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Crazy-paving Appearance at Thin-Section CT: Spectrum of Disease and Pathologic Findings¹

¹ From the Dept of Radiology, Osaka University Medical School, Japan (T.J., H.N.); Dept of Radiology, Vancouver Hospital and Health Sciences Centre and University of British Columbia, 855 W 12th Ave, Vancouver V5Z 1M9, Canada (T.J., N.L.M.); Dept of Radiology, Kyoto University Medical School, Japan (H.I.); First Dept of Internal Medicine, Kumamoto University School of Medicine, Japan (K.I.); Dept of Radiology, Ehime University Medical School, Japan (J.I.); Dept of Radiology, National Kinki Chuo Hospital for Chest Diseases, Osaka, Japan (M.A.); and Dept of Pathology, Izumisano Municipal Hospital, Osaka (T.N.). From the 1996 RSNA scientific assembly. Received Apr 2, 1998; revision requested Jun 29; final revision received Sep 8; accepted Oct 26. Address reprint requests to N.L.M.

	Abstract

TOP Abstract Introduction MATERIALS AND METHODS RESULTS DISCUSSION References

 
PURPOSE: To determine the spectrum of diseases associated with a fine reticular pattern superimposed on areas of ground-glass opacity (ie, "crazy-paving" appearance) at thin-section computed tomography (CT) and to determine the underlying pathologic features.

MATERIALS AND METHODS: In the in vivo study, the cases of 46 patients (21 male, 25 female; age range, 13–82 years) were retrospectively reviewed, with special attention paid to the size and extent of the reticular network. In the in vitro study, the thin-section CT findings in 20 inflated and fixed lungs were precisely correlated with the gross appearance, contact radiograph findings, stereomicroscopic views, and histologic findings.

RESULTS: In the in vivo study, 15 different diseases were identified, including alveolar proteinosis, adult respiratory distress syndrome, acute interstitial pneumonia, diffuse alveolar damage superimposed on usual interstitial pneumonia, and drug-induced pneumonitis. In the in vitro study, the fine networks at pathologic analysis were due to an alveolar filling process (n = 10), an interstitial fibrotic process (n = 7), or a combination of interstitial and intraalveolar processes (n = 3). Twelve (60%) cases did not have thickening of the interlobular septa within the areas of the crazy-paving appearance.

CONCLUSION: The crazy-paving appearance is a nonspecific finding seen in a variety of interstitial and airspace lung diseases.

Index terms: Computed tomography (CT), comparative studies, 60.126, 60.1292, 68.11, 68.12118 • Computed tomography (CT), thin-section, 68.12118 • Lung, CT, 60.12118 • Lung, diseases, 60.2061, 60.2075, 60.213, 60.2173, 60.23, 60.4123, 60.413, 60.47, 60.632, 60.71 • Lung, infection, 60.20 • Pneumonia, acute interstitial, 60.213 • Proteinosis, pulmonary alveolar, 60.791 • Respiratory distress syndrome, adult, 60.413

	Introduction

TOP Abstract Introduction MATERIALS AND METHODS RESULTS DISCUSSION References

 
The "crazy-paving" appearance consists of a network of a smooth linear pattern superimposed on an area of ground-glass opacity on thin-section computed tomographic (CT) scans. This finding has been considered to be strongly suggestive of alveolar proteinosis (1). In our daily clinical practice, however, we have found that diseases other than alveolar proteinosis can have this appearance at thin-section CT. Recently, it has been shown that mucinous bronchoalveolar carcinoma and lipoid pneumonia can produce this pattern also (2,3).

The linear network in the crazy-paving pattern is believed to be owing to thickening of interlobular septa (1,4). Recently, Kang et al (5), on the basis of the findings in a single case, suggested that the network in the crazy-paving appearance in alveolar proteinosis can be due to an accumulation of periodic acid–Schiff–positive material in the airspaces adjacent to the interlobular septa rather than to thickening of the septa. The purpose of this study was to assess the spectrum of diseases that can cause the crazy-paving appearance on thin-section CT scans and to determine the pathologic findings responsible for this appearance by using precise radiologic-pathologic correlation.

	MATERIALS AND METHODS

TOP Abstract Introduction MATERIALS AND METHODS RESULTS DISCUSSION References

 
In Vivo Study
Between January 1991 and August 1996, 5,123 patients underwent thin-section CT at the Osaka University Medical School. The CT scans were reviewed by two radiologists (T.J., K.I.) to determine the number of cases that had a crazy-paving pattern. Forty-six (0.9%) (21 male patients, 25 female patients; age range, 13–82 years; mean age, 52 years) of the 5,123 patients had the crazy-paving pattern at thin-section CT. The diagnoses were based on direct pathologic proof of the pulmonary lesion obtained from results of autopsy (five cases), open-lung biopsy (one case), video-assisted thoracoscopic biopsy (one case), surgery (one case), transbronchial biopsy (17 cases), or detailed clinical correlation (21 cases).

CT scanning was performed with either a model 9800 scanner (GE Medical Systems, Milwaukee, Wis) or a HiSpeed Advantage scanner (GE Medical Systems) without the administration of an intravenous contrast medium. The scans were obtained at end inspiration by using 1.5- (9800 scanner) or 1.0-mm (HiSpeed Advantage scanner) collimation and at 15- or 20-mm intervals through the chest, with the patient in a supine position. The scans were reconstructed by using a high-spatial-frequency (bone) algorithm. CT was performed at 140 kVp and 200 mAs. The scans were viewed at window settings appropriate for pulmonary parenchyma (ie, window width, 1,200–1,500 HU; window level, -700 to -550 HU).

Two radiologists (T.J., K.I.) retrospectively reviewed the cases of the 46 patients and paid special attention to the size of the network and the extent of the crazy-paving appearance. The observers did not know the diagnosis when they reviewed the CT findings. Analysis of the thin-section CT scans was performed by both radiologists together at the same time, and final interpretation of the findings was reached by consensus. An assessment of the size of the network was obtained by measuring the maximum and minimum sizes of networks in each case. An assessment of the extent of the crazy-paving appearance was obtained by counting the number of pulmonary segments that had this finding.

The size of networks and the numbers of pulmonary segments with the crazy-paving appearance were compared between patients who had alveolar proteinosis and the remaining patients by using the Mann-Whitney U test.

In Vitro Study
Between March 1987 and August 1996, 361 lungs obtained at autopsy were inflated and fixed (6). These lungs were distended through the main bronchus with fixative fluid that contained polyethylene glycol 400, 95% ethyl alcohol, 40% formalin, and plain water in proportions of 10:5:2:3. The specimens were immersed in the fixative for 2 days. The fixed lungs were then air dried.

After inflated fixation of the lungs, the first screening thin-section CT examination was performed with a model 9800 scanner or HiSpeed Advantage scanner by using a high-spatial-resolution algorithm and the following parameters: 140 kVp, 200 mAs, 1.5- or 1.0-mm thickness, 5-mm intervals, and a 16- to 22-cm field of view. Twenty of the lungs obtained at autopsy—seven with diffuse alveolar damage, six with pulmonary hemorrhage, three with cardiogenic edema, two with bacterial pneumonia, and two with postinfectious organizing pneumonia—showed the crazy-paving appearance at thin-section CT. The seven patients who had diffuse alveolar damage at autopsy had a clinical diagnosis of adult respiratory distress syndrome (ARDS). The ARDS in these patients occurred after major trauma or surgery. Selected areas of these lungs were cut into 2-cm-thick transverse sections, and serial thin-section CT scans of these sections were obtained at 1-mm thickness and a 16- to 22-cm field of view by using the CT equipment previously described.

After the CT studies, selected areas smaller than 7 x 5 cm were cut into serial, 1-mm-thick sections to correspond to the specimen CT sections by using a microslicer (DTK-3000W; Dosaka EM, Kyoto, Japan). Contact radiography was performed of each pathologic section with a fine-grain film (Softex; Fuji Medical, Tokyo, Japan) at 10 kVp, 1,260 mAs, and a 30-cm distance between the tube and film. When histologic confirmation was needed, serial 20-µm-thick microscopic sections were obtained from the 1-mm-thick specimens and stained with hematoxylin-eosin and elastic-van Gieson solution.

The thin-section CT scans were directly compared with the stereomicroscopic views, contact radiographs, and histologic sections in the same areas by two radiologists (T.J., K.I.) and one pathologist (T.N.); special attention was paid to the pathologic basis of the crazy-paving appearance and to the interlobular or intralobular location of the underlying process.

	RESULTS

TOP Abstract Introduction MATERIALS AND METHODS RESULTS DISCUSSION References

 
In Vivo Study
The 46 patients who had the crazy-paving appearance at thin-section CT had 15 different underlying diseases. These patients included the following: eight patients with ARDS (Fig 1), seven with bacterial pneumonia, five with alveolar proteinosis (Fig 2), five with acute interstitial pneumonia, three with drug-induced pneumonitis, three with radiation pneumonitis, three with pulmonary hemorrhage, two with chronic eosinophilic pneumonia (Fig 3), two with diffuse alveolar damage superimposed on usual interstitial pneumonia (ie, accelerated deterioration of usual interstitial pneumonia), two with cardiogenic edema, two with mycoplasma pneumonia, one with obstructive pneumonia, one with tuberculosis, one with pneumonia caused by Pneumocystis carinii, and one with bronchiolitis obliterans organizing pneumonia. The ARDS was secondary to trauma in six patients and occurred after surgery in two patients. The patient with tuberculosis had an exudative pneumonic pattern similar to that seen in bacterial pneumonia (Table).

View larger version (126K): [in this window] [in a new window]   Figure 1. Thin-section CT scan of right upper lobe in a 32-year-old man with ARDS shows a fine reticular pattern superimposed on a background of ground-glass opacity—that is, the crazy-paving pattern. This pattern is best seen in the posterior segment of the right upper lobe, particularly in the region circumscribed by the arrows. Fluid within the major fissure (arrowheads) also is seen.

View larger version (141K): [in this window] [in a new window]   Figure 2. Thin-section CT scan targeted to the left upper lobe in a 41-year-old man with alveolar proteinosis shows the crazy-paving appearance. The pattern consists of a reticular network superimposed on a background of ground-glass opacity. This pattern is best seen in the anterior segment of the left upper lobe in the region circumscribed by the arrows. The minimum and maximum sizes of each frame of the network are 2 and 7 mm, respectively.

View larger version (131K): [in this window] [in a new window]   Figure 3. Thin-section CT scan of right lower lobe in a 65-year-old woman with chronic eosinophilic pneumonia. The crazy-paving pattern is present in the right lower lobe, particularly in the region circumscribed by the arrowheads. The minimum and maximum sizes of each frame of the network are 2 and 6 mm, respectively.

There was no significant difference in the minimum size of the networks between alveolar proteinosis (mean ± SD, 2.0 mm ± 0.4) and the other processes (2.0 mm ± 0.5) (P = .29). There also was no significant difference in the maximum size of networks between alveolar proteinosis (5.7 mm ± 1.4) and the other processes (5.6 mm ± 1.8) (P = .11) (Fig 3).

The number of pulmonary segments involved in alveolar proteinosis (13.0 ± 5.8) was significantly greater than that in the other processes (5.9 ± 4.3) (P = .015). However, in three of eight patients with ARDS, in both the patients with diffuse alveolar damage superimposed on usual interstitial pneumonia, in one of five patients with acute interstitial pneumonia, and in one of three patients with drug-induced pneumonitis, the crazy-paving appearance was found in more than 10 segments.

In Vitro Study
Pathologically, there were three types of processes that resulted in fine networks. The first one, type 1, was an alveolar filling process (ie, airspace disease), which occurred in 10 cases (Fig 4). Six cases of pulmonary hemorrhage, two cases of bacterial pneumonia, and two cases of postinfectious organizing pneumonia were included in this type. The second process, type 2, was an interstitial fibrotic process, which occurred in seven cases (Fig 5). All of the seven cases included in this type were those of diffuse alveolar damage due to ARDS secondary to trauma or surgery. The third process, type 3, was a combination of both interstitial and intraalveolar diseases, and it occurred in three cases (Fig 6). All three cases included in type 3 were those of cardiogenic pulmonary edema.

View larger version (149K): [in this window] [in a new window]   Figure 4a. Postmortem findings in a 41-year-old woman with alveolar hemorrhage. (a) Thin-section CT scan of the left lower lobe demonstrates the crazy-paving appearance, which is best seen in the region circumscribed by the arrows. (b) Contact radiograph at the same level as in a reveals fine networks. The box encloses the region of the lung that is magnified in c. (c) Magnified view of the boxed area in b. The frames of fine linear networks in a correspond to the irregular lines on this contact radiograph. (d) Photomicrograph corresponding to b (hematoxylin-eosin stain; original magnification, x0.4). Diffuse hemorrhage can be seen in the alveoli. The fine network in a corresponds to the sites of relatively more marked deposition of hemorrhagic materials. The box outlines the region of the lung that is magnified in e. (e) Magnified view of the boxed area in d (hematoxylin-eosin stain; original magnification, x40). Normal interlobular septa (arrows) can be seen. The fine network is owing to the linear deposition of hemorrhagic materials within the airspaces.

View larger version (220K): [in this window] [in a new window]   Figure 4b. Postmortem findings in a 41-year-old woman with alveolar hemorrhage. (a) Thin-section CT scan of the left lower lobe demonstrates the crazy-paving appearance, which is best seen in the region circumscribed by the arrows. (b) Contact radiograph at the same level as in a reveals fine networks. The box encloses the region of the lung that is magnified in c. (c) Magnified view of the boxed area in b. The frames of fine linear networks in a correspond to the irregular lines on this contact radiograph. (d) Photomicrograph corresponding to b (hematoxylin-eosin stain; original magnification, x0.4). Diffuse hemorrhage can be seen in the alveoli. The fine network in a corresponds to the sites of relatively more marked deposition of hemorrhagic materials. The box outlines the region of the lung that is magnified in e. (e) Magnified view of the boxed area in d (hematoxylin-eosin stain; original magnification, x40). Normal interlobular septa (arrows) can be seen. The fine network is owing to the linear deposition of hemorrhagic materials within the airspaces.

View larger version (201K): [in this window] [in a new window]   Figure 4c. Postmortem findings in a 41-year-old woman with alveolar hemorrhage. (a) Thin-section CT scan of the left lower lobe demonstrates the crazy-paving appearance, which is best seen in the region circumscribed by the arrows. (b) Contact radiograph at the same level as in a reveals fine networks. The box encloses the region of the lung that is magnified in c. (c) Magnified view of the boxed area in b. The frames of fine linear networks in a correspond to the irregular lines on this contact radiograph. (d) Photomicrograph corresponding to b (hematoxylin-eosin stain; original magnification, x0.4). Diffuse hemorrhage can be seen in the alveoli. The fine network in a corresponds to the sites of relatively more marked deposition of hemorrhagic materials. The box outlines the region of the lung that is magnified in e. (e) Magnified view of the boxed area in d (hematoxylin-eosin stain; original magnification, x40). Normal interlobular septa (arrows) can be seen. The fine network is owing to the linear deposition of hemorrhagic materials within the airspaces.

View larger version (216K): [in this window] [in a new window]   Figure 4d. Postmortem findings in a 41-year-old woman with alveolar hemorrhage. (a) Thin-section CT scan of the left lower lobe demonstrates the crazy-paving appearance, which is best seen in the region circumscribed by the arrows. (b) Contact radiograph at the same level as in a reveals fine networks. The box encloses the region of the lung that is magnified in c. (c) Magnified view of the boxed area in b. The frames of fine linear networks in a correspond to the irregular lines on this contact radiograph. (d) Photomicrograph corresponding to b (hematoxylin-eosin stain; original magnification, x0.4). Diffuse hemorrhage can be seen in the alveoli. The fine network in a corresponds to the sites of relatively more marked deposition of hemorrhagic materials. The box outlines the region of the lung that is magnified in e. (e) Magnified view of the boxed area in d (hematoxylin-eosin stain; original magnification, x40). Normal interlobular septa (arrows) can be seen. The fine network is owing to the linear deposition of hemorrhagic materials within the airspaces.

View larger version (188K): [in this window] [in a new window]   Figure 4e. Postmortem findings in a 41-year-old woman with alveolar hemorrhage. (a) Thin-section CT scan of the left lower lobe demonstrates the crazy-paving appearance, which is best seen in the region circumscribed by the arrows. (b) Contact radiograph at the same level as in a reveals fine networks. The box encloses the region of the lung that is magnified in c. (c) Magnified view of the boxed area in b. The frames of fine linear networks in a correspond to the irregular lines on this contact radiograph. (d) Photomicrograph corresponding to b (hematoxylin-eosin stain; original magnification, x0.4). Diffuse hemorrhage can be seen in the alveoli. The fine network in a corresponds to the sites of relatively more marked deposition of hemorrhagic materials. The box outlines the region of the lung that is magnified in e. (e) Magnified view of the boxed area in d (hematoxylin-eosin stain; original magnification, x40). Normal interlobular septa (arrows) can be seen. The fine network is owing to the linear deposition of hemorrhagic materials within the airspaces.

View larger version (110K): [in this window] [in a new window]   Figure 5a. Postmortem findings in a 65-year-old woman with diffuse alveolar damage. (a) Thin-section CT scan of the left lobe of the lung demonstrates the crazy-paving appearance (arrows), which is most marked in the left lower region but is also seen in other portions of the left lobe. (b) Contact radiograph at the same level as in a shows fine linear networks. The box corresponds to the region of the lung that is magnified in c. (c) Magnified view of the boxed area in b. The frames of fine linear networks in a correspond to the irregular lines on this contact radiograph. (d) Photomicrograph corresponding to b (hematoxylin-eosin stain; original magnification, x0.4). The boxed area outlines the region of the lung that is magnified in e. (e) Magnified view of the boxed area in d (hematoxylin-eosin stain; original magnification, x40). In both the contact radiographs (b and c) and d, relatively severe fibrotic areas (short arrows) are situated at the border of acini and secondary pulmonary lobules. Centriacinar airspaces (long arrows) and airways (curved arrows) are dilated. The contrast between the periacinar fibrosis and the dilatation of centriacinar airspaces causes the fine networks seen in a. No thickening of interlobular septa was evident histologically.

View larger version (138K): [in this window] [in a new window]   Figure 5b. Postmortem findings in a 65-year-old woman with diffuse alveolar damage. (a) Thin-section CT scan of the left lobe of the lung demonstrates the crazy-paving appearance (arrows), which is most marked in the left lower region but is also seen in other portions of the left lobe. (b) Contact radiograph at the same level as in a shows fine linear networks. The box corresponds to the region of the lung that is magnified in c. (c) Magnified view of the boxed area in b. The frames of fine linear networks in a correspond to the irregular lines on this contact radiograph. (d) Photomicrograph corresponding to b (hematoxylin-eosin stain; original magnification, x0.4). The boxed area outlines the region of the lung that is magnified in e. (e) Magnified view of the boxed area in d (hematoxylin-eosin stain; original magnification, x40). In both the contact radiographs (b and c) and d, relatively severe fibrotic areas (short arrows) are situated at the border of acini and secondary pulmonary lobules. Centriacinar airspaces (long arrows) and airways (curved arrows) are dilated. The contrast between the periacinar fibrosis and the dilatation of centriacinar airspaces causes the fine networks seen in a. No thickening of interlobular septa was evident histologically.

View larger version (132K): [in this window] [in a new window]   Figure 5c. Postmortem findings in a 65-year-old woman with diffuse alveolar damage. (a) Thin-section CT scan of the left lobe of the lung demonstrates the crazy-paving appearance (arrows), which is most marked in the left lower region but is also seen in other portions of the left lobe. (b) Contact radiograph at the same level as in a shows fine linear networks. The box corresponds to the region of the lung that is magnified in c. (c) Magnified view of the boxed area in b. The frames of fine linear networks in a correspond to the irregular lines on this contact radiograph. (d) Photomicrograph corresponding to b (hematoxylin-eosin stain; original magnification, x0.4). The boxed area outlines the region of the lung that is magnified in e. (e) Magnified view of the boxed area in d (hematoxylin-eosin stain; original magnification, x40). In both the contact radiographs (b and c) and d, relatively severe fibrotic areas (short arrows) are situated at the border of acini and secondary pulmonary lobules. Centriacinar airspaces (long arrows) and airways (curved arrows) are dilated. The contrast between the periacinar fibrosis and the dilatation of centriacinar airspaces causes the fine networks seen in a. No thickening of interlobular septa was evident histologically.

View larger version (152K): [in this window] [in a new window]   Figure 5d. Postmortem findings in a 65-year-old woman with diffuse alveolar damage. (a) Thin-section CT scan of the left lobe of the lung demonstrates the crazy-paving appearance (arrows), which is most marked in the left lower region but is also seen in other portions of the left lobe. (b) Contact radiograph at the same level as in a shows fine linear networks. The box corresponds to the region of the lung that is magnified in c. (c) Magnified view of the boxed area in b. The frames of fine linear networks in a correspond to the irregular lines on this contact radiograph. (d) Photomicrograph corresponding to b (hematoxylin-eosin stain; original magnification, x0.4). The boxed area outlines the region of the lung that is magnified in e. (e) Magnified view of the boxed area in d (hematoxylin-eosin stain; original magnification, x40). In both the contact radiographs (b and c) and d, relatively severe fibrotic areas (short arrows) are situated at the border of acini and secondary pulmonary lobules. Centriacinar airspaces (long arrows) and airways (curved arrows) are dilated. The contrast between the periacinar fibrosis and the dilatation of centriacinar airspaces causes the fine networks seen in a. No thickening of interlobular septa was evident histologically.

View larger version (140K): [in this window] [in a new window]   Figure 5e. Postmortem findings in a 65-year-old woman with diffuse alveolar damage. (a) Thin-section CT scan of the left lobe of the lung demonstrates the crazy-paving appearance (arrows), which is most marked in the left lower region but is also seen in other portions of the left lobe. (b) Contact radiograph at the same level as in a shows fine linear networks. The box corresponds to the region of the lung that is magnified in c. (c) Magnified view of the boxed area in b. The frames of fine linear networks in a correspond to the irregular lines on this contact radiograph. (d) Photomicrograph corresponding to b (hematoxylin-eosin stain; original magnification, x0.4). The boxed area outlines the region of the lung that is magnified in e. (e) Magnified view of the boxed area in d (hematoxylin-eosin stain; original magnification, x40). In both the contact radiographs (b and c) and d, relatively severe fibrotic areas (short arrows) are situated at the border of acini and secondary pulmonary lobules. Centriacinar airspaces (long arrows) and airways (curved arrows) are dilated. The contrast between the periacinar fibrosis and the dilatation of centriacinar airspaces causes the fine networks seen in a. No thickening of interlobular septa was evident histologically.

View larger version (105K): [in this window] [in a new window]   Figure 6a. Postmortem findings in a 58-year-old man with cardiogenic edema. (a) Thin-section CT scan demonstrates the crazy-paving appearance (arrows) in the left lower lobe of the lung. (b) Contact radiograph at the same level as in a shows the fine networks. (c) Photomicrograph corresponding to b (hematoxylin-eosin stain; original magnification, x40). Each frame of network in the crazy-paving appearance at thin-section CT histologically was composed of either edematous thickening of interlobular septa (short arrows) or intraalveolar edema (long arrows) distributed along the border unit structures (acini and secondary lobules).

View larger version (148K): [in this window] [in a new window]   Figure 6b. Postmortem findings in a 58-year-old man with cardiogenic edema. (a) Thin-section CT scan demonstrates the crazy-paving appearance (arrows) in the left lower lobe of the lung. (b) Contact radiograph at the same level as in a shows the fine networks. (c) Photomicrograph corresponding to b (hematoxylin-eosin stain; original magnification, x40). Each frame of network in the crazy-paving appearance at thin-section CT histologically was composed of either edematous thickening of interlobular septa (short arrows) or intraalveolar edema (long arrows) distributed along the border unit structures (acini and secondary lobules).

View larger version (143K): [in this window] [in a new window]   Figure 6c. Postmortem findings in a 58-year-old man with cardiogenic edema. (a) Thin-section CT scan demonstrates the crazy-paving appearance (arrows) in the left lower lobe of the lung. (b) Contact radiograph at the same level as in a shows the fine networks. (c) Photomicrograph corresponding to b (hematoxylin-eosin stain; original magnification, x40). Each frame of network in the crazy-paving appearance at thin-section CT histologically was composed of either edematous thickening of interlobular septa (short arrows) or intraalveolar edema (long arrows) distributed along the border unit structures (acini and secondary lobules).

	DISCUSSION

TOP Abstract Introduction MATERIALS AND METHODS RESULTS DISCUSSION References

 
The crazy-paving appearance has been considered to be highly suggestive of alveolar proteinosis (1). However, in the present study, 15 different diseases showed this appearance at thin-section CT. Five diseases were typically airspace diseases, and the remaining 10 were interstitial or "mixed" diseases. Thus, the crazy-paving appearance is a nonspecific pattern. Although alveolar proteinosis involved more pulmonary segments than did the other diseases, the CT scans obtained in patients with ARDS, diffuse alveolar damage superimposed on usual interstitial pneumonia, acute interstitial pneumonia, and drug-induced pneumonitis also showed a widely distributed crazy-paving appearance.

The network of the crazy-paving appearance has been postulated to correspond histologically to thickening of the interlobular septa (1,4). Recently, Kang et al (5) suggested that the network of the crazy-paving appearance in alveolar proteinosis might be due to an accumulation of periodic acid–Schiff–positive material in the airspaces adjacent to the interlobular septa. In the current study, we found that the pattern could be caused by alveolar filling processes, interstitial fibrotic processes, or a combination of interstitial and alveolar processes. The interstitial fibrotic processes in the cases in our study were considered to correspond to the "intralobular interstitial thickening" described by Webb et al (7).

In general, areas of reticular opacity at thin-section CT are believed to be derived from pure interstitial pulmonary processes such as intralobular interstitial thickening and interlobular septal thickening (7–10). In contrast, pure alveolar filling processes are considered to cause airspace consolidation and partial alveolar filling processes at thin-section CT and thereby result in areas of ground-glass opacity (11–15). In our present study, except for the cases of pulmonary edema, the pathologic findings of the networks of the crazy-paving appearance were found to be similar to those of areas of ground-glass opacity seen around the networks; however, there was a slight increase in the severity of the pathologic process at the borders of unit structures such as acini or secondary pulmonary lobules. Therefore, the presence of areas of reticular opacity does not necessarily represent interstitial abnormalities such as interlobular septal thickening or intralobular interstitial thickening.

Our study has several limitations. Although the crazy-paving appearance was originally found in alveolar proteinosis, we were not able to include this disease in the radiologic-pathologic correlation of lung specimens in our in vitro study. This is not surprising, because pulmonary proteinosis is a rare disease with a good prognosis and is often diagnosed by using bronchoalveolar lavage or transbronchial lung biopsy (16). The second limitation of the study is that we were unable to obtain in vivo CT scans in any of the patients in whom we performed postmortem CT. However, the goal of our radiologic-pathologic correlative study was to establish the pathologic basis of the crazy-paving appearance. We believe that the use of postmortem lungs was a reasonable and meaningful means to reach this goal.

In conclusion, the crazy-paving pattern on thin-section CT scans is a nonspecific finding. The networks in the areas of the crazy-paving appearance are not necessarily due to thickening of interlobular septa or the presence of intralobular fibrosis. The appearance can also be caused purely by airspace disease, in which case the appearance is owing to linear deposition of material within the airspaces. The frames of the networks are situated at the borders of unit structures such as acini or pulmonary secondary lobules. Although the crazy-paving pattern is nonspecific, the various disease entities that cause this appearance can often be distinguished by their clinical findings. For example, the clinical presentation of patients with alveolar proteinosis is markedly different from that of patients with ARDS or drug-induced pneumonitis.

	Footnotes

 
Abbreviation: ARDS = adult respiratory distress syndrome

Author contributions: Guarantors of integrity of entire study, T.J., H.I.; study concepts and design, T.J., H.I.; definition of intellectual content, H.I., N.L.M.; literature research, T.J., K.I.; clinical studies, K.I., J.I., M.A.; experimental studies, T.J., H.I., T.N.; data acquisition, T.J., K.I., T.N.; data analysis, T.J., H.I., T.N.; statistical analysis, T.J., K.I.; manuscript preparation, T.J., N.L.M.; manuscript editing and review, N.L.M., H.I., H.N.

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TOP Abstract Introduction MATERIALS AND METHODS RESULTS DISCUSSION References

 

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