MEDIASTINAL MASSES

Navdeep singh

Anterior mediastinal masses

prevascular - Thymic masses

- Retrosternal thyroid

- Teratoma

- Lymph nodal mass

precardiac - Epicardial fat pad

- Morgagni ‘ s hernia

- pleuropericardial cyst

- Anterior mediastinal masses in the prevascular region can obliterate the anterior junction line.

Intrathoracic thyroid mass on (A) AP and (B) lateral radiographs. This benign multinodular goitre is predominantly posterior to the trachea with components to either side, resulting in forward displacement and narrowing of the trachea.

THYROID MASSES Well-defined usually spherical or lobular

intrathoracic masses which are continuous with the thyroid gland.

All thyroid masses displace the trachea, (narrowing). Descends anterolaterally or rarely posteriorly.

Calcification – round, well defined = benign amorphous cloud like =

malignant Radionuclide imaging CT- Size, shape & position (higher

attenuation) Benign and malignant = ?

THYMUS

Thymic cyst Thymic hyerplasia Thymoma Lymphoma Thymic carcinoid Thymolipoma.

Thymic cyst producing an anterior mediastinal mass on (A) AP and (B) lateral chest radiographs, filling in the normal retrosternal window and widening the mediastinum. (C) The cystic nature is best demonstrated by CT.

THYMOMA most common primary tumour of the

anterior mediastinum in adults. Average age is 50, rare under 20. Association - myasthenia gravis,

hypogammaglobulinaemia and red cell aplasia.

Most thymomas (90%) arise usually anterior to the ascending aorta, lying above the right ventricular outflow tract and pulmonary artery.

Imaging – usually spherical or oval in shape and may show lobulated borders. They may contain one or more cysts and a few are predominantly cystic. Calcification, punctate or curvilinear, may be seen.

CT is the most sensitive technique. The diagnosis depends on identifying a focal

swelling/ asymmetry rather than applying a specific measurement.

show homogeneous density and uniform enhancement after contrast injection.

Thymoma presenting on a chest radiograph obtained before orthopaedic surgery in an otherwise asymptomatic elderly female patient. There is a large anterior mediastinal mass (A) with coarse calcification visible on (B) the lateral view and (C) contrast-enhanced CT.

Invasion of the mediastinal fat and adjacent pleura may be identified with invasive thymomas.

Remote pleural metastases resulting from transpleural spread are a feature of invasive thymomas.

MRI - On T1-weighted images, thymomas have a signal intensity similar to that of muscle and the adjacent normal thymic tissue.

On T2-weighted images, the signal intensity increases and may make it difficult to distinguish a thymoma from adjacent mediastinal fat.

Invasive thymoma in a young man. (A) Shows a lobular anterior mediastinal mass associated with a pleural effusion. (B) Image obtained through the lower chest demonstrates mixed soft tissue (arrows) and fluid attenuation owing to transpleural spread.

Germ cell tumour Derived from primitive germ cell elements

left behind after embryonal cell migration.

Mediastinum – most common extragonadal site (anterior mediastinum)

Secrete HCG and alpha fetoprotein.

Germ cell tumour

Mature teratoma (benign) Seminoma Malignant teratoma Embryonal carcinoma Choriocarcinoma Endodermal sinus tumour

Mature teratoma – most common mediastinal germ cell tumour.

All ages – particularly young adults (F>M) Presentation – mostly asymptomatic - incidentally diagnosed on X-

ray, CT. - may cause cough, dyspnea,

pain

Imaging – - Well defined, rounded or lobulated mass

in the anterior mediastinum. - fat and calcification present - variable appearence

Teratoma in a young man undergoing an immigration chest radiograph. (A) There are no specific features on the plain radiograph to indicate the nature of the mass. (B) CT demonstrates that the opacity visible on the chest radiograph is well defined and contains soft tissue and fat densities.

Malignant germ-cell tumours are usually seen in young adults. ( M>F)

Seminoma is most common. Symptomatic due to mass effect and

invasion. X-ray findings – similar except appear

more lobular. Fat and calcification rarely seen. CT – asymmetrical mass, obliterated fat

planes - heterogeneous enhancement.

Malignant germ-cell tumour in a 25 year old man presenting with chest pain, dyspnoea, malaise and features of pericardial tamponade. The CT shows a lobular asymmetrical mass with low attenuation areas corresponding to necrotic tumour intersected by neoplastic septation.

Posterior Mediastinal Masses

Esophageal lesions, hiatal hernia Foregut duplication cyst Descending aorta aneuyrsm Neurogenic tumour Paraspinal abscess Lateral meningocele Extramedullary haematopoiesis

Foregut duplication cysts

Bronchogenic cyst -solitary asymptomatic mediastinal masses which may present at any age.

Have thin fibrous capsule and are lined with respiratory epithelium and contain cartilage. Cyst contents - thick mucoid material.

Located adjacent to trachea Mostly asymptomatic Complication – infection, haemorrhage

Imaging - spherical or oval masses with smooth outlines, along the course of trachea and bronchi.

Unilocular, can project in middle or posterior mediastinum.

Calcification rare. They can displaces carina forward and

oesophagus backwards.CT- size, shape nd position -thin walled masses with contents of

uniform attenuation ( 0 HU), may show higher HU(prot.

Bronchogenic cyst. (A) Bronchogenic cyst in right paratracheal area in a young asymptomatic man. (B) In this instance the CT attenuation was almost the same as that of the other soft tissue structures and it was not possible to predict the cystic nature of the mass. The cyst was surgically removed.

Oesophageal duplication cyst on (A) chest radiography and (B) CT. This case shows the typical features of a well-defined spherical mass projecting from the mediastinum.

Oesophageal duplication cyst Uncommon, mostly present in childhood. presence of smooth muscle in the walls

and contain mucosa resembling GIT. Imaging findings- similar to

bronchogenic cyst - except that the wall of the lesion may be

thicker, - may assume a more tubular shape, - and it may be in more intimate contact

with the oesophagus. - may cause extrinsic compression on

barium.

Neurogenic tumours most common tumours to arise in the

posterior mediastinum. peripheral nerves – neurofibroma, schwannoma, malignant tumours of nerve sheath

origin. Tumours arising from sympathetic

ganglia.

Peripheral nerve tumours typically originate in an intercostal nerve in the paravertebral region.

Neurofibromas and Schwannomas present as well-defined round or oval posterior mediastinal masses.

Pressure deformity causing a smooth, scalloped indentation on the adjacent ribs, vertebral bodies etc.

The scalloped cortex is usually preserved and is often thickened.

This coronal T1-weighted, spin-echo image demonstrates the tumour well and shows that it does not enter the spinal canal or encroach significantly on the adjacent foramina.

P

IMAGING - The rib spaces and the intervertebral foramina may be widened by the tumour.

CT - homogeneous or heterogeneous enhancement after intravenous contrast medium. Punctate foci of calcification may be seen.

MRI - Variable T1-weighted signal intensity that may be similar to spinal cord.

- high signal intensity peripherally and low signal intensity centrally (target sign) on T2-W.

- 10% may extend appear as dumb-bell-shaped masses with widening of the affected neural foramen.

Neuroenteric cyst Result from incomplete separation of the

foregut from the notochord in early embryonic life.

Cyst wall contains both gastrointestinal and neural elements with an enteric epithelial lining.

Communication with the subarachnoid space or the gastrointestinal tract may be present.

Vertebral body anomalies such as butterfly or hemivertebra.

produce pain and are often found early in life

Radiologically, a neurenteric cyst is a well-defined, round, oval or lobulated mass in the posterior mediastinum between the oesophagus and the spine. Appearances on CT and MRI are similar to those of other foregut duplication cysts, with MRI being the investigation of choice for demonstrating the extent of intraspinal involvement.

Lateral thoracic meningocele

protrusions of the spinal meninges through an intervertebral foramen.

associated with neurofibromatosis. asymptomatic mass, often with pressure

deformity of the adjacent bone. Indistinguishable on plain radiographs

from neurofibromas. CT and MRI can both indicate the correct

diagnosis by showing the mass to be fluid filled rather than solid.

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