Mature fat cells are admixed with variably sized follicles.
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Follicular cells line oval structures filled with adipose cells.
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Colloid distends some of the follicles. The cellular features are bland.
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Adenolipomas of the thyroid is characterized by fat infiltration within a follicular adenoma. Along with thyrolipomatosis and diffuse thyrolipomatosis, adenolipomas are rare entities. Only a few cases have been reported in the literature (Kim).
These neoplasms should be distinguished from lipid-rich follicular adenomas/carcinomas. For example, the clear cell variant of follicular adenoma/carcinomas may contain abundant glycogen or lipid within its cytoplasm. Usually, the clear cells have a vacuolated foamy cytoplasm and should not be mistaken for mature fat cells seen within an adenolipoma (Ge).
Thyrolipomas and thyrolipomatosis are benign entities with excellent prognosis (Ge).
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 Dec;13(6):384-9.
Kim HS, Yun KJ. Adenolipoma of the thyroid gland: report of a case with diagnosis by fine-needle aspiration cytology. Diagn Cytopathol. 2008 Apr;36(4):253-6.