Indian Journal of Pathology and Microbiology

CASE REPORT
Year
: 2010  |  Volume : 53  |  Issue : 2  |  Page : 305--307

Ectopic cervical thymoma mimicking as papillary thyroid carcinoma: A diagnostic dilemma


Abhijit Thakur1, Frederic Sebag1, Catherine De Micco2, Eveline Slotema1, Francois Jean Henry1,  
1 Department of Endocrine Surgery, University Hospital La Timone, 264, Rue Saint-Pierre, 13385 Marseille, France
2 Department of Pathology, Hospital Nord, Marseille, France

Correspondence Address:
Abhijit Thakur
Department of Endocrine Surgery, University Hospital La Timone, 264, Rue Saint-Pierre, 13385 Marseille
France

Abstract

Ectopic cervical thymomas are often confused with thyroid or parathyroid swellings due to their anatomical positioning. Predominant epithelial thymoma can be misdiagnosed as papillary thyroid carcinoma on fine needle aspiration and lymph node metastasis of epithelial tumor on frozen section. Predominantly lymphocytic thymomas have often been misinterpreted as Hashimoto«SQ»s thyroiditis or malignant lymphoma, either by fine needle aspiration or on frozen section analysis. If cytology is doubtful and is not correlating with clinical, anatomical and surgical findings; immunohistochemistry is a very important tool in such cases to give final answer. Thyroid cell specific proteins such as thyroglobulin, thyroid transcription factor-1, thyroperoxidase and dipeptidyl aminopeptidase-4, neuroendocrine markers chromogranin, calcitonin and parathyroid hormone could be used to rule out thyroid or parathyroid origin. We present such rare case of ectopic cervical thymoma mimicking as papillary thyroid carcinoma.



How to cite this article:
Thakur A, Sebag F, Micco CD, Slotema E, Henry FJ. Ectopic cervical thymoma mimicking as papillary thyroid carcinoma: A diagnostic dilemma.Indian J Pathol Microbiol 2010;53:305-307


How to cite this URL:
Thakur A, Sebag F, Micco CD, Slotema E, Henry FJ. Ectopic cervical thymoma mimicking as papillary thyroid carcinoma: A diagnostic dilemma. Indian J Pathol Microbiol [serial online] 2010 [cited 2022 Dec 6 ];53:305-307
Available from: https://www.ijpmonline.org/text.asp?2010/53/2/305/64294


Full Text

 Introduction



Thymoma is a tumor derived from thymic epithelium and is composed of a mixture of epithelial and lymphoid cells. Thymomas are commonly located in the anterior mediastinum. [1] The incidence of ectopic thymoma is about 4%. [1] The thymus gland is derived from third and fourth branchial clefts and during its development, it descents from neck to mediastinum. Various abnormalities such as hypoplasia, failure of descent and dislocation of thymic tissues occur along the path of this descent. [2]

The following sites of ectopic thymus were recorded in a study of 100 thymus glands in patients with myasthenia gravis: cervical area, 10%; perithymic area, 37%; left and right pericardiophrenic fat pads, 7% each; aortopulmonary window, 33%; and aortocaval groove 4%. [3] Ectopic cervical thymomas are often confused with thyroid or parathyroid swellings due to their anatomical positioning. Predominant epithelial thymoma can be misdiagnosed as papillary thyroid carcinoma on fine needle aspiration. [4],[5] Predominantly, lymphocytic thymomas have often been misinterpreted as Hashimoto's thyroiditis or malignant lymphoma, either by fine needle aspiration or on frozen section analysis. [6] We found two such cases of epithelial predominant thymoma mimicking as thyroid carcinoma in literature and one case of confusion of lymph node metastasis in frozen section. [4],[5],[7] There are some reports of lymphocyte predominant thymoma mimicking as lymphoma. [6]

 Case Report



A 64-year-old female with known case of hypothyroidism for 20 years, euthyroid on substitutive dose of levothyroxine presented in March 07 with ultrasound evidence of an extracapsular, heterogeneous, hypoechoic, partially calcified nodular formation of 12 x 8 mm in the anterolateral neck close to the left inferior thyroid pole. The thyroid was homogenous with reduced volume. Thyroid function tests, serum calcium and parathormone were all normal. We suspected thyroid or parathyroid origin of the swelling.

A fine needle aspiration, realized in January 2007, exhibited few epithelial cells with round or slightly elongated nuclei and no colloid. Monoclonal anti-thyroperoxidase antibodies 47 was negative, favoring extra-thyroid origin of the swelling. The possibility of parathyroid origin of the mass was considered.

Repeated ultrasound-guided fine needle aspiration in May 2007, showed tight nests of elongated epithelial cells associated with few lymphocytes and no colloid. Cells possessed scanty cytoplasm and overlapping ovoid nuclei exhibiting pale chromatin, longitudinal grooves and intranuclear inclusions of cytoplasm characteristic of papillary thyroid carcinoma [Figure 1]. The cells were negative with monoclonal anti-thyroperoxidase antibodies 47 and dipeptidyl aminopeptidase-4 cytoenzymology. The cytological findings were highly suggestive of papillary carcinoma of thyroid, though the cells were negative for thyroid and parathyroid immune markers. Absence of immune markers is possible due to scanty cellular aspirate or loss of differentiation, which is difficult to comment upon fine needle aspiration. A diagnosis of papillary thyroid carcinoma was suggested.

Patient was explored with transverse cervicotomy in August 2007 with consent for total thyroidectomy. A 1.5 x1 cm swelling, posterior-inferior to the left lower pole of thyroid was found. It was located in thyro-thymic ligament and comprised of a well-defined capsule with scattered calcifications; the core of swelling comprised of partially cystic soft grayish tissue. Frozen section in a noncalcified area showed nests of epithelial cells possessing pale, ovoid nuclei surrounded by lymphoid tissue, consistent with a diagnosis of lymph node metastasis by a thyroid carcinoma possessing a follicular architecture.

However, the picture was not unequivocal and other possibilities such as parathyroid or thymic tumors could not be excluded. On definite histology, the tumor was within the involuted thymic lobe. It was surrounded by a thick, largely calcified fibrous capsule including some epithelial nests. The core area was composed of a well-differentiated mature lymphoid tissue admixed with anastomotic strands of epithelial cells. Epithelial cells appeared round or elongated with scanty cytoplasm and overlapping pale, ovoid nuclei. Small pseudo-glandular cavities mimicking thyroid follicles resulted in cribriform pattern within epithelial nest [Figure 2] and [Figure 3]. However, immunohistochemistry showed the absence of thyroglobulin, chromogranin and thyroid transcription factor-1, definitely excluding the thyroid or parathyroid origin of this tumor. The diagnosis of type A thymoma without significant invasive features was thus retained.

 Discussion



On fine needle aspiration smears, epithelial component of thymoma shares several features with papillary thyroid carcinoma; ovoid crowded pale nuclei sometimes containing groves or intranuclear inclusion bodies [Figure 1]. [4],[5] If there is enough material to perform immunocytochemistry, the total absence of thyroid cell specific proteins such as thyroglobulin, thyroid transcription factor-1, dipeptidyl aminopeptidase-4 or thyroperoxidase and the absence of neuroendocrine markers such as chromogranin, calcitonin or parathyroid hormone should help to exclude a primitive thyroid or parathyroid tumor. [8],[9] However, scanty cellular aspirate and loss of differentiation in the tumor with a loss of thyroid-specific proteins can cause confusion in reporting fine needle aspiration cytology as occurred in our case, where the picture was so peculiar of papillary thyroid carcinoma that immunocytochemistry was overlooked because of the above reasons [Figure 1].

Frozen section examination was of limited value in our case, since the epithelial tissue surrounded by lymphocytes that was observed could not be clearly distinguished from an epithelial tumors lymph node metastasis. [7]

A cut-through complete specimen is very necessary to get final diagnosis, which can exhibit the characteristics of thymoma. The histology in our case showed the absence of thyroid or parathyroid tissues markers that allowed the final diagnosis of type A thymoma (WHO classification) [Figure 2] and [Figure 3]. [10]

Epithelial predominant cervical thymoma is confused with papillary thyroid carcinoma on fine needle aspiration and occasionally can be confused with lymph node metastasis of epithelial tumor in frozen section. [4],[5],[7] Lymphocyte-predominant cervical thymomas are confused with malignant lymphomas and occasionally with Hashimoto's thyroiditis. [6]

If cytology is doubtful and is not correlating with clinical, anatomical and surgical findings, immunohistochemistry is a very important tool in such cases to give the final answer. Thyroid cell specific proteins such as thyroglobulin, thyroid transcription factor-1, thyroperoxidase and dipeptidyl aminopeptidase-4, neuroendocrine markers chromogranin for parathyroid and medullary thyroid carcinoma, calcitonin specific for medullary thyroid and parathyroid hormone specific for parathyroid could be used to find the origin of malignant cells as immunohistochemistry markers. [8],[9]

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