Fatty tissue is not usually present within the thyroid gland. Only a few fat‑containing thyroid lesions have been reported to date, and thyrolipoma is the most common fat‑containing lesion of the thyroid gland. Thyrolipomatosis is a condition characterized by diffuse mature adipose cell infiltration of the normal thyroid gland. In this report, we describe what is, to the best of our knowledge, the 12th documented case of thyrolipomatosis, and review the fat‑containing lesions of the thyroid gland. A 68‑year‑old Japanese woman presented with a neck mass that had first been noticed ~7 years earlier. A computed tomography scan revealed diffuse thyroid gland enlargement and total thyroidectomy was performed. The histopathological examination revealed that mature fatty tissue was diffusely distributed throughout the thyroid gland, as well as among the hyperplastic follicles. Capsular formation or amyloid deposition were not observed. Nuclear grooves or intranuclear cytoplasmic inclusions were not observed. Accordingly, thyrolipomatosis was diagnosed. Albeit rare, various neoplastic and non‑neoplastic thyroid lesions may contain mature fatty tissue. Therefore, thyrolipomatosis must be included in the differential diagnostic consideration of fat‑containing lesions of the thyroid gland.

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