Dramatic regression of an inflammatory urachal pseudotumor mimicking adenocarcinoma under conservative medical therapy

Abstract

Inflammatory pseudotumors (IPTs) are rare benign lesions that often mimic malignancy, posing diagnostic and therapeutic challenges, especially in uncommon sites such as the urachus. We report a 66-year-old woman with a firm peri-umbilical mass initially suggestive of invasive urachal adenocarcinoma. Despite aggressive imaging features, biopsy revealed fibro-inflammatory tissue without neoplasia. The lesion regressed almost completely under antibiotics and anti-inflammatory therapy, with sustained remission. This case illustrates that IPTs, even when radiologically aggressive, may respond to conservative management, underscoring the importance of multidisciplinary evaluation and follow-up to avoid unnecessary radical surgery.

1. Introduction

Inflammatory pseudotumors (IPTs) are rare benign lesions with a prominent inflammatory component that frequently mimic malignant tumors in both their clinical and radiologic presentation.^1,2 Their aetiology remains uncertain, with infectious, autoimmune, and post-inflammatory mechanisms all being implicated.² Because they often appear as aggressive, infiltrative masses, IPTs can easily lead to diagnostic confusion and even radical surgery when malignancy is suspected.1, 2, 3 Although surgical resection has long been considered the standard of care, conservative treatments such as antibiotics or anti-inflammatory drugs have occasionally resulted in regression. However, complete resolution of a large, aggressive-appearing lesion under medical therapy alone is exceptional, particularly in unusual sites such as the urachus.

2. Case presentation

A 66-year-old woman with diabetes and mild overweight presented with a one-month history of a peri-umbilical abdominal mass and abdominal heaviness. The mass, located in the anterior abdominal wall centered on the umbilicus, was firm, ill-defined, measured about 6 cm, and produced a visible bulge.

Contrast-enhanced abdominopelvic CT (Fig. 1) revealed a subparietal soft tissue lesion with irregular infiltrative margins invading the rectus abdominis muscles (Fig. 1a). It measured 53 × 35 × 60 mm, enhanced heterogeneously, appeared to infiltrate the bladder dome, and followed the urachal tract (Fig. 1b). Surrounding micronodular infiltration of the epiploic fat and enhancing subparietal nodules suggested peritoneal carcinomatosis (Fig. 1c). The findings were most consistent with an infiltrating urachal adenocarcinoma. A chest CT scan was performed and showed no secondary suspect lesions.

Fig. 1.

Contrast-enhanced abdominopelvic CT images. a: Axial section showing a heterogenous enhanced lesion with irregular infiltrative margins invading the rectus abdominis muscles. b: Sagittal reconstruction demonstrating the extension of the lesion along the urachal tract and the infiltration the bladder dome. c: Axial section revealing micronodular epiploic fat infiltration and enhancing subparietal nodules consistent with peritoneal carcinomatosis.

Ultrasound-guided percutaneous biopsies were performed, showing a fibro-inflammatory reaction with abundant myofibroblastic proliferation, dense plasmacytoid infiltrate, foamy histiocytes, necrosis, and suppuration (Fig. 2). The immunohistochemistry profile was added: spindle myofibroblastic cells were positive for smooth muscle actin (SMA) and CD68, and negative for ALK-1 and cytokeratin; mitoses were rare and cellular atypia minimal, consistent with a benign inflammatory pseudotumor rather than an inflammatory myofibroblastic tumor (IMT). Because bladder dome involvement was suspected, cystoscopy was carried out, revealing a 3 cm nodule that was resected. Histology confirmed inflammatory mucosal changes without neoplasia.

Fig. 2.

Histological section (H&E, × 200) showing a myofibroblastic proliferation with mixed inflammatory infiltrate composed of lymphocytes, plasma cells, and foamy histiocytes, consistent with an inflammatory pseudotumor.

Despite these results, suspicion of malignancy remained high, and a delayed surgical resection was planned. Meanwhile, the patient was prescribed celecoxib 100 mg twice daily and amoxicillin–clavulanic acid 1 g three times daily for one month. The antibiotic choice was guided by a positive urine culture for Escherichia coli sensitive to amoxicillin–clavulanate.

Follow-up CT after medical therapy showed near-complete regression, with only a 12 × 12 × 23 mm fusiform residual lesion at the urachal remnant (Fig. 3). The suspected peritoneal nodules and the palpable mass had disappeared. Based on this clinical and radiological improvement, and negative histology, a diagnosis of inflammatory urachal pseudotumor responsive to conservative therapy was made. Surgery was deferred, and medical treatment stopped.

Fig. 3.

Axial contrast-enhanced CT scan at one-month follow-up showing near complete regression of the previously infiltrative urachal mass.

At three months, the patient was asymptomatic, with unchanged residual findings on CT. Long-term follow-up is ongoing. A six-month CT scan is planned, followed by annual imaging for at least two years.

3. Discussion

This case report underlines the diagnostic and management challenges posed by inflammatory pseudotumors (IPTs). The patient presented with a large urachal mass that, on imaging, appeared highly suspicious for adenocarcinoma. The lesion demonstrated irregular contours, marked enhancement, infiltration of the anterior abdominal wall, and apparent invasion of the bladder dome. In addition, micronodules were initially interpreted as peritoneal carcinomatosis, further reinforcing the malignant impression. Such radiological aggressiveness may be associated with IPTs, which have long been recognized as formidable mimickers of malignancy across various organ systems.¹ The lung and orbit are classically the most frequently reported sites, although IPTs have been described in nearly every organ, including the liver and pancreas, making diagnosis even more complex. Urachal involvement remains extremely rare.

Histological evaluation, however, revealed the key to the diagnosis. The percutaneous biopsies showed a fibro-inflammatory reaction with abundant myofibroblastic proliferation and dense plasmacytoid infiltrate, along with foamy histiocytes and areas of necrosis and suppuration. Immunohistochemistry demonstrated positivity for SMA and CD68, and negativity for ALK-1 and cytokeratin, with minimal atypia and rare mitoses, confirming a benign inflammatory pseudotumor rather than IMT. Coffin et al. emphasized that extrapulmonary IPTs often mimic malignancy histologically and radiologically yet behave as benign lesions with limited proliferative potential.⁴ The presence of myofibroblastic proliferation and inflammatory infiltrates in our case explains the intense radiologic enhancement and the apparent tissue invasion, both related to inflammation rather than neoplastic spread.

This paradox between malignant imaging features and benign histology is well documented in IPTs. Limited sampling can sometimes fail to reveal diagnostic features, but in this case, the histologic findings were sufficiently characteristic to support an inflammatory myofibroblastic pseudotumor rather than an adenocarcinoma.^1,3 Despite this, the aggressive clinical and radiological presentation naturally maintained a high index of suspicion, prompting consideration of delayed surgical resection.

The literature shows that although surgery is often curative, certain IPTs regress spontaneously or after medical therapy. Narla et al. stressed that while surgical excision remains the mainstay, conservative treatment can be effective when histology excludes malignancy.¹ Barabino et al. reviewed multiple cases of hepatic IPTs that underwent complete regression with conservative management — including antibiotic therapy in some instances — suggesting an infectious or inflammatory mechanism in selected cases.² Patnana et al. further highlighted the broad behavioural spectrum of IPTs, ranging from self-limiting inflammatory lesions to more cellular, sarcoma-like myofibroblastic proliferations.³

Our case stands out for its remarkable clinical course: a large, radiologically aggressive urachal mass showing near-complete regression within one month of combined antibiotic and NSAID therapy. The associated peritoneal micronodules, initially considered carcinomatosis, also resolved completely. Levy et al. previously reported a similarly dramatic regression of a hepatic IPT mimicking a malignant biliary tumor.⁵ This supports the concept that even IMT-type pseudotumors, when primarily inflammatory, can respond to conservative treatment. The rapid and complete regression under medical therapy suggests that in this patient, the myofibroblastic proliferation was part of a reactive inflammatory process rather than a neoplastic one.

These findings reinforce the notion that IPTs represent a histopathologic continuum ranging from purely inflammatory pseudotumors to true inflammatory myofibroblastic tumors with variable autonomy.2, 3, 4 The benign clinical evolution in our patient, the absence of recurrence, and the total disappearance of radiologic abnormalities after medical therapy confirm the inflammatory nature of the lesion and justify a conservative approach.

Altogether, this case supports the growing evidence that not all IPTs require immediate surgical excision. When histology demonstrates a benign inflammatory or myofibroblastic pattern and the patient's condition is stable, a trial of medical therapy under close monitoring is justified. This strategy can spare patients from unnecessary radical procedures, especially when malignancy has not been definitively proven.

4. Conclusion

Inflammatory pseudotumors continue to challenge clinicians because of their malignant mimicry on imaging and their often-inconclusive histology. Our case demonstrates that even a lesion with features highly suggestive of urachal adenocarcinoma can undergo complete regression under conservative treatment. This exceptional outcome stresses the need for a cautious, multidisciplinary approach in which medical therapy may be considered when malignancy is not histologically proven. By avoiding unnecessary radical surgery, such an approach may offer patients both safety and cure, provided that rigorous follow-up is maintained.

CRediT authorship contribution statement

Sami Chebbi: Conceptualization, Formal analysis, Investigation, Project administration, Writing – original draft. Houssem Bel Hadj Alouane: Formal analysis, Supervision, Validation, Writing – review & editing. Mohamed Amine Oueslati: Conceptualization, Investigation, Validation. Imen Helal: Resources, Visualization, Writing – review & editing. Sami Ben Rhouma: Supervision.

Consent

Signed consent was obtained from the patient.

Conflicts of interest

The authors declare that there are no conflicts of interest regarding the publication of this article.