Multinodular goiter with adipose metaplasia: A case report Worapop Suthiwartnarueput, MD Department of Pathology and Forensic Medicine Faculty of Medicine, Thammasat University, Thailand Introduction The presence of adipose tissue within the thyroid gland has been reported in wide range of conditions such as adenolipoma, thyrolipomatosis, goiter, papillary carcinoma, lymphocytic thyroiditis and heterotopic nest. Several theories have been proposed such as metaplastic change from stromal fibroblasts or neoplastic thyrocytes, massive steatosis of the follicular cells, and developmental abnormality[1,2]. The author describes a rare case of multinodular goiter with adipose metaplasia which has a few reported cases[3,4]. Case report An 82-year-old woman presented with a 60-year history of midline neck mass with gradual onset of compressive symptom for the past several months. CT of the neck showed diffuse thyroid enlargement with features suggestive of multinodular goiter extending to the superior mediastinum. Total thyroidectomy was performed. Gross examination revealed a huge thyroid gland with nodular surface measuring 14 x 9.8 x 5 cm. and weighing 320.5 g. Serial sections showed diffuse colloidal tan-brown nodules of 1-6.2 cm. in size, grossly compatible with multinodular goiter, with calcifications in the isthmus (Fig. 1). Histologic sections showed multinodular goiter with scattered adipocytic infiltration (Fig. 2), degenerative change and calcifications (not shown). There was an encapsulated firm white-tan mass on the right lobe measuring 3.8 cm. in the maximal extent (white arrow in Fig. 1) Histologic sections revealed follicular adenoma without fatty infiltration (Fig. 3). Figure 1 Gross pathology of the thyroid gland. Cut surface shows diffuse tan-brown colloidal nodules ranging from 1-6.2 cm. in size , grossly compatible with multinodular goiter, with calcifications in the isthmus. The arrow indicates a 3.8-cm. encapsulated firm white-tan mass on the right lobe histologically shows follicular adenoma (see fig. 3). Discussion Fatty infiltration of the thyroid has been described in various conditions as aforementioned. Recently, Ge et al classified the fat-containing lesions of the thyroid into three patterns: (1) adipose tissue within the follicular adenoma (thyrolipoma); (2) adipose tissue diffusely infiltrating the thyroid (thyrolipomatosis); and (3) adipose tissue involving both follicular adenoma and surrounding thyroid tissue[5]. In this case, there are scattered fatty infiltration in the multinodular goiter with degenerative change and dystrophic calcifications. No fatty infiltration of the surrounding thyroid is seen. Although there is one follicular adenoma. No fatty infiltration is identified in this adenoma. Therefore, the final diagnosis is multinodular goiter with adipose tissue infiltration, most likely from adipose metaplasia, with one follicular adenoma. To the author’s knowledge, the infiltrating adipocytes are most likely from metaplastic transformation either from stromal fibroblasts or thyrocytes, as a consequence of prolonged degenerative process. It is incompatible with thyrolipomatosis and thyrolipoma due to absence of fatty infiltration of the surrounding thyroid and absence of fatty infiltration of the follicular adenoma, respectively. Figure 2 Histopathology of goiter with adipose metaplasia. Figure 2A shows proliferation of benign follicles of various sizes with fibrous capsule, diagnostics of nodular goiter (100x). Figure 2B to 2D show adipocytic infiltration scattered among benign follicles in the goiter, suggestive of adipose metaplasia (2B; 100x, 2C; 200x, 2D; 400x). Figure 3 Histopathology of follicular adenoma. The sections show proliferation of microfollicles and normofollicles with thick fibrous capsule, compatible with follicular adenoma. No adipocytic infiltraition is seen. (200x) References 1. Schröder S, Böcker W. Lipomatous lesions of the thyroid gland: a review. Appl Pathol 1985;3(3):140-9. 2. Sanuvada RVS, Chowhan AK, Rukmangadha N, Patnayak R, Yootla M, Amancharla LY. Thyrolipomatosis: an inquisitive rare entity. Gland Surg 2014;3(14). 3. Metthew M, Gard S. A thyroid nodule with adipose metaplasia in a nodular goiter: a case report. Indian J Pathol Microbiol 2007;50(2):369-70. 4. Soda G, Baiocchini A, Nardoni S, Bosco D, Melis M. Benign tumors of heterotopic tissue in the thyroid gland: a report of two cases of lipomatous lesions. J Exp Clin Cancer Res 2000;19(2):245-8. 5. Ge Y, Luna MA, Cowan DF, Truong LD, Ayala AG. Thyrolipoma and thyrolipomatosis: 5 case reports and historical review of the literature. Ann Diagn Pathol 2009;13:384-9.