[Abstract] Objective To investigate the imaging features of acute interstitial pneumonia (AIP). Methods A series of imaging data of 7 cases of AIP confirmed by open lung biopsy or clinically comprehensive diagnosis were reviewed and analyzed. In the middle stage, the above lesions rapidly expanded from the periphery of the lung to the mid-axis level and from the mid- and lower lung to the upper lung, and the interstitial system of the lung was significantly changed, showing the thickening of the interlobular septa, intralobular septa and mid-axis interstitium. The interstitial fibrosis of the lung in the advanced stage is rapidly developing and accompanied by progressive destruction of lung tissue and lung structures. Conclusion The imaging manifestations of AIP are relatively characteristic, and the rapid imaging changes, especially the rapid interstitial fibrosis and destruction of lung structure, are the key to suggest the diagnosis. Lei Zhidan, Department of Radiology, Henan Provincial People’s Hospital
[Keywords] Acute interstitial pneumonia, diffuse alveolar injury
Open-chest lung biopsy, diagnostic imaging
Imaging Diagnosis of Acute Interstitial Pneumonia.
A Report of 7 Cases With Literature Review
LEI Zhi-dan, GE Ying-hui, WEN Ze-jun, TANG Xue-yi
(Department of Radiology, Henan Provincial People’s Hospital, Zhengzhou, 450003, China)
[Abstract] Objective To discuss imaging features of acute interstitial pneumonia (AIP). Methods Serial imaging materials of 7 cases’ AIP which were proved by open-lung biopsy or clinical comprehensive diagnosis were Results In the early stage of AIP, the ground-glass opacities and consolidations were loosely distributed over the bilateral peripheral zones of middle or lower In the middle phase of AIP, these opacities and consolidations progressed quickly into the axial plane or the upper pneumal zones. In the middle phase of AIP, these opacities and consolidations progressed quickly into the axial plane or the upper pneumal zones, and the interlobular septums, the intralobular interstitiums, the axial interstitiums all thickened. In the late phase of AIP, the pulmonary interstitial fibrosis and the pulmonary architectural injury progressed rapidly. AIP possesses relative imaging feature, and the imaging variation advancing sharply, particularly the pulmonary interstitial fibrosis and the progressive pneumal architectural injury are the funishing diagnostic evidences. AIP possesses relative imaging feature, and the imaging variation advancing sharply, particularly the pulmonary interstitial fibrosis and the progressive pneumal architectural injury are the funishing diagnostic evidences.
[Key words] Acute interstitial pneumonia Diffuse alveolar damage Open-lung biopsy Diagnostic imaging
Acute interstitial pneumonia (AIP) is a form of interstitial pneumonia of unknown etiology, with an acute onset and an extremely poor prognosis. Since it was first proposed by Katzenstein et al [1] in 1986, it has been repeatedly reported in the domestic and international literature in recent years [2-6], but the diagnosis of AIP is still a difficult problem. By retrospectively analyzing the imaging data of 7 cases of AIP series treated by our hospital during the six years from 1998 to 2004, the author aimed to discuss the imaging diagnosis and differential diagnosis of this disease.
1 Materials and methods
Among the 7 cases of AIP, 3 cases were confirmed by comprehensive clinical diagnosis and 4 cases were confirmed by open-chest lung biopsy. All 7 cases had a healthy cough with no obvious cause, 4 cases had fever with sore throat, 1 case had malaise, 5 cases had progressive dyspnea within 2 weeks, and 2 cases had marked dyspnea in the third week, and Velcro sounds in the middle and lower lungs could be detected after 2-3 weeks. All 7 cases had chest radiographs and/or CT examinations in the early, middle and late stages of AIP. 7 cases came from different hospitals with different grade of X-ray and CT equipment and different examination methods. However, all 7 cases had chest radiographs and/or CT examinations at our hospital at week 4 or 5.
2 Results
The imaging changes of AIP were progressively aggravated with the changes of the disease, and the manifestations of AIP in 7 cases were as follows: in the early stage, the main manifestations were scattered patchy solid shadows and ground glass shadows in the periphery of the bilateral middle and lower lungs, and none of the cases showed interstitial thickening such as septal lines; in the middle stage, the above lesions spread rapidly and showed diffuse distribution of ground glass shadows and solid shadows bilaterally, accompanied by interstitial thickening; in the late stage, the lesions In the late stage, the lesions deteriorate rapidly, the interstitial fibrosis progresses rapidly, and the destruction of lung structures is rapidly aggravated, even forming end-stage lung. The specific changes are shown in Table 1.
Table 1, imaging manifestations of 7 cases of AIP (cases)
Time (weeks) Ground glass shadow and solid shadow Interstitial thickening Stretch bronchiectasis Structural destruction of lung Distortion of bronchovascular bundles Collapse of lung Pneumothorax
1 6 0 0 0 0 0 0 0
2 7 2 0 0 0 0 0 0 0
3 7 7 1 0 1 0 0 0
4 7 7 6 6 6 6 2 1
3 Discussion
3.1 Overview
AIP is a severe respiratory disease of unknown etiology with an acute course and poor prognosis. It was originally a subtype of idiopathic pulmonary fibrosis (IPF), which was still classified as a subtype of IPF by Katzenstein [7] until 1998. In recent years, due to its clinical and pathological uniqueness, the American Thoracic Society and the European Respiratory Society have considered AIP as an interstitial disease distinct from IPF [8].
3.2 Clinical features and pathological manifestations of AIP
The incidence of AIP is much lower than that of IPF, and it usually develops around 50 years of age, with no difference between men and women. The onset of the disease is sudden and without obvious causes, and the initial symptoms may be similar to those of respiratory tract infection, such as cough, sputum, headache, and malaise, etc., and then respiratory distress can occur within a few days or 1-2 weeks, and the disease rapidly falls into respiratory failure. The mortality rate is high (33%-75%) and the majority of deaths occur within 3-4 weeks [3]. Only one case in our group was cured, which also indicates its high mortality rate. Wet rales can be heard in both lungs in the early stage, and Velcro rales can be heard in the middle and late stages with cyanosis and accelerated respiratory rate. The treatment of AIP is usually with glucocorticoids and mechanical ventilation, but the results are generally poor.
The pathology of AIP is characterized by mechanized diffuse alveolar injury in both lungs and is divided into an acute phase and a mechanized phase. The acute phase (exudative phase) occurs 1-2 weeks after the onset of the disease and is characterized by damage to the alveolar epithelium and basement membrane, with exudate containing fibroblasts, inflammatory cells, giant eosinophils, fibrin and detached epithelial cells, resulting in edematous changes in the alveolar cavity and interstitial lung. The proliferative phase occurs within 2-3 weeks and is characterized by thickening of the interstitial system. Fibroblast proliferation is prominent during this period, and extensive fibrosis of the alveolar septum and alveolar cavity is seen.
Although there is no uniform diagnostic criteria for AIP, combined with clinical and pathological features, the author believes that the comprehensive clinical diagnosis of AIP is based on: (1) unknown etiology and no obvious cause; (2) onset in normal subjects (no previous history of pulmonary disease); (3) sudden onset, rapid progression, and rapid descent into respiratory failure; (4) wet rales are heard in the lungs at the initial stage, and Velcro rales are heard in the middle and late stages; (5) (5) predominance of neutrophils in bronchoalveolar lavage fluid; (6) poor prognosis due to poor hormonal and ventilation therapy; (7) pathological features of diffuse alveolar injury and mechanization on lung tissue biopsy; (8) imaging manifestations of progressive interstitial fibrosis and acute destruction of lung structures. However, due to the rapid progression of AIP, it is more difficult to obtain a basis for lung histopathology. Therefore, imaging manifestations have an important reference role in the diagnosis of this disease.
3.3 Imaging features and their differential diagnosis
The imaging changes of AIP are often progressive, and each stage of its performance is characterized: (1) Early stage is usually within 1-2 weeks of onset, and the imaging performance of the 7 cases in this group was similar within 2 weeks, i.e., mainly exudative changes, whose distribution was characterized by scattered peripheral patchy solid shadows and ground glass shadows in the middle and lower lungs bilaterally. (2) In the middle stage (within 2-3 weeks), imaging at week 3 in four of the seven AIP cases and at weeks 2 and 3 in the other two cases was consistent with the middle stage presentation, with rapid progression of exudative lesions and extensive thickening of the interstitial system, which was consistent with the pathologic overlap of exudation and mechanization. In the late stage (after 3-4 weeks), fibrosis progresses rapidly, manifesting as acute interstitial fibrosis and progressive destruction of lung tissue and pulmonary structures, especially with a specificity of distended bronchial dilatation that is rare in other forms of acute diffuse lung disease [2,9]. In our group, five cases showed these manifestations after week 4 and one case after 3 weeks, further suggesting that worsening fibrosis with severe destruction of lung structures is the main manifestation and main feature of the late stage of AIP. Combining the above imaging characteristics of early, middle and late stages of AIP, the author believes that the rapidly progressive imaging change process is a more characteristic manifestation of AIP, and thus the analysis of the series of imaging data is the basis for proposing the diagnosis of this disease. Since the main role of HRCT is to optimally display the microstructure of the lung [10], and it is better than conventional CT and chest radiographs in showing interstitial changes, HRCT scan examination can be given priority during the whole process of lesion development, thus helping to judge the interstitial changes of the lung at an early stage and to detect the pattern of AIP image changes in time, providing an early basis for early treatment.
Since acute respiratory distress syndrome (ARDS) and severe acute respiratory syndrome (SARS) have similar clinical and pathological manifestations to AIP, the first two are the most important diseases to be differentiated from AIP. ARDS is often secondary to severe intrapulmonary or extrapulmonary disease [11], and the imaging presentation is “white lung” with less fibrosis than AIP, less destruction of lung structures than AIP, and less traction bronchiectasis. must have an epidemiological basis and the efficacy of high-dose hormone therapy combined with ventilation is more certain [12]. Also the more extensive distraction bronchiectasis helps to differentiate AIP from them.
In conclusion, the imaging manifestations of AIP are relatively characteristic, and although there is no basis for pathology, combined with the patient’s clinical symptoms, the diagnosis of AIP can be considered.
The diagnosis of AIP can be considered in combination with the clinical symptoms of the patient, which can provide help for further clinical pathological diagnosis and treatment.
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