Respiratory Diseases and the Fire Service

Certain features of the high-resolution chest CT may support a specific
diagnosis of interstitial lung disease or suggest alternatives. The overall pattern
of disease is very important in the classification. Certain diseases such as
sarcoidosis and hypersensitivity pneumonitis tend to have the abnormalities
distributed in a pattern that corresponds to bronchovascular bundles, the
conglomeration of airways and attendant blood vessels and lymphatics.
Hypersensitivity pneumonitis often is skewed toward a more upper-lobe
distribution. In sharp contrast, idiopathic pulmonary fibrosis has a characteristic
basilar (lower lung) distribution of disease. Pulmonary fibrosis appears on
the CT scan as ‘reticular’, a type of abnormality characterized as increased
relatively linear thin white lines. Active inflammation tends to cause a more
dense and coarse increase in radiodensity appearing as nonlinear patchy
areas of increased white attenuation on the chest CT which may fill in alveolar
spaces completely and can be referred to as ‘ground glass opacities’. Ground
glass opacities are characteristically seen in hypersensitivity pneumonitis,
nonspecific interstitial pneumonia and during the acute exacerbation phase
of idiopathic pulmonary fibrosis. More dense consolidation is often indicative
of infection or cryptogenic organizing pneumonia. Advanced disease may be
described as honeycombing due to its resemblance to the internal wax structure
of a beehive. This finding when pronounced may add to the probability of the
underlying disease process being idiopathic pulmonary fibrosis. Another finding
known as traction bronchiectasis refers to the enlargement of airways in the
periphery of the lung that are being tethered open by the centripetal forces
exerted when extensive scarring occurs in the substance of the lung tissue.
Radionuclide scanning with isotopes such as radioactively tagged gallium
can be useful to demonstrate active lung inflammation. Gallium is injected
into the patient’s vein, after which a scan of the chest is done to assess the
distribution of the gallium within the lung. Areas of inflammation “light up”
on the scan; but this test lacks specificity.
Pulmonary function tests show a restrictive pattern, which means that
measured lung volumes and rates of airflow from the lung on forced expiration
are both reduced. The diffusing capacity, a test measuring the ability of gases
to transfer from the atmosphere into the bloodstream, is usually reduced, even
prior to the development of restriction.
In the majority of cases, a surgical lung biopsy is required to obtain sufficient
lung tissue so that a specific diagnosis may be rendered. 3 Generally this
biopsy requires general anesthesia and can be obtained via video-assisted
thoracoscopy, where three tiny incisions are made in the chest wall, through
which the thoracic surgeon can insert a fiberoptic camera and tools to perform
the biopsies (Figure 2-7.2). The procedure is safe for most people but can
sometimes be obviated if the chest CT is diagnostic for a specific entity such
as what is known as usual interstitial pneumonia. It is often not recommended
to individuals who have increased risk for surgical procedures due to other
medical conditions.
Specific pathological findings are seen in the surgical lung biopsy specimens
obtained from individuals with idiopathic interstitial lung diseases. Cryptogenic
organizing pneumonia shows marked inflammation in the alveolar spaces
along with plugs of fresh fibrous connective tissue extending into the lumen
of small airways. Usual interstitial pneumonia, the histologic correlate of
124
Chapter 2-7 • Pulmonary Fibrosis and Interstitial Lung Disease