Pediatrics: Mediastinal Masses

Question 1

What characteristics of a thymus should raise suspicion for cancer?

Answer 1

• Abnormal size (e.g. large thymus in a 15 y/o)
• Heterogeneous appearance
• Calcification
• Compression of airway or vascular structure

Question 2

What causes thymus rebound?

Answer 2

An acute stressor (pneumonia, radiation, chemotherapy, burns, corticosteroid therapy etc.)

Note: The stressor actually causes the thymus to shrink, but after it will rebound to normal or above normal size (and can be FDG avid on PET).

Question 3

What is the most common abnormal mediastinal mass in children?

Answer 3

Lymphoma

Note: The thymus if the most common thing identified as a mediastinal mass, but is normal.

Question 4

Anterior mediastinal mass with calcifications in a child (no prior treatment)…

Answer 4

Think teratoma

Note: Lymphomas can calcify following treatment.

Question 5

Starting at what age should an anterior mediastinal mass make you concerned about lymphoma?

Answer 5

10 years

Note: After age 10, the thymus should be fairly small. Look for cervical lymphadenopathy.

Question 6

Pt has an extra gonadal germ cell tumor…

Answer 6

Think Klinefelter’s syndrome (47 XXY)

Question 7

What are the major germ cell tumors that can arise in the anterior mediastinum?

Answer 7

• Teratoma
• Seminoma
• Non-seminomatous germ cell tumors

Question 8

Large anterior mediastinal cystic mass with macroscopic fat and calcification…

Answer 8

Teratoma (germ cell tumor)

Question 9

Large anterior mediastinal solid mass that “straddles the midline” and appears lobulated…

Answer 9

Think seminoma (germ cell tumor)

Note: Lymphoma could also look like this.

Question 10

Large anterior mediastinal mass with regions of hemorrhage and necrosis +/- invasion of the pulmonary parenchyma…

Answer 10

Think non-seminomatous germ cell tumor

Question 11

Middle mediastinal lymphadenopathy…

Answer 11

Think granulomatous disease (fungal infection/tuberculosis) or lymphoma

Question 12

Adolescent with hilar adenopathy, splenomegaly, and fatigue…

Answer 12

Think mononucleosis (EBV/CMV infection)

Question 13

What are the major categories of duplication cysts you may find in the mediastinum?

Answer 13

• Bronchogenic
• Enteric
• Neuroenteric (posterior mediastinal)

Question 14

Middle mediastinal cyst adjacent to the airway…

Answer 14

Think bronchogenic duplication cyst

Question 15

Mediastinal cyst that abuts the esophagus…

Answer 15

Think enteric duplication cyst

Question 16

You see an air-fluid level in what you assume is a mediastinal enteric duplication cyst…

Answer 16

Normal finding (communication with the esophageal lumen is common)

Question 17

What is the most common posterior mediastinal mass in a child under 2 y/o…

Answer 17

Neuroblastoma

Question 18

Posterior mediastinal mass in a child under the age of 10…

Answer 18

Think malignancy (most likely neuroblastoma)

Note: Posterior mediastinal masses in children over age 10 are more often benign.

Question 19

Posterior mediastinal mass in a child over age 10…

Answer 19

Think benign lesions:

• Ganglioneuroma/neurofibroma (round masses)
• Neuroentric cyst (if cystic)
• Extramedullary hematopoiesis (if there is coarse bone trabeculation or history of anemia)

Question 20

What is the difference between a ganglioneuroma, ganglioneuroblastoma, and a neuroblastoma?

Answer 20

Cellular differentiation and aggression:

• Neuroblastoma (undifferentiated, aggressive)
• Ganglioneuroblastoma (intermediate differentiation/aggression)
• Ganglioneuroma (most differentiated/least aggressive)

Note: The aggressive neuroblatomas mostly occur in kids under the age of 10.

Question 21

Askin tumor

Answer 21

A primitive neuroectodermal tumor of the chest wall (considered as part of the Ewing sarcoma spectrum)

Question 22

Imaging appearance of an Askin tumor

Answer 22

Large, heterogeneous mass with enhancing solid components arising from the chest wall that tends to displace adjacent structures (rather than invade them) early on (though invasion does occur if they get large)

Question 23

Posterior mediastinal cyst in a pt with scoliosis…

Answer 23

Think neuroenteric cyst

Note: These are usually associated with a vertebral anomaly (scoliosis, hemivertebrae, split cord, etc.).

Question 24

Bilateral, smooth, sharply-demarcated soft tissue densities around the spine in the lower mediastinum…

Answer 24

Think extra medullary hematopoiesis

Note: Look for hepatosplenomegaly.

Question 25

Common causes of extra medullary hematopoiesis

Answer 25

• Myeloproliferative disorders
• Bone marrow infiltration (e.g. sickle cell disease)

Question 26

What type of lymphoma is most common in children?

Answer 26

Hodgkins (4x more common than non-Hodgkins)

Question 27

Hodgkins lymphoma involves the _____ in 90% of cases

Answer 27

Thymus

Question 28

Best way to differentiate a normal thymus from lymphoma

Answer 28

Age:

Under 10 y/o = thymus

Over 10 y/o = lymphoma

Question 29

Water density cystic structure in the anterior mediastinum…

Answer 29

Think lymphangioma

Question 30

Rounded posterior mediastinal mass in a pt over age 10…

Answer 30

Think ganglioneuroma or neurofibroma

Question 31

Huge mass in the chest (e.g. taking up an entire hemithorax or nearly the entire thorax)…

Answer 31

Think Askin tumor, AKA primitive neuroectodermal tumor of the chest wall, AKA Ewings spectrum (usually older than 10 y/o; look for rib erosions)

Think pleuropulmonary blastoma (if pt is less than 2 y/o)