Cytological Features of a Lymphoepithelial Cyst

Soonchunhyang Medical Science 20(2):131-135, December 2014

pISSN: 2233-4289 I eISSN: 2233-4297

CASE REPORT

Cytological Features of a Lymphoepithelial Cyst Collected from Fine Needle Aspiration of the Thyroid Gland That Mimicked Papillary Thyroid Carcinoma: A Case Report In Ho Choi1, Sun-Wook Kim2, Jee Soo Kim3, Young-Lyun Oh4 Department of Pathology, Soonchunhyang University Seoul Hospital, Soonchunhyang University College of Medicine, Seoul; Departments of 2Medicine, Surgery, and 4Pathology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea

1 3

Since its first description in 1989, lymphoepithelial cyst of the thyroid gland (LEC-T) has been generally considered a branchial cleft derivative similar to its presentation in other sites, including thymus, parathyroid, and pancreas. However, its characterization has mainly focused on histologic and sonographic findings, and cytological findings are generally described simply or left out entirely. Fine needle aspiration cytology (FNAC) of our case showed large tissue fragments of epithelial cells on a background of lymphocytes. Some areas showed sheets or small nests of squamoid cells, which were closely admixed with clusters of lymphoid cells. Squamous cells contained relatively moderate to large amounts of eosinophilic cytoplasm and vesicular nuclei with occasional nuclear grooves that lacked intranuclear inclusions. Some cells demonstrated keratinization and nuclear atypia. Herein, we describe FNAC findings of LEC-T and review other possible diagnoses. Keywords: Thyroid gland; Branchioma; Cyst; Cell biology

INTRODUCTION The lymphoepithelial cyst of the thyroid gland (LEC-T) has been

CASE REPORT 1. Patient history

generally considered as a branchial cleft derivative, and it has been

A 54-year-old woman with no previous medical problems visited

unusual occurring site like other unusual sites such as the thymus,

hospital due to a palpable neck mass. Laboratory findings showed

oral cavity, parotid gland, and pancreas [1]. Since the first report of a

increased microsomal antibody (1,175.4 μ/mL; normal, 0-60 μ/mL)

LEC-T in 1989, its histological resemblance to branchial cleft cysts

but normal findings in other thyroid function test, parathyroid hor-

and embryological branchial cleft derivatives in the thyroid, thy-

mone, and calcitonin. Sonographically, the mass was a 1.6-cm, ir-

mus, and parathyroid have led to general consensus of its branchial

regular, calcified, hypoechoic nodule (Fig. 1A) in the inferior pole of

origin [2]. Although there have been several reports of histological

the right thyroid with multiple hypoechoic lesions in bilateral cervi-

and immunohistochemical findings of LEC-T [1], its cytological

cal lymph nodal enlargement. Due to suspicion for malignancy, so-

characteristics have been described in only a few reports [3-5]. Here-

no-guided FNAC and BRAF study (result: not detected) were per-

in, we describe the cytological findings on fine needle aspiration cy-

formed. Computed tomography revealed a 1.4-cm, mildly enhanc-

tology (FNAC) of a 54-year-old woman with LEC-T mimicking

ing soft-tissue mass in the right thyroid lobe (Fig. 1B) with multiple

papillary thyroid carcinoma (PTC).

suspicious metastatic nodes. Total thyroidectomy was performed due to concern for thyroid cancer.

Correspondence to: Young-Lyun Oh Department of Pathology, Samsung Medical Center, Sungkyunkwan University School of Medicine, 81 Irwon-ro, Gangnam-gu, Seoul 135-710, Korea Tel: +82-2-3410-2805, Fax: +82-2-3410-0025, E-mail: [email protected] Received: Sep. 30, 2014 / Accepted after revision: Oct. 27, 2014

© 2014 Soonchunhyang Medical Research Institute This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/).

http://jsms.sch.ac.kr

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Choi IH, et al. • Cytology of Lymphoepithelial Cyst in Thyroid Gland

2. Cytological findings of lymphoepithelial cyst of the

on a background of lymphocytes (Fig. 2A). Most of these syncytial

thyroid gland

fragments demonstrated overwhelming cellularity with no notice-

FNAC of LEC-T showed large tissue fragments of epithelial cells

able architectural configuration. However, focal areas showing a

A

B

Fig. 1. Radiologic findings of a lymphoepithelial cyst of the thyroid gland. (A) Ultrasonography reveals a 1.6-cm, irregular, hypoechoic nodule in the inferior pole of the right lobe and multiple hypoechoic lesions in the mid and superior poles. (B) Computed tomography reveals a 1.4-cm, mildly enhanced soft-tissue mass in the right lobe and heterogeneous attenuation in the parenchyma of both lobes.

A

B

C

D

E

F

Fig. 2. Fine needle aspiration cytology of the lymphoepithelial cyst of the thyroid gland. (A) Syncytial tissue fragments are present in the lymphocytic background. (H&E, × 12.5). (B) Cellular fragments show papillary-like configuration with fibrovascular stroma (H&E, × 40). (C) Area suggesting squamous metaplasia is identified in the tissue fragments (H&E, × 100). (D) Squamous components (left side) and clusters of lymphoid cells (center and superior side) are closely blended (H&E, × 200). (E) Some areas of squamous cells show unorganized arrangement and mild cellular atypia (H&E, × 400). (F) Several small solid cell nests and detached cells are intermingled with lymphocytes (H&E, × 400).

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Soonchunhyang Medical Science 20(2):131-135

Cytology of Lymphoepithelial Cyst in Thyroid Gland • Choi IH, et al.

papillary-like configuration with fibrovascular stroma (Fig. 2B) and

background of Hashimoto’s thyroiditis.

suggesting squamous metaplasia were also noted (Fig. 2C). Sheets of squamoid cells were closely admixed with clusters of lymphoid cells (Fig. 2D). These cells contained relatively moderate to large amounts

3. Histological findings of lymphoepithelial cyst of the thyroid gland

of eosinophilic cytoplasm and vesicular nuclei, which varied in size

Grossly, the resected specimen showed a multinodular, yellowish-

from micro- to macronucleoli. Nuclear grooves were occasionally

gray, solid lesion (Fig. 3A, arrowhead) in the inferior pole of the right

present, but intranuclear inclusions were not identified. Some cells

thyroid lobe. The surrounding parenchyma of both lobes showed

demonstrated keratinization and nuclear atypia (Fig. 2E). Small sol-

multiple tiny, patchy lesions. Microscopically, the lesion consisted of

id nests and single squamoid cells were dispersed on the back-

labyrinth-like cystic spaces lined by squamous epithelial cells with

ground of lymphocytes (Fig. 2F). Scattered lymphocytes showed

florid lymphoid hyperplasia forming follicles and germinal cen-

polymorphous features without atypia, but eosinophils were not

ters (Fig. 3B, C). Some squamoid cells had solid or pseudopapillary

easily recognized. FNAC was interpreted as suspicious for PTC on a

architectures (Fig. 3D, E), and several necrotic foci with cholesterol

A

B

C

D

E

F

G

H

I

Fig. 3. Macroscopic and microscopic findings of the lymphoepithelial cyst of the thyroid gland. (A) Grossly, the specimen has a multinodular, yellowish-gray, solid lesion (arrowhead). (B-F) The lesion is a labyrinth-like cystic lesion lined by squamous epithelial cells with florid lymphoid hyperplasia and focal desquamating keratin. The epithelial components show solid and papillary architecture. Some damaged cellular lesions shows lymphocytic and eosinophilic infiltration (H&E stain; B, × 12.5; C,× 100; D&E,× 200; F, × 400). (G) The p63 is positive in the squamous components (× 200). (H) Ki-67 proliferation index is less than 2% (× 200). (I) Opposite lobe contains a 0.2-cm papillary microcarcinoma, follicular variant (H&E, × 200). Soonchunhyang Medical Science 20(2):131-135


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Choi IH, et al. • Cytology of Lymphoepithelial Cyst in Thyroid Gland

crystals and calcification were also noted. Some damaged areas of

roid gland is known to show mucin-producing cells, intermediate

the squamous epithelium demonstrated cellular atypia and an in-

cells, and squamous cells on FNAC, consistent with salivary gland

filtration of lymphocytes and eosinophils (Fig. 3F). The squamous

origin. However, the present case showed no glandular differentia-

elements showed positivity for p63 (Fig. 3G). Indeed, Ki-67 prolif-

tion or eosinophilia.

eration index of theses squamous elements was less than 2%, sug-

Most cases of squamous cell carcinoma of thyroid are present

gesting a benign lesion (Fig. 3H). No atypical lymphoid tissue was

with primary papillary carcinoma or anaplastic carcinoma of thy-

identified. The surrounding parenchyma showed lymphocytic in-

roid, remaining rare cases with pure squamous cell carcinoma (less

filtration with lymphoid aggregation. Incidentally, a minute PTC

than 1% of all thyroid cancer). Consequentially, the aspiration cy-

(0.2 cm), follicular variant was found in the opposite lobe but was

tology of squamous cell carcinoma in thyroid, whether the pure

not detected during preoperative radiologic examinations (Fig.

form or the combined form with papillary or anaplastic carcinoma,

3I). No lymph node metastasis was noted.

can show large sheets of squamous epithelium. However, it usually shows marked nuclear atypia, frequent mitoses, and necrotic back-

DISCUSSION

ground comparing to LEC-T; therefore, absence of these atypical findings may help identify the true diagnosis of LEC-T.

LEC-T has been postulated to originate from solid cell nests of

Among the other neoplasms, squamous metaplasia is occasion-

the thyroid gland, which are derivatives of the embryonic ultimo-

ally seen in PTCs (range, 20% to 40%), including conventional and

branchial body [6], and are associated with chronic or Hashimoto’s

Warthin-like variant (W-PTC) [9]. If syncytial tissue fragments of

thyroiditis. Previous reports about LEC-T focused on its histologi-

epithelial cells with abundant cytoplasm with or without papillary

cal and sonographic findings, and almost all cases demonstrated

architecture are closely admixed with lymphoid tissue, a specimen

benign sonographic findings with rare calcification [4,5]. Other-

can be mistaken for W-PTC. Our case showed squamoid syncytial

wise, previous reports of cytological features of LEC-T on FNAC

fragments closely intermingled with lymphoid tissue, matching

were sparsely documented and simple, despite the practical useful-

histological findings showing the squamous epithelium and sub-

ness of FNAC today [3-5].

epithelial lymphoid aggregates (Figs. 2D, 3C). W-PTC can show

The key feature of the present case is squamous metaplasia with a

predominant cystic change, but it usually occurs in the lateral lobe

lymphocytic background. Large syncytial clusters or small solid

and is composed of Hurthle cells [10], which is opposed to present

nests of squamous epithelial cells and clusters of lymphoid cells were

case having no oncocytic cells on FNAC. Indeed, no case of the

closely mixed (Fig. 2C-F). A variety of thyroid lesions can exhibit

Warthin-like variant of PTC with extensive squamous metaplasia

squamous differentiation, and it is problematic and challenging to

has been reported in literature of thyroid FNAC.

differentiate metaplastic from neoplastic origin. Nodular, tumor-

Although some authors have insisted that LEC-T should be con-

like squamous metaplasia can appear as an evolution of Hashimoto’

sidered for solid thyroidal masses with respiratory epithelium on

s thyroiditis and nodular goiter [7,8]. However extensive squamous

FNAC [5], cases without respiratory cells and extensive lymphocyte

metaplasia is rarely present on thyroidal FNAC and requires a thor-

and squamous tissue fragments may still be malignant, especially

ough approach to diagnosis and treatment [7].

when some cells show PTC-like nuclei. Additionally, microscopic

Given squamous metaplasia with lymphocytic background on

findings with mild nuclear atypia squamous metaplasia on lym-

cytology, several other entities can be considered in the differential

phocytic background and the additional radiologic findings suspi-

diagnosis, including mucoepidermoid carcinoma, squamous cell

cious for lymph node metastasis like present case led to the misdi-

carcinoma, and Warthin-like variant of PTC. High-grade muco-

agnosis of PTC, in spite of the first impression of lymphocytic thy-

epidermoid carcinoma can exhibit malignant cells similar to squa-

roiditis with extensive squamous metaplasia.

mous or anaplastic carcinoma. In particular, sclerosing mucoepi-

To conclude, it is important to know the cytological pitfalls of

dermoid carcinoma with eosinophilia often occurs on the back-

LEC-T, which may hinder correct diagnosis and prevent appropri-

ground of Hashimoto’s thyroiditis, and its cytological findings are

ate conservative management. Identifying the definite cytological

characterized by tissue fragments of squamous cells with varying

atypia of squamous cells and nuclei of PTC may help cytopatholo-

degrees of differentiation. Mucoepidermoid carcinoma of the thy-

gists to make the diagnosis of LEC-T as opposed to malignancy.

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