This is an interesting and difficult case to me. I don't know what it is yet. A few clarifying questions first - Where exactly of the lesion? Is it in the upper neck or lower (close to sternoclavicular joint?) neck? Is it close or associated to thyroid gland? Are there epithelia-lined cystic areas or mature adipocytes in the lesion? Is the eosinophilic material amyloid, osteoid or just collagen? How easy is it to find mitoses?

I do not think this is PHAT or pleomorphic hyalinized angiectatic tumor of soft tissue (软组织多形性透明变性血管扩张性肿瘤). The characteristics of PHAT are absent (such as ectatic vessels with fibrin thrombi and large pleomorphic cells in myxoid stroma containing inflammatory cells). 

To entertain the possibility of ectopic hamartomatous thymoma (异位性错构性胸腺瘤), one has to see mature adipocytes, squamous epithelial nests/anastomosing trabeculae/cords, and epithelia (squamous or glandular)-lined cystic spaces in addition to spindle cells. I have not seen these elements on the photos.

It appears that AE1 is positive in at least some neoplastic cells. Though unlikely, I wish to rule out medullary thyroid carcinoma.
abin译：
这个病例有意思，难。我还不知道这是什么，先要知道几个问题：病变的确切部位？在颈的上部还是下部（靠近胸锁关节）？邻近或与甲状腺有关吗？病变是否存在衬覆上皮的囊性区或脂肪细胞？是嗜酸性淀粉样物质，还是骨样或就是胶原？核分裂是否易见？
我认为不是软组织多形性透明变性血管扩张性肿瘤(PHAT or pleomorphic hyalinized angiectatic tumor of soft tissue)。没有PHAT的特征（如扩张的血管伴纤维素性血栓，大的多形性细胞和含炎细胞的粘液样间质）。
至于异位性错构性胸腺瘤，必须看到成熟脂肪、鳞状上皮巢/吻合的小梁或索，以及衬覆上皮（鳞状或腺上皮）的囊腔，还有梭形细胞。在图中未见这些成分。
至少部分肿瘤细胞似乎AE1阳性。尽管不太像，我还是想排除甲状腺髓样癌。