indicating dye or fluid spill from the fallopian tube. Panel C shows a large cystic mass originating from the left adnexal region, marked with an asterisk symbol. Panel D shows surgical dissection of the cystic mass with hair-like material within the lesion, consistent with a dermoid cyst. Four-panel intraoperative laparoscopic images labeled A through D showing findings within the pelvic cavity. Intraoperative findings: laparoscopic view of the pelvic cavity showed bilateral endometriomas ( A ), (L: left ovary, and R: right ovary), bilateral tubal spill (patency test) ( B ). After further identification and reposition, a large cystic mass originating from the left adnexal region ( C ), (with asterisk, *), with a component of hair identified within the mass, suggestive of a dermoid cyst ( D ). Further exploration revealed a normal-sized uterus. A 7×4 cm cystic mass was noted in the right ovary and a 6×4 cm cystic mass in the left ovary. Both masses were adherent to the posterior pelvis and posterior uterine surface, consistent with bilateral endometriomas and grade II–III pelvic adhesions. During adhesiolysis, hair was identified within the cyst cavity, which had initially been presumed to be a paratubal cyst, suggesting a dermoid cyst. Due to the large size of the dermoid cyst, the procedure was subsequently converted to laparotomy. Intraoperatively (laparotomy, shown in Figure 3 ), a 16×15 x 4 cm grayish-white cystic mass with a regular smooth surface was seen originating from the left Fallopian tube, and left salpingectomy was performed. Bilateral adhesiolysis and cystectomy of both endometriomas were completed, evacuating approximately 70 mL (right) and 40 mL (left) of chocolate-colored fluid, with complete removal of the cyst capsules. Estimated blood loss was approximately 100 mL, with intraoperative urine output of 300 mL. The patient tolerated the procedure well and was transferred to recovery in stable condition. Figure 3 Laparotomy exploration findings: a left cyst mass originating from the left Fallopian tube ( A ), with a smooth external surface was found ( B ). Panel A shows the large cystic mass during laparotomy exploration, attached to the left adnexal region. The mass has a rounded shape with a smooth external surface and prominent superficial blood vessels. Surrounding surgical tissue and instruments are present in the operative field. Panel B shows the excised cyst mass placed on a measurement grid. The specimen maintains a smooth outer surface with areas of blood staining and attached tissue near one edge. Two-panel surgical photographs showing a large left Fallopian tube cyst mass with a smooth external surface. Laparotomy exploration findings: a left cyst mass originating from the left Fallopian tube ( A ), with a smooth external surface was found ( B ). Histopathological examination ( Figure 4 ) of the left fallopian surgical specimen revealed a MCT arising from the left fallopian tube. The cyst wall is composed of ectodermal components, characterized by stratified squamous epithelium with bland nuclei. Mesodermal elements were identified, including cartilage with normal-appearing chondrocytes and smooth muscle tissue without atypia. Endodermal components were also present, represented by respiratory-type epithelium with unremarkable nuclei. No primitive neuroectodermal structures were observed. The subepithelial layer showed fibrous collagenous stroma with infiltration of lymphocytes and histiocytes. The cyst lumen contained keratinous debris, and adnexal skin structures were identified within normal limits. No evidence of malignancy was detected. Figure 4 Histopathological results (H&E stain, ×40). Ectoderm ( A and B ): ( A ) Hair shafts (black arrow) with surrounding foamy macrophages (white arrow) and multinucleated giant cell reaction (yellow arrow). ( B ) Walthard cell nests (asterisk, *) and glial cells nearby are present. Mesoderm ( C – E ): ( C ) Chondroid matrix, ( D ) Lamellar bone, ( E ) Fat cells (double dagger, ‡), and nerve bundle (dagger, †). Endoderm ( F and G ): ( F ) Glands lined by gastric-type (red arrow) and colonic-type epithelium are seen, ( G ) seromucous glands (delta, Δ). ( H ) showed a tubal structure lined by columnar epithelium with underlying fibromuscular stroma. Image A: Hematoxylin and eosin stained micrograph with purple cellular tissue and pink stromal bands. Arrows indicate pale structures and lumina. Image B: Dominated by pink, wavy stroma and darker purple tissue. Asterisk marks a focal region. Image C: Large blue-purple tissue with pale spaces, bordered by pink stroma. Image D: Dark pink tissue fragments diagonally crossing, with pink wavy stroma. Image E: Pink fibrous stroma with vacuole-like spaces. Symbols mark dense structures. Image F: Dense purple glandular structures with lumina. Red arrow points to duct-like structure. Image G: Clustered gland-like units with pale lumina and dark purple rings. Labels mark units. Image H: Large star-shaped lumen with dark purple lining, surrounded by pink stroma and smaller glandular profiles. Histopathology figure: 8 micrographs (A-H), H&E stain, glandular/stromal patterns, annotated on pale background. Histopathological results (H&E stain, ×40). Ectoderm ( A and B ): ( A ) Hair shafts (black arrow) with surrounding foamy macrophages (white arrow) and multinucleated giant cell reaction (yellow arrow). ( B ) Walthard cell nests (asterisk, *) and glial cells nearby are present. Mesoderm ( C – E ): ( C ) Chondroid matrix, ( D ) Lamellar bone, ( E ) Fat cells (double dagger, ‡), and nerve bundle (dagger, †). Endoderm ( F and G ): ( F ) Glands lined by gastric-type (red arrow) and colonic-type epithelium are seen, ( G ) seromucous glands (delta, Δ). ( H ) showed a tubal structure lined by columnar epithelium with underlying fibromuscular stroma. The other specimens with histopathological description: bilateral ovarian endometrioma: demonstrated fibrous connective tissue stroma with infiltration of lymphocytes and histiocytes, accompanied by vascular dilatation. Endometrial-type stroma was identified, along with hemosiderin deposition and hemosiderin-laden macrophages. No evidence of malignancy was observed. Based on the combined clinical, imaging, and histopathological data, the final diagnosis: Mature cystic teratoma a.r left fallopian tube; bilateral endometriomas; superficial endometriosis lesions; bilateral patent fallopian tubes; grade II–III pelvic adhesions.

Mature cystic teratoma (MCT), commonly referred to as a dermoid cyst, represents the most frequent benign ovarian germ cell tumor, accounting for 10–20% of all ovarian neoplasms and up to 60% of benign germ cell tumors in women of reproductive age. 1 , 2 Histologically, MCTs consist of well-differentiated tissues from embryonic germ layers. They commonly occur during the second to fourth decades of life and are often incidentally detected or identified during evaluation of pelvic pain or an adnexal mass. 3 In contrast, MCT arising from the fallopian tube or paratubal region is exceptionally rare. Primary tubal teratomas constitute less than 1% of teratomas within the female genital tract, with evidence largely limited to isolated case reports and small case series. 4 The rarity of this entity creates diagnostic challenges, especially in differentiating tubal or paratubal lesions from ovarian masses preoperatively. Its embryologic origin is thought to involve abnormal migration or sequestration of primordial germ cells along the Müllerian tract. 5 Tubal and paratubal teratomas are often asymptomatic and incidentally detected on imaging or during surgery. Symptomatic patients may present with lower abdominal pain with the imaging findings frequently mimic ovarian dermoid cysts, making definitive diagnosis dependent on intraoperative or histopathological evaluation. 6 Although malignant transformation occurs in approximately 1–2% of ovarian MCTs, most commonly into squamous cell carcinoma, 7 the malignant potential of tubal or paratubal teratomas remains uncertain due to their extreme rarity. Surgical excision remains the treatment of choice, with fertility preservation prioritized in reproductive-aged women. Several embryological theories have been proposed regarding the origin of tubal teratomas, including aberrant migration of primordial germ cells, ectopic displacement of germ cells during embryogenesis, and development from supernumerary ovarian tissue adjacent to the fallopian tube. However, the exact pathogenesis remains unclear due to the scarcity of reported cases. 8 This case report aims to describe the characteristics of a rare tubal mature cystic teratoma and to contribute to the limited literature on this uncommon adnexal pathology. This report was prepared in accordance with the CARE reporting guidelines.

This case emphasizes that mature cystic teratoma of the fallopian tube, albeit exceedingly rare, should be considered in the differential diagnosis of complex adnexal masses presumed to be ovarian in origin. Preoperative imaging and clinical findings may not reliably determine the anatomical origin of the lesion, particularly in the presence of concomitant pathologies such as endometriosis, hydrosalpinx, and pelvic adhesions, which may obscure diagnosis and complicate surgical planning. Therefore, meticulous intraoperative evaluation and histopathological confirmation remain essential for establishing a definitive diagnosis. Complete surgical excision with preservation of fertility should be prioritized in reproductive-aged women whenever feasible. Recognition of this rare entity and awareness of potential coexisting pelvic disease are essential for accurate diagnosis, appropriate operative planning, and optimal clinical outcomes.

Mature cystic teratoma (MCT), commonly referred to as a dermoid cyst, represents the most common benign ovarian germ cell tumor in women of reproductive age. 1 , 2 In contrast fallopian tube teratomas are extremely rare, with fewer about 70 cases recorded in the literature to date. 7 , 9 , 10 Similar to ovarian MCTs, these lesions are generally benign and predominantly occur during reproductive age; however, preoperative diagnosis remains challenging because most cases mimic ovarian adnexal masses. 11 In the present case, preoperative imaging suggested bilateral endometriomas, hydrosalpinx, and dermoid cyst, whereas intraoperative findings demonstrated a large cystic mass originating from the left fallopian tube rather than the ovary. Similar to previously reported cases, definitive diagnosis was established only intraoperatively and confirmed histopathologically. A comparison of previously reported extra-ovarian and fallopian tube teratoma cases is summarized in Table 1 . Table 1 Previously Reported Cases of Extra Ovarian Mature Cystic Teratoma Author/Year Age Presentation Preoperative Diagnosis Intraoperative Finding Size (cm) Management Key Point Baek et al, 2016 12 31 Adnexal mass Ovarian cyst Synchronous ovarian and tubal teratoma 2 x 2 x 15 Salpingectomy + ovarian cystectomy Coexisting ovarian pathology Chou et al, 2020 11 38 Infertility, abdominal discomfort Ovarian teratoma/teratocarcinoma Fimbrial teratoma 11 x 8 x 6 Laparotomy + excision Large fimbrial lesion mimicked ovarian tumor Kayastha et al, 2023 10 – Case 1 32 Infertility Ovarian dermoid cyst Tubal teratoma 1 x1 Laparoscopic excision Incidentally detected Kayastha et al, 2023 10 – Case 2 28 Incidental during cesarean section None Tubal teratoma Small teratoma Excision Incidental surgical finding Yang et al, 2023 13 71 Pelvic mass Adnexal mass Extragonadal MCT 7.4 x 5.4 Laparoscopic surgical excision Separate from ovaries Padula et al, 2024 14 40 Pelvic pain Tubal MCT suspected preoperatively Intratubal MCT 11 x 6 Salpingectomy Rare preoperative radiologic diagnosis Present case 34 Cyclical pelvic pain, abdominal mass Bilateral endometrioma, hydrosalpinx, dermoid cyst Left fallopian tube MCT with endometriomas 16 × 15 x 4 Salpingectomy + cystectomy Separate from ovaries, Diagnostic challenge due to concomitant pelvic pathology Previously Reported Cases of Extra Ovarian Mature Cystic Teratoma In the present case, preoperative hysterosalpingography (HSG) suggested left tubal occlusion and right hydrosalpinx, whereas intraoperative chromotubation demonstrated bilateral tubal patency This discrepancy may be explained by transient tubal spasm, technical limitations during HSG examination, or interpretation variability, all of which are recognized limitations of HSG assessment Intraoperative chromotubation under direct visualization is considered more reliable for evaluating tubal patency This finding highlights the importance of correlating radiologic findings with intraoperative assessment to avoid diagnostic misinterpretation. Dermoid cyst arises from totipotent primordial germ cells (composed of at least two, and frequently all three, embryonic germ layers). Ectodermal components predominate, accounting for the frequent presence of sebaceous material, keratin, hair follicles, and occasionally teeth or bone within the cyst cavity. 1 The characteristic Rokitansky protuberance (dermoid plug) corresponds to a mural nodule containing various tissue elements. Although the vast majority of MCTs are benign, malignant transformation occurs in approximately 1–2% of cases, most commonly to squamous cell carcinoma, and is more frequently observed in postmenopausal women. 2 , 7 Clinically, dermoid cysts are frequently asymptomatic and discovered incidentally during pelvic examination or routine ultrasonography. When symptomatic, patients may present with chronic pelvic pain, abdominal distension, or a palpable adnexal mass. Acute abdominal pain is most associated with adnexal torsion, a well-recognized complication attributable to the cyst’s lipid-rich content and relative buoyancy. 9 , 15 Less common complications include rupture leading to chemical peritonitis, infection, and, rarely, autoimmune hemolytic anemia. Serum tumor markers such as AFP, β-hCG, LDH, and CA-125 may be evaluated to exclude malignant germ cell tumors; however, these markers are typically within normal limits in MCT. 2 , 16 Preoperative diagnosis of dermoid cysts primarily relies on imaging studies, with ultrasonography serving as the first-line modality. Dermoid cysts characteristically appear as complex adnexal masses with echogenic components and posterior acoustic shadowing. 17 Pathognomonic sonographic signs include the “tip of the iceberg” sign (dense echogenic material obscuring deeper structures), the “dermoid mesh” sign (multiple hyperechoic linear interfaces caused by hair fibers), and a hyperechoic Rokitansky nodule projecting into the cyst lumen. 18 Fat–fluid levels may also be identified. Doppler examination typically demonstrates minimal to moderate internal vascularity unless complications such as torsion occur. 17 , 19 In cases where ultrasonographic findings are inconclusive, additional imaging modalities such as computed tomography (CT) or magnetic resonance imaging (MRI) may be useful to identify intralesional fat and improve diagnostic accuracy. 20 Despite these imaging characteristics, distinguishing between ovarian and extra-ovarian teratomas remains challenging preoperatively. Fallopian tube teratomas are particularly difficult to diagnose before surgery because they often present as adnexal masses that mimic ovarian dermoid cysts or other cystic lesions. As a result, the definitive diagnosis is frequently established only during surgical exploration or after histopathological examination. Management is individualized based on age, symptomatology, tumor size, imaging characteristics, and reproductive considerations. When the initial examination results indicate a high suspicion of ovarian germ cell tumours, surgical exploration is recommended to confirm the diagnosis and complete disease staging. Surgical removal is generally recommended for symptomatic lesions, cysts ≥5–6 cm because of torsion risk, rapidly enlarging masses, suspicion of malignancy, or postmenopausal status. 1 , 2 In reproductive-age women, laparoscopic ovarian cystectomy with maximal preservation of ovarian tissue is the preferred approach. Intraoperative rupture should be minimized to prevent peritonitis; copious peritoneal irrigation is recommended if spillage occurs. Oophorectomy may be considered in postmenopausal women or when ovarian preservation is not feasible. In the present case, the patient initially presented with symptoms suggestive of endometriosis and adnexal cystic masses. Preoperative imaging suggested bilateral endometriomas, hydrosalpinx, and a dermoid cyst. However, intraoperative findings revealed a large cystic mass originating from the left fallopian tube rather than the ovary. The presence of hair within the cyst cavity raised suspicion for a dermoid cyst, prompting conversion from laparoscopy to laparotomy for safe removal of the mass. Histopathological examination subsequently confirmed the diagnosis of MCT arising from the fallopian tube, demonstrating ectodermal, mesodermal, and endodermal components without evidence of malignancy. A comparison of previously reported extra-ovarian and fallopian tube teratoma cases is summarized in Table 1 . However, the coexistence of bilateral endometriomas, pelvic adhesions, and suspected hydrosalpinx in this patient further complicated preoperative localization of the mass and contributed to the diagnostic challenge. This case highlights the diagnostic challenge associated with rare adnexal tumors such as fallopian tube teratomas. Preoperative imaging may not reliably distinguish between ovarian and extra-ovarian origins, particularly when concurrent gynecological conditions such as endometriosis or hydrosalpinx are present. Therefore, intraoperative assessment and histopathological confirmation remain essential for establishing the definitive diagnosis. In this case, removal of the affected fallopian tube with preservation of the ovaries allowed adequate treatment while maintaining the patient’s fertility prospects. This case report has several limitations. First, additional imaging modalities such as CT or MRI were not performed preoperatively, which might have improved characterization of the adnexal mass and its anatomical origin. Second, serum tumor markers were not evaluated because imaging findings strongly suggested benign pathology without suspicious malignant features. Finally, as a single case report of a rare condition, the findings may not be generalizable to broader populations. Overall, this case contributes to the limited literature on fallopian tube MCT and emphasizes the importance of considering rare extra-ovarian teratomas in the differential diagnosis of complex adnexal masses, particularly in patients with coexisting gynecological pathology.