PMC10213382_01
T2-weighted magnetic resonance image of the neck in axial view showed a hyperintense mass on the left side of the neck, extending to prelaryngeal and prevertebral spaces (arrows).
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Magnetic resonance imaging of the neck done at the time of recurrence revealed an infiltrating soft tissue mass measuring 7.4 cm x 6.9 cm involving the left side of the neck extending into paravertebral space, encasing the left carotid artery and compressing the left jugular vein (Figure 1).
Gross examination of the thyroidectomy specimen showed a tumor measuring 8 cm x 7 cm x 6.5 cm, replacing the entire gland. No normal thyroid parenchyma was discernible. The cut surface appeared fleshy, grey-white in color with whorls and myxoid foci.
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Grossly, the specimen was distorted, replaced entirely by the tumor, and measured 8 cm x 7 cm x 6.5 cm (Figure 2).
Microscopic examination of core biopsy (H&E, 100x).
(A) revealed a low-grade spindle cell tumour having areas of fibrosis. Examination of the thyroidectomy specimen (H&E, 200x).
(B) showed that the tumor infiltrated the normal thyroid parenchyma at the periphery (black arrow).
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The tumour infiltrated the residual thyroid, which was within normal histological limits, and neck skeletal muscle bundles (Figure 3).
Immunohistochemical staining of the tumor cells showed (A) positivity for smooth muscle actin (black arrow; IHC, 200x) and (B) nuclear and cytoplasmic expression of beta-catenin (brown arrow; IHC, 200x).
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Immunohistochemical studies demonstrated that the cells were positive for smooth muscle actin (Scytek, 1A4, A00002) and desmin (Scytek, D33, A00007), and showed nuclear and cytoplasmic staining with beta-catenin (BD Biosciences, 14/Beta-Catenin, 610154), but were negative for pan-cytokeratin (Bio SB, AE1 & AE3, BSB 5433), CD34 (Spring Bioscience, QBEnd/10, E1281), and S-100 (Bio SB, 4C4.9, BSB 5919) (Figure 4).
Bi-directional Sanger sequencing performed on DNA extracted from the tumor block revealed a mutation at codon 45 of exon 3 (c.134C>T; p.S45F) of the beta-catenin (CTNNB1) gene (arrows).
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Bi-directional Sanger sequencing performed on DNA extracted from the tumor block revealed a mutation involving the beta-catenin (CTNNB1) gene (c.134C>T; p.S45F) (Figure 5).