Fig. 2. Multifocal thyroid gland invasion by ipsilateral metastasis of hypopharyngeal cancer without direct extension through the thyroid cartilage. (A) An approximately 3.5-mm primary mass lesion extending from the post-cricoid region to the pyriform sinus is noted without definite thyroid cartilage involvement (upper left). Multiple foci of metastatic thyroid gland invasion (thin arrows) are noted without direct connections to the primary lesion (thick arrow) on the coronal view of contrast-enhanced neck CT (upper right). Thyroid invasion of hypopharyngeal cancer at the mid-pole (lower left) and upper pole (lower right) of the thyroid gland are revealed without destruction of the surrounding soft tissue, including the cartilage. (B and C) Histological section showing no direct thyroid gland invasion. (B) Squamous cell carcinoma fully invaded the hypopharynx (thick arrow), but the fibroadipose tissue and thyroid cartilage are well preserved without cancer invasion (H&E, ×12). (C) There is no associated lesion between the metastasis of the upper pole of the thyroid (thin arrow) and primary tumor (H&E, ×12). The scale bar denotes 1 mm. (D) Histological section showing tumor emboli in the lymphatic channel (H&E, ×40). The scale bar denotes 0.25 mm. Thick arrow: tumor emboli. ThyC, thyroid cartilage; V, vessel; L, lymphatic channel.