Mediastinal masses commonly present in children and may pose diagnostic challenges, particularly with limited sampling. This article aids the pathologist by reviewing the hematologic differential diagnosis of a pediatric mediastinal mass, along with ancillary testing useful for rendering the correct diagnosis. A review of the more common lymphomas is presented, including classic Hodgkin lymphoma, T-lymphoblastic leukemia/lymphoma, and primary mediastinal (thymic) large B-cell lymphoma, along with brief mentions of less common entities such as gray zone lymphoma and thymoma as well as non-neoplastic conditions such as benign cysts and infections.
Pediatric mediastinal masses are often due to hematologic malignancy.
Most common pediatric hematologic malignancies in the mediastinum include T-lymphoblastic leukemia/lymphoma, classic Hodgkin lymphoma, and primary mediastinal large B-cell lymphoma.
Although biopsy of the mediastinal mass is sometimes required, alternate sources such as pleural fluid, peripheral blood, and/or extramediastinal tissue biopsy can help establish the diagnosis.
The timely diagnosis of mediastinal masses in children is of critical importance. Although the mass may produce no symptoms, more commonly at least some respiratory symptoms are present, including dyspnea, cough, or orthopnea, although fatigue, fever, and pain may also be presenting symptoms. Mediastinal masses can present at any age in children, although neural tumors are much more common in very young children (<5 years) and lymphomas and germ cell tumors are more commonly seen in older children.
The differential diagnosis of pediatric mediastinal masses is diverse, and 70% to 75% are malignant. The precise anatomic location of the mass can be very helpful. The anterior mediastinum is often the site of lymphomas, germ cell tumors, and thymic lesions, whereas the posterior mediastinum gives rise more exclusively to neurogenic tumors, which are outside the scope of this review. The middle mediastinum can demonstrate general lymphadenopathy from a variety of tumors, or be the site of benign etiologies such as bronchogenic cysts.
The distribution of findings in pediatric mediastinal tumors differs somewhat from that in adults, with most studies demonstrating a predominance of non-Hodgkin lymphoma, classic Hodgkin lymphoma (CHL), and neuroblastoma/ganglioneuromas. , , Table 1 summarizes the distribution of mediastinal biopsy diagnoses at our institution; however, a limitation of this review is that we included direct mediastinal biopsies only, and did not account for diagnoses obtained through other means, such as peripheral lymph nodes, pleural effusions (PE), or extramediastinal tissue biopsies.