Autopsy Diagnosis: Diffuse aspiration bronchiolitis (foreign material and aspergillus)

Comment: This elderly man had a brief episode of pneumonia followed 4 months later by a prolonged bout of acute lung injury (ARDS) from which he recovered sufficiently to leave the hospital. He had several subsequent brief episodes of bronchitis/pneumonia and died of C. difficile colitis 9 months after his first brief pneumonia. At the time of the prolonged pneumonia, no cause was identified, and a diagnosis of acute interstitial pneumona was made on the basis of acute respiratory failure and consistent histology.


Acute Interstitial Pneumonia

Synonyms: Hamman-Rich syndrome; accelerated interstitial pneumonia; fulminant idiopathic pulmonary fibrosis; idiopathic, organizing, diffuse alveolar damage [1]

Introduction: Hamman and Rich described cases of idiopathic, rapidly progressing interstitial fibrosis with death by 6 months after onset [2]. Recently, these cases have been separated from cases of chronic idiopathic pulmonary fibrosis and given the name acute interstitial pneumonia (AIP). Its prognosis is somewhat better than that of idiopathic pulmonary fibrosis, and when it responds to treatment, it does not progress [1].

Clinical features: AIP presents as adult respiratory distress of unknown cause but with a more gradual onset than most cases with a known cause. Typically, it begins like a viral URI with cough, fever, and myalgias followed by progressive dyspnea and respiratory failure usually over a period of a week, but up to 2 months. Men and women are equally affected and most are young or middle-aged adults, but the disease can occur at any age [1]. Leukocytosis (mean 24 k/µl) is usually present [1], and the sedimentation rate is increased [3]. ANA and RF are sometimes present [3]. Most patients receive antibiotics as well as steroids. A similar disease occurs in patients with immune or autoimmune disease [3], but these patients have been excluded in studies of the idiopathic variety [1, 4].

Radiologic changes: The changes are similar to those of ARDS, but differ from the reticulation and honeycombing of usual interstitial pneumonia. Radiographs in 9 patients showed bilateral air-space opacification that was usually diffuse but sometimes patchy. HRCT showed ground glass attenuation and consolidation. Ground glass opacities were bilateral and patchy or diffuse. Bilateral consolidation was present in 2/3 and was basilar or diffuse. Subpleural honeycombing, present in 3/9, was attributed to underlying UIP. The one patient who survived more than 3 months showed clearing except for subpleural lines on the CT [5]. In another study, correlation of CT and histology indicated that areas that appeared normal by CT showed the exudative phase of alveolar damage with hyaline membranes. Ground glass opacities indicated either exudative or proliferative phases, but ground glass associated with traction bronchiectasis indicated the proliferative phase [6].

Microscopic features: Although the disease is acute, biopsies are taken in the subacute, organizing phase. The histologic features vary throughout the biopsy, but no normal lung is present. At low power, widened alveolar walls encroach in an irregular way on air spaces, but some alveolar ducts are enlarged because of alveolar collapse. At higher magnification, the walls are widened by non-collagenized, loose granulation tissue with scattered inflammatory cells; lymphocytes, plasma cells, and a few PMNs. Air spaces are lined by type II cells that show frequent atypia and focal squamous metaplasia. Air spaces contain some blood and scattered inflammatory cells including PMNs. Granulation tissue is also present in air spaces or bronchioles. It often becomes epithelialized and incorporated into the interstitium. Hyaline membranes may be seen focally, and acute or organizing thrombi occasionally occur in small to medium-sized arteries. These occlusions may represent in situ thrombi, but thromboembolism cannot be excluded [7]. No features in the biopsy predict pulmonary function or survival [1].

Summary of Pathologic Changes [1, 4]:

Differential diagnoses:

  1. Acute eosinophilic pneumonia: primarily an alveolar pneumonia with many eosinophils in exudate
  2. Acute exacerbation of usual interstitial pneumonia. When acute lung injury is superimposed on a chronic interstitial pneumonia, the acute process may predominate and the old scar, overlooked [8]. The clinical history and an EVG stain showing old, dark pink scar and new, light pink granulation tissue should make the distinction [4]. A CT scan may show evidence of scar and honeycombing.
  3. ARDS of known cause; e.g., aspiration

Outcome: Histologic resolution may occur as in the present patient, or healing with scar may occur. In one study of 29 patients (mean age 50) 12/29 (42%) survived, some with decreased function. The disease is not progressive [1, 4]. Of the 8 patients in Katzenstein's series (mean age 28), only one survived. The others died within 6 months [4].

Conclusions in the present case: This case emphasizes the fact that histologic changes of severe ARDS with extensive organization may resolve. In addition, it is possible, although speculative, that aspiration of gastric contents was the cause of all of the pneumonic and bronchitic problems in this man with a history of gastroesophageal reflux. Other common causes of ARDS--sepsis, pneumonia, and trauma--were excluded, and evidence of particulate aspirated material may be absent in a single lung biopsy. His good outcome from his pulmonary disease can be related to his lack of liver disease, multiorgan failure, and sepsis [9]. Finally, hospital discharge does not signify a "cure" for those with severe ARDS. Aspirative bronchiolitis, which was documented at autopsy, occurred because of the loss of gag reflex that was noted after extubation. The clinical aspects of aspiration pneumonia have been reviewed recently [10], and the pathologic features vary from a granulomatous bronchiolitis [11] to the changes of diffuse alveolar damage.

References

1. Olson J, Colby T, Elliott C. Hamman-Rich syndrome revisited. Mayo Clin Proc 1990; 65:1538-1548.

2. Hamman L, Rich A. Acute diffuse interstitial fibrosis of the lungs. Bull Johns Hopkins Hosp 1944; 74:177-212.

3. Pratt D, Schwartz M, May J, Dreisin R. Rapidly fatal pulmonary fibrosis: the accelerated variant of interstitial pneumonitis. Thorax 1979; 34:587-593.

4. Katzenstein A, Myers J, Mazur M. Acute interstitial pneumonia. A clinicopathologic, ultrastructural, and cell kinetic study. Am J Surg Pathol 1986; 10:256-267.

5. Primack S, Hartman T, Ikezoe J, Akira M, Sakatani M, Müller N. Acute interstitial pneumonia: radiographic and CT findings in nine patients. Radiology 1993; 188:817-820.

6. Ichikado K, Johkoh T, Ikezoe J, Takeuchi N, Kohno N, Arisawa J, Nakamura H, et al. Acute interstitial pneumonia: high-resolution CT findings correlated with pathology. AJR 1997; 168:333-338.

7. Tomashefski J Jr, Davies P, Boggis C, Greene R, Zapol W, Reid L. The pulmonary vascular lesions of the adult respiratory distress syndrome. Am J Pathol 1983; 112:112-126.

8. Kondoh Y, Taniguchi H, Kawabata Y, Yokoi T, Suzuki K, Takagi K. Acute exacerbation in idiopathic pulmonary fibrosis. Analysis of clinical and pathologic findings in three cases. Chest 1993; 103:1808-1812.

9. Doyle R, Szaflarski N, Modin G, Wiener-Kronish J, Matthay M. Identification of patients with acute lung injury. Predictors of mortality. Am J Respir Crit Care Med 1995; 152:1818-1824.

10. Shifrin R, Choplin R. Aspiration in patients in critical care units. Radiol Clin N Am 1996; 34:83-96.

11. Matsuse T, Oka T, Kida K, Fukuchi Y. Importance of diffuse aspiration bronchiolitis caused by chronic occult aspiration in the elderly. Chest 1996; 110:1289-1293.

Case 9--Clinical summary

Comments: mw6825@itsa.ucsf.edu

Table of Contents

Copyright 1997 by Martha L. Warnock

Last revised 8/14/97