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Asbestos Exposure is a common occupational hazard.
o
Asbestos is a term that is used to describe a set of
fibrous dusts.
o
Inhalation of these particles results in localized
fibrous plaques on the viscera and diaphragm (see arrow
on first pic.; is the hallmark of asbestosis), pleural
effusions, and interstitial fibrosis (particularly of
the lower lobes).
o
May
also predispose to bronchogenic carcinomas and malignant
mesotheliomas.
o
Malignant mesotheliomas (above) can arise from both the
visceral or parietal pleura and the peritoneum.
o
It
is usually associated with extensive pleural effusion
and direct invasion of thoracic structures.
o
Symptoms seen in patients are similar to silicosis.
o
Pathology:
§
Asbestosis is marked by diffuse pulmonary interstitial
fibrosis with the appearance of asbestos bodies that
appear as golden brown, beaded rods with translucent
centers and asbestos fibers coated with an iron
containing proteinaceous material.
§
Ferruginous body is the term given to macrophages that
have engulfed the asbestos fibers.
§
Honeycomb lung is the characteristic feature; usually
there is no involvement of the hilar nodes.
§
Microscopically the interstitial spaces then to be
thickened with fibrous tissue; this results in the
constriction of the airways.
§
These bodies are found in the parenchyma of the lungs
and sputum and can be identified with stains for iron.
§
Ferruginous bodies are not pathogenic; the actual
pathogenicity is due to the uncoated fibers.
·
The
Mediastinum:
o
Is
the space in the center of the chest bounded by:
thoracic inlet superiorly, diaphragm inferiorly, sternum
anteriorly, spine posteriorly, pleura laterally.
o
It
is a very important region because it contains important
structures such as the heart, lungs, thymus,
thyroid/parathyroid, and many lymph nodes.
o
Neoplasms in this region have a tendency to metastasize
to nearby structures or to the lymph nodes.
·
Mediastinal tumors:
o
Neoplasms within the mediastinum are geographically
distributed.
Anterior Mediastinum
§
Thymomic and thyroid tumors
§
Lymphoma
§
Germ
cell tumor
§
Carcinoid
§
Metastatic carcinoma* (most common)
§
Lipoma
Middle Mediastinum (very few diseases)
§
Sarcoma of heart and pleura
§
Lymphoma
Posterior Mediastinum
§
Neural tumors; schwannoma, neurofibroma
§
Ganglioneuroblastoma
·
Thymoma is a general term used to describe tumors of the
thymic epithelial cells.
o
One
of the more common primary tumors of the anterior
mediastinum.
o
Patients present with cough, dysphagia hoarseness etc.
o
They
may arise in the anterior superior mediastinum* neck
thyroid, etc.
o
Within the tumors are also lymphocytes that are
actually benign components of the tumors.
o
Thymomas are generally surrounded by a dense fibrous
capsule (see arrow).
o
The
capsule is used to divide the thymoma into three
different types
If
it remains within its capsule it is a benign tumor.
§
Benign tumors
are typically the type of thymoma seen.
A
thymoma that spreads beyond its capsule is a
malignant tumor and is referred to as a thymic
carcinoma.
The
term atypical thymoma is used when the malignancy
of the tumor is indeterminate.
o
Symptoms of a benign tumor are related to the mass of
the tumor, and are as follows (we saw some of these
before):
Cough
Dyspnea
Chest Pain
Dysphagia
Hoarsness
Stridor
o
There are now seven or eight different cell types that
result in thymomas and malignancy can also be related to
the cell type. [Another point of classifying besides the
capsule]
o
Myasthenia Gravis is an acquired autoimmune disorder
resulting in acetylcholine receptor deficiency.
o
Why
talk about this disease?
o
Because:
65%
of patient with this disorder have thymic lymphoid
hyperplasia
15%
of patients with myasthenia gravis have a thymic
neoplasm; while 33% of all patients with a thymoma have
myasthenia gravis.
The
have a large mediastinal mass and most of the time it
has to be removed. Usually benign
Removal seems to include symptoms of disease.
·
Mediastinal Germ cell tumors:
o
Most
arise in the gonadal tissue
o
10%
of germ cell tumors show up in the anterior mediastinum
and are considered malignant (see below).
o
The
most affected patient population are males in
their 30s
o
Now
just because a tumor is classified as benign doesnt
mean it doesnt have malignant potential. So any male
patient that presents with a teratoma of the anterior
mediastinum must be monitored for potential progression
to malignancy.
o
There are blatantly malignant neoplasms that may be
present:
1)
Seminoma of the mediastinum (which is histologically
indistinguishable from a seminoma of the testis).
2)
Outright germ cell carcinoma
3)
Other carcinomas
·
Posterior mediastinal tumors:
Are
usually of Neural Origin
o
Schwannoma
o
Neurofibroma
o
ganglioneuroma
o
ganglioneuroblastoma
o
neuroblastoma
o
The
picture on the right is an example of a posterior
mediastinal tumor that is hemorrhagic and necrotic.
Usually this indicates that the tumor is malignant and
metastatic
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