case_images: PMC10213382_01
case_images: 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).
case_images: JAFES-38-1-120-g001.jpg
case_images: PMC10213382_01_JAFES-38-1-120-g001.jpg
case_images: f0001
case_images: 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).
case_images: 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.
case_images: JAFES-38-1-120-g002.jpg
case_images: PMC10213382_01_JAFES-38-1-120-g002.jpg
case_images: f0002
case_images: Grossly, the specimen was distorted, replaced entirely by the tumor, and measured 8 cm x 7 cm x 6.5 cm (Figure 2).
case_images: 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).
case_images: JAFES-38-1-120-g003.jpg
case_images: PMC10213382_01_JAFES-38-1-120-g003.jpg
case_images: f0003
case_images: The tumour infiltrated the residual thyroid, which was within normal histological limits, and neck skeletal muscle bundles (Figure 3).
case_images: 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).
case_images: JAFES-38-1-120-g004.jpg
case_images: PMC10213382_01_JAFES-38-1-120-g004.jpg
case_images: f0004
case_images: 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).
case_images: 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).
case_images: JAFES-38-1-120-g005.jpg
case_images: PMC10213382_01_JAFES-38-1-120-g005.jpg
case_images: f0005
case_images: 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).