Middle and Posterior Mediastinal Masses for Radiology Board Review

Review of middle and posterior mediastinal masses for radiology board review. Download the free study guide for this episode by clicking here.

Show Niotes/Study Guide:

Middle and Posterior Mediastinal Masses. Matt Covington, MD

Listen to the associated podcast episode(s) available at theradiologyreview.com or on your favorite

podcast directory.

What are the most common middle mediastinal masses?

The most common middle mediastinal masses consist of enlarged lymph nodes, foregut

duplication cysts and aortic arch anomalies. Lymphadenopathy should be the first thing to

consider for middle mediastinal masses but you must exclude other processes as well.

What are two fat containing masses that can present in the middle mediastinum?

Lipomas and esophageal fibrovascular polyps are fat containing masses that can present in the

middle mediastinum.

What are some vascular processes that can present as middle mediastinal masses?

Aortic arch anomalies such as aortic arch duplication and interrupted inferior vena cava with

azygous continuation can present as middle mediastinal masses.

What are some subtypes of foregut duplication cysts?

Mediastinal foregut duplication cysts are most often bronchogenic in etiology with respiratory

epithelium and have a propensity for infection which should be suspected if an air-fluid level is

seen. Bronchogenic cysts most commonly do not communicate with the bronchial tree and

therefore are not commonly air-filled. If you see an air-fluid level within a cyst, however, you

need to be concerned about the possibility of an infected bronchogenic cyst which can be a

manifestation as well that communication with the bronchial tree has now formed as a

sequelae of infection. On imaging look for a rounded fluid or soft tissue density mass that can

cause compression of adjacent structures and if airways are compressed is one cause of a

hyperlucent hemithorax. Sometimes you can see layering milk of calcium within the cyst.

Mediastinal foregut duplication cysts can also be of esophageal origin and these may have a

propensity to bleed due to ectopic gastric mucosa and normally have pseudostratified columnar

epithelium. Esophageal foregut duplication cysts are more common on the right aspect of the

mediastinum. These can cause symptoms of dysphagia due to esophageal compression.

Note that neurenteric cysts also exist in the posterior mediastinum and are rare but have a

hallmark of communication with the spinal canal and associated vertebral body anomalies.

1Middle and Posterior Mediastinal Masses. Matt Covington, MD

Listen to the associated podcast episode(s) available at theradiologyreview.com or on your favorite

podcast directory.

What are common differential considerations for posterior mediastinal masses?

Most posterior mediastinal masses have a neurogenic etiology to include neuroblastomas,

schwannomas and neurofibromas. Other considerations include extramedullary hematopoiesis

in the setting of various causes of anemia, lymphadenopathy, neurenteric cysts as already

discussed, meningoceles, descending aortic anomalies such as an aortic aneurysm, and bone

processes related to the vertebrae to include discitis/osteomyelitis, Ewing sarcoma,

chondrosarcoma and so forth.

A more extensive list of posterior mediastinal masses that are neurogenic tumors include

neurofibromas, malignant peripheral nerve sheath tumors, schwannomas, paragangliomas,

pheochromocytomas, chemodectomas, neuroblastomas, ganglioneuroblastomas and

ganglioneuromas. You don’t need to memorize all of these but I point this out to drive home

the association between posterior mediastinal masses and neurogenic tumors.

Lastly, don’t forget about hernias to include hiatal hernias and Bochdalek hernias that can

present, although not exclusively, as a posterior mediastinal mass.

What is the cervicothoracic sign?

Basically, if you have a mass that arises above the level of the clavicles, and there is lung tissue

anterior to the mass, then the location is in the posterior mediastinum. Note that the anterior

mediastinum does not arise above the level of the clavicles.

What are causes of anemia that can be associated with extramedullary hematopoiesis?

Causes of anemia that can be associated with extramedullary hematopoiesis can include

leukemia and lymphoma, myelofibrosis, polycythemia vera, sickle cell disease, hereditary

spherocytosis and thalassemia.

True or false? Extramedullary hematopoiesis can present as a fat-containing mass.

True. Fat can be seen within sites of extramedullary hematopoiesis, especially if long-standing.

What must one consider prior to biopsy of a mass that may be related to extramedullary

hematopoiesis?

Sites of extramedullary hematopoiesis may bleed as a result of biopsy. On a board exam

question be cautious before recommending biopsy of a site of extramedullary hematopoiesis

and, if tissue sampling must be performed, fine needle aspiration may be a better option

compared to core needle biopsy.

2Middle and Posterior Mediastinal Masses. Matt Covington, MD

Listen to the associated podcast episode(s) available at theradiologyreview.com or on your favorite

podcast directory.

Besides the posterior mediastinum, what other locations can be involved with

extramedullary hematopoiesis?

Extramedullary hematopoiesis can also commonly affect the liver and spleen and less

commonly affect other tissues to include the adrenal glands, lungs, breasts, GI tract, skin,

kidneys, brain and so forth. Perirenal soft tissue masses that can look similar to renal

lymphoma can occur and is one way this can be tested on board exams. Also note that bony

expansion, such as rib expansion, can occur.

What are differential considerations for masses that don’t respect assigned mediastinal

boundaries?

Note that mediastinal boundaries are arbitrary and there are no actual soft tissue structures or

tissue planes that isolate tissues to one compartment versus another. However, when you see a

mediastinal processes that crosses or encompasses multiple mediastinal compartments

consider infection such as mediastinitis, malignancy to include primary lung malignancy,

liposarcoma, and metastatic disease, mediastinal hematomas, and lymphangiomas.

What is a testable link between pancreatitis and middle mediastinal masses?

Occasionally, pancreatitis can cause a mediastinal fluid collection—an intrathoracic pancreatic

pseudocyst—that can present as a mediastinal mass.

What is Castleman disease?

Castleman disease is angiofollicular lymph node hyperplasia which is a benign type of B-cell

lymphoproliferation that causes a solitary or multicentric hypervascular lymphoid hyperplasia,

with unicentric involvement being most common. If unicentric, classic presentation is in a

younger population presenting with a thoracic mass (though can less commonly be seen in the

neck or abdomen/pelvis) and if multicentric think older population with coexisting HIV and

human herpesvirus 8 (HHV-8).

Treatment for unicentric Castleman disease is often surgical and multicentric may include

surgery, chemotherapy, steroids and possibly antivirals. Note that there is a POEMS syndrome

association with Castleman disease and multicentral disease often has additional symptoms to

include fevers, night sweats, weight loss, and hepatosplenomegaly.

Diagnosis of Castleman disease is made by lymph node excision or biopsy following exclusion of

other causes of lymphadenopathy.