A case of inflammatory myofibroblastic tumor of the urinary bladder with emergency clinical symptoms similar to bladder cancer

A 55-year-old man was admitted for ongoing gross hematuria and bladder tamponade. Computed tomography revealed a mass near the right sidewall of the bladder, along with massive blood clots. The patient was diagnosed as having bladder cancer based on laboratory findings and emergency clinical symptoms. Thus, emergency transurethral resection of the bladder tumor was performed. Pathological examination revealed an inﬂammatory myoﬁbroblastic tumor (IMT). No tumor progression was observed during the 6-month follow-up period. Owing to its rarity, IMT has not been well characterized clinically and radiologically, and thus, it is very difficult to diagnose IMT accurately without pathological examinations.


Introduction
Inflammatory myofibroblastic tumor (IMT) of the bladder is a rare intermediate soft tissue tumor that is, composed of myofibroblastdifferentiated spindle cells accompanied by numerous inflammatory cells, plasma cells, and/or lymphocytes. IMT was first described in 1980 by Roth. 1 Although IMT mainly occurs mainly in the lungs, it can also be found in the head and neck soft tissue, abdominal cavity, omentum, retroperitoneum, and other organs. 2 The most common symptoms of IMT of the bladder include gross hematuria and dysuria.
It is believed that multiple causes such as urinary tract infection, prior history of surgery or instrumentation, diabetes mellitus, trauma, steroids, and immune disorders can lead to IMT development. 2 However, the definitive pathogenesis of IMT is unclear and remains under discussion.
It is difficult to accurately diagnose such a rare disease based on findings of only imaging examinations and clinical symptoms. The final identification of IMT often depends on histopathological features and immunohistochemical profiles.
According to the World Health Organization classification, IMT is designated as a tumor of intermediate biological potential owing to its low risk of distant metastasis. 2 Surgical resection is the treatment of choice, and prognosis depends on local metastasis. 2 Here, we report a case of IMT of the bladder that was clinically indistinguishable from urothelial carcinoma of the bladder.

Case presentation
A 55-year-old man, with no significant medical history, was admitted to the emergency room for ongoing gross hematuria with bladder tamponade. Blood examination results indicated a low hemoglobin level (6.2 g/L: 13.5-17.6g/L), and blood pressure was also low (78/60 mmHg). The patient was infused with two units of red blood cells (200 ml plasma transfusion) and also underwent continuous bladder irrigation to avoid catheter obstruction, which prevented blood clot formation. Abdominal and pelvic computed tomography scan revealed a mass near the right sidewall of the bladder and massive blood clots. (Fig. 1). Based on clinical symptoms and imaging findings, the patient was diagnosed as having bladder cancer, and underwent emergency transurethral resection of the bladder tumor (TURBT). His clinical symptoms improved, and he was discharged to home on the postoperative day.
Pathological results showed the infiltration of a neoplasm, mainly composed of spindle cells with bland nuclear morphology and some with nuclear atypia arranged in fascicles in a vascular myxoid edematous background. A mixed population of inflammatory cells composed of lymphocytes, plasma cells, eosinophils, and neutrophils was present between neoplastic cells. Immunohistochemistry results were positive for vimentin, smooth muscle actin, Cytokeratin AE1/AE3, and anaplastic lymphoma kinase (ALK). (Fig. 2). Considering the sarcomatoid features and for excluding undifferentiated/sarcomatoid carcinoma, examed examination results desmin, epithelial membrane antigen, HHF35, and P63 were negative. The Ki67 proliferative activity was approximately 50%-70% in hotspot areas. Thus, the tumor was E-mail address: hyperzector555@med.showa-u.ac.jp.   diagnosed as an IMT of the bladder. Subsequent follow-up cystoscopy was performed every 3 months after surgery. The first follow-up revealed no tumor recurrence or symptoms such as dysuria.

Discussion
IMT is composed of myofibroblast-differentiated spindle cells and is accompanied by numerous inflammatory cells, plasma cells, and lymphocytes. The most common site involved is the lungs, and the involvement of bladder is rare. 2 A systematic review by Teoh et al. evaluated 182 cases of IMT of the bladder and reported that patients had a mean age of 38.9 years and that hematuria and dysuria were common clinical manifestations, with some patients also experiencing severe anemia. 3 IMT of the bladder has a local tumor recurrence rate of only 4% after surgery, and only one patient with distant metastases has been reported. 2 Since Hojo et al. showed an association between IMT and the ALK gene, many studies have reported the translocations of the ALK gene and expression of the ALK protein in IMTs with positive ALK immunostaining in 33%-89% of cases. 4 To further study the IMT of the bladder, we reviewed relevant case reports published since 2010, including our own case (Table 1). 2 The patient age ranged from 3 to 71 (mean 36.5) years, and females were represented more than males (ratio 15:11). Hematuria (n = 21) was a common clinical symptom in patients. The most common first treatment option was TURBT (n = 19), followed by partial cystectomy (n = 10). There were five cases of emergency surgery owing to severe hematuria, and three cases had hypovolemic shock. ALK positivity was observed in 20 of the 26 cases.
Since IMT of the bladder is a rare tumor, it is difficult to suspect IMT based only on symptoms and imaging findings as it has not been well studied. The characteristics and causes of IMT of the bladder are expected to become further clear with the accumulation of more studies in the future.

Conclusion
IMT of the bladder is a very rare tumor, and often presents with unpredictable clinical behavior. Thus, it requires complete surgical resection and regular monitoring of clinical outcomes.
We recommend clinical and radiological follow-up for monitoring the recurrence and metastasis of IMT of the bladder.

Consent
Written informed consent was obtained from the participant for the publication of this case report. A copy of the written consent is available for the editorial review.

Disclosure of sources of financial support
None.

Declaration of competing interest
Authors have no conflict of interest to declare.