Thoracic Imaging 2003 - Society of Thoracic Radiology

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radiologic, and histopathologic findings. Because the clinical
findings of HP mimic multiple other diseases, a high degree of
clinical suspicion and a thorough occupational and environmental
history are essential for accurate diagnosis. There is no single
pathognomonic feature for HP; rather, diagnosis relies on a
constellation of clinical, radiologic, and pathologic findings.
The HRCT findings of HP provide important clues and frequently
point clinicians towards the correct diagnosis. In particular
the finding of profuse centrilobular nodules of ground glass
attenuation is strongly suggestive of this diagnosis. Another
strongly suggestive pattern is the combination of ground glass
attenuation with air trapping (18, 19).
Although hypersensitivity pneumonitis is commonly classified
into acute, subacute and chronic subsets, patients with longstanding
symptoms may often be radiologically indistinguishable
from those with more acute presentations. However, about
50% of patients with chronic HP present with evidence of reticular
abnormality, traction bronchiectasis, or honeycombing suggestive
of lung fibrosis. These findings may predominate in the
upper, mid or lower zones. The challenge for the imager is to
distinguish these patients from patients with other fibrotic lung
conditions, particularly idiopathic pulmonary fibrosis (20) and
nonspecific interstitial pneumonia. In patients with CT evidence
of lung fibrosis, the presence of associated centrilobular
nodules or air trapping should suggest HP. Several series have
reported that emphysema is a common CT finding on followup
of patients with hypersensitivity pneumonitis, even in nonsmokers
(18, 21). However, the radiologic characteristics of this type
of emphysema remain poorly characterized. Distinction
between chronic HP and other conditions can be important,
because the CT findings of chronic HP can be reversible with
appropriate management including removal of the antigen.
New occupational diseases
With the increasing complexity of occupational exposures, it
is not surprising that new occupational diseases continue to be
identified. Two recent examples are flock-workers’ lung (22)
which produces a diffuse ground glass pattern, and flavor-workers
lung which produces a pattern of constrictive bronchiolitis
(23).
Summary
Challenges for the radiologist in occupational lung disease
include detection and characterization of the abnormality, and
recognition of new and evolving lung diseases.
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