Middle Mediastinal Mass

Eric J. Crotty, MD

DIFFERENTIAL DIAGNOSIS

Common

Lymphoma
Bronchogenic Cyst

Less Common

Lymphadenopathy
Vascular Anomalies

Rare but Important

Postoperative Complications
Pericardial Lesions
Malignant Tumors

ESSENTIAL INFORMATION

Helpful Clues for Common Diagnoses

Lymphoma
- Usually occurs with confluent multicompartment disease that involves anterior mediastinum
- Most commonly involves paratracheal > hilar > subcarinal groups
- Homogeneous or heterogeneous soft tissue attenuation and signal intensity on CT and MR
- May compress or invade superior vena cava (SVC), esophagus, tracheobronchial tree, and pericardium
- SVC more often compressed without associated obstruction, but invasion may lead to SVC syndrome
- Bronchial involvement may lead to lobar collapse
- Pericardial involvement can result in pericardial effusion
Bronchogenic Cyst
- May have bronchial or esophageal origin
- Most commonly paratracheal or subcarinal
- Collapse or hyperlucency may occur as result of bronchial compression
- Usually round or oval with smooth contour
- Homogeneous density on radiograph and attenuation on CT
  - Classically fluid attenuation but may be of higher attenuation due to high protein content
  - Wall of cyst is thin and does not enhance unless complicated by infection
- Variable low T1 and homogeneously increased T2 signal on MR
  - Characteristically thin and nonenhancing wall unless infected

Helpful Clues for Less Common Diagnoses

Lymphadenopathy
- Usually related to infection in pediatric population
- Most common inciting organism depends on geographic location
- Consider primary tuberculosis (TB), histoplasmosis, coccidioidomycosis, and blastomycosis
  - TB and histoplasmosis may have lymph nodes with low-attenuation centers on contrast-enhanced CT in acute phase
  - Calcification of lymph nodes indicates more remote disease
Vascular Anomalies
- Most commonly due to congenital anomalies of aorta and its branches
  - Findings are more apparent on positive contrast studies of esophagus
  - Anomalous vessels are most easily seen on CT and MR
- Convexity to right of trachea on radiograph may be due to right aortic arch or double aortic arch
- Posterior impression/anterior bowing of trachea on lateral radiograph may be due to
  - Diverticulum of Kommerell related to aberrant subclavian artery
  - Passage of aorta across midline posterior to trachea and esophagus
- Dilatation of ascending aorta
  - Seen in congenital aortic valvar or supravalvar stenosis (Turner syndrome and Williams syndrome)
  - Also may be seen in connective tissue disorders (Ehlers-Danlos and Marfan syndrome)
  - Convexity along right mediastinal border on chest radiograph
  - Dilatation of ascending aorta best seen on CT and MR
- Pulmonary arterial lesions are less common
  - Anomalous origin of left pulmonary artery from right pulmonary artery (pulmonary arterial sling)
  - Left pulmonary artery passes between trachea and esophagus
  - Passage of LPA between trachea and esophagus is best appreciated on CT and MR but also well seen on positive contrast studies of esophagus
- Pulmonic valve stenosis may lead to poststenotic dilatation of main pulmonary arterial segment
  - Convexity in aortopulmonary window on radiography
  - Seen as dilatation of MPA on CT and MR
- May also involve azygous vein and anomalous pulmonary venous drainage
  - Azygous vein enlargement leads to convexity above right main bronchus
  - Most commonly related to azygous continuation of IVC
  - May also be secondary to obstruction of SVC
  - Supracardiac type of anomalous pulmonary venous return leads to “snowman” appearance of mediastinum on radiograph

Helpful Clues for Rare Diagnoses

Postoperative Complications
- Some fluid always present in operative bed following cardiac surgery
  - Usually resolves in early days following surgery with gradual decrease in size of mediastinum
- Concern if radiograph demonstrates increased widening of mediastinum
  - May be hematoma, seroma, or infection
- Hematoma may be associated with pseudoaneurysm at surgical site
  - Contrast protrusion from vessel lumen on CT with signal changes of denatured blood and flow void on MR
Pericardial Lesions
- Pericardial effusion is seen as enlargement of cardiac silhouette with “water bottle” configuration on radiography
  - Lungs usually clear
  - “Fat pad” sign on lateral chest radiograph is rarely seen due to relative lack of fat in mediastinum in pediatric population
  - May be secondary to infection (most commonly viruses), following surgery or trauma, or related to neoplasia (lymphoma)
- Pericardial cyst consists of various-sized loculations of fluid
  - Rounded convexity, most commonly in right cardiophrenic angle on radiography
  - Loculated fluid attenuation and signal on CT and MR respectively
- Pericardial tumors are uncommon
Malignant Tumors
- Both primary and secondary malignant tumors are very rare, excluding lymphoma
- Consider carcinoid, melanoma, rhabdomyosarcoma, malignant germ cell tumors, squamous cell carcinoma in patients with respiratory papillomatosis

Image Gallery

Posteroanterior radiograph shows a lobulated middle mediastinal mass

with loss of the normal thin right paratracheal stripe

and nonvisualization of the outline of the aortic arch

Coronal CECT shows the lobulated contour of the middle mediastinum

due to involvement with lymphoma. Hodgkin and non-Hodgkin lymphoma cannot be differentiated by imaging.

(Left) Axial CECT shows a somewhat heterogeneous mass in the anterior

, middle

, and posterior

mediastinum and in the right hilum

. There are also bilateral pleural effusions

. Lymphoma most commonly involves the anterior mediastinum but can involve the other mediastinal compartments. Pleural effusions are common. (Right) Coronal CECT shows the tumor involving the subcarinal