Click on Images for Enlarged View
Findings: The chest radiograph (not shown) was interpreted as normal. The high resolution CT (HRCT) scan shows subtle, scattered ground glass opacities throughout both lungs. No evidence of significant adenopathy or pleural fluid.
Diagnosis: Hypersensitivity pneumonitis. Transbronchial biopsies negative for MAC or other bacterial infection. Pathology revealed inflammatory cells with scattered non caseating granulomas, consistent with hypersensitivity pneumonitis.
Discussion: The finding of ground glass opacities in the lung on HRCT carries a long differential diagnosis. This includes UIP,DIP, and LIP, as well as diagnoses such as sarcoidosis, PCP and hypersensitivity pneumonitis. Ground glass opacities were initially felt to represent an active alveolitis, and therefore be a marker for treatable disease. Further radiologic-pathologic correlation, however, has shown that it can represent fibrosis at the intralobular, or microscopic level.
Hypersensitivity pneumonitis can be incited by a number of factors. Though the most common inciting antigens are the thremophilic Actinomycetes species, avian proteins (bird fanciers lung), drugs and chemicals are also commonly cited agents.
Clinically, the patient generally complains of dyspnea and cough, chills and fever 4-8 hours after exposure. Symptoms typically last from 12-60 hours but will often recur with repeated exposure. With chronic exposure, chronic cough, fatigue and anorexia can develop. Age at diagnosis, duration of antigen exposure and number of repeated exposures are the most important predictive values for long term sequelae.
Pathologically, a lymphocytic infiltrate with ill defined, non-caseating granulomas are seen microscopically. BAL results show increased cell counts, which are predominantly lymphocytic. While the process is predominantly interstitial, an active alveolar component is often present. As the process becomes more chronic, interstitial fibrosis is more commonly seen.
The CT and HRCT findings in hypersensitivity pneumonitis have been described. In general, acute, subacute and chronic stages have been described. The acute phase is characterized by wide-spread air space consolidation. The sub-acute stage is characterized by centrilobular nodules, with the development of predominantly upper lobe fibrosis in the chronic stage. A recent review of 17 patients with the diagnosis of hypersensitivity pneumonitis was performed. the most common CT finding was ground glass opacities in 11 of 14 patients. Six of 14 had evidence of centrilobular nodules. Unlike the chest radiograph findings which often suggest a lower zone predominance, the lungs appear diffusely involved on CT scan. HRCT is both more sensitive and specific than the plain radiograph in the diagnosis of hypersensitivity pneumonitis.
References:
Webb, WR,Muller NL, Naidich, DP High Resolution CT of the Lung
Philadelphia, Lippincott Raven 1996.
Hasleton, PS, Hypersensitivity Pneumonitis, in Spencers Pathology of the Lung,
New York, Mc Graw-Hill 1996.
Hansell, DM and Moskovic, E. High ResolutionComputed Tomography in Extrinsic
Allergic Alveolitis. Clin. Rad. (1991) 43, 8-12.
Submitted by: