In a 17-year-old girl with erythema nodosum and abnormal mediastinal silhouette, which condition is most likely diagnosed?

The diagnosis of sarcoidosis is supported in this scenario due to the presence of erythema nodosum and an abnormal mediastinal silhouette. Erythema nodosum is often associated with a variety of conditions, but when seen in conjunction with findings suggestive of enlarged lymph nodes or other abnormalities in the mediastinum, sarcoidosis becomes a strong consideration. This granulomatous condition is known for affecting young adults, particularly women, and can lead to a clinical picture that includes skin lesions like erythema nodosum, along with pulmonary and lymphatic involvement.

Sarcoidosis typically presents with a characteristic pattern on imaging studies, such as hilar lymphadenopathy, which can alter the mediastinal silhouette. It can also manifest with systemic symptoms and extra-pulmonary manifestations, making it a fitting diagnosis for this presentation.

Conditions such as Hodgkin disease, teratomas, or thymomas could also present with an abnormal mediastinal silhouette; however, they are less commonly associated with erythema nodosum. Hodgkin lymphoma may present with lymphadenopathy and systemic symptoms but lacks a direct association with erythema nodosum. Teratomas are usually solid masses rather than causing diffuse symptoms like those seen