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Mediastinal Mass
ANATOMY
The mediastinum is a
narrow, vertically oriented
structure that resides
between the medial
parietal pleural layers of the
lungs.
Mediastinal Divisions
superior
anterior
middle
posterior
The superior mediastinum :
The space between the thoracic inlet 
and the superior aspect of the aortic arch
All mediastinal structures above an
imaginary line drawn between the sternal
angle and the fourth thoracic
intervertebral disk on the lateral chest
The anterior mediastinum is the space
anterior to the heart
and great vessels on the lateral chest
radiograph. It is bordered
anteriorly by the sternum and
posteriorly by the pericardium
Anterior mediastinum:
Internal mammary vessels
 Internal mammary and
 prevascular lymph nodes
 Thymus
Middle mediastinum
Heart and pericardium
 Ascending and transverse aorta
 Main and proximal right and left
 pulmonary arteries
 Confluence of pulmonary veins
 Superior and inferior vena cava
 Trachea and main bronchi
 Lymph nodes and fat within mediastinal
: Posterior mediastinum
Descending aorta
 Esophagus
 Azygos and hemiazygos veins 
Thoracic duct
 Sympathetic ganglia and intercostal
Localize to the mediastinum
The following characteristics indicate that a lesion originates
within the mediastinum:
Unlike lung lesions, a mediastinal mass will not contain air 
bronchograms.
The margins with the lung will be obtuse. 
Mediastinal lines (azygoesophageal recess, anterior and 
posterior junction lines) will be disrupted.
There can be associated spinal, costal or sternal 
abnormalities.
LEFT: A lung mass abutts the mediastinal surface and creates
acute angles with the lung.
RIGHT: A mediastinal mass will sit under the surface of the
mediastinum, creating obtuse angles with the lung.
On the x-ray on the left there is a lesion that has an
acute border with the mediastinum.
This must be a lung mass (pancoast tumor)
The chest radiograph on the right shows a lesion with an
obtuse angle to the mediastinum.
This must be a mediastinal mass( thymoma )
.
Utility of MDCT, MR, and PET in the Evaluation of
:Mediastinal Masses
MDCT = MR
Confirming the presence of a mass versus tortuous 
vascular structure
Localization of mass to anterior, middle, or posterior 
compartment
Suspected aneurysm or vascular anomaly 
Detection of fluid
MDCT = MR = US 
Detection of calcium
CT 
 Tracheal involvement
MDCT > MR
 Involvement of spinal canal MR > MDCT
 Thoracic inlet lesions
MR = MDCT
 Contraindication to iodinated contrast
MR > MDCT
 Percutaneous biopsy of mediastinal mass
CT ,US
Thyroid Masses
 In a small percentage of patients with thyroid disease
extension of the thyroid through the thoracic inlet into the
superior mediastinum may occur.
 usually discovered as incidental findings on chest radiographs;
 a minority of patients will present with complaints of dyspnea
or dysphagia
 Thyroid goiters arising from the lower pole of the thyroid or
the thyroid isthmus can enter the superior mediastinum anterior
to the trachea (80% of cases) or to the right and posterolateral to
the trachea (20% of cases).
: On chest radiographs
An anterosuperior mediastinal mass typically
deviates the trachea laterally and either
posteriorly (anterior masses) or anteriorly
(posterior masses)
 Radioiodine studies should be performed as
the initial imaging procedure, although falsenegative results do occur.
CT findings:
(1) well-defined margins,
(2) continuity of the mass with the cervical thyroid,
(3) coarse calcifications,
(4) cystic or necrotic areas,
(5) baseline high CT attenuation (because of intrinsic iodine
content),
(6) intense enhancement (>25 H) and prolonged enhancement
MR is useful in depicting the longitudinal extension of thyroid
goiters without the use of intravenous contrast.
Thymomas or thymic epithelial neoplasms
Second most common primary mediastinal
neoplasms in adults after lymphoma.
 Arise from thymic epithelium and contain
varying numbers of intermixed lymphocytes.
Traditional classification
Thymomas, which are histologically benign but may be either
encapsulated (noninvasive) or invasive,
thymic carcinomas, in which the epithelial component shows
signs of frank malignancy.
WHO has recently classified these neoplasms based upon the
morphology of the epithelial component and the ratio of
epithelial cells to lymphocytes.
The classification system divides these neoplasms into types A,
AB, B1, B2, B3, and C, with a spectrum of histologic changes
ranging from the classic encapsulated thymoma (A), to thymic
carcinoma (C),
The average age at diagnosis of thymoma is 45 to 50;
Rare in patients under the age of 20.
Most often associated with myasthenia gravis,
Other autoimmune diseases associated with thymoma :
 pure red cell aplasia,
 Graves disease,
Sjogren syndrome ,
hypogammaglobulinemia.
Patients with myasthenia gravis, 10% to 28% have a
thymoma,
Patients with thymoma (30% to 54%) have or will develop
myasthenia
On chest radiographs, •
Thymomas are seen as round or oval, smooth or 
lobulated soft tissue masses near the origin of the
great vessels at the base of the heart
CT is best for characterizing thymomas and detecting
local invasion
Higher-grade thymomas(types B3 and C) tend to show
larger size, more irregular margins, heterogeneous
enhancement, regions of necrosis,
mediastinal nodal metastases, and calcification.
 Invasion of the thymic capsule 33% to 50% of patients.
In the majority of these patients, this determination
cannot be made by CT or MR .
 Local invasion of pleura, lung, pericardium, chest wall,
diaphragm, and great vessels occurs in 10% to 15% of
patients.
.
 Contiguity of a thymoma with the adjacent chest wall or
mediastinal structures cannot be used as reliable evidence of
invasion of these structures.
 Drop metastases to dependent portions of the pleural space
are a recognized
 Extrathoracic metastases are rare,
 Transdiaphragmatic spread of a pleural tumor into the
retroperitoneum has been described.
Tt is important to image the entire thorax and upper abdomen in
any patient with suspected invasive disease
: Thymic cyst
 May be congenital or acquired.
 Congenital unilocular thymic cysts are remnants of the
thymopharyngeal duct.
 Acquired multilocular thymic cysts are postinflammatory
associated with AIDS, prior radiation or surgery, and autoimmune
conditions(myasthenia gravis,aplastic anemia,sjogren syndrom)
in these latter conditions, clinical and radiologic distinction of
multilocular thymic cyst from thymoma may be difficult
two conditions can coexist
Differentioal diagnose;
 cystic degeneration of a
thymoma
 lymphoma
 germcell neoplasm
 lymphangioma
The CT shows an anterior mediastinal mass with water
density attenuation.
This is typical for a thymic cyst.
Thymic Carcinoid
Neuroendocrine tumors of the thymus are rare malignant
neoplasms arise from thymic cells of neural crest origin ([APUD]
or Kulchitsky cells).
 The most common histologic type is carcinoid tumor,
 Ranges in differentiation and behavior from typical carcinoid
to atypical carcinoid to small cell carcinoma.
 40% of patients have Cushing syndrome
 The carcinoid syndrome is uncommon.
 This lesion is indistinguishable from thymoma on plain
radiographs and CT scans.
Thymic hyperplasia
Enlargement of a thymus that is normal on gross and histologic
examination.
 occurs primarily in children as a rebound effect in response to
an antecedent stress, discontinuation of chemotherapy, or
treatment of hypercortisolism.
 An association with Graves disease has also been noted
 Found in 60% of patients with myasthenia gravis.
 Most patients with thymic hyperplasia have normal or diffusely
enlarged glands on CT
: Thymic Lymphoma
Thymus is involved in 40% to 50% of patients
with the nodular sclerosing subtype of Hodgkin
disease.
 Its radiographic appearance is
indistinguishable from that of other solid
neoplasms arising within the thymus.
 The presence of lymph node enlargement in
other portions of the mediastinum or anterior
Lymphoma
Most common primary mediastinal neoplasm in adults.
Hodgkin disease involves the thorax in 85% of patients at the
time of presentation (25% of patients with limited to the
mediastinum at the time of diagnosis).
 The majority (90%) of patients with intrathoracic involvement
have mediastinal lymph node enlargement( most commonly
involves the anterior mediastinal and hilar )
 The anterior mediastinum is the most frequent site of a
localized nodal mass in patients with Hodgkin disease(
particularly nodular sclerosing )
Isolated enlargement of mediastinal or hilar nodes outside the
anterior mediastinum should suggest an alternative diagnosis.