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The purpose of this study was to evaluate the high-resolution computed tomographic (HRCT) findings of five adult patients (either immunocompromised or immunocompetent) with herpes simplex virus (HSV) pneumonia. We retrospectively assessed HRCT images of 5 patients (all male patients, age range 39-70 years; mean 62 years) with HSV pneumonia. The specific pathological findings that allowed for a definite diagnosis of HSV pneumonia included the presence of intranuclear inclusion bodies on haematoxylin and eosin staining, or positive immunohistochemical staining. High-resolution CT scans (HiSpeed Advantage or LightSpeed QX/i, GE Healthcare) using 1- or 1.25-mm collimation at 10-mm intervals without intravenous contrast medium injection were assessed, in particular for the presence and distribution of parenchymal abnormalities including ground-glass attenuation, airspace consolidation, nodules and interlobular septal thickening. In two patients, pathological specimens were obtained from open lung biopsy or bronchoscopic biopsy, and were correlated with HRCT findings. Three HRCT patterns of pulmonary abnormalities were identified in our series of HSV pneumonia: predominant areas of diffuse or multifocal ground-glass attenuation, predominant areas of multifocal peribronchial consolidations, and a mixed pattern of both. Histopathologically, areas of ground-glass attenuation seen on HRCT corresponded to diffuse alveolar damage in one patient who underwent open lung biopsy. No specific differences in HRCT findings were seen between the immunocompromised and the immunocompetent patients. In patients suspected of having an acute lower respiratory infection, whether immunocompromised or immunocompetent, a possibility of HSV pneumonia can be included in differential diagnoses when diffuse or multifocal areas of ground-glass attenuation and/or consolidations are seen on HRCT.

Giant fibrovascular polyp of the esophagus is a rare intraluminal benign tumor that is covered with normal esophageal mucosa, which consists of fibrous tissue, adipose tissue, and vascular structures. We report a case of a giant fibrovascular polyp of the esophagus in which feeding vessels were well visualized within the stalk of the mass at contrast-enhanced helical computed tomography.

The purpose of this study was to describe the CT findings of focal organizing pneumonia and to compare the findings with pathology. CT findings of histologically proven focal organizing pneumonias in 26 consecutive patients were analyzed. In 17 patients who had undergone surgical resections, the findings were correlated with pathology. Focal organizing pneumonias appeared as a nodule (n= 13) or a mass (n=13), ranging from 9 mm to 66 mm in diameter. Ground-glass opacity was seen in 6/13 (46%) nodules and 6.5/13 (50%) masses (k=.48) with an extent ranging from 5% to 75% (mean, 16%). In 4/26 (15%) patients, the extent was more than 50% of the lesion. They showed smooth (n=4), lobulated (n=8), spiculated (n=1), or lobulated and spiculated margin (n=13). On correlative analysis, nodule or mass on CT consisted histologically of intraalveolar exudate or microabscess, chronic inflammatory cell infiltration, fibrotic nodules, and polypoid granulation tissue in the alveolar or bronchiolar spaces. Ground-glass opacity consisted of interstitial fibrosis and chronic inflammatory cell infiltration and intraalveolar polypoid granulation tissue. Focal organizing pneumonia may simulate a lung cancer with variable appearances on CT and the findings reflect underlying histopathology of the disease.

The purpose of this study was to describe the clinical, computed tomographic (CT), and pathologic findings of large cell neuroendocrine carcinoma (LCNEC) of the lung. CT and pathologic findings as well as clinical features of surgically proven LCNEC of the lung were reviewed retrospectively in 11 consecutive patients (eight men and three women; mean age, 63 years; range, 44-77 years). Chest CT showed peripheral mass or nodule (n = 8) and central mass with distal atelectasis (n = 3). Six tumors were accompanied by mediastinal (n = 3) and hilar (n = 3) lymph node enlargement at CT. On pathologic examination, all resected tumors showed necrosis of variable extent (mean: 38%, range; 10-70%). The areas of intrinsic lipoid pneumonia and tumor emboli in two patients appeared at CT as areas of ground-glass opacity surrounding the tumor. Mediastinal nodal metastases were seen in three (27%) patients. Pathologic staging of 11 patients was IB in six, IIA in one, IIB in one, IIIA in two, and IIIB in one. Follow-up data showed extrathoracic metastases in four patients at mean follow-up period of 15 months. One patient died of distant metastasis 5 months after the surgery. CT findings of LCNEC of the lung are nonspecific and similar to those of other non-small cell lung cancers and extrathoracic metastasis is seen in approximately one third of the patients with follow-up study.

Purpose: The aim of our study was to evaluate the frequency of the crescent sign on follow-up radiographs in patients with invasive pulmonary aspergillosis, correlated with initial CT and clinical findings., Method: Retrospective analysis of serial chest radiographs was performed to see the frequency of the crescent sign in 21 consecutive patients with pathologically proved invasive pulmonary aspergillosis. The appearance of the crescent sign was correlated with the pattern of parenchymal lesions on initial CT scans, the presence and duration of neutropenia, and underlying diseases., Results: The crescent sign was seen in 10 of 21 patients (48%) on follow-up radiographic examinations. It was seen in patients with initially large [consolidation or mass; 9/11 (82%) patients] rather than small [nodule(s); 1/10 (10%) patients] parenchymal lesions (p = 0.002) on CT. The sign appeared in 7 of 17 (41%) patients with neutropenia 1-10 days after recovery from neutropenia. It appeared in three of four patients (75%) without neutropenia 4--8 days after treatment with amphotericin B. The appearance was not related to the duration (32 days in patients with crescent sign and 17 days without sign) of the neutropenic period (p > 0.05). The sign was seen in 8 of 15 (53%) patients with acute myelogenous leukemia and 2 of 6 (33%) patients with other diseases (p > 0.05)., Conclusion: The crescent sign appears in about half of patients with invasive pulmonary aspergillosis with recovery from neutropenia, especially when the initial lesion is a consolidation or mass on CT scans.

Objective: The purpose of our study was to describe and compare the CT and pathologic findings of atypical thymoma and thymic carcinoma., Materials and Methods: Twenty-seven consecutive patients (14 men, 13 women ranging in age from 22 to 77 years [mean age, 52 years]) with pathologically proven atypical thymoma (n = 9) and thymic carcinoma (n = 18) constituted the study population. The chest CT findings in each of the 27 patients were reviewed retrospectively in consensus by two chest radiologists. These findings were correlated with pathologic findings., Results: The tumors were located in the anterior mediastinum, and most tumors had a lobulated margin (24/27, 89%). Atypical thymomas were significantly smaller (mean, 4.7 cm) than thymic carcinomas (mean, 7.2 cm) (p = 0.041) on CT. The findings of invasion of the great vessels, lymph node enlargement, extrathymic metastases, and phrenic nerve palsy were seen only in patients with thymic carcinoma. The frequencies of necrosis, intratumoral calcification, pleural effusion, pleural implants, pericardial effusion, and obliteration of the mediastinal fat plane were not significantly different between atypical thymomas and thymic carcinomas (p > 0.05). Various histologic subtypes were included in thymic carcinoma. The tumor necrosis and calcification seen on CT were confirmed at pathologic examination., Conclusion: When a large thymic tumor appears with invasion of the great vessels, lymph node enlargement, phrenic nerve palsy, or extrathymic metastases on CT, thymic carcinoma rather than atypical thymoma should be considered.

We report the imaging findings in two patients with proliferating trichilemmal tumors. In the first patient, the tumor arose on the lower lip, a very unusual location for this type of tumor, and showed malignant transformation with metastasis to a regional lymph node. It was seen as a poorly marginated soft-tissue mass with isointense signal on T1-weighted MR images and hyperintense signal on T2-weighted images. Large areas of high signal intensity caused by necrosis were also found within the tumor on T2-weighted images. After i.v. administration of contrast material, the mass showed significant enhancement, with considerable portions remaining unenhanced. In the second patient, the tumor originated from a preexisting trichilemmal cyst and occurred in the hair-bearing area of the posterior part of the neck. CT scans showed a well-encapsulated cystic mass that contained multiple speckled calcifications in a wall of variable thickness. There were several foci of smooth soft-tissue elevations from the inner wall of the mass, which corresponded histologically to proliferating portions of trichilemmal cyst.

Typical CT findings of active postprimary pulmonary tuberculosis include centrilobular nodules and branching linear structures (tree-in-bud appearance), lobular consolidation, cavitation, and bronchial wall thickening. The CT findings of inactive pulmonary tuberculosis include calcified nodules or consolidation, irregular linear opacity, parenchymal bands, and pericicatricial emphysema. The typical appearance of primary tuberculosis on CT scans is homogeneous, dense, well-defined segmental or lobar consolidation with enlargement of lymph nodes in the hilum or the mediastinum. Miliary nodules may be seen in primary and postprimary tuberculosis. On CT, tuberculomas appear as a nodule with surrounding satellite nodules and internal cavitation on CT. Atypical radiologic manifestations of tuberculosis, encountered in as many as one third of the cases of adult-onset tuberculosis, are single or multiple nodules or masses, basilar infiltrates, miliary tuberculosis with diffuse bilateral areas of ground-glass opacity, and reversible multiple cysts. Underlying histopathologic findings of typical and atypical CT findings of tuberculosis are caseating granulomas or pneumonia in the active phase and fibrosis and dystrophic calcification in the inactive phase.

Purpose: To determine the frequency of extrathoracic metastases in T1 non-small-cell lung cancer., Method: Ninety patients with T1 lung cancer identified on CT were included. Extrathoracic metastases were evaluated at the time of initial diagnosis and during a 1-year follow-up study. The frequency of metastases was compared in terms of cell type (squamous or nonsquamous), size (<2 cm or >2 cm), and the initial CT findings of the tumor., Results: Extrathoracic metastases were identified in 12 (13%) of 90 patients at the time of diagnosis and in 10 patients at the 1-year follow-up study (total, 22 of 90 [24%] patients). Tumors with ground-glass opacity on CT were associated with a significantly lower prevalence of metastases (p = 0.042). The area of ground-glass opacity was seen in 1 of 13 (85%) patients with bronchioloalveolar carcinoma and in 12 of 53 (23%) patients with adenocarcinoma other than bronchioloalveolar carcinoma (p < 0.001). There was no significant difference in the prevalence of metastases between squamous and nonsquamous cell carcinoma, between tumors smaller than 2 cm (n = 17) and larger than 2 cm in diameter (n = 73) and between tumors with or without mediastinal nodal metastases (p>0.05)., Conclusion: Extrathoracic metastases were apparent at the initial examination in 13% of patients and at the 1-year follow-up examination in 11% of patients. The prevalence is significantly lower in tumors with ground-glass opacity.

Rationale and Objectives: The aim of our study was to assess the image quality, radiation dose, and clinical applicability of low-dose, volumetric helical CT in the evaluation of bronchiectasis., Methods: Volumetric helical CT scans (120 kVp, 3-mm collimation, pitch of 2, and reconstruction interval of 2 mm) were obtained through the thorax at four levels of tube current: 150, 100, 70, and 40 mA. There were a total of 12 patients who underwent CT scan either for suspected bronchiectasis or for lung cancer screening, with three patients allocated to each current level. Five radiologists assessed and compared image quality of the helical CT scans obtained at the various exposure levels. Radiation doses of helical CT performed with four different current settings and of high-resolution CT (120 kVp, 170 mA, 1-mm collimation, and 10-mm intervals) were measured. The diagnostic usefulness of the 40-mA helical CT images was compared with that of high-resolution CT by two observers in 52 patients with known or suspected airway diseases., Results: With helical CT, there was no significant difference in image quality among the four different levels of current (P > 0.05). Radiation doses associated with the 40-, 70-, 100-, and 150-mA helical techniques were 3.21 mGy (range, 3.02-3.57), 4.81 mGy (range, 3.89-5.93), 6.46 mGy (range, 6.01-7.31), and 10.4 mGy (range, 8.93-12.1), respectively, whereas that of high-resolution CT was 2.17 mGy (range, 1.90-2.67). Of 52 patients, 44.5 and 47 patients (the mean of positive interpretations by the five observers) were diagnosed with bronchiectasis at high-resolution and low-dose helical CT, respectively. Of 928 segments, bronchiectasis was seen in 152.5 segments on high-resolution CT and in 193.5 segments on helical CT. The interobserver agreement (k-values) was acceptable for both techniques., Conclusions: With acceptable images and similar radiation dose, low-dose volumetric helical CT at 40 mA may offer more information than does high-resolution CT in the evaluation of bronchiectasis.

Objective: To describe the HRCT findings of cytomegalovirus (CMV) pneumonia in non-AIDS immunocompromised patients, Materials and Methods: This retrospective study involved the ten all non-AIDS immunocompromised patients with biopsy-proven CMV pneumonia and without other pulmonary infection encountered at our Medical Center between January 1997 and May 1999. HRCT scans were retrospectively analysed by two chest radiologists and decisions regarding the findings were reached by consensus., Results: The most frequent CT pattern was ground-glass opacity, seen in all patients, with bilateral patchy (n = 8) and diffuse (n = 2) distribution. Other findings included poorly-defined small nodules (n = 9) and consolidation (n = 7). There was no zonal predominance. The small nodules, bilateral in eight cases and unilateral in one, were all located in the centrilobular region. Consolidation (n = 7), with patchy distribution, was bilateral in five of seven patients (71%). Pleural effusion and bilateral areas of thickened interlobular septa were seen in six patients (60%)., Conclusion: CMV pneumonia in non-AIDS immunocompromised patients appears on HRCT scans as bilateral mixed areas of ground-glass opacity, poorly defined centrilobular small nodules, and consolidation. Interlobular septal thickening and pleural effusion are frequently associated.

Objective: We describe the chest CT and pathologic findings of semiinvasive pulmonary aspergillosis in six patients., Conclusion: Semiinvasive pulmonary aspergillosis should be considered in the mildly immunocompromised patient with CT findings that reveal persistent parenchymal abnormalities. Patterns include consolidation and mass.

Purpose: The purpose of this work was to describe the CT findings of pathologically confirmed bronchus-associated lymphoid tissue (BALT) lymphoma in 10 patients., Method: The CT examinations of 10 patients with pathologically proven BALT lymphoma were reviewed retrospectively by two radiologists. Evaluated findings included number and distribution of lesions. We also assessed other CT findings such as presence of airspace consolidation, nodules, ground-glass attenuation, bubble-like radiolucencies, air bronchogram, bronchial dilatation, and lymphadenopathy., Results: Pulmonary lesions were revealed as airspace consolidation in six patients (60%) and nodule(s) in six (60%). Multiplicity of disease was seen in seven patients (70%) and bilateral lung lesions in six (60%). Areas of ground-glass attenuation were seen in seven patients (70%). Bubble-like radiolucencies were present in five patients (50%) and air bronchogram in nine (90%). Findings of bronchial dilatation and lymphadenopathy were seen in three patients (30%)., Conclusion: BALT lymphomas usually appear as airspace consolidation or nodules with air bronchogram or adjacent ground-glass attenuation at CT. These findings are similar to previous descriptions of pseudolymphomas. Multiple bilateral lesions are common in BALT lymphoma. Bubble-like radiolucencies have not been described previously and can be an additional finding of BALT lymphoma.

Objective: We assessed serial changes in high-resolution CT findings and pulmonary function in patients with nonspecific interstitial pneumonia with fibrosis., Materials and Methods: Serial high-resolution CT findings in 13 patients with biopsy-proven nonspecific interstitial pneumonia with fibrosis (mean follow-up period, 11 months) and pulmonary function tests (mean follow-up period, 11 months) were retrospectively analyzed. On CT, the presence and extent of ground-glass opacity, irregular linear opacity, honeycombing, and consolidation were assessed., Results: On initial CT, all patients had areas of ground-glass opacity (mean +/- SD, 21.6% +/-14.4) and irregular linear opacity (5.0% +/- 5.2). The areas of ground-glass opacity decreased significantly on follow-up CT (13.5% +/- 10.5, p = .003). The areas of irregular linear opacity decreased slightly (4.2% +/- 5.2, p > .05). Initial forced vital capacity (69.4% +/- 16.0) improved significantly on follow-up examination (83.9% +/- 16.5) (p = .003). The decrease in the extent of ground-glass opacity on CT correlated significantly with changes in forced vital capacity (r = -.702, p = .007) and diffusing capacity for carbon monoxide (r = - .597, p = .031)., Conclusion: In patients with nonspecific interstitial pneumonia with fibrosis, areas of ground-glass opacity decrease on follow-up high-resolution CT, and the extent of decrease correlates significantly with that of functional improvement.

Purpose: To determine the radiographic and computed tomographic (CT) findings and clinical features of mucoepidermoid carcinoma of the tracheobronchial tree., Materials and Methods: Chest radiographic and CT findings and clinical features of 12 histopathologically proved mucoepidermoid carcinomas in 12 consecutive patients (five male, seven female; age range, 9-72 years; mean age, 36 years) were reviewed retrospectively., Results: The tumors were located at the distal trachea (n = 1) or at a main (n = 2), lobar (n = 1), or segmental (n = 8) bronchus. On chest radiographs, the tumors appeared as central masses with post-obstructive pneumonia or peripheral atelectasis in four patients and as solitary pulmonary or endotracheobronchial nodules in eight. At CT, the tumors were all smoothly oval (n = 6) or lobulated (n = 6) in shape (ranging 9-40 mm in diameter), adapting to the branching features of the airways. Punctate calcification within the tumor was seen in six patients. Neither metastasis nor recurrence was seen after the surgical resection (follow-up of 8-103 months; mean, 30 months)., Conclusion: Mucoepidermoid carcinoma of the tracheobronchial tree, usually located in a segmental bronchus, appears at CT as a smoothly oval or lobulated airway mass. It adapts to the branching features of the airways.

Neurilemomas and neurofibromas appear as round soft tissue masses at CT. Variable enhancement with either homogeneity or heterogeneity is seen in neurilemomas. Attenuation of the tumors on enhanced CT depends on histology: the extent of Antoni A or B tissue and the amount of myxoid or cystic degeneration or hemorrhage. Neurofibromas are usually homogeneous low attenuation lesions on unenhanced CT. They show homogeneous enhancement or early central blush on enhanced scan. The extent of enhancement depends on the proportions of tumor components: nerve sheath cells, collagen bundles, and areas of myxoid degeneration. Malignant nerve sheath tumors show variable attenuation. Bony destruction, pleural effusion, and metastatic pulmonary nodules may also occur. Ganglioneuromas appear as oblong homogeneous low attenuation lesions on both enhanced and unenhanced CT. This low attenuation is due to their pathologic components, with an abundant amount of myxoid matrices and a relatively small amount of ganglion cells. Neuroblastomas appear as aggressive soft tissue lesions with calcification. Ganglioneuroblastomas may appear with features in between those of ganglioneuromas and neuroblastomas. The typical location of the posterior mediastinum or the aortopulmonary window and high enhancement with administration of contrast medium at CT suggest the diagnosis of paragangliomas.

Purpose: The purpose of our study was to compare the findings seen on HRCT with those from pathologic examination in patients with diffuse micronodular lung disease (DMLD)., Method: Forty consecutive patients with biopsy-proven DMLD (each nodule being <5 mm in diameter and occupying more than two-thirds of lung volume on chest radiograph) were included. High resolution CT (HRCT) scans were analyzed with particular attention to the location of nodules in and around the secondary pulmonary lobule (centrilobular, perilymphatic, and random) and the zonal distribution. The findings were compared to pathology., Results: CT scans showed centrilobular nodules in the patients with diffuse panbronchiolitis (n = 4), infectious bronchiolitis [n = 4; Hemophilus influenzae (n = 3) and Mycoplasma pneumoniae (n = 1)], hypersensitivity pneumonia (n = 3), bronchogenic disseminated tuberculosis (n = 3), pneumoconiosis (n = 1), primary lymphoma of the lung (n = 1), and foreign body-induced necrotizing vasculitis (n = 1). They demonstrated perilymphatic nodules in the patients with pneumoconiosis (n = 5), sarcoidosis (n = 2), and amyloidosis (n = 2). They demonstrated micronodules of random distribution in the patients with miliary tuberculosis (n = 9) and pulmonary metastasis (n = 5). Upper and middle zonal predominance was seen in two of two patients with sarcoidosis and in two of six patients with pneumoconiosis. The CT location of nodules in the secondary pulmonary lobule represented the location and nature of the lesion on pathologic examination., Conclusion: By showing the distribution of micronodules in and around the secondary pulmonary lobule, HRCT enables the narrowing of the differential diagnosis of DMLD. CT findings reflect gross morphologic features of pathologic examination.

Purpose: To evaluate prospectively the usefulness of thin-section computed tomography (CT) in the prediction of biopsy-proved invasive pulmonary aspergillosis in patients with neutropenia., Materials and Methods: In 11 consecutively seen neutropenic patients, 12 open-lung biopsies were performed prospectively for suspected angioinvasive (n = 10) or airway-invasive (n = 2) pulmonary aspergillosis. Thin-section CT findings in the patients with angioinvasive pulmonary aspergillosis were reviewed, and the findings were compared with those of other diseases., Results: Five of 12 biopsy specimens were positive for angioinvasive pulmonary aspergillosis; none was positive for airway-invasive pulmonary aspergillosis. In five (50%) of 10 cases, suspicion of angioinvasive pulmonary aspergillosis proved to be correct. The most common CT findings were segmental areas of consolidation plus ground-glass attenuation (four of five cases [80%]) and at least one nodule surrounded by a halo (two of five cases [40%]). Segmental areas of consolidation plus ground-glass attenuation were seen as isolated findings in three and mixed findings with nodules that have a surrounding halo in one case. In two patients, at least one nodule with a halo was an isolated finding in one patient and a mixed finding in one patient. Mucormycosis, organizing pneumonia, and pulmonary hemorrhage produced similar findings., Conclusion: At thin-section CT, segmental areas of consolidation plus ground-glass attenuation or at least one nodule with the halo sign were seen in patients with invasive pulmonary aspergillosis. The findings were nonspecific, however, and can be seen in neutropenic patients with mucormycosis, organizing pneumonia, or pulmonary hemorrhage.

Purpose: To assess the role of spiral computed tomographic angiography (CTA) in renal artery evaluation., Materials and Methods: The authors prospectively performed both CTA and intraarterial digital subtraction angiography (IA-DSA) in 50 consecutive patients (24 males and 26 females) who ranged between 9 and 77 years old (mean, 39.3 years), in whom renovascular hypertension was suspected (n = 32) or who were potential renal donors (n = 18). The major scan parameters of CTA were 3-mm collimation, 4-5-mm/sec table speed, and 2-mm reconstruction interval. Both CTA and IA-DSA images were blindly interpreted by two radiologists with respect to the number of accessory renal arteries and the location and severity of renal artery stenosis., Results: CTA demonstrated 27 of 28 accessory renal arteries (detection rate = 96%). For the detection of stenoses greater than 50% (37 of 127 renal arteries, at 40 sites), the sensitivity and specificity of CTA were 90% and 97%, respectively. For the detection of stenoses greater than 50% in the main renal arteries (32 of 99 main renal arteries, at 32 sites), the sensitivity and specificity of CTA were 100% and 97%, respectively., Conclusion: CTA is a reliable and accurate screening modality for the evaluation of renal arteries in patients with suspected renovascular hypertension and in potential renal donors.

Objective: The purpose of our study was to determine the diagnostic accuracy of computed radiography of the chest in the detection of paraesophageal varices and to describe the characteristic radiographic findings., Subjects and Methods: From June 1995 through May 1997, in 100 consecutive patients, portal hypertension was diagnosed through both clinical and radiologic evidence. Computed radiographs of the chest and hepatic helical CT scans of these 100 patients with portal hypertension and 20 control subjects were analyzed by two chest radiologists and one abdominal radiologist, who were not aware of the results of the other study., Results: On CT, paraesophageal varices were seen in 38 (38%) of 100 patients with portal hypertension. Overall, the sensitivity, specificity, and accuracy of chest computed radiography in the detection of paraesophageal varices were 53% (20/38), 90% (74/82), and 78% (94/120), respectively. In the patients with paraesophageal varices, splenomegaly (29/38, 76%), lateral displacement or obliteration of the inferior portion of the azygoesophageal interface (18/38, 47%), obliteration or nodularity of the inferior portion of the descending thoracic aorta interface (9/38, 24%), lateral displacement of the right inferior paraspinal interface (6/38, 16%), lateral displacement of the left inferior paraspinal interface (4/38, 11%), and varices in the left inferior pulmonary ligament (1/38, 3%) were seen on chest computed radiographs. Paraesophageal varices smaller than the diameter of the descending thoracic aorta (usually <2.5 cm) were not detected., Conclusion: Although chest computed radiography is only moderately sensitive for paraesophageal varices, the findings are characteristic when well developed, with a limited differential diagnosis. Splenomegaly, whether detected clinically or radiographically, eliminates most other diagnostic possibilities.

The most common high resolution CT (HRCT) findings of bronchiolitis are centrilobular nodules and branching linear structures in the secondary pulmonary lobules or areas of air trapping. These findings can be helpful in suggesting the presence of bronchiolitis. However, they are nonspecific because there are overlapping features among various kinds of bronchiolitis. Bronchiolar or peribronchiolar inflammation appears as centrilobular nodule, while bronchiolectasis filled with secretions manifests with branching linear structure on HRCT. Air trapping is secondary to bronchiolitis. Proliferative bronchiolitis with the findings of patchy areas of consolidation or ground-glass opacity can be distinguished from other bronchiolitis. Mineral dust-induced bronchiolitis and peribronchiolar lesions in sarcoidosis present with perilymphatic (centrilobular plus perilobular) micronodules in the secondary pulmonary lobule. Bronchiolitis in hypersensitivity pneumonia appears with poorly defined centrilobular nodules, associated with ground-glass opacity and air trapping.