Abdominal wall desmoid tumor postcesarean section: A case report

A 35-year-old multiparous woman (G2P2) presented to our institution with a progressively enlarging, painful mass in the infraumbilical region. Her obstetric history included 2 Cesarean sections performed 10 and 4 years prior to presentation. She reported a 1-year history of chronic, noncyclical pain unrelated to menstruation. No family history of FAP or connective tissue disorders was noted. Palpation demonstrated a firm, tender, ill-defined mass (approximately 10 cm) located within the infraumbilical abdominal wall and fixed to the underlying layers beneath the prior surgical scar ( Fig. 1 ). Fig. 1 Clinical photograph showing the palpable infraumbilical mass overlying the prior surgical scar (lateral view). Fig 1 dummy alt text Clinical photograph showing the palpable infraumbilical mass overlying the prior surgical scar (lateral view). Initial ultrasound showed a nonspecific, hypoechoic mass within the rectus abdominis muscle. Pelvic MRI revealed a lobulated mass (94 × 56 × 64 mm) with T1 and T2 hypointensity ( Fig. 2 A), restricted diffusion (Fig. 2C and D), and progressive, homogeneous enhancement (Fig. 2B) . The lesion exhibited infiltrative margins invading the linea alba and rectus sheath with extension toward the anterior uterine wall. Subsequent CT confirmed these findings without providing additional diagnostic value, and an ultrasound-guided core needle biopsy was performed. Fig. 2 Magnetic resonance imaging (MRI) of the abdominal wall mass. (A) Axial T2-weighted image showing a lobulated mass with predominant hypointense signal (arrow). (B) Sagittal T1-weighted fat-saturated postcontrast image demonstrating progressive, homogeneous enhancement and (C, D) Axial diffusion-weighted imaging (DWI) and corresponding apparent diffusion coefficient (ADC) map, revealing restricted diffusion within the lesion (arrows). Fig 2 dummy alt text Magnetic resonance imaging (MRI) of the abdominal wall mass. (A) Axial T2-weighted image showing a lobulated mass with predominant hypointense signal (arrow). (B) Sagittal T1-weighted fat-saturated postcontrast image demonstrating progressive, homogeneous enhancement and (C, D) Axial diffusion-weighted imaging (DWI) and corresponding apparent diffusion coefficient (ADC) map, revealing restricted diffusion within the lesion (arrows). Histopathological analysis showed a proliferation of bland, spindle-shaped cells in long, interlacing fascicles within an abundant collagenous stroma, without significant cellular atypia or increased mitotic activity ( Fig. 3 ). Nuclear beta-catenin expression confirmed the diagnosis, whereas estrogen (ER) and progesterone (PR) receptor staining were negative. A multidisciplinary tumor board recommended conservative management with NSAIDs and active surveillance, given the tumor's biology and patient preference. Follow-up confirmed symptomatic relief and stable disease on imaging. Fig. 3 Histopathological examination (H&E, 200x) showing a proliferation of bland, spindle-shaped cells arranged in long, interlacing fascicles within an abundant collagenous stroma. Nuclei are elongated and regular without significant atypia or mitosis, characteristic of desmoid-type fibromatosis. Fig 3 dummy alt text Histopathological examination (H&E, 200x) showing a proliferation of bland, spindle-shaped cells arranged in long, interlacing fascicles within an abundant collagenous stroma. Nuclei are elongated and regular without significant atypia or mitosis, characteristic of desmoid-type fibromatosis.

ASA: Conceived and designed the case report, collected the data, wrote the manuscript. MS, CM, FZL, YO, RL, SA: Participated in the imaging data analysis and interpretation, and critically reviewed the manuscript. NE, HH: Managed the surgical aspects of the case and critically reviewed the manuscript for clinical accuracy. All authors have read and approved the final manuscript.

All procedures performed in this study involving a human participant were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. 1. Which immunohistochemical marker is most specific for confirming the diagnosis of desmoid-type fibromatosis? A) Estrogen Receptor (ER) B) Progesterone Receptor (PR) C) Nuclear beta-catenin D) CD117 (c-kit) Answer: C. Nuclear translocation and accumulation of beta-catenin, resulting from CTNNB1 or APC mutations, is a hallmark of DTF and serves as the definitive diagnostic marker. 2. What is the primary reason for the current shift toward conservative management (active surveillance) in abdominal wall DTF? A) These tumors have a high metastatic potential. B) Postsurgical recurrence rates are high (20%-30%) and spontaneous stabilization can occur. C) Surgery is technically impossible in the abdominal wall. D) DTF always regresses completely without treatment. Answer: B. Due to significant local recurrence rates after surgery and the documented biological tendency of some tumors to stabilize or regress spontaneously, active surveillance is now the preferred first-line approach. 3. Which imaging modality is considered the gold standard for characterizing the tissue composition and infiltrative extent of a desmoid tumor? A) Grayscale ultrasound B) Contrast-enhanced CT C) Magnetic resonance imaging (MRI) D) Positron emission tomography (PET-CT) Answer: C. MRI provides superior soft-tissue contrast, allowing for the identification of collagen-rich areas (T2 hypointensity) and precise mapping of fascial and muscular infiltration. Which immunohistochemical marker is most specific for confirming the diagnosis of desmoid-type fibromatosis? A) Estrogen Receptor (ER) B) Progesterone Receptor (PR) C) Nuclear beta-catenin D) CD117 (c-kit) Answer: C. Nuclear translocation and accumulation of beta-catenin, resulting from CTNNB1 or APC mutations, is a hallmark of DTF and serves as the definitive diagnostic marker. What is the primary reason for the current shift toward conservative management (active surveillance) in abdominal wall DTF? A) These tumors have a high metastatic potential. B) Postsurgical recurrence rates are high (20%-30%) and spontaneous stabilization can occur. C) Surgery is technically impossible in the abdominal wall. D) DTF always regresses completely without treatment. Answer: B. Due to significant local recurrence rates after surgery and the documented biological tendency of some tumors to stabilize or regress spontaneously, active surveillance is now the preferred first-line approach. Which imaging modality is considered the gold standard for characterizing the tissue composition and infiltrative extent of a desmoid tumor? A) Grayscale ultrasound B) Contrast-enhanced CT C) Magnetic resonance imaging (MRI) D) Positron emission tomography (PET-CT) Answer: C. MRI provides superior soft-tissue contrast, allowing for the identification of collagen-rich areas (T2 hypointensity) and precise mapping of fascial and muscular infiltration.

Written informed consent was obtained from the patient for the publication of this case report and accompanying images.

Abdominal wall desmoid-type fibromatosis should be suspected in women presenting with a solid, noncyclical parietal mass and a history of Cesarean section. MRI is the superior imaging modality for characterization and local staging. Diagnosis is confirmed by nuclear beta-catenin positivity. Management should be individualized, with a growing emphasis on conservative strategies such as active surveillance and NSAIDs for symptomatic control, reserving surgery for refractory or threatening cases. Teaching point: Abdominal wall desmoid tumors post-Cesarean section can present with a significant delay; definitive diagnosis requires histopathology with nuclear beta-catenin staining, as imaging findings can be nonspecific and mimic other conditions like scar endometriosis.

This case illustrates a classic sporadic abdominal wall DTF, where the 4-year latency following Cesarean section aligns with reported intervals ranging from months to several years [ 5 , 6 ]. The differential diagnosis for a painful abdominal wall mass in this demographic is broad. Scar endometriosis is the primary mimic, typically presenting with cyclical pain exacerbating during menstruation—a feature absent in our patient [ 8 ]. Imaging plays a pivotal role in differentiation. While ultrasound is a useful first-line tool, MRI is the modality of choice. The signal characteristics observed in this case—specifically low signal intensity on T2-weighted images—are suggestive of high collagen content and fibrosis, a hallmark of DTF, although signal heterogeneity is common [ 4 ]. The infiltrative pattern observed on MRI, involving the rectus sheath and linea alba, correlates with the locally aggressive nature of the disease [ [13] , [14] ]. Histopathology remains the gold standard for diagnosis. The identification of nuclear beta-catenin accumulation is highly specific for DTF, resulting from CTNNB1 or APC gene mutations that prevent protein degradation. This mechanism leads to nuclear translocation and constitutive activation of the Wnt signaling pathway [ 9 ]. Despite the established association with pregnancy history, the tumor in this patient demonstrated negative ER and PR expression. This suggests that Wnt pathway dysregulation, rather than current hormonal status, remains the primary driver of tumor progression in some cases [ [9] , [15] ]. Management has shifted from aggressive surgery toward active surveillance or medical therapy [ 10 ], due to high postsurgical recurrence rates (20-30%) and the potential for spontaneous stabilization or regression [ 11 , 16 ]. In symptomatic patients, medical therapies including NSAIDs, hormonal agents (e.g., tamoxifen), or low-dose chemotherapy are validated options [ 11 , 12 ]. In this case, the use of NSAIDs provided adequate symptom control, validating the decision to defer surgery.

Desmoid-type fibromatosis (DTF) is a rare monoclonal, fibroblastic proliferation characterized by infiltrative growth and a tendency for local recurrence, but lacking metastatic potential [ 1 , 2 ]. While DTF can occur sporadically or in association with Familial Adenomatous Polyposis (FAP), abdominal wall locations are strongly linked to prior surgical trauma and the hormonal environment of pregnancy [ [2] , [3] , [4] ]. Specifically, the trauma of Cesarean sections is a well-documented risk factor [ 5 , 6 ]. Diagnosing abdominal wall DTF in the postpartum period presents a specific challenge, as it mimics other postoperative complications such as scar endometriosis, hematomas, or sarcomas [ 4 , 7 ]. Accurate diagnosis relies heavily on Magnetic Resonance Imaging (MRI) for tissue characterization and definitive histopathology demonstrating nuclear beta-catenin expression [ 8 , 9 ]. Management paradigms for DTF have shifted significantly in recent years. Current guidelines increasingly favor conservative approaches—including active surveillance and medical therapy—over upfront radical surgery, aiming to minimize morbidity without compromising oncological outcomes [ [10] , [11] , [12] ]. We present a case of abdominal wall DTF diagnosed 4 years post-Cesarean section, managed successfully with a conservative approach.