Congenital Thymic Cyst: Antenatal Diagnosis and Postnatal Management.

Thymic cyst is regarded as a rare anomaly, accounting for about 3% of all anterior mediastinal masses. It can be either congenital or acquired. Congenital thymic cysts are usually asymptomatic, with about 50% found incidentally in childhood or adolescence. We report a case of 1-month 23-day-old male baby who was antenatally diagnosed at 32 weeks' gestation. Spontaneous resolution did not take place in the antenatal or neonatal period; instead, there was an increase in size on follow-up imaging. The baby was successfully managed by surgical excision.

INTRODUCTION

Thymic cysts are regarded as rare, accounting for about 3% of all anterior mediastinal masses.[1] It can be either congenital or acquired.[1] Thymic cysts have been described in the neonatal and pediatric literature, and to our knowledge, there are only two reports of antenatally detected intrathoracic thymic cysts. de Miguel Campos et al.[2] reported the first case in which a specific antenatal diagnosis and identification of the thymic origin was not possible. McEwing and Chaoui[3] reported the second case of a thymic cyst detected in a fetus at 22 weeks' gestation, which showed spontaneous resolution in the postnatal period. We report a case of 1-month 23-day-old male baby who was antenatally diagnosed at 32 weeks' gestation. Magnetic resonance imaging (MRI) showed the cyst to be pericardial/thymic cyst. Antenatal intervention was also considered in this case as in Lee et al.[4] but was not done as the cyst was not obstructing the airway. Lower segment cesarean section (LSCS) was done for obstetrical reasons. Postnatally, he was followed with imaging. The cyst was managed with surgical excision. The histopathology confirmed this cyst to be of thymic origin.

CASE REPORT

A 1-month 23-day-old male baby admitted with antenatally diagnosed left thoracic cyst. Antenatal MRI at 32 weeks of gestation revealed a tubular cystic structure draping the fetal heart along its left side, measuring 2.8 cm × 1.5 cm. The lesion seems to be outside the lung parenchyma, abutting the mediastinal pleura [Figure 1]. The possibility of both pericardial and thymic cysts was considered. Fetal echo suggested a pericardial cyst. The baby was born full-term LSCS uneventfully. Birth weight was 3.6 kg. Postnatal ultrasound (USG) and MRI performed on day 3 of life were suggestive of cystic swelling on the left side of chest possibly a cystic lymphangioma. Barium swallow study was normal. Contrast-enhanced computed tomography chest at 1 month 15 days of age revealed a well-defined large cystic density mass in the left anterior mediastinum which appeared to be arising from thymic gland, measuring 4.1 cm × 3.4 cm × 4.4 cm extending from the thoracic inlet till the left atrial appendage showing internal septae and irregular iso- to hyper-dense contents and mild enhancement. No calcification or fat density is seen in it. This lesion was abutting the anterior wall of arch of aorta and left lateral wall of main pulmonary artery and left pulmonary artery. Right half of the thymus showed homogenous enhancement measuring 5.1 cm × 4.7 cm × 3.0 cm and was adherent to this cystic lesion and extending in the suprasternal region [Figure 2]. Keeping the possibility of hemorrhagic thymic cyst, an USG-guided fine-needle aspiration cytology was performed. Microscopic examination revealed inflammatory changes – lymphocytes, neutrophils, and scattered hemosiderin laden cyst macrophages in a hemorrhagic background. The patient was taken up for surgery due to increase in size of the cyst. Left thoracoscopy converted to left thoracotomy and excision of the cyst was done. Cyst appeared blue; multiseptated was probably thymic origin. Normal thymus was also seen on the right of the cyst. The baby tolerated the procedure well. Chest tube was removed after 24 h. Postchest tube removal, the X-ray showed full expansion of both lungs. His postoperative period was uneventful. Histopathology was suggestive of benign thymic cyst [Figure 3a and b].

Figure 1

Antenatal magnetic resonance imaging showing left thoracic cyst likely pericardial/thymic cyst

Figure 2

Postnatal contrast-enhanced computed tomography chest showing thymic cyst

Figure 3

Histology slide. (a) Cystic lesion showing thymic tissue, (b) CD3-positive lymphocytes

The baby is now 15 months old and weighing 13 kg.

DISCUSSION

Congenital thymic cysts are usually asymptomatic, with about 50% found incidentally in childhood or adolescence period.[1] Complications are rare unless they are large or occur in an aberrant cervical gland. Respiratory complications, vocal cord paralysis, dysphagia, and compression of the brachiocephalic vein have been reported.[3] However, most congenital cysts are small.[3] Postnatally, sonography, computed tomography,[5] and MRI[1] may play a role in diagnosis and identification of the thymic origin. However, despite optimal imaging, the origin of the cyst may be difficult to establish, particularly when very large.

Resection of a thymic cyst is optimal for the prevention or treatment of complications and because neoplasia cannot be definitively excluded.[6] Wang et al.[7] reported clinical features, diagnosis, and video-assisted thoracoscopic surgery (VATS) in 108 patients of thymic cyst. In one patient, VATS was converted to a thoracotomy due to severe pleural adhesion and difficulty of surgical exposure of thymic cyst. They identified 7 (6.5%) postoperative complications: atrial fibrillation in three patients, chylothorax in two patients, and pneumonia in two patients. All complications were resolved after conservative treatment.

Fetal mediastinal cystic lesions are rarely reported. de Miguel Campos et al.[2] reported an intrathoracic cyst detected prenatally. Postnatal imaging with sonography and computed tomography suggested a possible thymic origin, and MRI allowed the specific diagnosis.[2] Prenatally described mediastinal lesions include bronchogenic cysts, esophageal duplication cysts, neurenteric cysts, congenital hiatal hernias, cystic neuroblastoma, cystic teratoma, pericardial cysts, and cystic lymphangioma.[5] Congenital thymic cysts are rare in the neonatal and pediatric population but should be considered in the differential diagnosis.

CONCLUSION

Any cystic lesion between the lung parenchyma and the pericardium which has no communication with the esophagus should be investigated further. In this case, the cyst did not have spontaneous resolution in the antenatal and neonatal period; instead, there was an increase in size on follow-up imaging. The baby was successfully managed by surgical excision.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.