Inflammatory myofibroblastic tumour of the bladder

Definition

 Postoperative spindle cell nodule is a similar lesion occurring after a surgical procedure4. Similar lesion has been reported in the vagina, ureter, urethra and prostate10. It is unclear whether this lesion is truely neoplastic. Inflammatory myofibroblastic tumour of the bladder has been shown to have a t(2;5) translocation involving the ALK-1 gene, and so may be a variant of inflammatory myofibroblastic tumour: this entity was first identified in the lung, but is now known to occur at a range of sites.

Synonyms

Inflammatory pseudotumour, inflammatory pseudosarcomatous fibromyxoid tumour, nodular fasciitis, pseudomalignant spindle cell proliferation, pseudosarcomatous myofibroblastic tumour, reactive pseudosarcomatous response.

Clinical features

This is usually a tumour of adults with a male predominance10, rarely of children7. Patients present with haematuria, pelvic pain, obstructive symptoms or recurrent cystitis2,10. There is often a history of smoking, prior surgery or instrumentation10.

Macroscopic appearance

The most common is the is the dome of the bladder10. The tumour may be polypoidal10 or form a submucosal mass2. The tumour commonly appears gelatinous2.

Histopathology

This is a variably cellular spindle cell tumour. Stellate cells are seen. The cells do not show hyperchomasia or frank atypia10. A single nucleolus is commonly present within each nucleus10. Some nuclei may show a red-brown inclusion10. As at other sites, three patterns occur. Most cases show a mix of patterns7. There are mitoses (3 to 38/10 HPF7) but no abnormal mitotic figures. Atypia is lacking. There may be limited necrosis7. There is a mixed inflammatory infiltrate. The tumour shows a myxoid background with myxoid hypocellular areas near the mucosal surface and greater cellularity more deeply10. Arcing blood vessels may be seen10.

Immunohistochemistry (with differential diagnoses for comparison)

Ultrastructure

The features are those of myofibroblastic cells. Fibronexus junctions are specific to myofibroblastic cells but are not often to be found.

Molecular cytogenetics

• Cytogenetic abnormalities at 2p23, the site of the ALK-1 gene, have been reported8. ALK gene translocations examined by FISH are seen in 4 of 6 cases in each of two studies1,10.

Differential diagnosis

• Inflammatory myofibroblastic tumour of childhood: is associated with constitutional symptoms. This lesion is more cellular with a dense infiltrated of lymphocytes and plasma cells. There are ganglion-like cells and the lesions show calcification. There is rarely positivity for cytokeratins. This is a tumour of low malignant potential10.

• Postoperative spindle cell nodule

• Sarcomatoid urothelial carcinoma: may be myxoid. There is marked cytological atypia, abnormal mitoses, non-myxoid areas of greater cellularity. There is often a malignant epithelial component. p53 staining tends to be strong. Staining for cytokeratins may be weak. ALK-1 is negative.

• Leiomyosarcoma: may be myxoid and may show positivity for cytokeratins. A delicate vascular network and an inflammatory infiltrate are lacking. ALK-1 is negative. p53 staining may be strong. Any cytokeratin positivity is focal and weak.

• Rhabdomyosarcoma: positive for myogenin and Myo-D1. May be positive for ALK-19.

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Management

Treatment has variously been by transurethral resection, or partial or total cystectomy10.

Prognosis

The prognosis is good; local resection is adequate. Recurrences may occur10, possibly more often in ALK-1 positive cases7. The tumour does not metastasis10. Unresected lesions may massively enlarge to cause death by obstruction, not metastasis4.

References

1 Freeman, A., N. Geddes, et al. (2004). "Anaplastic lymphoma kinase (ALK 1) staining and molecular analysis in inflammatory myofibroblastic tumours of the bladder: a preliminary clinicopathological study of nine cases and review of the literature." Mod Pathol 17(7): 765-71.

2 Jones, E. C., P. B. Clement, et al. (1993). "Inflammatory pseudotumor of the urinary bladder. A clinicopathological, immunohistochemical, ultrastructural, and flow cytometric study of 13 cases." Am J Surg Pathol 17(3): 264-74.

3 Coyne, J. D., G. Wilson, et al. (1991). "Inflammatory pseudotumour of the urinary bladder." Histopathology 18(3): 261-4.

4 Iczkowski, K. A., J. H. Shanks, et al. (2001). "Inflammatory pseudotumor and sarcoma of urinary bladder: differential diagnosis and outcome in thirty-eight spindle cell neoplasms." Mod Pathol 14(10): 1043-51.

5 Chan, J. K., W. Cheuk, et al. (2001). "Anaplastic lymphoma kinase expression in inflammatory pseudotumors." Am J Surg Pathol 25(6): 761-8.

6 Cook, J. R., L. P. Dehner, et al. (2001). "Anaplastic lymphoma kinase (ALK) expression in the inflammatory myofibroblastic tumor: a comparative immunohistochemical study." Am J Surg Pathol 25(11): 1364-71.

7 Tsuzuki, T., C. Magi-Galluzzi, et al. (2004). "ALK-1 expression in inflammatory myofibroblastic tumor of the urinary bladder." Am J Surg Pathol 28(12): 1609-14.

8 Hojo, H., W. A. Newton, Jr., et al. (1995). "Pseudosarcomatous myofibroblastic tumor of the urinary bladder in children: a study of 11 cases with review of the literature. An Intergroup Rhabdomyosarcoma Study." Am J Surg Pathol 19(11): 1224-36.

9 Cessna, M. H., H. Zhou, et al. (2002). "Expression of ALK1 and p80 in inflammatory myofibroblastic tumor and its mesenchymal mimics: a study of 135 cases." Mod Pathol 15(9): 931-8.

10 Harik LR, Merino C, Coindre JM, et al. Pseudosarcomatous Myofibroblastic Proliferations of the Bladder: A Clinicopathologic Study of 42 Cases. Am J Surg Pathol 2006; 30:787-794

This page last revised 13.7.2006.

©SMUHT/PW Bishop