Download radiological examination of the mediastinum and diaphragm.

RADIOLOGICAL
EXAMINATION OF THE
MEDIASTINUM AND
DIAPHRAGM.
DEPARTMENT OF ONCOLOGY
AND RADIOLOGY
PREPARED BY I.M.LESKIV
• Abnormalities can be seen on either plain
films or CT. Metastatic disease to the
chest may involve one or more of the
following: lungs; pleura; lymph nodes;
local invasion; bony skeleton.
• Lymph nodes
• CT is accurate in the detection of enlarged hilar
and mediastinal lymph nodes. (CT will detect
nodes I cm in size and smaller, but nodes < I cm
are less likely to be metastatic.)
• Lymphangitis carcinomatosa — secondary
deposits in central lymph nodes may produce
lymphatic congestion with a linear pulmonary
pattern radiating outwards from the hilar glands,
septal lines and pleural effusions.
• Local invasion
• Pericardium to give malignant pericardial
effusion; superior vena cava compression
or obstruction; phrenic nerve paralysis;
Pancoast's tumour.
•Diaphragm
• The diaphragm consists of a thin sheet of muscle with a smooth
upward convexity, the right usually lying in a higher position than the
left. On a chest film, the inferior surface of the diaphragm is not
visualized as it blends with the surfaces‘ of the liver and spleen.
• CAUSES OF A UNILATERAL ELEVATED DIAPHRAGM
• Above diaphragm: phrenic nerve palsy; infiltration from bronchial
carcinoma or mediastinal tumour.
• Diaphragm: eventration, more common on the left and results from
deficiency or atrophy of muscle.
• Below diaphragm: right diaphragm elevation; liver or subphrenic
abscess, liver secondary deposits.
• CAUSES OF BILATERAL ELEVATED DIAPHRAGMS
• Obesity.
• Hepatosplenomegaly. Within the abdomen: ascites, pregnancy,
abdominal masses.
• A congenital defect in the diaphragm, more common on
the left, allows bowel protrusion into the thoracic cavity
and usually results in respiratory distress. Herniation
may occur at three sites though those causing neonatal
respiratory distress are usually of the Bochdalek type.
• • Foramen of Bochdalek: posterior diaphragm.
• • Foramen of Morgagni: anterior diaphragm.
• • Oesophageal hiatus.
• RADIOLOGICAL FEATURES
• Antenatal ultrasound examination often detects the
herniation. A chest X-ray illustrates either cyst-like
changes or the typical appearance of multiple bowel
loops in the thorax. Mediastinal shift is away from the
affected side. Abdominal films may show absence or
paucity of bowel loops.
• TREATMENT
• Surgical repair of the diaphragm, but pulmonary
hypoplasia and pulmonary hypertension cause a
significant mortality.
•
A mediastinal mass due to a hiatus hernia is usually easy to diagnose on
plain films because it often contains air and may have a fluid level, best
seen on the lateral view. A film taken after a mouthful of barium has been
swallowed will easily confirm or exclude the diagnosis of hiatus
hernia.
Hiatus hernia, (a) Lateral and (b) PA chest films show the characteristic
retrocardiac density containing an air-fluid level (arrows).
Masses in the right cardiophrenic angle anteriorly are
virtually never of clinical significance. They are nearly all
either large fat pads, benign pericardial cysts or hernias through the
foramen of Morgagni
Fat pads in both cardiophrenic angles. Note
the loss of clarity of the adjacent cardiac
outline - an example of the silhouette sign.
The anterior location was confirmed on the
lateral view
• Paralysis of a hemidiaphragm. This results from
disorders of the phrenic nerves, e.g. invasion by
carcinoma of the bronchus. The signs are
elevation of one hemidiaphragm which on
fluoroscopy or ultrasound shows paradoxical
movement, i.e. it moves upward on inspiration
Carcinoma of the bronchus at the left hilum
causing collapse of the left upper lobe and
paralysis of the left phrenic nerve. The elevated
left hemidiaphragm is too high to be due to the
lobar collapse; it is due to phrenic nerve
involvement by the tumour at the left hilum.
Eventration of the diaphragm. This
is a congenital condition in which
the diaphragm lacks muscle and Localized eventration of the diaphragm. There is
becomes a thin membranous a smooth localized elevation of the medial half of
sheet. Except in the neonatal the right hemidiaphragm (arrows). On the lateral
period it is almost always an view the eventration involved the anterior half of
incidental finding and does not the right hemidiaphragm.
cause symptoms. When the whole
of one hemidiaphragm is involved,
almost invariably the left, that
hemidiaphragm is markedly
elevated. On fluoroscopy or
ultrasound, the hemidiaphragm
may remain fixed during inspiration
and expiration, but when more
severely involved it moves
paradoxically and cannot be
distinguished from paralysis. The
eventration may only involve part
of one hemidiaphragm, resulting in
a smooth 'hump
MEDIASTINAL MASS
• The mediastinum is that part of the chest bounded by
the sternum at the front, thoracic spine at the back and
laterally by the medial surfaces of visceral pleura. It can
be divided into: anterior mediastinum: anterior to the
pericardium; middle mediastinum: the heart, aortic root
and pulmonary vessels; posterior mediastinum: behind
the posterior pericardial surface.
Mediastinal compartments.
Although the mediastinum is categorized
into compartments, masses may freely
cross from one part to another.
• RADIOLOGICAL FEATURES
• Usually, a mediastinal mass is suspected
on a plain chest film; a lateral film may be
helpful; further evaluation is carried out by
CT/MRI for anatomical localization. The
presence of cystic lesions, calcification, fat
and vascular structures are all more
accurately assessed than by plain films.
• •
Anterior mediastinal masses (three Ts—thyroid, thymus and
teratodermoids)
Retrosternal thyroid: the mass is well defined and may be lobulated.
Exten
sion into the mediastinum is to a varying degree up to the carina.
Thymic tumours: these may be benign or malignant and frequently
associ
ated with myasthenia gravis.
• Teratodermoids: these tumours are usually benign but have a
malignant potential. Occasionally fat, rim calcification, bone
fragments and teeth may be identified.
• •
Middle mediastinal masses
• Lymphadenopathy: lymphoma, metastases, sarcoid or tuberculosis.
• •
Posterior mediastinal masses
• Neurogenic tumours arising from intercostal nerves and sympathetic
• chain.
• Neurofibromas (nerve sheath tumours).
• Ganglioneuroma (sympathetic nerve cell tumours).
• The anterior (A), middle (M) and posterior (P) compartments of the
mediastinum. The divisions are arbitrary and do not correspond to those used
by anatomists. The anterior mediastinum refers to the structures anterior to the
trachea and the major bronchi. The posterior mediastinum refers to structures
posterior to a line joining the anterior boundary of the vertebral bodies.
ANTERIOR: 1.Thyroid tumour, Thymic tumour or cyst, Teratoma/Dermoid cyst,
Lymphadenopathy, Aortic aneurysm.
2. Pericardial cyst, Fat pad, Morgagni hernia
MIDDLE: 3. Thyroid tumour, Lymphadenopathy, Bronchogenic cyst, Aortic aneurysm. 4.
Hiatus hernia
POSTERIOR: 5. Neurogenic tumours, Soft tissue mass of vertebral infection or
neoplasm, Lymphadenopathy, Aortic aneurysm
Computed tomography scanning provides a much clearer
idea of the position, shape and size of any mass than is
possible from the plain chest radiograph; occasionally the
CT density even enables a specific diagnosis to be made.
Magnetic resonance imaging provides more information
than CT only in highly selected cases.
Intrathoracic thyroid
masses (goitres) are the
most frequent cause of a
superior mediastinal mass.
The characteristic feature
is that the mass extends
from the superior
mediastinum into the neck
and almost invariably
compresses or displaces
the trachea.
Retrosternal goitre, (a) The plain chest film
shows a large superior mediastinal mass
narrowing the trachea, (b) A radionuclide
scan in the same patient shows the level of
the clavicles on the right, confirming that the
mass is due to thyroid tissue, (c) CT scan,
in another patient, showing a bilateral
superior mediastinal mass that was shown
on adjacent sections to be contiguous with
the thyroid gland in the neck and to have
the same density as thyroid tissue. Note the
compression of the trachea.
• Lymphadenopathy is the next most
frequent cause of a
mediastinal swelling.
Lymphadenopathy may occur in
any of the three compartments and
it is often possible to diagnose
enlarged lymph nodes from their
lobulated outlines
and the multiple locations involved
Superior mediastinal lymph node
enlargement. Note the bilateral lobular
masses.
Extensive mediastinal lymphadenopathy (caused b
lymphoma) shown by CT scanning.
• Hilar lymphadenopathy may cause enlargement of the hilar
shadows, the lymph nodes appearing as well-defined, lobulated
masses. Nodal enlargement has to be differentiated from hilar
vascular prominence (as in pulmonary hypertension). Difficulty may
be encountered in distinguishing between them on chest
radiography, though CT with contrast or MRI accurately identifies the
abnormality.
• CAUSES OF BILATERAL HILAR GLAND ENLARGEMENT
• Sarcoidosis: commonest cause, usually resolving spontaneously.
• Lymphoma: mediastinal glands are more frequently involved than
hilar.
• Tuberculosis: enlargement is usually asymmetrical and often
associated with mediastinal glandular involvement.
• Metastases.
• CAUSES OF UNILATERAL HILAR GLAND ENLARGEMENT
• Bronchial carcinoma.
• Lymphoma.
• Tuberculosis.
Bilateral hilar adenopathy. The enlarged hila are clearly lobular in
outline and there is also enlargement of the right paratracheal nodes
(arrow). The diagnosis in this patient was malignant lymphoma.
• Neurogenic tumours
are by far the
commonest causes
of a posterior
mediastinal mass.
Pressure deformity
of the adjacent ribs
and thoracic spine is
often visible.
*Certain tumours, such as dermoid
cysts and thymomas, are, for
practical purposes, confined to
the anterior mediastinum.
Thymoma, (a) CT and (b) MRI (Tl-weighted) show a lobular
mass (arrows) in the left side of the thymus
a
b
Dermoid cyst (cystic teratoma) (arrows) shown by CT to contain fat. In
this cyst the fat can be seen floating in the upper third of the cyst.
Note that the density of part of the cyst is the same as subcutaneous
fat.
• Neurofibroma in posterior mediastinum. The
MRI shows the neurofibroma (arrows) lying
against the spine, but not growing into the
spinal canal.
• Calcification occurs in many conditions but almost never in malignant
lymphadenopathy. Occasionally, the calcification is characteristic in
appearance, e.g. in aneurysms of
the aorta
Calcification in an aneurysm arising from
the descending aorta. The arrows point to
the distinctive curvilinear calcification
within the mass, which is in intimate
contact with the aorta.
Aneurysm of the descending aorta. The lumen has
been opacified by intravenous contrast
enhancement. The unopacified component is a
blood clot lining the aneurysm.