A 38-year-old woman undergoes routine chest X-ray for a persistent dry cough. Imaging reveals a 3 cm mass in the anterior mediastinum. She is asymptomatic with normal vital signs. What is the most appropriate next step in management?

## Clinical Context An anterior mediastinal mass in a young adult is a common incidental finding. The anterior mediastinum is bounded anteriorly by the sternum, posteriorly by the pericardium and great vessels, and contains the thymus, lymph nodes, and fat. The differential diagnosis includes thymoma, thymic hyperplasia, lymphoma, germ cell tumors, and thyroid masses. ## Why Contrast-Enhanced CT Is the Best Next Step **Key Point:** Contrast-enhanced CT chest is the standard imaging modality for characterizing anterior mediastinal masses because it: - Defines the mass location, size, density, and enhancement pattern - Assesses involvement of adjacent structures (pleura, pericardium, great vessels) - Evaluates for lymphadenopathy and distant metastases - Guides the decision between observation, biopsy, or surgery - Determines resectability and surgical approach **High-Yield:** The anterior mediastinum is the most common site for mediastinal masses in adults. The **4 T's mnemonic** for anterior mediastinal masses: - **T**hymoma / **T**hymic hyperplasia - **T**eratoma (germ cell tumor) - **T**errible lymphoma - **T**hyroid (ectopic thyroid or goiter) **Mnemonic:** **AAAA** — Anterior mediastinal masses require: - **A**ssessment by CT - **A**nalysis of resectability - **A**ppropriate biopsy if needed - **A**ctual tissue diagnosis before treatment ## Management Algorithm ```mermaid flowchart TD A["Anterior mediastinal mass on CXR"]:::outcome --> B["Contrast-enhanced CT chest"]:::action B --> C{"Mass characteristics?"}:::decision C -->|Small, fat-density, no enhancement| D["Observe with follow-up imaging"]:::action C -->|Enhancing, concerning features| E{"Resectable?"}:::decision E -->|Yes| F["Surgical resection ± biopsy"]:::action E -->|No| G["Percutaneous or endoscopic biopsy"]:::action G --> H["Tissue diagnosis guides treatment"]:::outcome ``` ## Why Other Options Are Incorrect - **Observation alone:** While small, stable masses may be observed, a 3 cm mass requires characterization first. Observation without imaging assessment delays diagnosis of potentially aggressive tumors (lymphoma, germ cell tumor). - **Immediate surgical biopsy:** Premature and risky. CT defines the mass anatomy, vascularity, and resectability, allowing the surgeon to plan the safest approach. Blind biopsy risks hemorrhage and incomplete diagnosis. - **Empirical chemotherapy:** Dangerous and inappropriate. Chemotherapy is not first-line for all mediastinal masses; tissue diagnosis is mandatory. Treating without histology may harm the patient if the mass is benign or requires surgery.