Middle Compartment Mass

Christopher M. Walker, MD

DIFFERENTIAL DIAGNOSIS

Common

Lymphadenopathy
- Infection
- Sarcoidosis
- Lymphoma
- Lung Carcinoma and Extrathoracic Metastases
Foregut Duplication Cysts
Hiatal Hernia

Less Common

Aortic Aneurysm
Lipomatosis
Mediastinal Goiter

Rare but Important

Esophageal Masses
Mediastinitis
Mediastinal Hemorrhage
Tracheal Neoplasms

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Anatomic boundaries of middle mediastinum on lateral radiograph
- Anterior boundary
  - Line drawn along anterior tracheal wall and posterior heart border
- Posterior boundary
  - Line drawn 1 cm behind anterior margin of vertebral bodies
- Contents include trachea, superior vena cava, mid aortic arch, lymph nodes, and esophagus
Middle mediastinal mass deviates these normal radiographic lines and measurements
- Right paratracheal stripe ≤ 4 mm
- Concave interface in aortopulmonary window
- Reverse S contour of azygoesophageal recess
- Posterior tracheal stripe ≤ 6 mm on lateral radiograph
Components to consider in differential diagnosis
- Density of lesion (fat, calcium, soft tissue, fluid)
- Number of lesions
- Clinical history

Helpful Clues for Common Diagnoses

Lymphadenopathy
- Right paratracheal stripe thickening usually indicates lymphadenopathy
- Subcarinal lymphadenopathy
  - Convexity in superior azygoesophageal recess
- Calcified nodes
  - Dense calcification usually from prior granulomatous infection
  - Rim calcification, “eggshell” appearance with sarcoidosis, silicosis, and treated lymphoma
- Necrotic or low-density nodes
  - Tuberculosis and histoplasmosis
  - Lymphoma, thymoma, metastases, and lung carcinoma
- Enhancing lymphadenopathy
  - Vascular metastases (renal, thyroid, and melanoma)
  - Tuberculosis
  - Castleman disease
Foregut Duplication Cysts
- Round and well circumscribed
- Highly variable Hounsfield units depending on fluid content
- Bronchogenic cysts commonly subcarinal in location
  - Less commonly peripheral, hilar
- Esophageal duplication cyst location
  - Paraesophageal or within esophageal wall
Hiatal Hernia
- Convexity of lower azygoesophageal recess
- Easily diagnosed on CT by protrusion of stomach through esophageal hiatus

Helpful Clues for Less Common Diagnoses

Aortic Aneurysm
- Definitions
  - Dilated ≥ 4 cm
  - Aneurysmal ≥ 5 cm
  - High risk of rupture ≥ 6 cm
  - Saccular are focal outpouchings and are associated with trauma or infection
  - Fusiform is circumferential
  - Annuloaortic ectasia is a dilated aortic root and associated with Marfan syndrome
- CT or MR are diagnostic
Lipomatosis
- Causes include
  - Obesity, long-term steroid therapy, Cushing disease
- Radiographs show smooth mediastinal widening without compression of trachea
- CT shows homogeneous fat causing bulging of mediastinal contours
Mediastinal Goiter
- Radiographs reveal upper mediastinal mass with deviation of trachea
- CT demonstrates connection to thyroid
  - Coronal images very helpful
- Enhance avidly with contrast and are high in density on pre-contrast exams

Helpful Clues for Rare Diagnoses

Esophageal Masses
- Varices are secondary to portal hypertension
  - Abnormal convexity of lower azygoesophageal recess or paravertebral widening
  - CT with contrast is diagnostic and easily differentiates from hiatal hernia or tumor
Mediastinitis
- Associated with sternotomy, esophageal perforation, or spread of infection
- Radiographs show widened mediastinum
- CT findings include
  - Diffuse fat stranding replacing normal mediastinal fat
  - Pneumomediastinum
  - Fluid collections
- Difficult to differentiate normal postoperative appearance from mediastinitis
  - Resolution of expected fluid collections occurs within 2-3 weeks after surgery
Mediastinal Hemorrhage
- Causes include
  - Acute aortic injury or venous bleeding secondary to severe blunt or penetrating trauma
  - Aneurysm or dissection rupture
- Radiographs show nonspecific mediastinal widening
- High-attenuation (blood density) fluid within mediastinum
- Hematoma not adjacent to aorta is secondary to venous bleeding
- Retrosternal hematoma in anterior compartment
Tracheal Neoplasms
- Usually secondary to primary squamous cell carcinoma or adenoid cystic carcinoma
- Uncommonly single or multiple metastases from
  - Melanoma, breast carcinoma, colon carcinoma, or adjacent tumor extension
- CT features include
  - Polypoid, sessile, or circumferential lesion
  - Adenoid cystic carcinoma usually originates from posterolateral wall
  - Important to define extraluminal extent of disease for surgical planning

Image Gallery

Coronal CECT shows subcarinal lymphadenopathy

and right lower lung consolidation

in this patient with bacterial pneumonia.

Axial NECT shows multiple calcified lymph nodes within the right paratracheal space

in this patient with prior histoplasmosis infection.

(Left) Axial CECT shows features of adenopathy in sarcoidosis. There is diffuse mediastinal adenopathy

in the prevascular and paratracheal spaces. Lower sections revealed bilateral symmetric hilar lymphadenopathy. (Right) Axial CECT shows subcarinal lymphadenopathy

in this asymptomatic patient. The symmetry of lymphadenopathy and age of the patient are important differential considerations to make the correct diagnosis.

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