The infant’s story began deceptively. From the age of two months she had persistent tachypnea, an abnormally rapid breathing rate that in babies is most often attributed to minor respiratory infections. When a chest radiograph was obtained at four months, it showed widening of the mediastinum, the central compartment of the chest between the lungs. In infants this finding is frequently benign: the thymus, an organ of the immune system that sits just behind the breastbone, is naturally large in early life and gradually shrinks over the following years. The radiograph was therefore interpreted as a prominent but normal thymic shadow, and the child was followed without further intervention. Only in retrospect, the reporting team notes, did the contour and extent of the opacity on those early films appear atypical for simple thymic prominence.

By six months of age the picture had changed decisively. The baby’s respiratory distress worsened, prompting referral to a tertiary care center, where a repeat radiograph showed marked progression of the mediastinal widening along with mass effect and reduced aeration of the right lung. Chest computed tomography was ordered to characterize the lesion. The differential diagnosis at that point included thymic enlargement, lymphoma, and germ cell tumor, the broad categories that account for most masses in the anterior mediastinum of young children. The CT scan delivered a near-definitive answer: a large mass containing fat, cystic spaces, and calcifications, a combination of tissue densities highly characteristic of a mature teratoma. The scan also revealed the tumor’s dangerous anatomy. It was compressing the superior vena cava, the large vein returning blood from the head and arms to the heart, and pressing on the right heart itself. It had also collapsed the posterior segment of the right upper lobe by squeezing shut the segmental bronchus that ventilates it.

Teratomas are among the strangest tumors in medicine. They arise from germ cells, the primitive cells capable of forming an entire organism, and are composed of mature tissues derived from more than one embryonic layer. Most teratomas occur in the ovaries or testes, with other common sites including the sacrococcygeal region at the base of the spine and the retroperitoneum behind the abdominal organs. Within the chest, the anterior mediastinum is by far the most frequent location. Under the microscope, these tumors can contain an astonishing menagerie of structures: in this case, pathologists identified neuroglial tissue, adipose tissue, hyaline cartilage, skeletal muscle, respiratory-type epithelium, mucinous gastric-type glands, and even structures resembling ovarian follicles and kidney glomeruli, all coexisting within a single encapsulated mass. Focal nephrogenic rests, primitive kidney-forming tissue, were also present, and the tumor showed immunohistochemical positivity for the Wilms tumor 1 protein. Despite this bizarre composition, mature teratomas are histologically benign; their danger lies almost entirely in what they compress.

That danger announced itself dramatically. Several hours after the CT scan, the infant became irritable, her face puffed up, and she stopped breathing. The episode improved with repositioning and supplemental oxygen, a pattern that immediately raised concern for mediastinal mass syndrome. The syndrome arises because a large anterior mediastinal mass behaves like a plug in a hydraulic system. In an awake, spontaneously breathing child, respiratory muscle activity and airway tone help keep the compressed airway patent and assist venous return to the heart. When sedation or general anesthesia abolishes spontaneous respiration, when the child is placed supine, or when positive-pressure ventilation is applied, the already narrowed airway can collapse further and venous return can be critically impaired. The result can be abrupt, irreversible cardiorespiratory arrest, sometimes within minutes of induction. Anesthesiology literature has documented this phenomenon for decades, and it is the reason anterior mediastinal masses occupy a special place of caution in pediatric perioperative medicine.

The anesthetic plan crafted for this infant reflects nearly every principle that the specialty has developed for this scenario. Two units of cross-matched packed red blood cells were prepared before surgery. Standard monitoring was established, and anesthesia was then induced by inhalation with sevoflurane rather than by intravenous agents, allowing a gradual, controllable transition to unconsciousness while the child continued to breathe on her own. Once an adequate depth was achieved, the team placed a central venous line in the left femoral vein and an arterial line in the right femoral groin under ultrasound guidance, deliberately choosing femoral vessels because catheters inserted in the neck or arms might have passed through the compressed superior vena cava or failed to provide reliable access. Ketamine and atropine were administered intravenously to support hemodynamics and heart rate, and the trachea was intubated with an uncuffed 4.0-millimeter tube while spontaneous respiration was preserved. Crucially, muscle relaxants were withheld entirely at this stage, because paralyzing a child whose airway is held open only by her own respiratory effort can precipitate the very collapse the team feared.

With the airway secured and the child breathing spontaneously, sevoflurane was discontinued and maintenance anesthesia switched to isoflurane. The infant was turned into the left lateral decubitus position, lying on her left side, a posture that shifts the mediastinum and can partially relieve compression, and handed to the surgical team. Through a right thoracotomy, an incision between the ribs into the right chest, surgeons completely excised a well-encapsulated mass measuring approximately 20 by 5 centimeters in its longest dimensions; the gross specimen measured 10 by 7.5 by 6 centimeters and contained a cystic area of clear fluid. The operation lasted from 12:30 in the afternoon until 3:00 p.m., during which the infant received 100 milliliters of packed red blood cells and 400 milliliters of normal saline. Only after the tumor had been removed, and the compression eliminated, did the team administer a neuromuscular blocking agent and transition to controlled mechanical ventilation. A chest tube was placed and the right lung re-expanded satisfactorily.

The outcome underscores the value of this approach. The infant was successfully extubated on the first postoperative day, discharged in good condition on postoperative day five, and remained asymptomatic with normal respiratory status at three-month follow-up. Her case fits a recognizable pattern across the small published literature on infantile anterior mediastinal teratomas with airway or cardiovascular compromise. A five-month-old reported in 2018 was managed with a one-lung ventilation strategy to protect against compression at the carina and bronchi. A two-month-old reported in 2022, who presented with cough, noisy breathing, and cardiac displacement, underwent deliberate right-mainstem intubation without paralysis, with sternotomy and cannulation access prepared in advance, and was likewise extubated on day one and discharged on day five. A three-month-old reported in 2024 carried a congenital teratoma weighing twice her body weight and was managed with a staged approach of sedated imaging and percutaneous drainage before definitive thoracotomy. Across these independently reported cases, the recurring elements are nonspecific respiratory symptoms preceding diagnosis, spontaneous-ventilation induction with muscle relaxants withheld until the surgeon is ready, and generally favorable outcomes when those principles are followed.

The diagnostic lesson may be the most broadly applicable one. In infancy, the thymus is a large, soft organ that routinely produces impressive mediastinal shadows on plain radiographs, and distinguishing a pathological mass from normal thymic tissue on a single supine film is genuinely difficult. Features that should raise suspicion include atypical contours, interval growth between studies, mass effect on adjacent structures, and persistent unexplained tachypnea. Cross-sectional imaging with computed tomography, particularly the identification of fat, fluid, and calcification within a lesion, can settle the question, but only if the lesion is suspected in the first place. The authors of the report emphasize that heightened clinical vigilance in infants with persistent tachypnea and mediastinal widening, combined with early multidisciplinary planning among pediatric pulmonology, radiology, anesthesiology, and surgery, is essential to prevent the catastrophic anesthetic complications that anterior mediastinal masses can produce. For this one infant, that vigilance arrived just in time, and a tumor that had been silently growing since early infancy was removed before it could claim her airway for good.

Subject of Research: Anesthetic and surgical management of a giant anterior mediastinal mature teratoma causing mediastinal mass syndrome in an infant

Article Title: Anterior Mediastinal Mature Teratoma Presenting With Mediastinal Mass Syndrome in a Six‐Month‐Old Infant: Diagnostic Pitfalls and Anesthetic Challenges

Article References: Khanbabaee, G. T., Shafiee, A., Ghomi, Z., Mahdavi, N. S., Mohajerzadeh, L., Nilipour, Y., & Mahdavi, S. A. (2026). Anterior Mediastinal Mature Teratoma Presenting With Mediastinal Mass Syndrome in a Six‐Month‐Old Infant: Diagnostic Pitfalls and Anesthetic Challenges. Clinical Case Reports, 14(10), Article e73618. https://doi.org/10.1002/ccr3.73618

Image Credits: AI Generated

DOI: 10.1002/ccr3.73618

Keywords: mature teratoma, anterior mediastinal mass, mediastinal mass syndrome, infant, pediatric anesthesia, thymus, superior vena cava compression, spontaneous ventilation, thoracotomy, germ cell tumor, chest radiography, computed tomography