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Huge Fetal Cervicomediastinal Thymic Cyst: Successful Antenatal Intervention for Vaginal Delivery The thymus is located in front of the heart and is an important immune organ that produces T cells. Congenital thymic cysts result from the degeneration of aberrant thymic tissue after the arrest of thymic primordium migration along the thymopharyngeal tract.1 Although congenital thymic cysts can occur anywhere from the neck to the mediastinum, most are in the neck.2 If such a cyst is in the cervicomediastinal area, it is difficult to distinguish from other cystic masses, such as lymphangiomas and bronchogenic cysts.3 They are often diagnosed as a result of the deformity that develops with cyst growth because congenital thymic cysts are asymptomatic.4 A large cyst can compress the adjacent organs and cause tracheal obstruction and a mediastinal shift. Such cysts need to be removed surgically.5 To our knowledge, 2 cases of fetal thymic cysts have been reported prenatally. Those cases did not need any additional intervention in utero because one cyst did not produce a mass effect,6 and the other did not change in size until delivery.2 There is no consensus on the in utero obstetric management of thymic cysts and which delivery mode is better because most are detected postnatally. Here we report antenatal intervention to prevent immediate postnatal complications from a large cervicomediastinal thymic cyst that extended from the upper neck to the diaphragm with a mediastinal shift, tracheal compression, and tachycardia. A 28-year-old healthy primigravida was referred after detection of a huge fetal mediastinal cystic mass during a sonographic examination at 38 weeks’ gestation. There was no history of medical, surgical, or familial disease. The initial fetal sonography (Accuvix XQ; Medison Co, Ltd, Hongcheon, Korea) showed a huge hypoechoic cystic mass with a septum measuring 64 × 23 × 32 mm extending from the neck into the diaphragm. The mass had welldefined borders with no connection to the heart, great vessels, or trachea. However, the mass displaced the heart to the left posterior thorax and compressed the trachea (Figure 1A). Fetal tachycardia was also present. Color Doppler sonography showed no blood flow in the mass. Fetal biometric measurements were appropriate for gestational age, and no other fetal findings were identified. Fetal magnetic resonance imaging (MRI) was performed the same day to evaluate the characteristics and anatomic connections of the mass to the surrounding tissues. It showed a 60 × 21 × 34-mm tubular cystic mass with J Ultrasound Med 2014; 33:917–921

a linear septum extending from the anterior neck beneath the tongue base to the anterior mediastinum above the diaphragm. It compressed the heart to the left posterior thorax (Figure 1B). The differential diagnosis of the cyst included a thymic cyst, lymphangioma, and a bronchogenic cyst. There was difficulty distinguishing these diagnoses because the cyst was too large for its origin to be established, and it had two septa. On the basis of the fetal sonography and MRI, we concluded that the cyst had a mass effect, causing the fetal tachycardia and mediastinal shift, and that the huge cyst would trigger respiratory distress immediately after delivery. Therefore, if we did not reduce the size of the cyst, we would have to perform a cesarean delivery for ex utero intrapartum treatment to avoid respiratory distress. In addition, the cyst might have ruptured during a normal vaginal delivery. Therefore, we performed sonographically guided aspiration to decompress the cyst immediately before vaginal delivery. Because percutaneous fetal intervention can be associated with complications, such as placental hemorrhage, rupture of the chorioamniotic membrane, maternal infection, and maternal-fetal hemorrhage,7 we obtained informed consent from the parents. The skin was prepared with a povidone-iodine solution and draped using standard sterile techniques, and the procedure was performed with sterile gel. A 22-gauge, 89-mm spinal needle (Hakko Co, Tokyo, Japan) was advanced into the cyst under direct sonographic guidance through the fetal anterior neck. Thirty milliliters of clear viscous fluid were aspirated from the cyst through the spinal needle. Cytologic examination revealed some mature squamous cells. After aspiration, fetal MRI and sonography were repeated and showed a marked decrease in the size of the cystic mass, which now measured 29 × 11 × 17 mm, and mass effects were now absent in the anterior neck and mediastinum (Figure 1, C and D). In addition, the tachycardia disappeared. Three days after the intervention, a female neonate weighing 3670 g was born by a normal vaginal delivery at 40 weeks’ gestation with Apgar scores of 8 and 9 at 1 and 5 minutes, respectively. Her condition was stable with no signs of respiratory distress. On physical examination, there was no palpable mass in the neck. Postnatal sonography showed a small cystic mass measuring 30 × 12 × 19 mm. At 31 days of age, a painless mass in the neck was noted. Sonography of the neck and chest showed a recurrence of the mass, measuring 78 × 31 × 40 mm. At 3 months of age, the cyst was removed surgically because it had collapsed the left lung totally and caused atelectasis of the right lower lung. The histologic findings confirmed the diagnosis of a unilocular thymic cyst with a stratified squamous epithelial lining.

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In conclusion, a huge cervicomediastinal thymic cyst can cause a mediastinal and tracheal shift and tachycardia in utero. Although there is no consensus on treatment in utero, antenatal aspiration from the cyst is a useful obstetric option, not only for decompressing the trachea and restoring the position of the heart and a normal heart rhythm but also for enabling a vaginal delivery.

Dongheon Lee, MD, Ji Yeon Lee, MD, Sunghun Na, MD, Jong Yun Hwang, MD Department of Obstetrics and Gynecology College of Medicine Kangwon National University Chuncheon, Korea

This work was supported by a research Grant from Kangwon National University. doi:10.7863/ultra.33.5.919

Figure 1. Huge cervicomediastinal thymic cyst on sonography and MRI. A, Transaxial sonography of the mediastinum showed that a huge cyst (arrow) displaced the heart. B, Fetal MRI showed that the cyst (white arrow) extended from the neck to the diaphragm and compressed the trachea (gray arrows). C and D, After intervention, the size of the cyst decreased, and the heart was restored to the original position. Also, it was shown that the trachea was decompressed on fetal MRI (D, gray arrowheads).

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References 1. 2.

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Johnsen NJ, Bretlau P. Cervical thymic cysts. Acta Otolaryngol 1976; 82:143–146. de Miguel Campos E, Casanova A, Urbano J, Delgado Carrasco J. Congenital thymic cyst: prenatal sonographic and postnatal magnetic resonance findings. J Ultrasound Med 1997; 16:365–367. Ozbey H, Ratschek M, Höllwarth M. Cervicomediastinal thymic cyst: report of a case. Surg Today 2005; 35:1070–1072. Nguyen Q, de Tar M, Wells W, Crockett D. Cervical thymic cyst: case reports and review of the literature. Laryngoscope 1996; 106:247–252. Hendrickson M, Azarow K, Ein S, Shandling B, Thorner P, Daneman A. Congenital thymic cysts in children: mostly misdiagnosed. J Pediatr Surg 1998; 33:821–825. McEwing R, Chaoui R. Fetal thymic cyst: prenatal diagnosis. J Ultrasound Med 2005; 24:127–130. Sudhakaran N, Sothinathan U, Patel S. Best practice guidelines: fetal surgery. Early Hum Dev 2012; 88:15–19.

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Huge fetal cervicomediastinal thymic cyst: successful antenatal intervention for vaginal delivery.

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