Mediastinal spaces and recesses

Mediastinal spaces and recesses are anatomically defined regions within the mediastinum the central compartment of the thorax that serve as landmarks for localizing pathology, guiding differential diagnoses, planning surgical or biopsy approaches, and understanding pathways of disease spread.

Key Mediastinal Spaces and Recesses

• Pretracheal space: located anterior to the trachea and posterior to the great vessels. It contains lymph nodes (stations 1, 2R, 2L, 4R) and is a common site for lymphadenopathy. Widening of the right paratracheal stripe on chest radiography indicates abnormality in this region.

• Aortopulmonary (AP) window: the space between the inferior surface of the aortic arch and the superior surface of the left pulmonary artery, lateral to the trachea and ligamentum arteriosum. It contains lymph nodes (station 5), the left recurrent laryngeal nerve, and fat. Convexity of the AP window reflection on radiography suggests a middle mediastinal abnormality.

• Subcarinal space: located immediately inferior to the tracheal carina, between the two main bronchi, and anterior to the esophagus. It contains station 7 lymph nodes and is a critical area for mediastinal staging of lung cancer, accessible by both EBUS-TBNA and EUS-FNA.

• Azygoesophageal recess: the interface between the subcarinal portion of the mediastinum and the right lower lobe, formed by the right pleural reflection as it contacts the azygos vein and esophagus. On CT, the normal adult configuration is concave; a convex contour may indicate subcarinal lymphadenopathy, foregut cysts, or esophageal pathology. In children under 3 years, a convex or straight contour is a normal variant (seen in 96% of cases).

• Retrosternal (prevascular) space: the space between the posterior surface of the sternum and the anterior pericardium/great vessels. It normally contains thymic tissue (especially in children), fat, and internal mammary vessels.

• Retropharyngeal and pretracheal spaces :these deep cervical fascial spaces are continuous with the mediastinum superiorly. The retropharyngeal space and the so-called "danger space" (space 4) provide direct pathways for infection spread from the head and neck into the posterior mediastinum, which is the anatomical basis for descending necrotizing mediastinitis.