What are the causes of right paratracheal fullness on imaging?

Right Paratracheal Fullness: Causes

Right paratracheal fullness on imaging most commonly represents paratracheal lymphadenopathy, mediastinal hemorrhage (in trauma), tracheal diverticulum, or less commonly, anatomic variants like azygos lobe or congenital anomalies.

Diagnostic Approach

The evaluation begins with measuring the right paratracheal stripe (RPS) width on chest radiography. A normal RPS measures 1-4 mm; widening to ≥5 mm reliably indicates pathology 1. When abnormal, CT chest with IV contrast is the definitive imaging modality to characterize the cause 2.

Primary Causes by Category

Mediastinal Lymphadenopathy

This is the most common pathologic cause. Enlarged paratracheal lymph nodes (>15 mm) appear as:

• Widening of the RPS (seen in 31% of cases) 3
• Convex lateral contour of the superior vena cava (47% of cases) 3
• Increased density posterior to the SVC (83% of cases) 3

CT demonstrates that enlarged nodes are typically anterolateral to the trachea and immediately posterior to the SVC, rather than directly lateral 3. This anatomic positioning explains the radiographic appearance.

Mediastinal Hemorrhage (Trauma Setting)

In blunt chest trauma, RPS width ≥5 mm on supine radiographs indicates mediastinal hemorrhage with 22.9% of these patients having major arterial injury on arteriography 4. This finding mandates urgent CT angiography or direct arteriography.

Tracheal Diverticulum

Right paratracheal air cysts represent tracheal diverticula in 98% of cases, characteristically located at the right posterolateral trachea at T1-T2 levels 5. Key features:

• Mean diameter: 10 mm axial, 14 mm vertical 5
• Associated with obstructive lung disease and emphysema 5
• CT may show a communicating channel with the trachea 5

Tracheal Pathology

• Tracheal masses, thickening, or stenosis
• CT chest with IV contrast optimally evaluates enhancement characteristics and relationship to adjacent structures 2

Anatomic Variants

• Azygos lobe: Rare congenital variant appearing as right paratracheal opacity 6
• Pulmonary agenesis: Can present as heterogeneous paratracheal mass with calcification 7

Other Mediastinal Causes

• Thyroid goiter extending into superior mediastinum 8
• Vascular abnormalities (aberrant vessels, aneurysms) 2
• Mediastinal infection 8

Adjacent Structure Involvement

• Pleural disease 1, 8
• Lung parenchymal opacification 8

Imaging Algorithm

1. Initial assessment: Chest radiography measures RPS width 1
2. If RPS ≥5 mm or clinical concern: CT chest with IV contrast is usually appropriate 2
   • Provides enhancement characteristics
   • Evaluates hilar/mediastinal adenopathy
   • Assesses relationship to vessels and adjacent structures
3. In trauma: If RPS ≥5 mm, proceed to CTA chest for vascular injury 4
4. For suspected vascular causes: CTA chest with IV contrast 2

Critical Pitfalls

• Don't dismiss RPS <5 mm in trauma: While reliable for excluding major injury, clinical correlation remains essential 4
• Recognize that air cysts signal underlying lung disease: Tracheal diverticula associate with obstructive physiology and emphysema 5
• Avoid limited neck CT alone: It risks missing the full extent of tracheal disease; combined neck and chest CT is preferred when upper tracheal involvement is suspected 2
• Consider rare anatomic variants: Azygos lobe and pulmonary agenesis can mimic pathologic masses 7, 6