Retropharyngeal Aberrant Thymus

Samir S. Shah, MD*; Stephen Y. Lai, MD, PhD‡; Eduardo Ruchelli, MD§; Ken Kazahaya, MD‡; and Soroosh Mahboubi, MDʈ

ABSTRACT. Introduction. Upper airway obstruction mus as it migrates caudally. Therefore, aberrant thymic from a retropharyngeal mass requires urgent evaluation. tissue may be found in any position along a line from the In children, the differential diagnosis includes infection, angle of the mandible to the sternal notch, and in the trauma, neoplasm, and congenital abnormalities. Aber- anterior mediastinum to the level of the diaphragm. In an rant cervical thymic tissue, although occasionally ob- autopsy study of 3236 children, abnormally positioned served on autopsy examination, is rarely clinically sig- thymic tissue was found in 34 cases (1%). The aberrant nificant. We present the case of an infant with respiratory thymus was most often located near the thyroid gland cases) but was also detected lower in the anterior 19 ؍ distress attributed to aberrant thymic tissue located in (n 8 ؍ cases), higher in the anterior neck (n 6 ؍ the retropharyngeal space. neck (n case). The 1 ؍ Case. A 6-week-old infant was brought to the emer- cases), and at the left base of the skull (n gency department for evaluation of stridor associated presence of thymic tissue in the retropharyngeal space in with periodic episodes of cyanosis. Lateral neck radio- our patient is more unusual given the typical embryo- graph revealed widening of the retropharyngeal soft tis- logic origin and descent of the thymus in the anterior sues. The patient’s symptoms did not improve with in- neck to the mediastinum. travenous ampicillin-sulbactam. Magnetic resonance Children with aberrant thymus may have associated imaging (MRI) performed on the seventh day of hospi- anomalies. Twenty-four of 34 children (71%) with aber- talization revealed a retropharyngeal mass that extended rant thymus detected at autopsy had features consistent to the carotid space. The mass was easily resected using with DiGeorge syndrome, and only 5 of the remaining 10 an intraoral approach. Microscopic examination demon- patients had a normal mediastinal thymus present. Our strated thymic tissue. A normal thymus was also ob- patient had normal serum calcium levels after excision served in the anterior mediastinum on MRI. The patient and a mediastinal thymus was visualized on MRI. recovered uneventfully and had no further episodes of Biospy is required for diagnosis of cervical thymus and stridor or cyanosis. should also be considered to exclude other causes. MRI is Discussion. Aberrant cervical thymic tissue may be helpful in delineating the presence, position, and extent cystic or solid. Cystic cervical thymus is more common, of thymic tissue. Immunologic sequelae or recurrence and 6% of these patients present with symptoms of dys- after resection of an aberrant cervical thymus has not pnea or dysphagia. Aberrant solid cervical thymus usu- been reported. Pediatrics 2001;108(5). URL: http://www. ally presents as an asymptomatic anterior neck mass. pediatrics.org/cgi/content/full/108/5/e94; retropharynx, thy- This case is unusual in that solid thymic tissue was mus, child. located in the retropharynx, a finding not previously reported in the English literature. Additionally, the patient presented in acute respiratory distress, and the ABBREVIATION. MRI, magnetic resonance imaging. diagnosis was confounded by the presence of mild laryngomalacia. In retrospect, our patient likely had symp- he differential diagnosis of a retropharyngeal toms of intermittent upper airway obstruction since mass in the infant is broad. Infections and neo- birth. The acute respiratory distress at presentation was likely the result of laryngomalacia exacerbated by the Tplasms, such as neuroblastoma or teratoma, presence of aberrant thymic tissue and a superimposed are the most common causes of retropharyngeal viral infection. mass in this population. Less common causes include Aberrantly located thymic tissue arises as a conse- ectopic thyroid, angioneurotic edema, congenital quence of migrational defects during thymic embryogen- myxedema, and lymphadenopathy associated with esis. The thymus is a paired organ derived from the third Langerhans’ cell histiocytosis or Kawasaki disease.1 and, to a lesser extent, fourth pharyngeal pouches. After We report the case of an infant with solid retropha- its appearance during the sixth week of fetal life, it ryngeal thymic tissue who presented with respira- descends to a final position in the anterior mediastinum, tory distress, an unusual presentation of an uncom- adjacent to the parietal pericardium. Aberrant thymic mon entity. tissue results when this tissue breaks free from the thy-

CASE REPORT From the Divisions of *General Pediatrics, ‡Otorhinolaryngology, §Pathol- The patient was a 6-week-old black boy brought to the emer- ogy, and ʈRadiology, Children’s Hospital of Philadelphia, Philadelphia, gency department with a 2-day history of coughing associated Pennsylvania. with cyanosis. His history was remarkable for noisy breathing Received for publication Mar 16, 2001; accepted Jun 13, 2001. since the first week of life that worsened with supine positioning Reprint requests to (S.S.S.) Children’s Hospital of Philadelphia, 34th St and and agitation. He had not been evaluated previously and had not Civic Center Blvd, Second Floor, Division of General Pediatrics, Philadel- required prior hospitalization. phia, PA 19104. E-mail: [email protected] On examination, the patient was in mild respiratory distress. PEDIATRICS (ISSN 0031 4005). Copyright © 2001 by the American Acad- There was audible stridor associated with periodic episodes of emy of Pediatrics. cyanosis. His temperature was 38.3°C; heart rate, 120 beats per http://www.pediatrics.org/cgi/content/full/108/5/Downloaded from www.aappublications.org/newse94 PEDIATRICS by guest on September Vol. 108 27, No. 2021 5 November 2001 1of3 minute; respiratory rate, 60 breaths per minute; blood pressure, 110/50 mm Hg; and percutaneous oxygen saturation, 100% in room air. Mild subcostal retractions were present, but the lungs were clear to auscultation. The abdomen was soft without hepa- tosplenomegaly or palpable mass. The remainder of the physical examination was normal. Laboratory analysis revealed a white blood cell count of 24 500/mm3 (0% band forms, 30% segmented neutrophils, and 57% lymphocytes). On cerebrospinal fluid examination there were 3 leukocytes/mm3 and 1360 erythrocytes/mm3; no bacteria were seen on Gram stain. Urinalysis revealed no protein or leukocyte esterase. Blood, cerebrospinal fluid, and urine cultures were ster- ile. Antigens of adenovirus; influenza A and B viruses; parainflu- enza virus types 1, 2, and 3; and respiratory syncytial virus were not detected by immunofluorescence of nasopharyngeal wash- ings. Hemoglobin, platelet count, serum electrolytes, blood urea nitrogen, creatinine, calcium, and prothrombin and partial throm- boplastin times were normal. Mild laryngomalacia was diagnosed by flexible laryngoscopy. A lateral neck radiograph revealed widening of the retropharyngeal soft tissues (Fig 1). Chest radiograph was normal. Intra- vascular contrast-enhanced computerized axial tomography of the neck demonstrated a nonenhancing soft-tissue mass in the left parapharyngeal region that was thought to represent an in- flammatory process with phlegmon. The patient was treated with ampicillin-sulbactam intravenously. Although the patient remained afebrile, a lateral neck radiograph repeated on the fifth Fig 2. MRI scan (sagittal T1-weighted image) of the neck demon- day of hospitalization was unchanged and the patient continued strating the retropharyngeal mass and the presence of normal to have frequent episodes of severe stridor associated with cya- mediastinal thymus. nosis. Therefore, magnetic resonance imaging (MRI) of the neck was performed under general anesthesia on the seventh day of hospitalization. MRI revealed a retropharyngeal mass (2.5 cm ϫ ␤-human chorionic gonadotropin, ferritin, and urine homovanillic 2.4 cm ϫ 0.7 cm) extending from the first to the second cervical acid and vanillylmandelic acid were normal. Ultrasound of the vertebrae, with extension to the left carotid space (Fig 2). A normal abdomen, including the kidneys, was normal. Biopsy of the ret- thymus was observed in the anterior mediastinum. ropharyngeal mass was performed on the 10th day of hospitaliza- Additional laboratory evaluation was performed because of tion. An intraoral approach was used and a well-circumscribed concern for neoplasm. Serum lactate dehydrogenase, uric acid, mass was easily resected. Microscopic examination demonstrated thymic tissue (Fig 3). The patient recovered uneventfully and was discharged from the hospital on the 13th day of hospitalization without stridor or further episodes of cyanosis. No imaging stud- ies were performed postoperatively.

DISCUSSION Upper airway obstruction from a retropharyngeal mass requires urgent evaluation. In children, the differential diagnosis includes infection, trauma, neoplasm, and congenital abnormalities.1 Aberrant cervical thymic tissue, although occasionally observed on autopsy examination, is rarely clinically signifi- cant. Aberrant cervical thymic tissue may be cystic or solid. Cystic cervical thymus is more common, and 6% of these patients present with symptoms of dys- pnea or dysphagia.2–5 Aberrant solid cervical thymus usually presents as an asymptomatic anterior neck mass.6–8 This case is unusual in that solid thymic tissue was located in the retropharynx, a finding not previously reported in the English literature. Addi- tionally, the patient presented in acute respiratory distress, and the diagnosis was confounded by the presence of mild laryngomalacia. In retrospect, our patient likely had symptoms of intermittent upper airway obstruction since birth. The acute respiratory distress at presentation was likely the result of laryngomalacia exacerbated by the presence of aberrant thymic tissue and a superimposed viral infection. Aberrantly located thymic tissue arises as a conse- quence of migrational defects during thymic embry- ogenesis. The thymus is a paired organ derived from Fig 1. Lateral neck radiograph demonstrating widening of the the third and, to a lesser extent, fourth pharyngeal retropharyngeal soft tissues. pouches. After its appearance during the sixth week

2of3 RETROPHARYNGEALDownloaded ABERRANT from www.aappublications.org/news THYMUS by guest on September 27, 2021 Fig 3. Microscopic section of resected mass demonstrating normal thymus. Small lymphocytes and Hassall’s corpuscle (arrow) are seen (hema- toxylin-eosin, ϫ25).

of fetal life, it descends to a final position in the intensity that becomes brighter in T2-weighted im- anterior mediastinum, adjacent to the parietal peri- ages. Immunologic sequelae or recurrence after re- cardium. Aberrant thymic tissue results when this section of an aberrant cervical thymus has not been tissue breaks free from the thymus as it migrates reported. caudally. Therefore, aberrant thymic tissue may be found in any position along a line from the angle of ACKNOWLEDGMENTS the mandible to the sternal notch, and in the anterior We thank Drs Robert Fern, Sogol Mostoufi-Moab, and Winona mediastinum to the level of the diaphragm.9 In an Chua for their assistance in the care of this patient and Dr Eric autopsy study of 3236 children, abnormally posi- Frehm for his review of the manuscript. tioned thymic tissue was found in 34 cases (1%). The REFERENCES aberrant thymus was most often located near the thyroid gland (n ϭ 19 cases) but was also detected 1. Zawin JK. Radiologic evaluation of the upper airway. In: Wetmore RF, ϭ Muntz HR, McGill TJ, eds. Pediatric Otolaryngology: Principles and Prac- lower in the anterior neck (n 6 cases), higher in the tice Pathways. New York, NY: Thieme; 2000:689–736 anterior neck (n ϭ 8 cases), and at the left base of the 2. Nowak PA, Zarbo RJ, Jacobs JR. Aberrant solid cervical thymus. Ear skull (n ϭ 1 case).10 The presence of thymic tissue in Nose Throat J. 1988;67:670–677 the retropharyngeal space in our patient is more 3. Tovi F, Mares AJ. The aberrant cervical thymus—embryology, pathol- ogy and clinical implications. Am J Surg. 1978;136:631–637 unusual given the typical embryologic origin and 4. Raines JM, Rowe LD. Progressive neonatal airway obstruction second- descent of the thymus in the anterior neck to the ary to cervical thymic cyst. Otolaryngol Head Neck Surg. 1981;89:723–725 mediastinum. 5. Guba AM, Adam AE, Jaques DA, et al. Cervical presentation of thymic Children with aberrant thymus may have associ- cysts. Am J Surg. 1978;136:430–436 6. Shah UK, Fuleihan NS, Handler SD, Kallman JE, Fear DR. Pathologic ated anomalies. Twenty-four (71%) of 34 children quiz case 2. Arch Otolaryngol Head Neck Surg. 1999;125:695–698 with aberrant thymus detected at autopsy had fea- 7. Spigland N, Bensoussan AL, Blanchard H, Russo P. Aberrant cervical tures consistent with DiGeorge syndrome, and only 5 thymus in children: three case reports and review of the literature. of the remaining 10 patients had a normal mediasti- J Pediatr Surg. 1990;25:1196–1199 nal thymus present.10 Our patient had normal serum 8. McLeod DM, Karandy EJ. Aberrant cervical thymus. Arch Otolaryngol. 1981;107:179–180 calcium levels postexcision and a mediastinal thy- 9. Richardson, MA, Sie KCY. The neck: embryology and anatomy. In: mus was visualized on MRI. Bluestone CD, Stool SE, Kenna MA, eds. Pediatric Otolaryngology. 3rd ed. Biospy is required for diagnosis of cervical thymus Philadelphia, PA: WB Saunders Company; 1996:1464–1479 and should also be considered to exclude other caus- 10. Bale PM, Sotelo-Avila C. Maldescent of the thymus: 34 necropsy and 10 3,11 surgical cases, including 7 thymuses medial to the mandible. Pediatr es. MRI is helpful in delineating the presence, Pathol. 1993;13:181–190 position, and extent of thymic tissue. A normal thy- 11. Pirkey WP. Epithelioma of undescended thymus in a child. Arch Oto- musinT1-weighted images has intermediate signal laryngol. 1954;59:237–240

Downloaded from www.aappublications.org/newshttp://www.pediatrics.org/cgi/content/full/108/5/ by guest on September 27, 2021 e94 3of3 Retropharyngeal Aberrant Thymus Samir S. Shah, Stephen Y. Lai, Eduardo Ruchelli, Ken Kazahaya and Soroosh Mahboubi Pediatrics 2001;108;e94 DOI: 10.1542/peds.108.5.e94

Updated Information & including high resolution figures, can be found at: Services http://pediatrics.aappublications.org/content/108/5/e94 References This article cites 9 articles, 0 of which you can access for free at: http://pediatrics.aappublications.org/content/108/5/e94#BIBL Subspecialty Collections This article, along with others on similar topics, appears in the following collection(s): Pulmonology http://www.aappublications.org/cgi/collection/pulmonology_sub Permissions & Licensing Information about reproducing this article in parts (figures, tables) or in its entirety can be found online at: http://www.aappublications.org/site/misc/Permissions.xhtml Reprints Information about ordering reprints can be found online: http://www.aappublications.org/site/misc/reprints.xhtml

Downloaded from www.aappublications.org/news by guest on September 27, 2021 Retropharyngeal Aberrant Thymus Samir S. Shah, Stephen Y. Lai, Eduardo Ruchelli, Ken Kazahaya and Soroosh Mahboubi Pediatrics 2001;108;e94 DOI: 10.1542/peds.108.5.e94

The online version of this article, along with updated information and services, is located on the World Wide Web at: http://pediatrics.aappublications.org/content/108/5/e94

Pediatrics is the official journal of the American Academy of Pediatrics. A monthly publication, it has been published continuously since 1948. Pediatrics is owned, published, and trademarked by the American Academy of Pediatrics, 345 Park Avenue, Itasca, Illinois, 60143. Copyright © 2001 by the American Academy of Pediatrics. All rights reserved. Print ISSN: 1073-0397.

Downloaded from www.aappublications.org/news by guest on September 27, 2021