A 35-year-old woman undergoes CT chest for recurrent cough and is found to have a posterior mediastinal mass. Which is the most common diagnosis?

Explanation

## Posterior Mediastinal Masses — Most Common Entity **Key Point:** Neurogenic tumours are the most common primary posterior mediastinal mass in adults, accounting for approximately 75% of posterior mediastinal masses. ### Mediastinal Compartments and Mass Distribution | Compartment | Primary Location | Most Common Mass | Frequency | |-------------|------------------|------------------|----------| | Anterior | Sternum to pericardium | Thymoma | 40–50% | | Middle | Pericardium, great vessels | Lymphoma, cysts | Variable | | Posterior | Vertebral bodies, nerve roots | Neurogenic tumour | 75% | **High-Yield:** The posterior mediastinum is bounded by the pericardium anteriorly and the vertebral bodies posteriorly. Neurogenic tumours arise from structures within this space: sympathetic chain, vagus nerve, and intercostal nerves. ### Neurogenic Tumours — Classification and Features **Mnemonic:** **Neurogenic Tumours of Posterior Mediastinum** - **Nerve sheath tumours:** Schwannoma (most common), neurofibroma - **Sympathetic chain tumours:** Neuroblastoma (children), ganglioneuroblastoma, ganglioneuroma (adults) - **Paraganglioma:** Phaeochromocytoma (rare) ### Clinical Presentation - Often **asymptomatic**, discovered incidentally on imaging (as in this case) - May present with back pain, chest pain, or radiculopathy if compressing nerve roots - Schwannoma: benign, slow-growing, well-encapsulated - Neuroblastoma: malignant, more common in children - Ganglioneuroma: benign, more common in adults **Clinical Pearl:** A posterior mediastinal mass in an adult is neurogenic until proven otherwise. The location (posterior, adjacent to vertebral bodies and nerve roots) is the key diagnostic clue. ### Anatomical Boundaries of Posterior Mediastinum - **Anterior:** Pericardium and oesophagus - **Posterior:** Vertebral bodies and posterior chest wall - **Lateral:** Mediastinal pleura - **Superior:** Thoracic inlet - **Inferior:** Diaphragm **Warning:** Do not confuse posterior mediastinal masses with anterior or middle mediastinal masses — location on imaging is critical for narrowing the differential diagnosis. ### Why Other Options Are Less Likely - **Oesophageal carcinoma:** Arises from the oesophagus itself (which lies in the middle/posterior mediastinum) but is not a primary mediastinal mass; it is a primary oesophageal malignancy that may extend into the mediastinum. - **Aortic aneurysm:** A vascular lesion, not a mass in the traditional sense; occurs in the middle mediastinum. - **Pericardial cyst:** A middle mediastinal lesion, not posterior; less common than neurogenic tumours.