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Radiology Quiz Case—Diagnosis

Radiology Quiz Case—Diagnosis Diagnosis: Ectopic thyroid tissue The radiographic differential diagnosis of the posterior mediastinal mass in the present case includes neurogenic tumors (eg, neurilemoma/schwannoma, neurofibroma, ganglioneuroma/ganglioneuroblastoma, neuroblastoma, and paraganglioma) and esophageal disease (eg, esophageal duplication cyst and primary esophageal neoplasm). Schwannoma of the right recurrent laryngeal nerve was the primary preoperative consideration, based on the uniform enhancement of the mass and its location in the tracheoesophageal groove. However, a computed tomography–guided biopsy of the mass revealed normal thyroid tissue that was completely separate from the thyroid gland. The computed tomographic scan also showed that the tissue was completely separate from the thyroid gland. In the operating room, the hypervascular mass was found in the paraesophageal region of the lower part of the right side of the neck. The right recurrent laryngeal nerve and thyroid gland were found to be separate from the mass, and the nerve was dissected free and preserved. Intraoperative frozen-section analysis demonstrated benign thyroid tissue. Grossly, the mass consisted of a 14.1-g multinodular goiter with an uninterrupted external capsule. Histopathologically, it was composed of benign thyroid architecture with normal colloid follicles (Figure 3). There was no evidence of malignancy or lymphadenopathy, so a thyroidectomy was not performed. Thyroid function was still normal 6 months after surgery. Figure 3. View LargeDownload Ectopic thyroid tissue is defined as thyroid cells that are located at sites other than anterior to the trachea in the midline area of the lower part of the neck.1 Ectopic thyroid tissue is an uncommon phenomenon, with a prevalence of 7% to 10% in autopsy studies.2 In patients with thyroid disease, the prevalence is 1/4000 to 1/8000. A knowledge of thyroid embryology is essential to understanding the location of ectopic thyroid tissue. At 3 weeks of gestation, the median thyroid anlage arises from a thickening in the midline anterior pharyngeal floor, between the first and second branchial arches. From this location, adjacent to the newly differentiating myocardial tissue, it migrates caudally, following the descent of the differentiating myocardium and great vessels. As it expands ventrally from the foramen cecum, it remains attached to the pharyngeal floor by an epithelial stalk: the thyroglossal duct. It then expands laterally to form the bilobed structure of the adult thyroid and reaches its final position in the seventh week of gestation. A lingual thyroid, located at the foramen cecum, is the most common form of ectopic thyroid tissue.1 Lingual thyroid constitutes 90% of all thyroid ectopias and is believed to represent a failure or arrest of normal developmental migration.1-4 In 75% of the patients, the lingual thyroid is the only functioning thyroid tissue. The development of symptoms is closely correlated with the size of the thyroid tissue and may include dysphagia, dyspnea, or dysphonia.1,3,4 Unsurprisingly, ectopic thyroid tissue is typically found along the trajectory of embryonal migration. Partial descent of the thyroid results in ectopic thyroid tissue anywhere along the thyroglossal tract. In contrast, excessive migration can lead to substernal ectopic thyroid tissue. Ectopic thyroid tissue may rarely be found in the piriform sinus; the submandibular, intrathymic, and intracardiac regions; the retroesophageal superior mediastinum; and the carotid sheath, as well as along the ascending aortic arch. Recently, benign thyroid tissue along the thyrothymic tract has been conceptualized as rests, or remnants of thyroid tissue, that underwent excessive caudal migration. Sackett et al5 found ectopic thyroid tissue caudal to the inferior pole of the thyroid in approximately 9% of 100 consecutive lower neck explorations. Nearly 90% of these "thyrothymic rests" were small (<1 cm in diameter), highlighting a unique feature of the present case. In general, an ectopic, nonmidline thyroid gland is very rare and, historically, quite controversial. In 1942, King and Pemberton6 found that 51 of 54 patients with laterally located thyroid tissue had metastatic thyroid carcinoma in their cervical lymph nodes. They concluded that laterally located ectopic thyroid tissue represents a metastatic extension of primary thyroid carcinoma in the ipsilateral lobe of the thyroid gland. More recent studies have challenged this theory, and the concept of benign thyroid tissue in the lateral aspect of the neck has become a well-recognized clinical entity.7,8 However, the pathogenesis of nonmidline thyroid ectopias remains controversial; both mechanical and migrational theories have been proposed. A common mechanical explanation suggests that tissue from a nodular goiter is sheared from the gland by movement of the neck muscles.4,6-8 The main controversy in the treatment of patients who have ectopic thyroid cells is whether such cells represent inclusions of metastatic thyroid tissue in cervical lymph nodes. This controversy began when histologically well-differentiated thyroid follicles were found in the lymph nodes of patients undergoing radical neck dissections for tumors of nonthyroid origin.9 Later, histopathologic criteria were developed to characterize benign lymph node inclusions. Despite these criteria, the concept of benign inclusions remains controversial, and many authors continue to advocate an aggressive search for a primary malignancy, including resection of the ipsilateral thyroid lobe.10 Clearly, if well-differentiated thyroid carcinoma is found in cervical nodes, the patient should undergo a total thyroidectomy and an ipsilateral neck dissection, followed by radioactive iodine ablation.11 Since the tissue identified in this case was not contained within a lymph node, no further therapy was indicated in our opinion. In the future, molecular pathology, such as proto-oncogene analysis, may assist in the clinical management of ectopic thyroid tissue.12 A presumed feature of malignancy is its clonal cellular origin. Using clonal analysis, Kakudo et al12 classified ectopic thyroid tissue as either monoclonal or polyclonal in origin, thus helping to identify the tissue as benign or neoplastic. Such diagnostic techniques eventually may direct the clinical treatment of patients who present with ectopic thyroid tissue. Residents and fellows in otolaryngology are invited to submit quiz cases for this section and to write letters to the ARCHIVES commenting on cases presented. Quiz cases should follow the patterns established. See "Instructions for Authors." Material for CLINICAL PROBLEM SOLVING: RADIOLOGY should be mailed to the Editor. Reprints not available from the authors. References 1. Basakis JGEl-Naggar AKLuna MA Thyroid gland ectopias. Ann Otol Rhinol Laryngol.1996;105:996-1000.PubMedGoogle Scholar 2. Arriaga MAMyers EN Ectopic thyroid in the retroesophageal superior mediastinum. Otolaryngol Head Neck Surg.1988;99:338-340.PubMedGoogle Scholar 3. Baik SHChoi JHLee HM Dual ectopic thyroid. Eur Arch Otorhinolaryngol.2002;259:105-107.PubMedGoogle Scholar 4. Kumar RSharma SMarwah AMoorthy DDhanwal DMalhotra A Ectopic goiter masquerading as submandibular gland swelling: a case report and review of the literature. Clin Nucl Med.2001;26:306-309.PubMedGoogle Scholar 5. Sackett WRReeve TSBarraclough BDelbridge L Thyrothymic thyroid rests: incidence and relationship to the thyroid gland. J Am Coll Surg.2002;195:635-640.PubMedGoogle Scholar 6. King WMPemberton JJ So called lateral aberrant thyroid tumors. Surg Gynecol Obstet.1942;74:991-1001.Google Scholar 7. Watson MGBirchall JPSoames JV Is "lateral aberrant thyroid" always metastatic tumor? J Laryngol Otol.1992;106:376-378.PubMedGoogle Scholar 8. Nishiyama RH Overview of surgical pathology of the thyroid gland. World J Surg.2000;24:898-906.PubMedGoogle Scholar 9. Nicastri ADFoote Jr FWFrazell EL Benign thyroid inclusions in cervical lymph nodes. JAMA.1965;194:1-4.Google Scholar 10. Moses DCThompson NWNishiyama RHSisson JC Ectopic thyroid tissue in the neck: benign or malignant? Cancer.1976;38:361-365.PubMedGoogle Scholar 11. Coleman SSmith JCBurkey BBDay TAPage RNNetterville JL Long-standing lateral neck mass as the initial manifestation of well-differentiated thyroid carcinoma. Laryngoscope.2000;110:204-209.PubMedGoogle Scholar 12. Kakudo KShan LNakamura YInoue DKoshiyama HSato H Clonal analysis helps to differentiate aberrant thyroid tissue from thyroid carcinoma. Hum Pathol.1998;29:187-190.PubMedGoogle Scholar http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Archives of Otolaryngology - Head & Neck Surgery American Medical Association

Radiology Quiz Case—Diagnosis

Archives of Otolaryngology - Head & Neck Surgery , Volume 130 (1) – Jan 1, 2004

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Publisher
American Medical Association
Copyright
Copyright © 2004 American Medical Association. All Rights Reserved.
ISSN
0886-4470
eISSN
1538-361X
DOI
10.1001/archotol.130.1.118
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Abstract

Diagnosis: Ectopic thyroid tissue The radiographic differential diagnosis of the posterior mediastinal mass in the present case includes neurogenic tumors (eg, neurilemoma/schwannoma, neurofibroma, ganglioneuroma/ganglioneuroblastoma, neuroblastoma, and paraganglioma) and esophageal disease (eg, esophageal duplication cyst and primary esophageal neoplasm). Schwannoma of the right recurrent laryngeal nerve was the primary preoperative consideration, based on the uniform enhancement of the mass and its location in the tracheoesophageal groove. However, a computed tomography–guided biopsy of the mass revealed normal thyroid tissue that was completely separate from the thyroid gland. The computed tomographic scan also showed that the tissue was completely separate from the thyroid gland. In the operating room, the hypervascular mass was found in the paraesophageal region of the lower part of the right side of the neck. The right recurrent laryngeal nerve and thyroid gland were found to be separate from the mass, and the nerve was dissected free and preserved. Intraoperative frozen-section analysis demonstrated benign thyroid tissue. Grossly, the mass consisted of a 14.1-g multinodular goiter with an uninterrupted external capsule. Histopathologically, it was composed of benign thyroid architecture with normal colloid follicles (Figure 3). There was no evidence of malignancy or lymphadenopathy, so a thyroidectomy was not performed. Thyroid function was still normal 6 months after surgery. Figure 3. View LargeDownload Ectopic thyroid tissue is defined as thyroid cells that are located at sites other than anterior to the trachea in the midline area of the lower part of the neck.1 Ectopic thyroid tissue is an uncommon phenomenon, with a prevalence of 7% to 10% in autopsy studies.2 In patients with thyroid disease, the prevalence is 1/4000 to 1/8000. A knowledge of thyroid embryology is essential to understanding the location of ectopic thyroid tissue. At 3 weeks of gestation, the median thyroid anlage arises from a thickening in the midline anterior pharyngeal floor, between the first and second branchial arches. From this location, adjacent to the newly differentiating myocardial tissue, it migrates caudally, following the descent of the differentiating myocardium and great vessels. As it expands ventrally from the foramen cecum, it remains attached to the pharyngeal floor by an epithelial stalk: the thyroglossal duct. It then expands laterally to form the bilobed structure of the adult thyroid and reaches its final position in the seventh week of gestation. A lingual thyroid, located at the foramen cecum, is the most common form of ectopic thyroid tissue.1 Lingual thyroid constitutes 90% of all thyroid ectopias and is believed to represent a failure or arrest of normal developmental migration.1-4 In 75% of the patients, the lingual thyroid is the only functioning thyroid tissue. The development of symptoms is closely correlated with the size of the thyroid tissue and may include dysphagia, dyspnea, or dysphonia.1,3,4 Unsurprisingly, ectopic thyroid tissue is typically found along the trajectory of embryonal migration. Partial descent of the thyroid results in ectopic thyroid tissue anywhere along the thyroglossal tract. In contrast, excessive migration can lead to substernal ectopic thyroid tissue. Ectopic thyroid tissue may rarely be found in the piriform sinus; the submandibular, intrathymic, and intracardiac regions; the retroesophageal superior mediastinum; and the carotid sheath, as well as along the ascending aortic arch. Recently, benign thyroid tissue along the thyrothymic tract has been conceptualized as rests, or remnants of thyroid tissue, that underwent excessive caudal migration. Sackett et al5 found ectopic thyroid tissue caudal to the inferior pole of the thyroid in approximately 9% of 100 consecutive lower neck explorations. Nearly 90% of these "thyrothymic rests" were small (<1 cm in diameter), highlighting a unique feature of the present case. In general, an ectopic, nonmidline thyroid gland is very rare and, historically, quite controversial. In 1942, King and Pemberton6 found that 51 of 54 patients with laterally located thyroid tissue had metastatic thyroid carcinoma in their cervical lymph nodes. They concluded that laterally located ectopic thyroid tissue represents a metastatic extension of primary thyroid carcinoma in the ipsilateral lobe of the thyroid gland. More recent studies have challenged this theory, and the concept of benign thyroid tissue in the lateral aspect of the neck has become a well-recognized clinical entity.7,8 However, the pathogenesis of nonmidline thyroid ectopias remains controversial; both mechanical and migrational theories have been proposed. A common mechanical explanation suggests that tissue from a nodular goiter is sheared from the gland by movement of the neck muscles.4,6-8 The main controversy in the treatment of patients who have ectopic thyroid cells is whether such cells represent inclusions of metastatic thyroid tissue in cervical lymph nodes. This controversy began when histologically well-differentiated thyroid follicles were found in the lymph nodes of patients undergoing radical neck dissections for tumors of nonthyroid origin.9 Later, histopathologic criteria were developed to characterize benign lymph node inclusions. Despite these criteria, the concept of benign inclusions remains controversial, and many authors continue to advocate an aggressive search for a primary malignancy, including resection of the ipsilateral thyroid lobe.10 Clearly, if well-differentiated thyroid carcinoma is found in cervical nodes, the patient should undergo a total thyroidectomy and an ipsilateral neck dissection, followed by radioactive iodine ablation.11 Since the tissue identified in this case was not contained within a lymph node, no further therapy was indicated in our opinion. In the future, molecular pathology, such as proto-oncogene analysis, may assist in the clinical management of ectopic thyroid tissue.12 A presumed feature of malignancy is its clonal cellular origin. Using clonal analysis, Kakudo et al12 classified ectopic thyroid tissue as either monoclonal or polyclonal in origin, thus helping to identify the tissue as benign or neoplastic. Such diagnostic techniques eventually may direct the clinical treatment of patients who present with ectopic thyroid tissue. Residents and fellows in otolaryngology are invited to submit quiz cases for this section and to write letters to the ARCHIVES commenting on cases presented. Quiz cases should follow the patterns established. See "Instructions for Authors." Material for CLINICAL PROBLEM SOLVING: RADIOLOGY should be mailed to the Editor. Reprints not available from the authors. References 1. Basakis JGEl-Naggar AKLuna MA Thyroid gland ectopias. Ann Otol Rhinol Laryngol.1996;105:996-1000.PubMedGoogle Scholar 2. Arriaga MAMyers EN Ectopic thyroid in the retroesophageal superior mediastinum. Otolaryngol Head Neck Surg.1988;99:338-340.PubMedGoogle Scholar 3. Baik SHChoi JHLee HM Dual ectopic thyroid. Eur Arch Otorhinolaryngol.2002;259:105-107.PubMedGoogle Scholar 4. Kumar RSharma SMarwah AMoorthy DDhanwal DMalhotra A Ectopic goiter masquerading as submandibular gland swelling: a case report and review of the literature. Clin Nucl Med.2001;26:306-309.PubMedGoogle Scholar 5. Sackett WRReeve TSBarraclough BDelbridge L Thyrothymic thyroid rests: incidence and relationship to the thyroid gland. J Am Coll Surg.2002;195:635-640.PubMedGoogle Scholar 6. King WMPemberton JJ So called lateral aberrant thyroid tumors. Surg Gynecol Obstet.1942;74:991-1001.Google Scholar 7. Watson MGBirchall JPSoames JV Is "lateral aberrant thyroid" always metastatic tumor? J Laryngol Otol.1992;106:376-378.PubMedGoogle Scholar 8. Nishiyama RH Overview of surgical pathology of the thyroid gland. World J Surg.2000;24:898-906.PubMedGoogle Scholar 9. Nicastri ADFoote Jr FWFrazell EL Benign thyroid inclusions in cervical lymph nodes. JAMA.1965;194:1-4.Google Scholar 10. Moses DCThompson NWNishiyama RHSisson JC Ectopic thyroid tissue in the neck: benign or malignant? Cancer.1976;38:361-365.PubMedGoogle Scholar 11. Coleman SSmith JCBurkey BBDay TAPage RNNetterville JL Long-standing lateral neck mass as the initial manifestation of well-differentiated thyroid carcinoma. Laryngoscope.2000;110:204-209.PubMedGoogle Scholar 12. Kakudo KShan LNakamura YInoue DKoshiyama HSato H Clonal analysis helps to differentiate aberrant thyroid tissue from thyroid carcinoma. Hum Pathol.1998;29:187-190.PubMedGoogle Scholar

Journal

Archives of Otolaryngology - Head & Neck SurgeryAmerican Medical Association

Published: Jan 1, 2004

Keywords: diagnostic radiologic examination,radiology specialty,thyroid tissue, ectopic

References