侵犯肌層之膀胱發炎性肌纖維母細胞瘤：病例報告

^1,3曾義翔、^1,3顧明軒、²潘競成、^1,3黃逸修

¹臺北榮民總醫院泌尿部

²臺北榮民總醫院病理檢驗醫學部

³國立陽明交通大學醫學院泌尿學科及書田泌尿科學研究中心

Muscle-invasive inflammatory myofibroblastic tumor of the urinary bladder: a case report

^1,3I-Hsiang Tseng, ^1,3Ming-Hsuan Ku, ²Chin-Chen Pan, ^1,3Eric Yi-Hsiu Huang

¹Department of Urology, ²Department of Pathology and Laboratory Medicine,

Taipei Veterans General Hospital, Taipei, Taiwan

³Department of Urology, College of Medicine and ShuTien Urological Research Center, National Yang Ming Chiao Tung University, Taipei, Taiwan

Introduction

Inflammatory myofibroblastic tumor (IMT) is a rare mesenchymal neoplasm characterized by proliferation of myofibroblastic spindle cells accompanied by inflammatory cell infiltration. Although IMT was first described in the lung, it has since been reported in a variety of extrapulmonary sites, including the urinary bladder. Bladder IMT is uncommon and accounts for less than 1% of all bladder tumors. Patients typically present with gross hematuria or irritative lower urinary tract symptoms, and imaging findings frequently resemble those of urothelial carcinoma. [1]

Histologically, IMT is composed of spindle-shaped myofibroblasts in a myxoid or collagenous stroma with mixed inflammatory infiltrates. Rearrangement of the anaplastic lymphoma kinase (ALK) gene is detected in approximately half of cases and serves as an important diagnostic marker for this entity. Despite being considered a tumor of intermediate biologic potential, IMT may demonstrate locally aggressive behavior, including invasion into the muscularis propria, which can mimic muscle-invasive bladder cancer. [2], [3]

Case presentation

A 60-year-old man with no history of smoking presented to our outpatient department due to gross hematuria with passage of blood clots. He denied dysuria, urinary frequency, or voiding difficulty. Urinalysis demonstrated ≥100 red blood cells per high-power field.

Ultrasonography of the lower abdomen revealed a 2.6 × 2.0 cm polypoid lesion with increased vascularity over the posterior wall of the urinary bladder and further CT image also reported the bladder lesion (Figure 1). Cystoscopy subsequently demonstrated a non-papillary bladder tumor located on the left posterior bladder wall (Figure 2).

The patient underwent transurethral resection of bladder tumor (TURBT) (Figure 2), and histopathological examination revealed an inflammatory myofibroblastic tumor characterized by proliferation of elongated spindle cells within an inflammatory and myxoid stroma. Immunohistochemical staining showed diffuse positivity for anaplastic lymphoma kinase (ALK) (Figure 3). Tumor cells were noted to invade the muscularis propria.

After discussing the treatment options, the patient elected to undergo surgical management. A robotic-assisted partial cystectomy was performed one month after the initial TUR-Bt. Initial cystoscopic evaluation identified the previous TUR-Bt scar on the posterior bladder wall near the left ureteral orifice. The lesion was carefully inspected, and the scar margin was delineated via cauterization. A double-J ureteral stent was inserted into the left ureteral orifice for protection. The robotic partial cystectomy was then performed; the lesion was identified and excised with adequate surgical margins (Figure 4). The bladder defect was closed in two layers, and a leak test confirmed a watertight closure. The postoperative course was uneventful, and the patient was discharged in stable condition on postoperative day 3. Pathological examination of the partial cystectomy specimen demonstrated chronic inflammation and fibrosis without residual tumor.

Cystography performed thirteen days after cystectomy showed no contrast leakage from the bladder repair site. The ureteral double-J stent and Foley catheter were subsequently removed.

Discussion

Inflammatory myofibroblastic tumor (IMT) is a rare mesenchymal neoplasm characterized by proliferation of myofibroblastic spindle cells accompanied by inflammatory cell infiltration. Although IMT was originally described in the lung, extrapulmonary involvement has been increasingly recognized, including the urinary bladder. Bladder IMT is uncommon and accounts for less than 1% of all bladder tumors. Patients most commonly present with gross hematuria, dysuria, or irritative urinary symptoms. Because imaging findings frequently resemble those of urothelial carcinoma, preoperative diagnosis can be challenging. [1]

Histologically, IMT is composed of spindle-shaped myofibroblasts arranged in fascicles or storiform patterns within a myxoid or collagenous stroma, accompanied by a mixed inflammatory infiltrate consisting of lymphocytes, plasma cells, and eosinophils. Immunohistochemically, tumor cells typically express smooth muscle actin and vimentin. Approximately 50–60% of IMTs demonstrate rearrangement of the anaplastic lymphoma kinase (ALK) gene, which is considered an important diagnostic marker for this entity. ALK immunoreactivity is particularly useful in distinguishing IMT from malignant spindle cell tumors such as leiomyosarcoma and sarcomatoid carcinoma. In the present case, diffuse ALK positivity supported the diagnosis of inflammatory myofibroblastic tumor. [2]

Although IMT is classified as a tumor of intermediate biologic potential, it may demonstrate locally aggressive behavior. Invasion of the muscularis propria has been reported in several cases and may mimic muscle-invasive bladder cancer. However, despite this infiltrative growth pattern, distant metastasis is rare and the overall prognosis is generally favorable following complete surgical excision.[3]

The mainstay of treatment for bladder IMT is complete surgical resection. Transurethral resection of bladder tumor (TURBT) may be sufficient for small lesions, but partial cystectomy is often considered when complete excision cannot be confidently achieved or when muscle invasion is suspected. Radical cystectomy is rarely necessary because most cases can be successfully managed with bladder-preserving surgery. [4]

Minimally invasive surgical techniques have increasingly been applied in the management of bladder tumors. Robotic-assisted partial cystectomy offers several advantages, including improved visualization, precise dissection, and reduced perioperative morbidity. In our case, robotic partial cystectomy was performed successfully, and pathological examination of the surgical specimen revealed no residual tumor, suggesting that the tumor had been completely removed during the initial TURBT. [5]

An important differential diagnosis of bladder inflammatory myofibroblastic tumor is postoperative spindle cell nodule (PSCN), a benign spindle cell proliferation that typically occurs following recent bladder instrumentation or surgery. PSCN shares overlapping histologic features with IMT, including spindle cell proliferation in a myxoid stroma. However, PSCN is generally considered a reactive lesion, whereas IMT is regarded as a true neoplasm and may demonstrate ALK gene rearrangements. Recognition of this distinction is important to avoid overtreatment and unnecessary radical surgery. [6]

Conclusions

Inflammatory myofibroblastic tumor of the urinary bladder is a rare spindle cell lesion that may clinically and radiologically mimic malignant bladder tumors. Accurate diagnosis relies on histopathological examination and immunohistochemical analysis, particularly ALK expression, to distinguish it from other spindle cell lesions such as postoperative spindle cell nodule and sarcomatoid carcinoma. Complete surgical excision with close follow-up is recommended, as these tumors may demonstrate locally aggressive behavior despite their generally favorable prognosis.

 ADDIN EN.REFLIST 1.         Laylo, J.C.V., N.L. Lim, and J.J.V. Remo, Inflammatory myofibroblastic tumor of the urinary bladder: A prognostically favorable spindle cell neoplasm. Urol Case Rep, 2021. 34: p. 101474.

2.         Choi, J.H., Inflammatory Myofibroblastic Tumor: An Updated Review. Cancers (Basel), 2025. 17(8).

3.         Teoh, J.Y., et al., Inflammatory myofibroblastic tumors of the urinary bladder: a systematic review. Urology, 2014. 84(3): p. 503-8.

4.         Hensley, P.J., et al., Clinicopathological analysis and outcomes of inflammatory myofibroblastic tumours of the urinary bladder. BJU Int, 2022. 130(5): p. 604-610.

5.         Chen, C., et al., Inflammatory Myofibroblastic Tumor of the Urinary Bladder: An 11-Year Retrospective Study From a Single Center. Front Med (Lausanne), 2022. 9: p. 831952.

6.         Lott, S., et al., Soft tissue tumors of the urinary bladder, Part I: myofibroblastic proliferations, benign neoplasms, and tumors of uncertain malignant potential. Hum Pathol, 2007. 38(6): p. 807-23.