Pediatric Chest: A Review of the Must-know Diagnoses

Shreya Sood, MD; Julia Rissmiller, MD; Anastasia Hryhorczuk, MD

Disclosures

Appl Radiol. 2018;47(4):4-14. 

In This Article

Mediastinal Masses

Pediatric mediastinal masses are best approached by considering the types of masses that may occur in each mediastinal compartment.

Anterior Mediastinum

The most common anterior mediastinal mass in children is lymphoma. Lymphomas are further classified into Hodgkin's lymphoma (HL) and non-Hodgkin's lymphoma (NHL). Both may present with nonspecific symptoms associated with mass effect on the mediastinal structures, including cough, dyspnea, dysphagia, SVC syndrome or hemoptysis. Lymphoma may also manifest with additional "B symptoms:" fever, night sweats, and weight loss.

At imaging, both HL and NHL can present as an enlarged conglomeration of intrathoracic lymph nodes. Roughly 85% of HL present within intrathoracic involvement, usually as an anterior mediastinal mass. On chest radiography, this may appear as mediastinal widening, displacement of the trachea, and loss of the retrosternal clear space. Less commonly, HL will present with pulmonary nodules, consolidation and pleural effusions.[16] In contrast, only about 50% of NHL demonstrates enlarged intrathoracic lymph nodes. Pulmonary findings in NHL are more diverse and may range from pulmonary nodules (which may cavitate), consolidation to interstitial thickening. Cross-sectional CT imaging of chest and body is essential for staging. Treatment generally involves chemotherapy and/or radiation, which may be started urgently in cases of airway or vascular compromise.

Intrathoracic germ cell tumors (GCT) arise following the arrested migration of primitive germ cells that remain in the anterior mediastinum rather than descending into the gonads. These tumors share similarities with primary tumors arising from the ovaries and testes. GCTs account for approximately 20% of pediatric mediastinal tumors.[18,19] Approximately 15% are malignant, which portends poor prognosis.[20]

Teratomas represent a subtype of GCT, comprising approximately 60% of all mediastinal germ cell tumors. If a child presents with calcified mediastinal mass, this is assumed to represent a teratoma until proven otherwise. Teratomas may be mature and benign or immature with malignant potential; imaging alone may not be able to determine whether a teratoma is malignant or benign. Cross-sectional imaging will often demonstrate a mass comprised of various densities, including fat, fluid and calcification. The presence of fat is virtually diagnostic of a teratoma (Figure 7).

Figure 7.

12-year-old male with chest pressure while lying down. (A) PA radiograph of the chest shows abnormal widening of the mediastinum, particularly along the right anterior mediastinum. (B) Lateral chest radiograph confirms presence of abnormal soft tissue in the anterior mediastinum which obliterates the retrosternal clear space (black arrow). Axial (C) and coronal (D) images from chest CECT in soft-tissue mediastinal windows demonstrates a circumscribed heterogeneous lesion arising from right anterior mediastinum with central macroscopic fat (*) surrounding low (cystic) density and an outer rind of soft tissue. The lesion causes mass effect on the other mediastinal structures, in particular the right heart with narrowing of the SVC. There are a few scattered foci of right pleural soft tissue/fluid due to rupture of the mediastinal mass, which occurred in the interim between radiography and chest CT. The mass was pathologically confirmed as a mature teratoma.

GCT and teratomas are usually asymptomatic until they are large, at which point they may cause respiratory distress and compromise the airway. Once they are detected in the mediastinum, the pelvis should also be assessed to exclude a primary gonadal tumor. Since malignant teratomas are often quite large, patients may require preoperative chemotherapy prior to surgical resection.[18,20]

Thymomas are infrequent in the pediatric population comprising only 1–2% of mediastinal masses in children.[16] As in adults, thymomas many present with paraneoplastic syndromes including myasthenia gravis, hypogammaglobulinemia or red cell aplasia.

Middle Mediastinum

The most common middle mediastinal masses in children are foregut duplication cysts. Mediastinal foregut duplication cysts are further classified into bronchogenic, esophageal and neurenteric cysts.

Bronchogenic cysts arise due to abnormal lung budding during ventral foregut development during the first trimester.[16] Most arise near the carina and right paratracheal region (Figure 8), though up to 20% are contained within lung parenchyma. Histologic examination reveals respiratory epithelial lining.

Figure 8.

18-month-old with abnormal chest x-ray. Axial T2 (A), T1 precontrast (B), and T1 postcontrast with fat-sat (C) MR images at the level of thoracic inlet demonstrate a T2 hyperintense, T1 hypointense, nonenhancing lesion posterior to the trachea in the upper mediastinum (arrows). There is no association with the adjacent vertebral body or extension into the neural foramen. This was pathologically confirmed to be a bronchogenic cyst.

Esophageal duplication cysts result from abnormal development of the posterior portion of the embryonic foregut. These often present with dysphagia and are commonly associated with the upper third of the esophagus. In rare cases, migration with the lung bud may lead to an intraparenchymal location. Histology reveals gut epithelia including submucosal and muscular layers.

Although neurenteric cysts are usually found in the posterior mediastinum, these lesions are typically classified with other foregut cysts and will be briefly covered here. Neurenteric cysts result when the neural crest and gastrointestinal tract fail to separate. These cysts may be associated with osseous abnormalities of the adjacent spine and will contain both GI and neural histologic elements.

On imaging, each of the foregut cysts appears as a fluid-filled, well-circumscribed round or oval mass. CT may demonstrate a lesion of water attenuation or slightly higher, depending on the amount of internal proteinaceous contents. No intralesional enhancement is seen, though peripheral enhancement may be present in the setting of infection/inflammation. Treatment is generally surgical resection, especially for symptomatic lesions.

Diffuse middle mediastinal adenopathy is generally due to lymphoma. However, unilaterally enlarged hilar lymph nodes are suggestive of infections, particularly, tuberculosis. Metastatic mediastinal adenopathy can also be considered in the correct clinical setting. If lymph nodes are calcified, osteosarcoma or treated lymphoma should be on the differential.

Posterior Mediastinum

As discussed above, neurenteric cysts should be strongly considered when a cystic mass is encountered in the posterior mediastinum. When a solid mass is identified, neurogenic tumors associated with the sympathetic chain should be high on the differential. These tumors exist on a spectrum, ranging from malignant neuroblastoma to ganglioneuroblastoma and benign ganglioneuroma. Of these entities, neuroblastoma is the most common, and represents the most common extra-cranial solid tumor of childhood.

Neuroblastomas arise from primitive neural crest cells. While most commonly seen in the adrenal gland, neuroblastomas also frequently arise in the posterior mediastinum. Systemic symptoms include irritiability, fever, weight loss and anemia. Cord symptoms such as bladder/bowel dysfunction or lower extremity weakness should suggest extension into the spinal canal or neural foramen.

Chest radiography may demonstrate abnormal paravertebral opacity with associated widening of intercostal spaces or rib erosions. CT or MRI scans may demonstrate intralesional calcification and extension into the neural foramen. Neuroblastomas are invasive and often encase vessels. These tumors may be vascular and demonstrate robust, albeit heterogeneous, enhancement. Due to neural origins and catecholamine production, nuclear scintigraphy using metaiodobenzylguanidine (MIBG) aids in detecting extent of tumor and distant metastases (Figure 9). Typically, thoracic neuroblastomas have a more favorable outcome than abdominal neuroblastomas.

Figure 9.

5-month-old male with left-sided Horner syndrome. Axial T1 precontrast (A), axial T2 (B), coronal T1 precontrast with fat sat (C), and coronal T1 post-contrast with fat sat (D, demonstrate a multilobulated mass (arrows)with heterogeneous enhancement in left lung apex and left supraclavicular region that encases the brachial plexus and narrows the left subclavian and left vertebral arteries. There is perineural spread, not well depicted on these select images. Anterior (E) and posterior (F) whole-body planar projections from 24-hour metaiodobenzylguanidine (MIBG) scan demonstrate increased uptake at the base of the left skull (arrowhead), left upper chest (straight arrow), patchy liver metastases (curved arrow) and mild uptake in proximal right thigh (hollow circle). The mass was biopsy-proven neuroblastoma.

Ganglioneuroblastomas are intermediate tumors with malignant potential that may demonstrate distant metastases, while ganglioneuromas are benign. Both tumor types tend to be more fusiform in appearance and smaller than neuroblastomas, as well as less invasive. These more mature tumors are also seen in slightly older children. Biopsy is required for conclusive diagnosis.

Comments

3090D553-9492-4563-8681-AD288FA52ACE

processing....