Cervical Thymic Cyst: Case Report
Introduction: Ectopia of thymic tissue in the neck is well known, while the ectopic thymic cysts are extremely rare. Literature enlists frequency of cervical thymic cysts from 0.3% to 1% of all congenital tumefactions in the neck area. They are usually diagnosed in early childhood. Case report: A nine-year-old girl was hospitalised at Department of Child Surgery, because of the painless cystic tumour at the left side of the neck. After the performed diagnostic procedures, a surgical exploration was done. The cystic tumour was dissected and sent to histopathological verification. During the histological analysis of the cyst wall, in the part that was 6 mm thick, thymic tissue was detected. Conclusion: Cervical thymic cysts must be considered in the differential diagnosis of cervical cystic formations, especially in child age and publications of case reports are important in order of caution when cervical cysts are examined.
簡介：頸部胸腺組織異位元是眾所周知的，而異位胸腺囊腫則極為罕見。文獻記載了頸部胸腺囊腫的發生率，佔所有先天性胸腺囊腫的0.3% ~ 1%。他們通常在兒童早期就被診斷出來。病例報導：一名9歲女孩因為頸部左側的無痛性囊性腫瘤在兒童外科住院。在完成診斷程式後進行手術探查，囊性腫瘤被切除並送組織病理學檢查。在厚達6mm的囊腫壁組織學分析中檢測到胸腺組織。結論：頸部胸腺囊腫必須考慮在頸部囊腫的鑒別診斷中。特別是兒童的年齡和個案報導，可以提醒頸部囊腫檢查時考慮到該病。
Keyword : Cyst; Neck; Thymus
Pharyngeal system anomalies are common congenital disorders. Anomalies of the second pharyngeal arch represent around 95% of all anomalies created due to pharyngeal system development disorder.1
Thymus is developed from the third pharyngeal arch and during the embryonic development thymus descends from the neck towards the anterior upper mediastinum. The embryonic development of the thymus explains the possibility of thymic tissue residue in the neck, most often diagnosed in childhood.2
Ectopia of thymic tissue in the neck is well known, while the ectopic thymic cysts in the neck are extremely rare.3
Literature enlists frequency of cervical thymic cysts from 0.3% to 1% of all congenital tumefactions in the neck area. They are usually diagnosed in early childhood, more commonly in boys. Considering the fact that these are rare lesions, the right diagnosis is not often set preoperatively. Surgical excision and histological analysis usually lead to diagnosis.4,5
In the paper we present a case of a nine-year-old girl with clinical, radiological and pathohistological characteristics of a cervical thymic cyst.
A nine-year-old girl was hospitalised at the Department of Child Surgery, due to diagnostics and treatment of painless cystic tumour at the left side of the neck. The cystic tumour was noticed by the parents 4 weeks prior addressing to a doctor, and since then they do not cite significant size changes. They deny trauma as an etiological factor, loss of weight and fever. The cystic tumour was clearly visible when the head of the patient was raised. The cystic tumour was positioned in the middle third of the neck, in front of anterior edge of the sternocleidomastoid muscle and it was elastic, painless, and mobile, did not fix the skin and the surrounding neck structures, and measured 5x3 cm.
The blood test results, as well as the biochemical analysis, were within the reference values.
Magnetic resonance showed that in the soft tissues on the left side of the neck, in the level from the third to the seventh cervical vertebral body, there was an oval, septated inhomogenic cystic tumour, well circumscripted from the surrounding neck structures, up to 6 cm in diameter, filled with liquid content, with suppression of the thyroid gland left lobe to the front and trachea to the right.
Scintigraphy of the thyroid gland was normal.
After the performed diagnostic procedures, a surgical exploration was done under general anesthesia. The patient was placed into spinal position with head rotated to the right. An incision was made on the skin, along the front edge of the left sternocleidomastoid muscle. Subcutaneous tissue has been dissected, as well as the platysma and superficial fascia of the neck. Medially from the left external jugular vein, along the front edge of the sternocleidomastoid muscle, central parts of the neck have been approached. A cystic tumour mass was detected, with the wider pole extending from the middle part of the cricothyroid cartilage. The tumour was dissected, separated from the musculus omohioideus and neck blood vessels (the left internal carotid artery and the left internal jugular vein). With a further tissue preparation between the esophagus and the trachea, the left recurrent laryngeal nerve was identified, which crosses the inferior left thyroid artery on the front and enters the larynx in the area of the cricothyroid cartilage, thereby preserving its integrity. Then the cyst was mobilised from the left superior thyroid artery which crossed its narrow part. After the separation of left superior thyroid artery, the origin of cystic tumour in the level of the pre-vertebral fascia of the third cervical vertebra was dissected.
The cystic tumour was sent to histopathological verification (Figure 1).
The postoperative recovery passed without complications.
Using a macroscopic examination, a cystic tumour was multilocular, measured 6x3.7x1.5 cm, with smooth external surface. Septa were widening from 0.2 to 0.6 cm with smooth inner surface, with lumen filled by yellowish liquid content.
During the histological analysis of the cyst wall, in the part that was 0.6 cm thick, thymic tissue has been detected, the remaining cyst wall as well as septa, were made from moderately cellular connective tissue, infiltrated with lymphocytes, while the interior surface of all parts was coated with flattened regular squamous epithelium (Figure 2).
After the cervical thymic cyst was diagnosed, thymic tissue has not been detected by the magnetic resonance of the thorax.
Pharyngeal system is created in the fourth week of the intrauterine development.1
Thymus is made from the ventrolateral surface of the third pharyngeal arch, in the sixth week of the intrauterine development. The thymus tissue residue, that may create cysts, can be found from the mastoid region to the anterior upper mediastinum.5
Thymic cysts are rare, especially with cervical localisation. They can be congenital and acquired; also they can be unilocular or multilocular. Unilocular cysts are congenital, they have a thin wall, with thymus tissue on the periphery. Multilocular cysts are acquired; their wall is made from abundant connective tissue and coated with multilayered squamous epithelium, single-layered cubical, cylindrical or multilayered cylindrical epithelium. The thymus tissue residue can be found in the cyst wall, hence facilitate setting the right diagnosis. The congenital are rarer than the acquired. The surgical excision is preferred treatment.3,6
There are numerous pathological changes that can be clinically manifested by cervical tumefaction. In paediatric age, congenital anomalies are the most frequent cause. In differential diagnosis, cervical bronchogenic cysts, branchial arches residue, lymphatic malformations, thyroglossal ducts, cystic teratoma, cysts of the parathyroid and thyroid gland and the thymus anomalies are considered.7
Clinically, the cysts are commonly asymptomatic, only 6-10% patients have symptoms, such as dysphagia, dyspnoea, stridor, pain, vocal paralysis caused by compression to the recurrent laryngeal nerve and hoarseness. Thymic cysts in the neck most often appear in the first decade of life, more commonly in boys, in the left half of the neck, placed deeply behind or in front of sternocleidomastoid muscle.3,8,9
In about half of cases, the cyst is in contact with mediastinal thymus.10
During respiratory infections, they can be enlarged. Computerised tomography and/or magnetic resonance of the neck and thorax, can help in setting the cyst diagnosis, its connection with mediastinum, as well as thymus existence in younger patients of paediatric age, to avoid immunological dysfunction. Surgical excision could be method of choice for treatment, and the final diagnosis is set via pathohistological examination.8
It is important to note that surgical treatment of the thymic cyst in the neck, without adequate radiological examination of the region of the neck and chest, in the adult age will not lead to disorders in the function of the immune system, but in childhood it can lead to immunodeficiency.
Surgical excision of the cervical thymic cyst should be performed with great precaution due to close anatomical relationships with neurovascular elements in the neck such as: the vagus nerve, the internal jugular vein, carotid artery, as well as the phrenic, hypoglossal and recurrent laryngeal nerves.2,5,7
In the given case, the thymus cyst in the neck has been diagnosed in a girl, nine years old, without connection with mediastinum, while in the subsequent examination thymus has not been found in the mediastinum.
Cervical thymic cysts must be considered in the differential diagnosis of cervical cystic formations, especially in child age. Publication of the case report is important in order of caution when cervical thymic cysts are examined.
Conflict of Interests
The authors declare that there is no conflict of interests.
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