The mediastinum is a central thoracic compartment encompassing those structures contained between the sternum anteriorly and the vertebral column posteriorly, the thoracic inlet superiorly and diaphragm inferiorly, and laterally by each pleural cavity. The mediastinum has classically but nonanatomically been further divided into three or four subdivisions (variable separation of a superior mediastinal component in addition to the anterior, middle, and posterior elements). The boundaries and contents of each can be seen in Fig. 23.1 and Table 23.1 . In 2017, the International Thymic Malignancy Interest Group (ITMIG) released a classification system for mediastinal masses based on cross-sectional imaging that has been applied to children as well as adults. ^, The ITMIG system divides the mediastinum into prevascular, visceral, and paravertebral compartments.

Anterior ( light blue ), middle ( light red ), and posterior ( light green ) divisions of the mediastinum on sagittal CT scan of the chest.

As with other childhood cancers, pediatric mediastinal tumors are rare. Almost 40% occur in children under 2 years of age, and approximately 40%–60% are malignant. Approximately 40%–50% of pediatric mediastinal masses will present in the posterior mediastinum, 30%–40% in the anterior mediastinum, and the remaining 10%–20% in the middle mediastinum. ^, Table 23.1 describes the usual masses found in each of the anterior, middle, and posterior mediastinal compartments. The most common anterior mediastinal masses are lymphomas. ^, The most common middle mediastinal masses are nonmalignant lymphadenopathy and lymphomas. Neurogenic tumors and foregut cysts are the most common posterior mediastinal masses.

The early embryo is a trilaminar disc connected to the yolk sac. The mediastinum contains elements of each layer—the outer ectoderm, middle mesoderm, and inner endoderm. The thyroid and thymus are mostly endodermal structures—the thyroid gland originates from the first and second pharyngeal pouches, and the thymus derives from the third pharyngeal pouches, which migrate to the anterior mediastinum and fuse together. The esophagus and tracheobronchial tree also derive from the endodermal germ layer. Around week 4, folding of the three-layered disc occurs through its ventral midline, resulting in tubularization. Between 4–6 weeks, a ventral bud from the foregut separates into the trachea and bronchi, combining with early lungs developing from surrounding mesoderm. The heart also develops from the mesodermal layer; lateral folding forms a primitive heart tube around week 3 of embryonic development, which twists and bends, forming four chambers around week 8. The maturing heart continues to develop and receive migrating neural crest cells from the ectodermal layer, which also migrate along the foregut to innervate the splanchnic organs and form the sympathetic chain. At roughly 17–20 weeks gestation, the heart is sufficiently formed to be seen on ultrasound.

Most mediastinal masses are found on incidental imaging performed for other reasons, sometimes prenatally ( Figs. 23.2 and 23.3 ), but more often on chest radiographs performed on a child who has a concurrent condition. Most symptomatic presentations are respiratory in nature, with features like dyspnea, orthopnea, cough, wheezing, and recurrent pulmonary infection. Less commonly, other compressive symptoms like Horner syndrome or superior vena cava syndrome are described. In young infants with pliable chest walls, bulging on exam is possible. Posterior mediastinal tumors involving the spinal cord can present with neurological symptoms such as sudden paraplegia. Rapid onset of symptoms may suggest a fast-growing mass, more typical of lymphoma.

This fetal echocardiogram on a 30-week gestational age baby shows a 4 × 4 cm intrapericardial teratoma (MASS) that is closely associated with the aortic root. The bulk of the mass is in the right chest and is in direct contact with the right atrium but does not cause any right atrial compression or systemic venous inflow or outflow obstruction. There is a large pericardial effusion ( asterisk ) around both the heart and the tumor. Following delivery, the baby was taken to the operating room for excision of the teratoma and recovered uneventfully.

This newborn with the prenatal diagnosis of an upper mediastinal cyst had respiratory distress at birth. These T2-weighted MR images show a large prevertebral mucus cyst that (A) displaces the trachea forward and (B) extends to both sides. In (A), deformation of the anterior vertebral bodies due to prolonged prenatal compression can be seen. This bronchogenic cyst was successfully removed thoracoscopically.

Diagnostic workup begins with a clinical history and physical exam, with special attention to respiratory symptoms and compressive phenomena like orthopnea, wheezing, stridor, Horner or superior vena cava syndrome, as well as any palpable lymph nodes. The mass is often initially seen on a plain chest radiograph, which shows a widened mediastinal shadow, and a lateral film can further identify the anterior-posterior location. The next step in workup is axial chest imaging with IV contrast–enhanced CT scan of the chest, which provides further detail including solid versus cystic nature, presence of calcifications (suggestive of neuroblastoma or teratoma), relation of the mass to vascular structures, compression of the tracheobronchial tree, and neural invasion. ^, If obtained, MRI may provide additional detail, especially for tumors of vascular origin. Fetal MRI may also be used for masses seen on prenatal ultrasound. Although not beneficial in most other etiologies, PET scan, combined with either CT or MRI, is used in the staging and management of lymphoma ( Fig. 23.4 ). Approximately one in five mediastinal foregut duplications have concurrent gastrointestinal duplications elsewhere, for which ultrasound or CT screening should be performed. Most mediastinal masses may be reliably differentiated by imaging characteristics. ^,

¹⁸ FDG PET (A) and PET/CT scan (B and C) of a 10-year-old boy with an anaplastic large-cell NHL. Extensive mediastinal and abdominal FDG uptake in the lymphoma is clearly seen. A biopsy was performed in the left cervical region ( arrows , A and C), avoiding a riskier procedure in the thorax or the abdomen. NHL , Non-hodgkin lymphoma.

Serum and urine biochemical tests may also help point toward etiology. For posterior masses, urine or serum metanephrines as well as urine vanillylmandelic acid and homovanillic acid may indicate a catecholamine secreting neuroblastoma. Alpha-fetoprotein and hCG should be obtained for suspected teratomas. Elevated LDH may suggest lymphoma but can also be elevated in neuroblastomas.

The next step for cystic masses (e.g., bronchogenic cysts and esophageal duplication cysts) is generally to proceed with excision in the absence of infection. For other masses, cell sampling should be sought for definitive diagnosis. Compression of the airway or major vessels by a mediastinal mass can render endotracheal intubation and general anesthesia potentially treacherous, and when possible, alternative sites for tissue harvest should be selected. Bone marrow, pleural fluid, and palpable peripheral nodes can be sampled under local anesthesia and light sedation. A multidisciplinary discussion (e.g., surgery, interventional radiology, oncology, anesthesia, intensivists, pulmonology) is essential and can facilitate timely workup. If these less invasive tests are not available or nondiagnostic, image-guided percutaneous fine-needle aspiration or core needle biopsy can sometimes also be performed without general anesthesia. An anterior approach through a Chamberlain procedure may be possible under local anesthesia and sedation for masses in the anterior mediastinum. Thoracoscopy or mediastinoscopy are generally used as a last resort. Empiric treatment is an alternative in extreme scenarios (steroids and or chemotherapy) . An algorithm is shown in Fig. 23.5 . Unexpected airway collapse from a mediastinal mass while under anesthesia is life-threatening event, and rotation of the patient to a lateral position (to take the weight of the mass off the airway), rigid bronchoscopy, sternal elevation (Rultract, Rultract Inc., Cleveland, OH), emergent anterior thoracotomy, or extracorporeal membrane oxygenation (ECMO)/bypass are possible options.

General algorithm for diagnosis of mediastinal masses in children.

Lymphoma is the third most common childhood malignancy following leukemia and tumors of the central nervous system, and it is the most prevalent of the mediastinal masses in children. Hodgkin lymphoma typically presents in children older than 10 years of age and may present with associated “B” symptoms (fever, weight loss, and night sweats) in addition to mass effect from bulky lymphadenopathy. Non-Hodgkin lymphomas (diffuse large B cell lymphoma, Burkitt lymphoma, anaplastic lymphoma, and lymphoblastic lymphoma) are more common in children younger than 10 years. The prognosis is generally favorable, and most children with lymphoma will survive into adulthood. Surgery for mediastinal lymphoma is generally limited to obtaining tissue for the diagnosis, as well as placing long-term vascular access. Principles for biopsy have been discussed in the diagnostic evaluation section ( Fig. 23.7 ).

Sagittal (A) and axial (B and C) contrast-enhanced CT images of a 7-year-old girl with a T-cell NHL. Cardiac insufficiency, superior vena cava syndrome, and severe dyspnea were the initial symptoms. The CT scan depicts a large mediastinal mass ( asterisks ) and a significant pericardial and pleural effusion. Diagnosis was made by cytometry analysis from the pericardial fluid.

The focus of this chapter is on surgical management; additional current references for the reader interested in novel genetic and biologic pathways and medical management of lymphomas are provided. ^, Continually updated information is also available through the National Cancer Institute. ^,

Neurogenic tumors most commonly arise in the posterior mediastinum and comprise about three-quarters of the solid masses in this location. Approximately 80% of neurogenic tumors are benign and include neurofibromas, schwannomas, and ganglioneuromas. Of the malignant neurogenic tumors of the mediastinum, the most common and clinically significant is neuroblastoma, which originates from the sympathetic chains on either side of the spine and may involve variable levels of ganglia. There may be tumor extension into the spinal canal through one or more foramina (a “dumbbell” tumor). Lower mediastinal neuroblastomas may extend intraabdominally, either through the aortic hiatus or the posterior diaphragm itself. Similarly, upper mediastinal neuroblastomas may have cervical extension. Although most presentations are either asymptomatic or minimally symptomatic and incidentally discovered, spinal cord involvement may cause neurological symptoms such as back pain, leg weakness, and bladder dysfunction. Disruption in the sympathetic nerve supply to the eye can cause oculosympathetic paresis (Horner syndrome [ipsilateral ptosis], miosis [pupillary constriction], and anhidrosis). Rare paraneoplastic syndromes are associated with neuroblastoma, including opsoclonus-myoclonus-ataxia and secretion of vasoactive intestinal peptide. Neuroblastoma metastasizes by both lymphatic and hematogenous pathways. Orbital metastasis can cause periorbital ecchymosis and may be initially misdiagnosed as trauma. Metastatic involvement of the liver may lead to hepatomegaly. Skin metastases are uncommon but present as firm, reddish, nontender nodules that when rubbed, blanch centrally with an erythematous outer ring (“blueberry muffin spots”). Ganglioneuroblastomas (discussed in Chapter 62 ) are considered a transitional tumor on the spectrum of ganglioneuroma to neuroblastoma with malignant potential.

In 2009 the International Neuroblastoma Risk Group developed the INRG staging system (INRGSS), a pretreatment evaluation based on clinical and image-defined risk factors. ^, Patients in low- and very-low-risk groups had a 5-year event-free survival greater than 80%, whereas high-risk patients had less than 50% 5-year event-free survival. Neuroblastomas of the thorax, including mediastinum, have more favorable biologic activity and clinical outcomes. ^, Age is also an important prognostic factor; infants younger than 18 months have significantly better outcomes. Neuroblastomas have very heterogenous behavior from aggressive, treatment-resistant progression to spontaneous regression without therapy, even in some patients with metastatic disease. The optimal therapy and role of surgical resection remain under intense investigation and are reviewed in detail in Chapter 62 .

Axial imaging will typically demonstrate a round or fusiform mass in the posterior mediastinum with paraspinal extension. Calcifications may be present. MRI provides additional detail regarding tumor relationship to neurological structures. Serum neuron-specific enolase, LDH, and ferritin should be checked. Urine should be collected and tested for vanillylmandelic and homovanillic acid. A nuclear medicine scan utilizing 131I-metaiodobenzylguanidine uptake should be performed to evaluate for bony and bone marrow metastasis. Direct bone marrow evaluation with biopsy is also needed for staging. Imaging may not be able to reliably differentiate ganglioneuromas from ganglioneuroblastomas and neuroblastomas, and diagnosis may not be confirmed until histopathologic analysis ( Figs. 23.8 and 23.9 ).

A 16-year-old patient presented with Horner syndrome and was found to have a right superior mediastinal mass. (A) MR image of the mass showing the ganglioneuroma ( asterisk ). (B) At thoracoscopy, the mass ( asterisk ) can be visualized cephalad to the azygous vein and just lateral to the superior vena cava ( arrow ). This ganglioneuroma was able to be removed thoracoscopically.

Two-year-old patient referred for a mediastinal mass discovered on a plain chest radiograph (A) for minor respiratory symptoms and abnormal auscultation. On the CT scan (B), the tumor occupied the majority of the left hemithorax and displaced all the structures to the right. It had extensive calcifications within it and was completely removed at thoracotomy. The final pathology was a ganglioneuroblastoma.

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