Retrotracheal Space Mass

Jud W. Gurney, MD, FACR

DIFFERENTIAL DIAGNOSIS

Common

Vascular Anomalies
- Aberrant Right Subclavian
- Aberrant Left Subclavian
- Double Aortic Arch
Substernal Goiter
Esophageal Disorders
- Zenker Diverticulum
- Achalasia
- Foreign Body

Less Common

Tracheal or Esophageal Masses
- Esophageal Carcinoma
- Esophageal Leiomyoma
- Tracheal Neoplasms
Nerve Sheath Tumors

Rare but Important

Mediastinal Cysts

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Retrotracheal space
- Lateral examination: Triangular area of lucency bounded
  - Posteriorly by spine (1st 4 thoracic vertebra)
  - Inferiorly by top of aortic arch
  - Anteriorly by posterior wall of trachea
  - Superiorly by thoracic inlet
- Trachea is straight; convex bowing anteriorly is considered abnormal
- Also known as Raider triangle after radiologist Louis Raider who originally described radiographic significance
- Lesions in retrotracheal space may not be evident on frontal radiographs
  - Lesions may widen or disrupt posterior junction line
- Lesions of retrotracheal space arise from normal contents
  - Esophagus, trachea, lymph nodes, lung, nerves (left recurrent laryngeal nerve, vagus nerve), thoracic duct
Posterior tracheal band (or tracheoesophageal stripe)
- Vertically oriented linear opacity < 4.5 mm in thickness (usually < 3 mm thickness)
- Visible on lateral radiograph in 50%
- Extends from thoracic inlet to carina
- Components: Posterior tracheal wall, anterior esophageal wall, and mediastinal soft tissue
- Tracheoesophageal stripe (TES) vs. posterior tracheal band (PTB); TES if
  - Stripe contains vertical fat radiolucency
  - Stripe passes below azygos arch

Helpful Clues for Common Diagnoses

Aberrant Right Subclavian
- Most common major aortic anomaly (0.5% of population)
- Arises as last branch from left aortic arch
- Origin often widened and known as diverticulum of Kommerell
  - Represents remnant of primitive distal right aortic arch
  - Seen in 60%
  - Aneurysmal when > 4 cm in diameter
- Associated abnormalities
  - Congenital heart disease (CHD): Conotruncal anomalies, ventricular septal defects
  - Down syndrome with CHD; 37% have aberrant right subclavian
- Surgical implications
  - Anomalous recurrent laryngeal nerve (nonrecurrent laryngeal nerve)
  - Thoracic duct may terminate on right
- Most patients asymptomatic
- Most common problem: Dysphagia (lusoria) from esophageal compression
Aberrant Left Subclavian
- Arises as last branch from right aortic arch
- Most common type of right aortic arch (0.05% of population)
- Associated abnormalities
  - Tetralogy of Fallot (70%)
  - Atrial septal defect or ventricular septal defect (20%)
  - Coarctation of aorta (7%)
Double Aortic Arch
- Most common vascular ring
- Rarely associated with congenital heart disease
- Results in tracheal &/or esophageal compression
- Right arch is larger and positioned higher than left
Substernal Goiter
- Represents up to 7% of mediastinal tumors
- Usually has tracheal deviation on frontal radiograph
- Posterior to trachea (25%), predominant on right side
- Calcification in 25%
- High attenuation at CT due to natural iodine
Zenker Diverticulum
- Pulsion diverticulum at pharyngoesophageal junction
- Descends into retrotracheal space posterior to trachea and esophagus
- Size variable (0.5-8 cm)
- May contain air or air-fluid level
- May have findings of chronic aspiration
Achalasia
- Primary motility disorder of smooth muscle or secondary (e.g., Chagas disease)
- Esophageal dilatation, usually marked, with air-fluid level in upper esophagus
- CT: Smooth narrowing of distal esophagus
- Smooth symmetric wall thickening (< 10 mm); any asymmetric thickening or frank mass consider carcinoma (pseudoachalasia)
Foreign Body
- Most common site of chronic esophageal foreign body is upper esophagus at level of thoracic inlet
- Coins: Seen en face frontal and in profile on lateral views
- CT useful for complications (perforation or abscess), may also be useful for nonradiopaque foreign body

Helpful Clues for Less Common Diagnoses

Esophageal Carcinoma and Leiomyoma
- Most common tumors of esophagus
- Widening of tracheoesophageal stripe and presence of air-fluid level most common findings
Tracheal Neoplasms
- Rare, 2/3 either squamous cell carcinoma or adenoid cystic carcinoma
- Adenoid cystic carcinoma more common in proximal 1/2 of trachea
- May have either focal mass of tracheal wall or diffuse thickening of PTB
Nerve Sheath Tumors
- Neurofibroma or schwannoma
- May occur along any peripheral nerve
- In retrotracheal space: Recurrent laryngeal nerve, vagus nerve, phrenic nerve

Helpful Clues for Rare Diagnoses

Mediastinal Cysts
- Includes bronchogenic cysts, esophageal duplication cysts, thymic cysts, and thoracic duct cysts
- None primarily located in region of retrotracheal space
- Thoracic duct cyst
  - Rare, expands with fatty meals
  - Thin-walled, low-attenuation fluid characteristic

Image Gallery

Axial CECT in the same patient shows partially thrombosed aneurysmal dilatation of diverticulum of Kommerell

Axial CECT more inferiorly shows partially thrombosed aneurysmal diverticulum of Kommerell

. The diverticulum of Kommerell may become aneurysmal or may be site of dissection.

(Left) Lateral radiograph shows a large mass in Raider triangle

. Note that the trachea is bowed anteriorly

. The most common cause of mass in retrotracheal triangle is aberrant right subclavian artery. (Right) Frontal radiograph shows a right paratracheal mass