DOI: 10.1148/radiol.2253010663
(Radiology 2002;225:746-750.)
© RSNA, 2002
Case 53: Adenolipoma of the Thyroid Gland1
Alexandra Borges, MD and
Ana Catarino, MD
1 From the Departments of Radiology (A.B.) and Pathology (A.C.), Instituto Português de Oncologia Francisco Gentil, Centro de Lisboa, Rua Prof Lima Basto, 1093 Lisbon Codex, Portugal. Received March 23, 2001; revision requested May 2; revision received July 9; accepted August 9. Address correspondence to A.B. (e-mail: borgesalexandra@hotmail.com).
Index terms: Diagnosis Please • Thyroid, neoplasms, 273.36
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HISTORY
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A 70-year-old man with a long-standing history of increased neck volume was examined in the Ear, Nose, Throat Clinic because he was complaining of dysphagia and dyspnea on exertion. His medical history was irrelevant except for a family history of goiter in several relatives. At clinical examination, an enlarged right thyroid gland lobe with a lobulated surface that was soft was detected. The gland was mobile with deglutition, but the inferior limit of the right lobe could not be palpated.
Laboratory findings disclosed normal thyrotropin, triiodothyronine, and thyroxine levels, and no antithyroid antibodies were detected. Fine-needle aspiration biopsy of the right lobe of the thyroid gland was performed without imaging guidance and revealed normal follicular cells and colloid and no neoplastic cells. Scintigraphic findings disclosed absence of activity at the site of the nodule.
The patient then underwent neck and mediastinal computed tomography (CT) to evaluate for intrathoracic component and airway patency. Additionally, magnetic resonance (MR) imaging of the neck and ultrasonography (US)-guided fine-needle aspiration biopsy were performed.
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IMAGING FINDINGS
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Transverse CT scans (Fig 1) showed a large nonhomogeneous nodule partially replacing the right lobe of the thyroid gland and extending inferiorly into the superior mediastinum along the prevascular space. This nodule had well-defined margins and contained several areas of low attenuation, which suggested fat, and a small calcification. There was slight tracheal displacement to the left side and a slight decrease in the transverse diameter of the tracheal lumen. The lesion was clearly separate from the esophagus. The left lobe of the thyroid gland showed no abnormalities.
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Figure 1a. Nonenhanced transverse CT scans through the (a) lower neck and (b) thoracic inlet (window width, 228 HU; window level, 43 HU) show a large nonhomogeneous nodule partially replacing the right lobe of the thyroid gland and extending inferiorly into the superior mediastinum along the prevascular space. The nodule is largely composed of fatty tissue (arrows in a) and shows a small calcification (arrow in b). Note the cleavage plane between the lesion and the esophagus (arrowhead in a). The attenuation value of the low-attenuation tissue was -106 HU.
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Figure 1b. Nonenhanced transverse CT scans through the (a) lower neck and (b) thoracic inlet (window width, 228 HU; window level, 43 HU) show a large nonhomogeneous nodule partially replacing the right lobe of the thyroid gland and extending inferiorly into the superior mediastinum along the prevascular space. The nodule is largely composed of fatty tissue (arrows in a) and shows a small calcification (arrow in b). Note the cleavage plane between the lesion and the esophagus (arrowhead in a). The attenuation value of the low-attenuation tissue was -106 HU.
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The possible presence of fat within the nodule put the initial diagnosis of colloid goiter in question, and additional MR imaging and US-guided fine-needle aspiration biopsy were performed to further characterize this lesion. At MR imaging (Fig 2a, 2b), a large heterogeneous nodule was seen replacing the right lobe of the thyroid gland. This nodule contained large irregular areas of T1-weighted hyperintensity that became hypointense on the fat-suppressed transverse spectral presaturation inversion-recovery T1-weighted MR image (Fig 2c), and these findings further indicated the presence of fat. The MR image showed the intrathyroid location of the lesion, its well-defined borders, and clear cleavage planes with adjacent anatomic structures.
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Figure 2a. (a) Transverse and (b) coronal T1-weighted MR images (repetition time msec/echo time msec, 490/13) and (c) transverse T1-weighted spectral presaturation inversion-recovery MR image (1,001/20) show a heterogeneous nodule that replaces the right lobe of the thyroid gland and contains large areas of T1-weighted hyperintensity (arrowheads in a and b) that became hypointense on the fat-suppressed image in c.
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Figure 2b. (a) Transverse and (b) coronal T1-weighted MR images (repetition time msec/echo time msec, 490/13) and (c) transverse T1-weighted spectral presaturation inversion-recovery MR image (1,001/20) show a heterogeneous nodule that replaces the right lobe of the thyroid gland and contains large areas of T1-weighted hyperintensity (arrowheads in a and b) that became hypointense on the fat-suppressed image in c.
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Figure 2c. (a) Transverse and (b) coronal T1-weighted MR images (repetition time msec/echo time msec, 490/13) and (c) transverse T1-weighted spectral presaturation inversion-recovery MR image (1,001/20) show a heterogeneous nodule that replaces the right lobe of the thyroid gland and contains large areas of T1-weighted hyperintensity (arrowheads in a and b) that became hypointense on the fat-suppressed image in c.
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No cervical, supraclavicular, or superior mediastinal lymphadenopathy was detected. A scan obtained at US-guided fine-needle aspiration biopsy (Fig 3) showed the heterogeneity of the nodule of the right lobe of the thyroid gland and large hyperechoic areas within the nodule, which reflected the fatty component. A reverberation artifact caused by the tip of the needle was seen in the middle of the hyperechoic component of the lesion.
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Figure 3. Image at US-guided fine-needle aspiration biopsy (7.5-MHz probe; 22-gauge needle) shows a nodule in the right lobe of the thyroid gland, with large hyperechoic areas and a needle tip within the hyperechoic component. Note the reverberation artifact (arrowheads) caused by the needle tip.
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DISCUSSION
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At both clinical examination and imaging studies of nodular thyroid lesions, findings usually are nonspecific and suggest extensive differential diagnoses. In most instances, these lesions require fine-needle aspiration biopsy or even excisional biopsy for a final diagnosis. The finding of macroscopic fat within a lesion of the thyroid gland considerably limits the list of possible differential diagnoses and is, therefore, an important imaging clue in this case.
Fat-containing lesions of the thyroid gland have been broadly categorized as (a) lesions containing macroscopic mature fatty tissue, such as in this case, and (b) lesions rich in microscopic intracellular fat vacuoles, or lesions that also are referred to as clear cell or lipid-rich neoplasms (1,2). The differential diagnoses that would be considered for the first group of lesions include lipomatous goiter (also known as adenolipomatosis or choristomatous adiposity), amyloid goiter, lymphocytic thyroiditis, Graves disease, adenolipoma, intrathyroid thymic or parathyroid lipoma, encapsulated papillary carcinoma, and liposarcoma (1,3–7). Occasionally, cervical lipomas may mimic nodules of the thyroid gland, particularly when they grow into the thyroid gland (8), but findings at multiplanar cross-sectional imaging can be used to resolve this issue in most cases.
Clues to the diagnosis that were based on the clinical history included the presence of a focal well-circumscribed lesion of the thyroid gland that was soft at palpation, with no associated symptoms of dysfunction of the thyroid gland. Laboratory findings confirmed the euthyroid state, and findings at scintigraphy disclosed absence of activity at the site of the nodule. The soft consistency of the lesion at palpation was the single most important clinical hint in regard to the diagnosis.
At CT, the presence of a single nodule of the thyroid gland was confirmed, and mediastinal extent and slight tracheal impingement were detected. The finding of large, irregular, low-attenuation components with negative Hounsfield units cast doubt on the initial diagnosis of colloid goiter, on the basis of results of the first blinded fine-needle aspiration biopsy without imaging guidance. The MR image showed a well-defined heterogeneous nodule of the thyroid gland that contained large areas of T1-weighted hyperintensity, which became hypointense with the fat-suppressed sequence. At imaging, the presence of a well-defined benign-appearing nodule of the thyroid gland with macroscopic fat admixed with islands of soft tissue is most consistent with four differential diagnoses: adenolipoma of the thyroid gland, intrathyroid thymic lipoma, intrathyroid parathyroid lipoma, and encapsulated papillary carcinoma.
Lipomatous and amyloid goiters manifest as diffuse fatty infiltration of the thyroid gland and not as a single focal nodule (2,9,10). Additionally, lipomatous goiters tend to manifest in patients at an earlier age as a diffuse swelling of the thyroid gland, whereas amyloid goiter is almost always associated with systemic amyloidosis (2,3,5,6).
Lymphocytic thyroiditis also is a diffuse inflammatory process and is accompanied by the presence of antithyroid antibodies, which were not present in this case. Graves disease is excluded because of the absence of activity at the site of the nodule and normal function of the thyroid gland.
Although intrathyroid thymic and parathyroid lipomas could have a similar imaging appearance, manifesting as single nodules of the thyroid gland and mainly composed of fat, we found no cases described in the English-language literature. However, if these diagnoses are in question, positive results with thyroglobulin immunostaining help to rule them out, because immunostaining of parathyroid and thymic tissue will have negative results (6,11–13).
In the literature (3,14), only three cases are described of encapsulated papillary carcinomas of the thyroid gland with a substantial amount of fatty tissue. This diagnosis could not be excluded on the basis of only clinical and imaging findings, although the fine-needle aspiration biopsy results were negative for neoplastic cells.
Liposarcomas of the thyroid gland also are rare, and only two cases have been described. Both of these cases were in patients who at clinical presentation had rapidly growing masses with aggressive clinical features (15,16).
Thus, on the basis of the clinical and imaging findings, adenolipoma of the thyroid gland was considered the most likely diagnosis. The patient underwent right hemithyroidectomy, and the diagnosis was confirmed at histopathologic analysis. Macroscopically, the entire tumor was 50 x 35 x 30 mm, and it compressed the adjacent thyroid tissue. On a cut section, the major bulk of the tumor was composed of large yellowish areas and contained, adjacent to its surface, a well-defined 12-mm-diameter white nodule with a smooth shiny surface. Microscopically (Fig 4), the white nodule was composed of hyperplastic follicles of the thyroid gland, and the bulk of the remaining tumor showed mature adipose tissue separated by thin fibrous septa. No degenerative features were seen within the fatty component, namely, calcification, hemorrhage, or fibrosis. No cellular atypia was seen in both tumor components except for the presence of rare mitotic figures within the follicular component. Also, there were no signs of vascular or capsular invasion. The final diagnosis was adenolipoma of the thyroid gland.
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Figure 4. Histologic specimen shows hyperplastic follicles (arrowheads) of the thyroid gland and mature adipose tissue (thick arrow) that make up the major bulk of the tumor. These two tumor components are separated by thin fibrous septa (thin arrows). (Hematoxylin-eosin stain; original magnification, x100.)
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Adenolipoma of the thyroid gland has been termed adenolipoma, thyrolipoma, or thyroid hamartoma (1). This tumor is composed of tissue of the thyroid gland and fat in different proportions and is usually encapsulated (5,6). Review of the few cases published so far in the English-language literature shows that the most common clinical symptoms are increased neck volume and/or symptoms of compression (4–6). All patients in whom thyroid gland function was evaluated were euthyroid, and all those who had a scintigraphic scan had an absence of activity at the site of the nodule (5,6). The amount of fat at gross inspection varied from 10% to 90% (2,3). In all cases, the lesions described were considered benign and were treated surgically (2,3,7). There are only two cases in the literature in which imaging studies, CT scans of the neck, and imaging findings similar to those in the case just described are mentioned (6,17).
The pathophysiologic features of this lesion are not known. Several different theories have been proposed to explain the presence of mature fat tissue within the thyroid gland. Normal thyroid glands may have a scanty amount of fat immediately adjacent to the capsule and along fibrous tissue septa but do not have fat tissue intermixed with the follicles (1,3). Additionally, fatty replacement, such as that seen in other organs (eg, the salivary gland, the breast, and the pancreas), is not a feature of parenchymal atrophy of the thyroid gland, and no correlation has been established between intrathyroid fat and nutritional status (6). Some authors consider the presence of intrathyroid fat as a developmental anomaly that results from entrapment of adipose tissue during encapsulation of the thyroid gland (3,4).
Such a process explains the presence of fat in some congenital goiters but not in acquired lesions of the thyroid gland where fat is limited to the lesion itself without involvement of adjacent parenchyma (6,7). Others consider the presence of fat as a metaplastic process that results from vascular changes that lead to local hypoxia and subsequent mesenchymal tissue metaplasia (3–6). This theory explains the presence of fat in certain diseases of the thyroid gland, such as amyloid and colloid goiter, but it is unlikely to explain the cause of macroscopic fat in the absence of other connective tissue degenerative changes or inflammation. Finally, a group of authors believe that the presence of fat in tumors of the thyroid gland is an integral neoplastic component of the tumors, which implies that such neoplasms are mixed epithelial and mesenchymal proliferations such as other tumors seen elsewhere, namely, benign mixed tumors of salivary gland origin (1,3,4). Cytogenetic studies could be of great help to solve this issue.
In a review article by Gnepp et al (3), only 17 cases of lesions of the thyroid gland that contained macroscopic fat were found at the Armed Forces Institute of Pathology, Washington, DC. In that review, adenomas of the thyroid gland, dyshormonogenetic goiter, lymphocytic thyroiditis, amyloid goiter, and encapsulated papillary carcinoma were the only lesions of the thyroid gland that contained a significant amount of mature fat. In a study by Autelitano et al (18) in which the authors examined thyroid glands sampled from 507 consecutive autopsies, five adenolipomas were incidentally found. Therefore, it is possible that these lesions are more common than expected but that they may not be detected when imaging studies are not performed. At blinded fine-needle aspiration biopsy, the fatty component may be missed, and these lesions can be categorized as colloid goiter or follicular adenoma (5).
The presence of macroscopic fat within the thyroid gland is easily detected at US, CT, and MR imaging, and this finding considerably limits the diagnostic possibilities. Also, with the exception of liposarcoma and encapsulated fat-containing papillary carcinoma, which are exceedingly rare lesions of the thyroid gland, nodules of the thyroid gland that contain macroscopic fat are benign, with important therapeutic and prognostic implications.
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FOOTNOTES
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Part 1 of this case appeared 4 months previously and may contain larger images.
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REFERENCES
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- LiVolsi VA. Unusual tumors and tumor-like conditions of the thyroid In: Surgical pathology of the thyroid. Major problems in pathology series, vol 22, chap 15. Philadelphia, Pa: Saunders, 1990; 323-350.
- Schroder S, Bocker W. Lipomatous lesions of the thyroid gland: a review. Appl Pathol 1985; 3:140-149.[Medline]
- Gnepp DR, Ogorzalek JM, Heffess CS. Fat-containing lesions of the thyroid gland. Am J Surg Pathol 1989; 13:605-612.[Medline]
- Laforga J, Vierna J. Adenoma of the thyroid gland containing fat (thyrolipoma): report of a case. J Laryngol Otol 1996; 110:1088-1089.[Medline]
- DeRienzo D, Truong L. Thyroid neoplasms containing mature fat: a report of two cases and review of the literature. Mod Pathol 1989; 2:506-510.[Medline]
- Schroder S, Bocker W, Hussellmann H, Dralle H. Adenolipoma (thyrolipoma) of the thyroid gland: report of two cases and review of the literature. Virchows Arch A Pathol Anat Histopathol 1984; 404:99-103.[CrossRef][Medline]
- Pagés B, Tiraskis B. Deux cas de thyrolipome. Ann Pathol 1985; 5:283-286.[Medline]
- Leonidas JR, Goldman JM, Wheeler MF. Cervical lipomas masquerading as thyroid nodules. JAMA 1985; 253:1436-1437.[Abstract]
- Simha M, Doctor V. Adenolipomatosis of the thyroid gland. Indian J Cancer 1983; 20:215-217.[Medline]
- Arslan A, Alic B, Uzunlar AK, Buyukbayram H, Sari I. Diffuse lipomatosis of the thyroid gland. Auris Nasus Larynx 1999; 26:213-215.[CrossRef][Medline]
- Ranaldi R, Goteri G, Bearzi I. Lipid-rich adenoma of the thyroid. Path Res Pract 1993; 189:1101-1106.
- Van Hoeven KH, Brennan MF. Lipothymoadenoma of the parathyroid. Arch Pathol Lab Med 1993; 117:312-314.[Medline]
- Ducatman BS, Wilkerson SY, Brown JA. Functioning parathyroid lipoadenoma: report of a case diagnosed by intraoperative touch preparations. Arch Pathol Lab Med 1986; 110:645-647.[Medline]
- Bisi H, Longatto Filho A, de Camargo RY, Fernandes VS. Thyroid papillary carcinoma lipomatous type: report of two cases. Pathologica 1993; 85:761-764.[Medline]
- Andrion A, Gaglio A, Dogliani N, Bosco E, Mazzucco G. Liposarcoma of the thyroid gland: fine-needle aspiration cytology, immunohistology, and ultrastructure. Am J Clin Pathol 1991; 95:675-679.[Medline]
- Nielsen VT, Knudsen N, Holm IE. Liposarcoma of the thyroid gland. Tumori 1986; 72:499-502.[Medline]
- Schroder S, Hagemann J, Bocker W. Adenolipoma of the thyroid (thyrolipoma): a case report of a rare fat cell tumor diagnosed by computed tomography. Rofo Fortschr Geb Rontgenstr Nuklearmed 1984; 141:239-240[German].
- Autelitano F, Santeusanio G, Mauriello A, et al. Latent pathology of the thyroid: an epidemiological and statistical study of thyroids sampled during 507 consecutive autopsies. Ann Ital Chir 1992; 63:761-781[Italian].[Medline]
Congratulations to the 50 individuals who submitted the most likely diagnosis (Adenolipoma of the Thyroid Gland) for Diagnosis Please, Case 53. The names and locations of the individuals, as submitted are as follows:
- Ken Baliga, Rockford, Ill
- Marcelo Bordalo Rodrigues, São Paulo, Brazil
- Eric L. Bressler, MD, Minnetonka, Minn
- Michael P. Buetow, MD, Okemos, Mich
- Peter Buetow, Bellingham, Wash
- Carlos Capiel, MD, Mar Del Plata, Argentina
- Thomas S. Chang, MD, Pittsburgh, Pa
- Daniel M. Chernoff, MD, PhD, Saratoga Springs, NY
- James W. Cole, MD, Cincinnati, Ohio
- Sebastian Costantino, MD, Mar Del Plata, Argentina
- Federico Dalla Torre, MD, Cipolletti, Rio Negro, Argentina
- Mustafa Kemal Demir, MD, Ataköy, Istanbul, Turkey
- Shella Farooki, MD, Dublin, Ohio
- Gabriel C. Fernández Pérez, Vigo, Spain
- Akira Fujikawa, Tokyo, Japan
- Christine M. Glastonbury, MD, San Francisco, Calif
- Thomas Grant, DO, Chicago, Ill
- Yukihiro Hama, MD, Tokorozawa, Japan
- Robert Hermans, MD, PhD, Leuven, Belgium
- Vinay Jain, Pontiac, Mich
- Eric Kinder, MD, Seattle, Wash
- Mitchell A. Klein, MD, Milwaukee, Wis
- Thorsten Krebs, MD, Ridgefield, Conn
- Mario Laguna, West Allis, Wis
- N. B. S. Mani, MD, Nassau, Bahamas
- Frank McKowne, MD, Vancouver, Wash
- Manabu Minami, MD, Tokyo, Japan
- Sankar Ranjan Mondal, Nassau, Bahamas
- Mizuki Nishino, MD, Kyoto, Japan
- Sanford M. Ornstein, MD, Phoenix, Ariz
- Harish Panicker, MD, Detroit, Mich
- Carlo L. E. Petralli, MD, Bruderholz, Switzerland
- Frank Pilleul, Lyon, France
- James Ravenel, MD, Charleston, SC
- Thomas Roeren, MD, PhD, Aarau, Switzerland
- Mourad Said, MD, Monastir, Tunisia
- Anthony J. Scuderi, MD, Johnstown, Pa
- Dr David Scullion, Harrogate, England
- Matt Shapiro, MD, Lowell, Mass
- Taro Shimono, MD, Osaka, Japan
- Paolo Siotto, MD, Cagliari, Italy
- R. Soler, MD, La Coruña, Spain
- Yoshito Tsushima, MD, Ohta, Gunma, Japan
- Kai Vilanova Busquets, Girona, Spain
- Christopher Vittore, MD, Rockford, Ill
- Jeff West, MD, Jacksonville, Fla
- Scott White, Rockford, Ill
- Tatsuya Yamamoto, Obama, Japan
- Joe Yut, Olathe, Kan
- Yu Zhang, Nagoya, Japan
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HISTORY
IMAGING FINDINGS
