Adenolipoma

Thyroid gland
Benign neoplasms
Adenolipoma

Author: Jian-Hua Qiao, M.D., FCAP
Editorial Board Member Review: Andrey Bychkov, M.D., Ph.D.

Revised: 5 January 2018, last major update August 2017

Copyright: (c) 2002-2018, PathologyOutlines.com, Inc.

PubMed Search: Adenolipoma [title]

Table of Contents

Cite this page: Qiao, J. H. Adenolipoma. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/thyroidadenolipoma.html. Accessed May 21st, 2018.

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):
1. Adipose tissue is present in the thyroid gland during embryogenesis
2. Adipocytes have a metaplastic origin from fibroblasts
3. 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

Images hosted on PathOut server:

Image contributed by Andrey Bychkov, M.D., Ph.D.

Thyroid lipoadenoma

Adipose metaplasia

Images contributed by Jian-Hua Qiao, M.D., FCAP

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