Thymic Cyst with Rare Clinical Presentations: Report of Ten Cases over 13 Years

Thymic cysts are usually found in the anterior mediastinum. They comprise 1 to 4.8% of all the mediastinal cysts [1, 2]. Thymic cysts can also be found in the neck [1, 3]. Cervical thymic cysts often appear as a mass in the lateral part of the neck. Investigations have shown that about fifty percent of the cervical thymic cysts can extend into the mediastinum [4, 5]. Although mediastinal thymic cysts are rarely symptomatic, dyspnea, cough and chest pain have been reported in some cases [1, 5]. Computed tomography (CT) scan of the cervical lesions can be used to identify the cystic nature and determine the extension of lesions to the mediastinum[1, 6, 7]. Fine needle aspiration (FNA) under CT guidance, video-assisted thoracoscopic surgery (VATS) and thoracotomy are common procedures for the management of thymic cysts[1, 7, 8]. The purpose of this study was to report rare clinical features, diagnostic workup and surgical approaches in the management and outcome of patients with thymic cyst.

n this retrospective study, we reviewed the data of ten patients with thymic cyst in Respiratory Inflammatory Diseases Research Center, Razi Hospital of Rasht, Iran, between 2000 and 2013. We collected data on presenting symptoms, signs, imaging features including chest X-ray (CXR), CT scan and magnetic resonance imaging (MRI), surgical approaches and outcome. Patients underwent various surgical approaches, dependent on the location of the cyst and final diagnosis was established for each patient by pathological examination.

Eight patients were symptomatic; three had dyspnea, chest pain and pleural effusion, simultaneously. Symptoms of other patients are shown in table 1. The most common tool for diagnosis was CT. CT was used in all patients for the diagnosis of unilocular or multilocular, unilateral or bilateral, extension or invasion of cyst and also pleural effusion or pneumothorax (Table 2). One patient had a huge bilateral thymic cyst (Figure 1). One patient had hydropneumothorax and three patients had hydrothorax (Figure 2, 3, 6, 7). Surgical approaches for cyst excision were postero-lateral thoracotomy, sternotomy and antero-lateral thoracotomy (Table 3). Complications occurred in one patient as left phrenic nerve damage. Mortality was zero. Recurrence of the thymic cyst was not detected in any of patients during 4 years follow up by evaluation of CXR, CT-scan and MRI. Moreover, outcome of patients including previous symptoms and signs, working and social activities was good.

Thymic migration, during fetal development, may cause deposition of thymic remnants in the anterior mediastinum and neck [5]. Nowadays, it is believed that thymic cysts are either congenital or acquired [1, 5]. Investigations have shown that about fifty percent of the cervical thymic cysts extend into the mediastinum and most are found in the anterior mediastinum [1, 4]; however, the incidence rate of the mediastinal thymic cysts is low and comprises up to 4.8% of all mediastinal masses [1].

For example, a study in Japan showed that of 108 mediastinal masses in children, the incidence rate of the thymic cysts was less than 1% [9]. Thymic cysts involve males 3 times more often than females and are often found in children. The mean age of our patients was 34 years, which illustrates that the thymic cysts can present in any age group. Thymic cysts may be unilobular (Figure 4, 5) or more frequently multilobular (Figure 1). Unilobular thymic cysts are usually found in the neck while multilobular are generally bigger and may extend into the mediastinum [10, 11]. Generally, thymic cysts are encompassed by a smooth fibrous capsule. Although the fluid of cysts is usually clear, it may be turbid or bloody in some cases [12]; in our study, the fluid of cysts in most of the patients was clear. Cholesterol clefts and foreign body granulomas may be found in cyst walls [9]. Four patients in our study had cholesterol granuloma (Figure 3, 5). It seems that unilocular thymic cysts are congenital or are caused by bronchial pouch remnant [1]. Multilocular cysts often result from an acquired inflammatory reactive process and have multiple adhesions to the adjoining structures [1, 10, 11]. The thymoma and thymic carcinoma were reported in the wall of the multilocular thymic cysts [1, 10] but none of our patients had thymoma or thymic carcinoma. Although most patients with thymic cyst are asymptomatic, symptoms can appear in some cases, usually between 5 and 7 years old [1, 5]. Eight of our patients had symptoms such as palpitation, dyspnea, chest pain, fever and neck mass. The symptoms of thymic cysts depend on their location. Cervical thymic cysts often appear with a mass in the lateral neck [3, 5]. Graeber et al, reported pain and vocal cord paralysis in the cysts which were located in the neck [13]; vocal cord paralysis was not detected in any of our cases. Allee and his colleagues found a thymic cyst accompanied with cardiac tamponade and pericarditis [14], which was also not found in our study. Similarly, Graeber et al reported four cases of dysphagia with large thymic cysts [13]; none of our cases had dysphagia. Gönülü et all reported five cases with dyspnea associated with very large thymic cysts in the hemi-thorax [15]; in our study, one patient had a huge thymic cyst in the right hemithorax who suffered from palpitation. Moreover, three patients had hydrothorax similar to a case reported by Lachanas [16]. Horner’s syndrome and intermittent brachiocephalic vein obstruction are other rare signs associated with thymic cysts [1]; these were not observed in our study. Although some investigators emphasized the advantage of ultrasonography in the evaluation of cervical thymic cyst, nowadays, most believe that CT of the neck and chest should be used to distinguish the cystic nature of the lesions and extension into the surrounding tissue [1, 5]. CT with contrast provides excellent visualization of thymic cysts and better margination with adjacent vessels. CT scanning was used for all of our cases. MRI and CT scan provide precise data on the position, depth and anatomical relationships of the cyst and demonstrate a connection between the cervical mass and the mediastinal thymus [6, 17] There is much controversy about the treatment methods for the unilocular congenital thymic cysts. Some believe that for the definitive diagnosis of the lesions, all should be resected [8]. Others believe that, intervention is often not necessary when typical CT findings exist for the thymic cyst [18]. Yet others suggest FNA under CT guidance  for similar conditions [1]. Malignant transformations are also indications for surgery [19]. All multilocular cysts should be resected by thymectomy to identify the neoplastic changes [1]. Multilocular cysts should also be removed because surgical resection is usually curative and can be performed safely through video thoracoscopy, median sternotomy or thoracotomy. Surgical excision is accomplished either by open methods or VATS [1, 9]. In our patients, surgical procedures were postero-lateral thoracotomy, antero-lateral thoracotomy and sternotomy. Although one of our patient developed left side phrenic paralysis but in most patients, surgical excision was curative without any long term recurrence and complications such as hemothorax, phrenic paralysis, wound, empyema and other infections.

Although thymic cysts are rare, they should be considered in the differential diagnosis of cervical or mediastinal masses. The true origin of these masses is unknown and preoperative diagnosis is difficult. The treatment of choice is complete excision of the cyst but a normal thymus in the mediastinum must be confirmed preoperatively to avoid the risk of total thymectomy. If cervical thymic cyst is in continuity with a normal thymus, preservation of the thymus should be considered, particularly in younger patients.

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