Case report: retentive fibroid tumor of the ileocecal region during pregnancy

Introduction

Background

Desmoid type fibromatosis (DTF), also known as aggressive fibromatosis or desmoid tumor, is a rare clonal fibroblastic-myofibroblastic proliferation characterized by infiltrative growth and a high propensity for local recurrence but an absence of metastatic potential. Classified as an intermediate (locally aggressive) soft tissue tumor, DTF has an estimated annual incidence of 2–4 per million population. The pathogenesis is closely linked to dysregulation of the Wnt/β-catenin signaling pathway, with somatic mutations in the CTNNB1 gene (1) serving as key molecular drivers. While these tumors can arise anywhere in the body, pelvic localization is uncommon. Their clinical presentation is highly variable, and diagnosis often poses a significant challenge, relying heavily on histopathological examination and the characteristic nuclear expression of β-catenin on immunohistochemistry.

Rationale and knowledge gap

The diagnostic dilemma intensifies when DTF occurs in pregnant women. The physiological changes of pregnancy, such as uterine enlargement and the common occurrence of pelvic masses like uterine fibroids, can obscure the true nature of an underlying desmoid tumor. Ultrasound, as the first-line imaging modality during pregnancy, has both advantages and limitations (2,3). It often lacks specificity in distinguishing placental abruption from more common conditions, which may lead to misdiagnosis.

While the co-occurrence of DTF and pregnancy has been sporadically reported, cases of ileocecal DTF presenting with direct vascular connections to the uterus, thereby masquerading as a gynecological mass, are exceedingly rare. This unique presentation represents a significant knowledge gap in both the radiological and clinical literature, underscoring the need for heightened awareness and detailed reporting of such atypical cases to inform diagnostic protocols.

Objective

This case report aims to describe the clinical, radiological, and pathological findings of a rare case of massive ileocecal DTF in a pregnant woman that was pre-operatively misdiagnosed as a uterine fibroid. We will elucidate the factors that contributed to the diagnostic confusion and highlight the critical role of immunohistochemistry in achieving a definitive diagnosis. By presenting this case, we intend to emphasize the importance of including DTF in the differential diagnosis of complex pelvic-abdominal masses during pregnancy and to advocate for a multidisciplinary approach to management in such challenging scenarios. We present this article in accordance with the CARE reporting checklist (available at https://acr.amegroups.com/article/view/10.21037/acr-2026-0054/rc).

Case presentation

A 32-year-old pregnant woman came for consultation at 6 weeks of pregnancy, presenting with no symptoms and no gastrointestinal symptoms. At 14 weeks of pregnancy, ultrasound and magnetic resonance imaging (MRI) showed: there was a huge (18.0 cm × 10.3 cm × 16.0 cm) hypoechoic mass above the uterus, accompanied by connecting blood vessels.

Present medical history: regular menstrual cycles with a 30-day cycle; moderate dysmenorrhea (negative). Last menstrual period was March 29, 2019. A home urine pregnancy test performed more than 30 days after the last menstrual period was positive. A pelvic mass was detected at another hospital at 6 weeks of gestation. Exploratory laparoscopy is recommended following termination of pregnancy.

Medical history: underwent resection of an ovarian teratoma in 2014; no history of major trauma or blood transfusions; parity G1P1; underwent one cesarean section in 2015.

Physical examination: temperature 36.7 ℃, pulse 80 bpm, respiratory rate 20 bpm, blood pressure 101/65 mmHg; general condition is good. Gynecological examination: vulva consistent with a married woman; vagina smooth; cervix slightly dilated; a mass approximately 20 cm in size palpable in the abdominal cavity, firm in consistency, with limited mobility; uterine borders indistinct; due to the mass, palpation of the uterine fundus was inconclusive; bilateral adnexal palpation was inconclusive.

Laboratory tests: CA125 61.46 U/mL, alpha fetoprotein (AFP) 18.25 U/mL.

Four ultrasound examiners in the author’s team underwent ultrasound scans, and this ultrasound examiner has 5 to 20 years of experience in gynecological ultrasound.

Ultrasound description: the fetus can be seen in the uterine cavity, the fetal crown-lump length is 2.7 cm, the fetal heart beating can be seen, the placenta is located in the anterior wall of the uterus, mainly in the middle and lower segments, and part reaches the posterior wall, the postplacental space is clearly visible, the placenta below covers the intrauterine opening, and multiple widening veins can be seen in the myometrium. The hypoechoic mass of 18.0 cm × 10.3 cm × 16.0 cm was visible above the uterus, with clear boundary and regular shape. The upper part reached the umbilical level, the left side reached the left midabdomen, and the right side occupied the right abdomen. Blood flow signals were visible inside and around the mass, and the boundary between the mass and the myometrium was not clear. Bilateral ovaries were not clear (Figure 1).

Figure 1 Ultrasonic image of a 32-year-old pregnant woman with a pelvic mass. (A) Fetal head (white arrow) is visible above the inner opening of the cervix. (B) The placenta (white arrow) covering the inner opening of the cervix. (C) The fetus was showed. (D) A hypoechoic mass (white arrow) above the uterus, which was indistinct from the uterus. (E) Clear boundary of mass and visible blood flow signal. (F) Blood flow signal could be seen inside the mass (white arrows), and a thick blood vessel could be seen around the mass, which seemed to be connected with the uterus. (G) Large blood vessels on the right side of the mass (white arrows).

Ultrasound result: second trimester, single fetus, equivalent to 14 W +5 D of pregnancy placenta previa state. Hypoechoic mass of abdominal pelvic cavity above the uterus, uterine fibroids? Please combine clinical.

Pelvic MRI suggested: pregnant uterus, placenta previa, huge abdominal cavity occupying, source undetermined, please combine with other gynecological examinations (Figure 2).

Figure 2 MRI image (A) On coronal T2-weighted images, the right ovary was poorly defined, whereas the left ovary appeared normal in morphology and signal (arrow: left ovary). (B) On sagittal view, the anterior lower edge of the placenta reaches the cervical internal cervix (arrow: lower edge of placenta). (C) Axial T2-weighted imaging demonstrates a mildly hyperintense (arrow: lesion mass). (D) T1WI shows lesion hypointensity. (E) DWI: no restricted diffusion (isointense signal), indicating low cellular density. (F) ADC map: no significant signal drop (ADC =×10⁻³ mm²/s), ruling out diffusion restriction. ADC, apparent diffusion coefficient; DWI, diffusion-weighted imaging; MRI, magnetic resonance imaging; T1WI, T1-weighted imaging.

Multidisciplinary team (MDT): the patient’s mass was huge and required surgical resection. The patient agreed to the surgical treatment and signed the relevant informed consent form to ensure the smooth operation. Contents of consultation in the whole hospital of MDT:

• Placenta centrale is in a low position, placenta accretion is not ruled out. Is there any indication for termination of pregnancy?
• Pelvic mass is huge, where is its source? Is the uterus outward, or is the exoplastic mass pressing on the uterus? How to deal with pelvic mass?

Conclusion of consultation: blood 4 U +200 mL plasma was prepared before surgery, tourniquet was prepared, uterine balloon was prepared, and stone level was low. Please ask the urological department to assist in placing the ureteral stent. Please prepare myxomatology to assist in the operation in advance. Please ask vascular interventional department to prepare uterine artery embolization.

Operation situation

Surgical records: the incision was made in the middle of the lower abdomen, the original cesarean scar was removed, and the abdominal cavity was successfully entered, no free fluid was found, the greater omentum was extensively adherent to the peritoneum of the pelvic cavity, the uterus was enlarged to the size of 16+ weeks gestation, and the texture was soft, the blood vessels in the original cesarean scar in the lower anterior wall of the uterus were open, the right adnexa was missing, the appearance and size of the left ovary were not abnormal, and the left fallopian tube was not abnormal. An upward exploration of the abdominal cavity showed a large tumor, about 30 cm × 25 cm in size, with smooth surface. Two thick blood vessels were seen connected to the surface of the uterus, with a diameter of about 0.3 cm, and no obvious adhesion to the surrounding tissues. The mass was connected to the ileocecal bowel, 5 cm wide, and could be released outside the abdominal cavity without adhesion to the surrounding organs, and no abnormality was observed in the appearance of the appendix. The greater omentum of local adhesion was slightly stiff, with a range of about 5 cm × 10 cm, and no obvious nodular implant disease was observed. Bilateral peritoneum and bilateral diaphragmatic peritoneum showed no tumor implantation. No obvious abnormality was observed on the surface of liver, spleen, gallbladder, stomach and lesser omentum. According to the exploration results, considering that the tumor originated from ileocecal part, the possibility of mesenchymal tumor was not excluded, tumor resection + ileocecal resection + partial omentum resection + hysterectomy was proposed. Please refer to Figure 3 for intraoperative images of the mass, as well as histopathological and immunohistochemical images.

Figure 3 Gross and histopathological features of the lesion. (A) Gross image of the mass. (B) Low magnification, diffuse growth of spindle cells was observed (HE ×10). (C) High magnification, spindle cell tumor with coarse collagen fibers, insignificant cell atypia, and no definite necrosis (HE ×40). (D) Immunohistochemistry of β-catenin showed positive cytoplasm and nuclei (a more specific marker of ligamentous fibromatosis). HE, hematoxylin-eosin.

Pathological results: (pelvic mass) spindle cell tumor, sparse cells, not obvious atypia, combined with immunohistochemistry, considered fibromatosis, size of 22 cm × 18 cm × 13 cm. No tumor was found in the broken end of small intestine and colonic end. No changes were observed in the appendix. No tumor was found in part of the omentum. (Placenta) The placenta in early pregnancy, villus development is reasonable, subfetal membrane focal bleeding and cellulose necrosis, other changes are not observed. Immunohistochemical results: CD34 (−), CD117 (−), S-100 (−), SMA (−), Desmin (−), Dog-1 (−), Ki-67 (+, <10%), β-catenin (nuclear⁺).

Diagnosis: spindle cell tumor in ileocecal part, second trimester (15+ weeks), placental previa, pregnancy with uterine scar. Differential diagnosis: (I) uterine fibroids: the uterus increases can be uniform or irregular, fibroid uterine larger or more disorders. It is mostly hypoechoic, with clear boundaries and distinct distinctions from the surrounding muscle layers. Larger fibroids may be accompanied by posterior echo attenuation, and the internal echoes may be vortex-like or heterogeneous. Circular or semi-circular blood flow signals can be seen around the tumor, and strip-shaped blood flow signals may be present inside. The blood flow originates from the uterus; (II) solid tumors: ovary mostly cystic or pouch or solid, with a clear demarcation between the uterus, visible around the bump on ovarian essence, rear always dense acoustic shadow; (III) small abdominal and retroperitoneal neoplasm: mobility, push technique with retroperitoneal organs (e.g., kidney, pancreas) synchronization. The mass often compresses or pushes the anterior abdominal organs (such as the pancreas, stomach, and intestinal tract), which can encircle and push the inferior vena cava and the abdominal aorta. During breathing, the mass moves synchronously with the vascular movement.

The doctor asked the patient to recheck the ultrasound regularly, and there is no abnormality found in the ultrasound examination semi-annually, and a total of four inspections were conducted. The possibility of recurrence has been ruled out.

All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Helsinki Declaration and its subsequent amendments. Written informed consent was obtained from the patient for publication of this case report and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Discussion

Clinical timeline (Figure 4)

Figure 4 Clinical timeline. LMP, last menstrual period; MDT, multidisciplinary team; MRI, magnetic resonance imaging.

2014: underwent open surgical resection of an ovarian teratoma.

2015: delivered a G1P1 infant via cesarean section.

March 29, 2019: patient’s last menstrual period. Self-administered urine pregnancy test was positive.

6 weeks into pregnancy in 2019 (May 3, 2019): a pelvic mass was detected at another hospital; exploratory laparotomy was recommended following termination of pregnancy.

At 14 weeks and 6 days of pregnancy (July 11, 2019): ultrasound and MRI revealed an 18.0 cm × 10.3 cm × 16.0 cm hypoechoic mass above the uterus; a preliminary diagnosis of uterine fibroid was made. The patient requested termination of pregnancy and removal of the mass.

MDT consultation: a surgical plan was formulated for termination of pregnancy and tumor resection.

On the day of surgery (July 16, 2019, 15 weeks and 4 days into the pregnancy): following termination of pregnancy, an exploratory laparotomy was performed, revealing a massive tumor originating from the ileocecal region with vascular connections to the surface of the uterus. Successful tumor resection, ileocecal resection, and partial omentectomy were performed.

On May 20, 2020, postoperative follow-up revealed no signs of tumor recurrence.

Key findings

This report presents a rare case of a large ileocecal DTF diagnosed during the second trimester of pregnancy. The tumor was of considerable size and located superior to the uterus. Preoperative ultrasonography mischaracterized it as a “hypoechoic mass above the uterus, suggestive of a uterine fibroid”. Its intimate anatomical relationship with the gravid uterus on imaging led to the misdiagnosis. Intraoperatively, the tumor was found to originate from the ileocecal region, with prominent vascular connections to the uterus, while exhibiting minimal adhesion or obstruction to surrounding bowel and other abdominal organs. Following a MDT assessment of maternal and fetal risks, surgical intervention was performed. MDT Discussion contents of the whole MDT hospital consultation: (I) central placental low status, not excluding the possibility of placental implantation, whether there is indication for termination of pregnancy, how to choose the method of termination of pregnancy? (II) the pelvic mass is huge. Where does it come from? Is the uterus facing out, or is it an exogenic mass pressing the uterus? How to deal with pelvic mass? The purpose is: cesarean section to take the fetus, remove the abdominal pelvic cavity mass, prevent massive hemorrhage. Operation time was nearly 5 hours. The diagnosis of ileocecal DTF was confirmed postoperatively by histopathology and immunohistochemistry. This case highlights that when encountering a large pelvic mass during pregnancy, the possibility of a gastrointestinal-origin DTF should be considered. Imaging modalities like ultrasound and MRI alone may be insufficient for accurately determining the tumor’s origin, and multidisciplinary collaboration is crucial for optimizing diagnostic and therapeutic decisions.

Strengths and limitations

The strengths of this case report include: (I) the rare tumor location and growth pattern—primary to the ileocecal region yet with vascular connections to the uterus—mimicked a uterine fibroid in the context of pregnancy, providing a classic example for clinical differential diagnosis; (II) it offers a comprehensive record of the entire process, from the discovery of the pelvic mass and imaging evaluation to MDT discussion and the formulation and execution of surgical strategy, thus clearly illustrating the multidisciplinary decision-making framework in managing tumors during pregnancy; (III) through histopathology and immunohistochemistry, common differential diagnoses such as gastrointestinal stromal tumor (GIST) were ruled out, reinforcing the key diagnostic features of DTF.

This report also has notable limitations: (I) as a single-case study, it cannot represent the general characteristics or prognosis of ileocecal DTF in pregnancy and serves only to provide clinical insights; (II) the postoperative follow-up period for this patient remains limited, precluding a comprehensive assessment of long-term risks for local tumor recurrence and its potential association with the timing of pregnancy termination and the extent of surgery; (III) the inability to obtain more preoperative evidence (e.g., via colonoscopy or image-guided biopsy) restricted the accuracy of preoperative characterization and risk assessment. These shortcomings need to be addressed through larger case series or multicenter studies.

Comparison with similar research

DTF is an intermediate-grade soft tissue tumor arising from fibroblasts/myofibroblasts, exhibiting clinical behavior between benign and malignant. It is characterized by local invasiveness, a high local recurrence rate, but rare distant metastasis. Its pathogenesis is multifactorial, involving genetic, endocrine, and physical factors such as trauma and surgery (4,5). Common sites include the abdominal wall and mesentery, while occurrence in the pelvis, particularly the ileocecal region, is less frequently reported. DTF complicating pregnancy in the ileocecal region is exceedingly rare, mostly documented as isolated case reports. Previous reports indicate that intra-abdominal or pelvic DTF can be misdiagnosed as uterine fibroids or ovarian tumors due to proximity to the uterus or ovaries, especially during pregnancy where uterine enlargement and altered blood supply can further obscure clues to the primary site (6). In the present case, the tumor originated from the ileocecal region, with a clear anatomical relationship to the bowel, yet on imaging it manifested as a large parauterine mass with vascular connections to the uterus, reinforcing the illusion of a uterine fibroid. Furthermore, despite its large size, this tumor did not cause significant intestinal obstruction or digestive symptoms, differing from some reports where enteric DTF may present with obstruction or abdominal pain as initial symptoms (7).

Pathologically, consistent with prior studies, our case showed diffuse or fascicular proliferation of spindle cells, collagen fiber hyperplasia, minimal cellular atypia, and scarce mitotic figures. Immunohistochemically, nuclear positivity for β-catenin served as a relatively specific marker aiding differentiation from GIST (8).

Explanations of findings

The preoperative misdiagnosis of this case as a uterine fibroid can be attributed to several factors. Firstly, the physiological enlargement and hypervascularity of the gravid uterus often lead to the categorization of any adjacent large soft tissue mass on routine ultrasound as a “uterine pathology”, particularly when prominent vessels connect the mass to the uterus, increasing the likelihood of misinterpreting it as a uterine or subserosal fibroid. Furthermore, the literature indicates that uterine sarcomas or malignant tumors that have metastasized to the myometrium are highly vascular, making them prone to misdiagnosis (9,10). Secondly, the ultrasound appearance of DTF lacks specificity, typically presenting as a hypoechoic mass with heterogeneous internal echotexture, including irregular anechoic areas, cable-like slightly hyperechoic strands, speckled strong echoes, and nodular echoes (11), which can resemble degenerating fibroids. In this case, the tumor’s location superior to the uterus, extending into both flanks, made it difficult to clearly delineate its continuity with the ileocecal region on imaging. Concurrently, the clinical context of the second trimester increased diagnostic sensitivity to “pregnancy with uterine fibroids”, while lowering suspicion for “pregnancy with enteric DTF”, further reinforcing the diagnostic bias.

Regarding therapeutic decisions, recent guidelines and consensus increasingly emphasize individualized management and an “active surveillance” strategy for DTF, recommending observation for asymptomatic or slow-growing lesions (12). However, for lesions that are large, anatomically complex, or pose potential risks of obstruction or compression—especially in the setting of pregnancy complicated by high-risk factors like placenta previa—conservative observation alone may not ensure maternal-fetal safety. The decision in this case to perform mid-trimester pregnancy termination combined with concurrent tumor and involved bowel resection, following MDT discussion, represents a compromise balancing maternal-fetal risks, local tumor control, and perioperative bleeding risks. It reflects the difficult choices clinicians often face between “tumor control” and “pregnancy preservation”.

Implications and actions needed

This case suggests that in the diagnosis and management of a large pelvic or abdominal mass during pregnancy, clinicians and radiologists/sonographers should include enteric and mesenteric DTF in the differential diagnosis, alongside the more common considerations of uterine fibroids and ovarian tumors. This is particularly important when the mass has ill-defined borders with the uterus, atypical imaging features, or there is a history of prior abdominal surgery.

For preoperative evaluation, in addition to routine ultrasound and MRI, colonoscopy and image-guided tissue biopsy should be considered, if feasible, to clarify the tumor’s nature and probable origin early, thereby informing the formulation of an individualized treatment plan.

From a management perspective, the handling of DTF in pregnancy should ideally rely on a MDT, including obstetrics, surgical oncology/gastrointestinal surgery, pathology, anesthesiology, interventional radiology, and neonatology, to achieve the optimal balance between maternal-fetal safety and tumor control. For patients with fertility desires who have small, asymptomatic lesions, continuation of pregnancy under close MDT-guided surveillance may be attempted. For lesions that are large, complex in location, or carry risks of bleeding or obstruction, as in this case, thorough communication with the patient and family regarding the benefits, risks, and expected outcomes of pregnancy termination and surgical resection is essential.

Future efforts should focus on accumulating more case series and conducting multicenter retrospective studies to delineate the clinical features and imaging manifestations of DTF in pregnancy, as well as the maternal-fetal outcomes associated with different management strategies. This will provide an evidence base for developing more practical management algorithms and follow-up protocols.

Conclusions

This case illustrates the diagnostic challenge of a rare ileocecal desmoid tumor mimicking a uterine fibroid during pregnancy. It underscores the need for a broad differential diagnosis of pelvic masses in pregnancy and highlights the critical role of multidisciplinary collaboration and immunohistochemical confirmation (β-catenin⁺) in guiding management. Individualized treatment balancing maternal safety and oncologic control remains paramount.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the CARE reporting checklist. Available at https://acr.amegroups.com/article/view/10.21037/acr-2026-0054/rc

Peer Review File: Available at https://acr.amegroups.com/article/view/10.21037/acr-2026-0054/prf

Funding: This study was supported by National Natural Science Foundation of China (No. 62371010); and General Project of Beijing Natural Science Foundation (No. 7262235).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://acr.amegroups.com/article/view/10.21037/acr-2026-0054/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Helsinki Declaration and its subsequent amendments. Written informed consent was obtained from the patient for publication of this case report and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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