PMC9256428_01
Pelvic magnetic resonance imaging showing the following: (a) sagittal T2-weighted spin-echo image: a round mass with very low homogeneous signal intensity in its central part is present; (b) sagittal 90 second postgadolinium T1-weighted fat-suppressed spin-echo image: the upper aspect of the mass enhances reflecting active disease and the nodular desmoid tumor exhibits minimal enhancement confirming its fibrous nature; (c) paracoronal T2-weighted; and (d) postgadolinium T1-weighted images showing right kidney hydronephrosis due to an extraureteral obstruction confirmed to be a desmoid tumor.
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fig1
Consequently, a pelvic magnetic resonance imaging (MRI) was requested (Figure 1).
(a) Macroscopic and (b) microscopic correlation of a poorly circumscribed lesion, with a white and whorled appearance, on the cut surface, that infiltrates the surrounding soft tissue (indicated by the green arrows). The tumor compresses the adjacent ureter (indicated by the red arrow).
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The lesion was solid, firm, and infiltrative, surrounding the ureter (Figure 2), right iliac vessels, and hypogastric nerve. In the Pathology Department, on gross examination, the lesion consisted of an infiltrative, fibroelastic tumor that measured approximately 5 cm on the long axis, with a white, whorled appearance and ill-defined borders, on the cut surface (Figure 2).
(a and b) Microscopically, the lesion consisted of a proliferation of relatively uniform spindle cells, arranged in long fascicles, with fusiform nuclei and inconspicuous nucleoli, in an abundant collagenous stroma, pointed by the black arrows. The tumor showed an infiltrative pattern of growth.
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fig3
Microscopically, the tumor was composed by an infiltrative growth pattern proliferation of bland spindle cells, arranged in long fascicles, with fusiform, uniform, nuclei, and inconspicuous nucleoli, with no cytological atypia, in a stroma with bundles of collagen (Figure 3).
The neoplastic cells expressed positive aberrant nuclear staining for beta-catenin and were negative for desmin.
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DOG1 and expressed positivity for beta-catenin (nuclear expression), favouring the diagnosis of fibromatosis (Figure 4). Due to the rarity of the diagnosis and the distinct treatment implications of such diagnosis, the case was sent for a second opinion to a national expertise pathologist of mesenchymal tumors that supported the diagnosis.