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Table of Contents
Definition / general | Essential features | Terminology | Epidemiology | Etiology | Clinical features | Diagnosis | Radiology description | Radiology images | Prognostic factors | Case reports | Treatment | Gross description | Gross images | Microscopic (histologic) description | Microscopic (histologic) images | Cytology description | Differential diagnosis | Board review question #1 | Board review answer #1Cite this page: Qiao JH. Adenolipoma. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/thyroidadenolipoma.html. Accessed February 18th, 2019.
Definition / general
- Follicular adenoma with mature adipose cells interspersed throughout the tumor (Lloyd: WHO Classification of Tumours of Endocrine Organs, 4th Edition, 2017)
- Adipocytes can be found in benign thyroid (adipose metaplasia), nonneoplastic goiter, benign (adenolipoma) and malignant follicular derived thyroid tumors (Am J Surg Pathol 1989;13:605, Ann Diagn Pathol 2009;13:384)
Essential features
- Rare benign neoplasm
- Usually well encapsulated; composed of variable combinations of follicular thyroid tissue (thyroid adenoma) and mature adipocytes
Terminology
- Adenolipoma = lipoadenoma (in the 4th edition of WHO classification, Lloyd: WHO Classification of Tumours of Endocrine Organs, 4th Edition, 2017)
- Also thyrolipoma, thyroid hamartoma
- In clinical settings (e.g. in studies based on imaging), thyrolipoma is often synonymous with thyrolipomatosis; however the latter term only points to the presence of adipose tissue in thyroid, which morphologically can be a diffusely distributed fat or lipoadenoma or even ectopic thymus / parathyroid
Epidemiology
- Extremely rare benign neoplasm of thyroid gland
- Fat containing nodules in thyroid found on CT in 1.2 - 2.8% of population (Neuroradiology 2013;55:1405, Pol J Radiol 2015;80:305)
Etiology
- Origin of adipocytes in thyroid tissue is unclear; hypotheses include (Ann Diagn Pathol 2009;13:384):
- Adipose tissue is present in the thyroid gland during embryogenesis
- Adipocytes have a metaplastic origin from fibroblasts
- Disturbance in the development of the primitive foregut
- Reported in Cowden syndrome (PTEN hamartoma tumor syndrome) (Ann Diagn Pathol 1999;3:331, Am J Clin Pathol 2015;144:322)
Clinical features
- Most common clinical manifestation is a slowly enlarging neck mass
- Large thyroid adenolipomas can cause obstructive symptoms, including airway obstruction
Diagnosis
- Diagnosis of thyroid adenolipoma is only possible after surgical resection by microscopic examination
Radiology description
- Imaging results (CT, ultrasound and MRI) of cold thyroid nodules are usually nonspecific with extensive differential diagnoses (Radiology 2002;225:746)
Radiology images
Images hosted on other servers:
Thyrolipoma on CT
MRI
Prognostic factors
- Prognosis is favorable with no evidence of recurrence (Ann Diagn Pathol 2009;13:384)
Case reports
- 35 year old woman with swelling in the neck (Indian J Pathol Microbiol 2008;51:521)
- 53 year old woman (Braz J Otorhinolaryngol 2014;80:542)
- 55 year old woman with a neck mass (Surg Today 2004;34:593)
- 65 year old woman with a 4 month history of a thyroid nodule (Diagn Cytopathol 2008;36:253)
- 65 year old woman with slow growing neck swelling (Pathol Int 1995;45:247)
- 68 year old woman (Histopathology 1986;10:91)
- 69 year old woman with a prominent cold nodule in multinodular goiter (Iran J Pathol 2016;11:456)
Treatment
- Surgical excision is curative
Gross description
- Variable sized thyroid goitrous / adenomatous nodules which can be focally calcified
- Soft and yellow pattern represents adipose tissue
Gross images
Images hosted on other servers:
Cut surface
Microscopic (histologic) description
- Variable proportion of mature adipocytes and thyroid follicles, from 10% to 90% of the whole lesion
- Groups of adipocytes in thyroid goitrous / adenomatous nodules
Microscopic (histologic) images
Contributed by Andrey Bychkov, M.D., Ph.D.
Thyroid lipoadenoma
Adipose metaplasia
Contributed by Jian-Hua Qiao, M.D.
Low power view shows clusters of mature adipocytes in a goitrous / adenomatous thyroid nodule
Intermediate power shows numerous mature adipocytes present
High power shows mature adipose tissue
High power view shows mature adipocytes in benign thyroid glandular / follicular elements
Images hosted on other servers:
Adenolipoma
Cytology description
- Mixed population of adipocytes and thyroid follicular cells (Diagn Cytopathol 2008;36:253)
Differential diagnosis
- Clear cell follicular adenoma (lipid rich variant): follicular cells with small round nuclei and abundant foamy or coarsely vacuolated cytoplasm, thyroglobulin immunostaining highlights cells of thyroid origin
- Parathyroid tissue and lesions (hyperplasia, tumors), especially on frozen section: birefringent crystals are absent (Ann Diagn Pathol 2009;13:384)
Board review question #1
The following statements about adenolipoma of the thyroid gland are correct, EXCEPT:
- Clinical presentation of adenolipoma is usually a slow growing neck mass
- Imaging studies of cold thyroid nodule are usually nonspecific with extensive differential diagnosis
- Large adenolipoma can cause airway obstruction
- Recurrence of adenolipoma after surgical resection is common
Board review answer #1
D. "Recurrence of adenolipoma after surgical resection is common" is incorrect - surgical resection of thyroid adenolipoma is curative with no recurrence or malignant potential
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