PMC9619336_01
AP radiograph shows a mass at the medial aspect of the left knee with soft tissue density similar to muscle (arrowheads).
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Initial radiographic evaluation showed soft tissue swelling corresponding to the location of the palpable mass (Fig. 1).
On axial MRI, the mass demonstrated slight T1 hyperintense signal relative to muscle (A), heterogeneous but primarily hyperintesne T2 signal (B), and heterogeneous enhancement on T1 post-contrast subtraction imaging (C).
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The mass demonstrated slight hyperintense T1 signal relative to muscle and heterogeneous, predominantly hyperintense T2 signal with enhancement on the post-contrast sequences (Fig. 2).
Histopathology of the first biopsy specimen (hematoxylin and eosin, 400x magnification) demonstrates a lesion composed of compact fascicles of monotonous spindle cells with overlapping nuclei and scattered wiry collagen bundles. These features are characteristics of a monophasic synovial sarcoma.
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Histopathologic analysis of the core needle specimens demonstrated a proliferation of monotonous spindle cells with overlapping nuclei and scattered wiry collagen bundles (Fig. 3).
Initial staging PET-CT MIP image (A) demonstrates abnormal hypermetabolism at the medial aspect of the left knee (arrowhead), which corresponds to the location of the biopsy-proven synovial sarcoma. There is a tiny focus of low-level hypermetabolism within the medial soft tissues of the proximal left thigh (arrow), which is in the same region as the subsequent biopsy-proven pleomorphic liposarcoma and therefore likely represents a very early synchronous manifestation of a second distinct primary soft tissue tumor. Subsequent staging PET-CT MIP image following clinical discovery of the left thigh mass (B), shows marked hypermetabolism of the large mass in the thigh (arrow) and low level hypermetabolism in the surgical resection bed at the medial aspect of the knee (arrowheads).
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Initial staging was performed with chest computed tomography (CT) and whole-body positron emission tomography (PET)-CT, which were interpreted as negative for metastatic disease (Fig. 4).
Initial axial fused PET-CT image (A) of the left thigh shows a tiny focus of low-level signal (arrow) along the surface of the adductor compartment musculature. There is a very subtle lesion with lower density compared to muscle (arrow) on the corresponding axial CT image (B). Subsequent axial and coronal CT imaging (C and D) show a large irregular mass centered within the adductor muscle compartment at the posteromedial aspect of the left thigh with areas of internal low density consistent with necrosis.
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The original staging PET-CT was reviewed retrospectively and a tiny focus of low-level hypermetabolism within the medial soft tissues of the proximal left thigh was identified, but the large mass was not present (Fig. 5).
Histopathology of the second mass (hematoxylin and eosin, 400x magnification) is composed of bizarre cells with large, hyperchromatic nuclei including pleomorphic lipoblasts showing nuclear indentation by clear vacuoles. These findings were consistent with a pleomorphic liposarcoma.
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There was no histologic resemblance to the previous SS at the knee (Fig. 6).