PMC4861885_01
Axial, T1-weighted, precontrast image shows the 9.7 x 5 cm mass (*) in the right ischiorectal fossa, abutting the labia, to be isointense to skeletal muscle.
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Contrast-enhanced MRI of the pelvis (Fig. 1) showed a 9.7 x 5 x 5.5 cm heterogeneous mass in the perineum on the right, involving the ischiorectal fossa and abutting the labia.
Axial T1 postcontrast image shows the mass (*) to enhance heterogeneously.
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The mass was heterogeneous but hypointense on T1-weighted sequences, hyperintense on STIR, and demonstrated heterogeneous contrast enhancement (Figure 2, Figure 3, Figure 4).
Coronal T1 postcontrast image shows the mass (*) to infiltrate the adjacent musculature, and have a poorly defined lateral margin (arrow).
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The mass was heterogeneous but hypointense on T1-weighted sequences, hyperintense on STIR, and demonstrated heterogeneous contrast enhancement (Figure 2, Figure 3, Figure 4).
Axial STIR image shows the mass to be relatively hyperintense to skeletal muscle.
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The mass was heterogeneous but hypointense on T1-weighted sequences, hyperintense on STIR, and demonstrated heterogeneous contrast enhancement (Figure 2, Figure 3, Figure 4).
A: Large soft-tissue mass with surrounding skin and fibroadipose tissue, measuring 17 x 10 x 8 cm. Attached skin measures 14 x 11.5 cm. Portion of the vagina and labia minora measures 4 x 3.5 cm. B: Sectioning of the specimen reveals a large multilobulated tumor measuring 8 x 6 x 5.5 cm. Note tan to slightly yellow gelatinous cut surface, with large areas of caseous necrosis. Tumor is well circumscribed, with a thin capsule.
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At surgery, the mass was found to be intimately involved with the right inferior pubic ramus, and grossly metastatic lymph nodes were visualized (Figs. 5A, B).
Nests of discohesive tumor cells (ovals) separated by thin fibrovascular septae (arrows), imparting alveolar appearance (A, 10X; B, 4X).
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Numerous fibrovascular septae separated the discohesive tumor cells into discrete nests, where the tumor cells appear to float in alveolar spaces (Figs. 6A, B).
Discohesive monomorphous small round tumor cells with numerous mitoses (arrows) (10X).
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The malignant neoplasm was composed of monomorphous round nuclei (Fig. 7) with deep eosinophilic cytoplasm.
Occasional multinucleate giant cell (arrow) (40X).
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A few multinucleated giant cells (Fig. 8) were also present.
Nuclear myogenin positivity in tumor cells (20X).
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Immunohistochemically, the tumor cells showed strong positivity for desmin and nuclear positivity for myogenin (Fig. 9) yet negativity for cytokeratin, synaptophysin, and chromogranin, establishing the diagnosis of alveolar rhabdomyosarcoma.
PET/CT image demonstrating foci of hypermetabolism within the postoperative bed and the right pelvic sidewall (arrows).
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A PET scan (Fig. 10) showed residual tumor deposits in the postoperative bed, consistent with high-grade malignancy by quantitative analysis.