Chest / Cardiac for Friday, April 11th, 2025

History

A 33 year old pregnant female at 38 weeks 2 days gestation presents for further evaluation after prenatal ultrasound demonstrated a new fetal chest mass. 

Images (Click any image to enlarge)

Question

What is the most likely diagnosis?

Your answer

Please log in to see your results.

Correct answer

Mediastinal Teratoma

Discussion

The mediastinal location of the mass and its complex features, including calcifications, makes mediastinal teratoma the most likely prenatal diagnosis, further supported with postnatal chest CT. Following fetal MRI, which raised high suspicion for mediastinal teratoma, the patient underwent a scheduled cesarian section with ex utero intrapartum treatment (EXIT) to ECMO procedure given the severe mass effect on the heart and obstructed left main stem bronchus. After stabilization, the tumor was resected through a median sternotomy and pathology confirmed congenital mature teratoma. The patient’s right thymic lobe was resected. 

Fetal  mediastinal teratomas typically arise from either the thymus or pericardium. Mediastinal/thymic origin teratomas are more likely to be in the anterior superior thorax superior to the heart and can extend to the sternum. Pericardial teratomas are more likely to be located on the right side of the heart. In the pericardial type, the mass moves in synch with the heart and attaches directly to the heart, which may be visualized on prenatal echocardiogram. Mature teratomas are the most common types of germ cell tumors in the mediastinum, with seminoma being the second most common. On imaging, germ cell tumors can have fluid, macroscopic fat and calcifications associated with soft tissue. Distinguishing between mature and immature teratomas on imaging is challenging. An enlarged, mostly solid, enhancing and necrotic mass with high alpha fetoprotein levels may favor a malignant teratoma.  

Teratoma is the most common congenital neoplasm, but mediastinal teratoma is rare in the fetus. In utero, these tumors may result in nonimmune hydrops leading to fetal demise, polyhydramnios, and preterm labor. Hydrops fetalis and polyhydramnios are poor prognostic signs. The diagnosis is often in the second or third trimester of gestation and a multidisciplinary approach including obstetricians, fetal imagers, neonatologists, and surgeons is critical to plan the delivery and postnatal care.

Differential diagnosis

• Congenital pulmonary airway malformation (CPAM) is unlikely due to the mediastinal location of the mass, the presence of calcifications, and the lack of appreciable cysts on ultrasound or MRI. CPAM are multicystic masses of lung with abnormal bronchial proliferation and are part of the spectrum of bronchopulmonary foregut malformations.
• Lymphatic malformations can occur in the anterior mediastinum but the imaging appearance consists of thin-walled cystic spaces with fluid attenuation. While there can be displacement of adjacent structures, lymphatic malformations often do not cause significant compression. If untreated, the malformation can grow over time. 
• Pleuropulmonary blastoma can rarely present in the fetus. It is a rare, aggressive malignant tumor of the lung periphery that involves the visceral pleura, mostly presenting prior to age 5. The tumors are more commonly right-sided, pleural-based and mixed solid-cystic in appearance without calcifications, and often with associated pleural effusion and mediastinal shift. Many patients have a mutation of the DICER1 gene. 

Additional images

References

• Oliver, E. R., Didier, R. A., Horii, S. C., Hedrick, H. L., Khalek, N., DeBari, S. E., Adzick, N. S., & Coleman, B. G. (2022). Fetal thoracic teratomas: Mediastinal or pericardial? Pediatric Radiology, 52(12), 2319–2328. https://doi.org/10.1007/s00247-022-05367-x
• Shahrzad, M., Le, T. S., Silva, M., Bankier, A. A., & Eisenberg, R. L. (2014). Anterior mediastinal masses. American Journal of Roentgenology, 203(2). https://doi.org/10.2214/ajr.13.11998
• Giancotti, A., La Torre, R., Bevilacqua, E., D'Ambrosio, V., Pasquali, G., & Panici, P. B. (2012). Mediastinal masses: a case of fetal teratoma and literature review. Clinical and experimental obstetrics & gynecology, 39(3), 384–387.
• Retrouvey, M., & Lam, C. (2024, August 27). Anterior Mediastinal Mass. STATdx. https://app.statdx.com/document/anterior-mediastinal-mass/7095ab45-ca72-4222-ad1b-f35240900cdd
• Edwards, E. (2021, February 17). Congenital Pulmonary Airway Malformation. STATdx. https://app.statdx.com/document/congenital-pulmonary-airway-malfor-/a8586aeb-51e7-4ee7-ab0b-3bc620b09e14
• Towbin, A. J. (2021, November 8). Pleuropulmonary Blastoma. STATdx. https://app.statdx.com/document/pleuropulmonary-blastoma/7acd2f73-2378-4848-8b47-a1c1fe378c9c