Cervical thymic cyst ? A Rare Neck Swelling in an Adolescent

Abstract

Cystic neck masses in adolescents pose a diagnostic challenge as they be neoplastic or non-neoplastic, congenital, inflammatory, or infectious. Detailed history and examination, anatomical location of the lesion may help narrow down the differential diagnosis of such masses. Cervical thymic cysts contribute to less than 1% cystic lesions in the neck. We present one such case and our management strategy.

Introduction

Cystic neck masses often pose a diagnostic challenge as they may be neoplastic or non-neoplastic, congenital, inflammatory, or infectious. Detailed history and examination, anatomical location of the lesion may help narrow down the differential diagnosis of such masses [1, 2]. This report describes one such cystic swelling in an adolescent girl, and our management strategy.

Case Report

A female aged 17 presented to the outpatient department with a two-week history of swelling in the neck, associated with pain which aggravated during upper respiratory tract infections. The swelling did not change in size and caused no pressure symptoms or weight loss. On examination, a firm smooth spherical 2 × 2 cm swelling with regular margins was noted in the left side of the neck extending superiorly 1 cm from the inferior border of the cricoid cartilage, inferiorly reaching up to medial end of the clavicle, medially pushing the trachea to the right and laterally up to the anterior border of sternocleidomastoid. It moved with deglutition but not on tongue protrusion. A clinical diagnosis of branchial cyst was made. Ultrasound neck revealed approximately 2.5*2.1 cm well-defined, predominantly solid spherical nodule with mixed echogenicity showing central and peripheral vascularity, micro and macrocalcifications, noted just below but separate from the left lobe of the thyroid. Fine Needle Aspiration Cytology (FNAC) of the swelling displayed sparse metaplastic squamous cells with foamy macrophages and scattered inflammatory cells in a proteinaceous background suggestive of branchial cyst.

Furthermore, a plain CT scan was performed which revealed a well-defined cystic lesion measuring approximately 1.7 * 3 cm noted close to the inferior pole of the thyroid at the level of C6-C7 vertebral level medially abutting the trachea with maintained fat planes (Fig. 1). There was no evidence of any mediastinal mass on the chest X-ray. Lab parameters were unremarkable. Surgical excision of the cyst was performed under general anaesthesia.

Fig. 1.

CT neck Axial view with an asterisk (*) showing lesion abutting trachea medially

Intraoperatively, the cyst was found lying inferior to the left lobe of the thyroid, medially abutting the trachea, and inferiorly there was a fibrous band extending into the mediastinum. The cyst had an irregular nodular surface with both solid and cystic components (Fig. 2). The cyst was resected en bloc, and the fibrous band was further clamped and ligated deep to the clavicle. The postoperative period was uneventful.

Fig. 2.

Specimen of the excised cyst

Histopathological evaluation revealed numerous cystic spaces lined partly by squamous epithelium with central multiple cholesterol granuloma. The cyst wall was fibrotic with thymic tissue comprising Hassall’s corpuscles which confirmed the diagnosis of thymic cyst (Fig. 3).

Fig. 3.

Histopathological analysis of (A) excised cyst showing thymic tissue (black arrow) (B) Hassall’s corpuscles (black arrow) (C) cholesterol clefts (black arrow) (D) squamous cells in the cyst wall (black arrow)

Discussion

Branchial cyst was the most likely clinical diagnosis in this patient; it is known to have a slight female preponderance manifesting in second to fourth decades of life, with left sided being more commonly involved than right, and worsening of symptoms during bouts of upper respiratory infection [3]. Lymphangioma was not considered despite the age at presentation, as it typically involves posterior triangle of neck [2] Cervical thymic cyst (CTC) was not suspected due to the rarity; it contributes to less than 1% of cystic lesions in the neck, and classically affects males in the first decade of life [4, 5]. Thyroid swelling was ruled out based on ultrasound findings.

Thymic cysts are postulated to originate from persistent embryonic thymopharyngeal ducts, arising from the ventral surface of the third pharyngeal pouch [3]. Until 2020, only around 100 cases of paediatric cervical masses have been diagnosed as thymic cysts, with a majority of the cases being asymptomatic and occurring before 20 years of age [6]. They usually present in the lateral infrahyoid neck, more often on the left side, with superior mediastinal extension in half of the cases [3, 7].

Computed tomography aids in differentiating thymic cysts from other neck lesions; magnetic resonance imaging is useful in detection of mediastinal thymus and comparison of soft tissue densities between the neck mass and thymus [4, 8]. Cervical thymic cysts are typically located in close relation to carotid sheath, between the carotid vessels and internal jugular vein, whereas branchial cysts are more superficial and lateral to the carotid sheath [4]. However, presence of thymic tissue remnants with Hassall’s corpuscles on histopathology establishes the diagnosis [3], which also distinguishes CTC from other cystic lesions of the neck [4]. The cystic fluid could be clear, or purulent. Congenital thymic cysts need to be distinguished from the multilocular type; the latter is acquired, originating from cystic dilatation of the medullary duct, with secondary inflammation [3]. Treatment of choice is complete surgical excision preferably with a transverse cervical incision [4]. Presence of thymic tissue in the mediastinum should ideally be confimed before thymic cyst excision to avoid immunosuppression [3]. Recurrence is uncommon in completely excised CTCs [8]; our patient recovered well without evidence of recurrence at two months postoperatively.

Conclusion

CTCs being relatively rare, are usually not considered in the differential diagnoses of cystic swellings in the anterior neck. Though imaging studies aid in detection, postoperative histopathologic examination clinches the diagnosis.

Author Contribution

All authors contributed to the conception and design. Material preparation, data collection was performed by PP. The first draft of the manuscript was written by PP, MNK. All authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Funding

No funding obtained.

Data Availability

Data transparent.

Code Availability

Not applicable.

Declarations

Conflict of Interest

The authors declare that they have no conflict of interest.

Ethics Approval

The report was approved by Institutional Ethics Committee, KMC Mangalore (IEC KMC MLR 04/2023/187). The report complies with the ethical standards as laid down in the 1964 Declaration of Helsinki and its later amendments or comparable ethical standards. No animals were involved.

Consent to Publish

Obtained.

Research involving Human Participants and/or Animals

The report was approved by Institutional Ethics Committee, KMC Mangalore (IEC KMC MLR 04/2023/187). The report complies with the ethical standards as laid down in the 1964 Declaration of Helsinki and its later amendments or comparable ethical standards. No animals were involved.

Informed consent

Written informed consent was obtained.