The external surface of the resection shows an erythematous edematous bladder dome region and a large mass attached superiorly.
Different viewpoint again shows the infiltrative mass.
The cut surface shows gray trabeculated muscularis of the bladder partially obscured by a fibrous ill defined mass.
Closer image shows the infiltrative nature of the mass replacing the muscularis.
Bladder muscularis is seen on the right. The lesion arises from even deeper portions of the bladder wall, in the region of the urachus.
This is a fibroblastic lesion with sclerosis admixed with a mixed chronic inflammatory infiltrate. Some chronic inflammatory cells are present.
The fibroblastic proliferation irregularly dissects into underlying submucosal fat.
Fascicles of spindle cells with scattered inflammatory cells are the key histologic features.
Beta catenin shows some cytoplasmic positivity. Nuclear staining is seen in deep fibromatosis (desmoid tumor) and nonspecific cytoplastic accumulation is seen in IMTs, low-grade fibromyxoid sarcoma, leiomyosarcomas and various fibrosarcoma variants (Bhattacharya).
A different ares shows a more myxoid quality to the stroma.
Normal transitional mucosa is seen to the far upper right; an underlying solid spindle cell mass infiltrates the muscularis propria but does not directly involving actual mucosa
Some areas manifest distinct fascicular growth, with elongated tapered spindle cells arranged in bundles
Among the spindle cell is a sprinkling of inflammatory cells.
The urachus is the remnant of the embryonic allantois (which drains the fetal bladder and assists with waste and gas exchange). Failure of this structure to close leads to a persistant connection between the bladder and the umbilicus. Cysts, diverticula and tumors can develop. The urachus is lined by urothelium and surrounded by connective tissue and smooth muscle. Cases of urachal adenocarcinoma and transitional cell carcinoma have been documented.
Mesenchymal tumors are exceptionally rare and includes desmoid tumors, leiomyomas and inflammatory myofibroblastic tumors (IMTs)(Nascimento). IMTs are low-grade neoplasms most often seen in the lung and abdomen of children and young adults. It is not entirely clear whether IMTs evolve from a reactive or neoplastic process, however, a subset of these tumors (usually seen in the children and younger adults) have demonstrated translocations involving the ALK (anaplastic lymphoma kinase) gene located on chromosome 2p23. This translocation often fuses the ALK gene with tropomyosin 3 or 4, creating constitutively active oncoproteins -- this overexpression of ALK protein can be detected on IHC, seen as ALK positivity (Tsuzuki).
IMTs are considered a low-grade neoplasm (borderline malignancy) and a minority of cases recur and a handful of cases have been metastatic.
Bhattacharya B, Dilworth HP, Iacobuzio-Donahue C et al. Nuclear beta-catenin expression distinguishes deep fibromatosis from other benign and malignant fibroblastic and myofibroblastic lesions. Am J Surg Pathol. 2005 May;29(5):653-9.
Nascimento AF, Cin PD, Cilento BG et al. Urachal Inflammatory Myofibroblastic Tumor With ALK Gene Rearrangement: A Study of Urachal Remnants. Urology 64: 140-4, 2004.
Tsuzuki T, Magi-Galluzzi C, Epstein JI et al. ALK-1 Expression in Inflammatory Myofibroblastic Tumor of the Urinary Bladder. Am J Surg Pathol (2004); 28(12): 1609-1614.