Ectopic subglottic thymic cyst: a rare cause of congenital stridor.

Abstract

We describe the case of a 10-day-old boy who was brought to the hospital with stridor and respiratory distress. He was diagnosed with stenosis caused by a subglottic cyst. After the cyst was removed endoscopically, the patient's symptoms resolved. Pathology identified the cyst as ectopic thymic tissue. This case is noteworthy because we believe it represents the first reported instance of ectopic thymic tissue in the subglottis.

Introduction

Stridor and respiratory distress in a full-term newborn should be evaluated for possible congenital anomalies of the laryngotracheal airway. Flexible fiberoptic laryngoscopy should be performed in all cases to carefully examine the supraglottic and subglottic areas. Flexible fiberoptic laryngoscopy allows for a dynamic evaluation of the glottic airway. If a conclusive diagnosis cannot be reached, direct rigid laryngoscopy and bronchoscopy with general anesthesia should be performed in the operating room, where definitive diagnosis and treatment may be achieved, In this article, we report a rare cause of congenital stridor caused by an ectopic thymic cyst in the subglottic area.

Case report

A 10-day-old boy, born full term via caesarean section and weighing 7 lb 11 oz, was discharged home with no complications. At home, his mother noticed that the infant's breathing had become progressively more congested. She sought medical advice from a pediatrician. At the first visit, the boy's abnormal breathing was attributed to a common cold. But despite conservative treatment, his symptoms progressed and began to interfere with his feeding. His noisy breathing was compatible with stridor, and the decision was made to admit the patient to the hospital for further evaluation.

Fiberoptic laryngoscopy at the bedside revealed that a cystic structure had caused a narrowing in the subglottic region. Rigid bronchoscopy was then performed to establish a definitive diagnosis and guide management. Bronchoscopy confirmed that the cyst at the base of the left subglottic area had caused significant narrowing of the airway and interfered with ventilation (figure 1). The cyst was removed by a microlaryngoscopic technique.

[FIGURE 1 OMITTED]

Pathologic examination revealed that the excised specimen was made up of a squamous epithelium-lined cyst that was surrounded by thymic tissue and Hassall's corpuscles (figure 2). A few mixed muco-serous glands were also present. These findings are consistent with the diagnosis of subglottic thymic cyst.

[FIGURE 2 OMITTED]

The patient recovered quickly, and both the respiratory distress and noisy breathing resolved. Follow-up laryngoscopy 3 weeks later showed a patent, well-healed subglottic mucosa and no evidence of recurrence (figure 3).

[FIGURE 3 OMITTED]

Discussion

Patients with congenital subglottic stenosis manifest with various types of symptoms, and the degree of their airway obstruction ranges from minimal to severe. Anteroposterior x-rays of the neck may show the classic narrowing of the subglottis (the "steeple sign"). Flexible fiberoptic laryngoscopy is indicated to rule out supraglottic, glottic, or subglottic pathology, such as vocal fold paralysis, laryngomalacia, and subglottic stenosis. The definitive diagnosis is often made in the operating room during flexible or rigid laryngoscopy. Subglottic cyst as a cause of subglottic stenosis in neonates is rare.

The three distinct types of subglottic cysts are congenital, retention, and inclusion. (1) To our knowledge, the presence of ectopic thymic tissue in the subglottis has not been previously reported. Ectopic thymic tissue is rarely of clinical significance. It is observed in approximately 1% of patients on autopsy. The ectopic tissue can be either cystic (more common) or solid. Mislocated (aberrant) thymic tissue is a consequence of a defect in the migration of the thymus during embryogenesis. (2) The thymus is derived from the third and fourth pharyngeal pouches. After the sixth week of fetal life, it descends to its final position in the anterior mediastinum adjacent to the parietal pericardium. Aberrant thymic tissue occurs when portions of the organ break free as the organ migrates caudally. Therefore, ectopic thymic tissue may be found in any position along a line from the angle of the mandible to the sternal notch, and in any location between the anterior mediastinum and the diaphragm.

Previously reported cases of ectopic thymic tissue have involved the neck, (3) the base of the skull, the anterior and posterior mediastinum, the pericardium, and the retro-pharyngeal space. (4) The position of the thymic tissue in the subglottic area in our patient is unusual in light of the typical embryologic origin and the descent of the thymus from the anterior neck to the mediastinum.

References

(1.) Arens C, Glanz H, Kleinsasser O. Clinical and morphological aspects of laryngeal cysts. Eur Arch Otorhinolaryngol 1997; 254:430-6.

(2.) Tovi F, Mares AJ. The aberrant cervical thymus. Embryology, pathology, and clinical implications. Am J Surg 1978;136:631-7.

(3.) Marra S, Hotaling AJ, Raslan W. Cervical thymic cyst. Otolaryngol Head Neck Surg 1995;112:338-40.

(4.) Shah SS, Lai SY, Ruchelli E, et al. Retropharyngeal aberrant thymus. Pediatrics 2001;108:E94.

From the Department of Pediatrics, Advocate Hope Children's Hospital. Oak Lawn, Ill.

Reprint requests: Javeed Akhter, MD, Pediatric Pulmonology and Allergy, Advocate Hope Children's Hospital, 4440 W. 95th St., Oak Lawn, IL 60453. Phone: [phone]; fax: [phone]; e-mail: [e-mail]