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Original Report |
1
Department of Radiology, Duke University Medical Center, Box 3808, Durham, NC
27710.
2
Department of Radiology, Hanyang University Hospital, 17 Haengdang-dong,
Sungdong-Ku, Seoul 1333-792, Korea.
3
Department of Radiology, Mayo Medical Institutions, 200 First St. S.E.,
Rochester, MN 55905.
4
Department of Medicine, Duke University Medical Center, Durham, NC
27710.
Received May 24, 2001;
accepted after revision July 5, 2001.
Address correspondence to H. P. McAdams.
Abstract
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CONCLUSION. The most common CT manifestations were increased attenuation and smooth thickening of airway walls. Tracheal or bronchial stenosis was less common. Airway collapse and lobar air trapping were seen in half of patients examined with expiratory CT.
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Respiratory tract involvement, though uncommon at presentation, occurs in up to 50% of patients with relapsing polychondritis sometime during the course of their illness [1]. Airway involvement is a poor prognostic sign and is the leading cause of death in affected patients [1]. Because of the morbidity and potential mortality of respiratory tract involvement, patients with relapsing polychondritis may be referred for CT of the lower respiratory tract [1, 3].
The CT findings of lower respiratory tract involvement by relapsing polychondritis have been previously reported in case reports or small series [3,4,5,6,7,8]. The purpose of this study was to report the CT findings of lower respiratory tract involvement in a larger group of patients with relapsing polychondritis.
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Because of the retrospective and multiinstitutional nature of the study, CT technique varied. Twelve scans were obtained on an electron-beam CT scanner with 6-mm collimation and 6-mm slice interval. Three scans were obtained on a single-slice helical CT scanner with collimation of 3-mm (n = 1) or 5-mm (n = 2); pitch of 2, and reconstruction interval of 3-mm (n = 1) or 5-mm (n = 2). All examinations were performed from the thoracic inlet to the diaphragm at end inspiration, without IV contrast material. Images obtained at soft-tissue window settings were available in all patients; images obtained at lung window settings were available in 11 patients. Six patients also had CT performed at end expiration.
Three radiologists simultaneously reviewed all CT images; findings were recorded by consensus. We reviewed CT scans, noting airway wall attenuation and thickness, airway narrowing, air trapping, and bronchiectasis. Tracheal or bronchial wall attenuation was compared with mediastinal soft tissue and recorded as either normal or increased. Airway wall thickness was assessed by comparing the thickness of the involved wall with that of proximal uninvolved airways. Wall thickness was recorded as either normal or increased; when increased, it was recorded as smooth or nodular and as circumferential or sparing the posterior membranous wall. Tracheal or bronchial narrowing was assessed by comparing the diameter of the involved segment with that of a corresponding uninvolved segment. Narrowing was recorded as present when more than 25% luminal diameter narrowing was present. Tracheal wall thickening or narrowing was recorded as focal if one third or less of the intrathoracic trachea was involved and as diffuse if more than one third was involved. Bronchial wall thickening or airway narrowing was recorded as focal if only lobar or segmental bronchus was involved and as diffuse if more than one lobar or segmental bronchus was involved. In all cases (even those recorded as diffuse), a portion of normal airway wall was always visible on CT for comparison.
Air trapping and airway collapse at end expiration was assessed only in the six patients with expiratory CT scans. Air trapping was defined visually when a segment or lobe failed to increase in attenuation appropriately at end expiration. When present, location and extent (segmental, lobar, or whole lung) were recorded. Air trapping involving less than a full bronchopulmonary segment was not recorded. Airway collapse was defined as present when the luminal diameter on expiration was less than 50% of the diameter on inspiration; when present, site of airway collapse was also noted. Bronchiectasis was assessed in the 11 patients with lung window settings available. Bronchiectasis was recorded as present or absent, using published criteria [9]; when present, extent (segmental, lobar, or whole lung) and location were recorded.
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Tracheal walls were thickened in 11 (73%) of 15 patients; wall thickening was characterized as smooth and diffuse in 10 (66%) of 15 patients (Figs. 1,2,3A,3B,4) and as focal and nodular in one (7%) (Fig. 5). Bronchial walls were thickened in 12 (80%) of 15 patients; wall thickening was characterized as smooth and diffuse in 11 (73%) of 15 patients and as focal and nodular in one (7%). Both tracheal and bronchial walls were thickened in 11 (73%) of 15 patients; one patient had bronchial wall thickening without tracheal involvement. Wall thickening typically spared the posterior membranous portion of the airway.
Tracheal narrowing was present in five (33%) of 15 patients. Three (20%) of 15 patients had focal subglottic tracheal stenosis (Fig. 6A,6B). Two (13%) of 15 patients had diffuse tracheal narrowing and narrowing of the main bronchi (Fig. 7A,7B). Two of these patients also had noncontiguous bronchial narrowing. The remaining patient with focal subglottic stenosis had no evidence of bronchial involvement.
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CT performed at end expiration was available in six patients and showed no evidence of air trapping in three (50%). Lobar air trapping was noted in the remaining three patients (50%), one of whom also had segmental air trapping. Analysis of the central airways in these three patients showed evidence of complete collapse of the left main bronchus at end expiration in the first patient (Fig. 6A,6B), complete collapse of both the left main bronchus and the right lower lobe bronchus in the second patient, and complete collapse of the left lower lobe bronchus and the superior segment of the right lower lobe bronchus in the third patient.
Two (18%) of the 11 patients who had lung window setting images had cylindric right upper lobe bronchiectasis, and a third patient had cylindric bronchiectasis involving the right upper lobe, middle lobe, and left upper lobe. Two of the three patients with bronchiectasis had no appreciable airway stenosis, whereas the third had both tracheal and bilateral bronchial stenoses.
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The second most common CT finding in our series was increased airway wall thickness, seen in 12 (80%) of 15 patients. Wall thickening was typically smooth and diffuse and spared the posterior membranous portion of the airway. This incidence and appearance of increased airway wall thickness were similar to the 78% reported by Tillie-Leblond et al. [3]. Luminal narrowing of the trachea or bronchi, perhaps surprisingly, was a less common CT feature in our series, seen in five (33%) and seven (47%) of 15 patients, respectively. Whereas diffuse or focal tracheal narrowing occurred with equal frequency, bronchial narrowing was uniformly diffuse. Overall, most patients with airway stenoses had involvement of both the trachea and main bronchi. The incidence of airway stenosis in our series was less than the 89% reported in the series of Tillie-Leblond et al. This discrepancy may be partly due to differences in CT criteria used to define stenosis. Tillie-Leblond et al. defined stenosis as present when any degree of luminal diameter narrowing was noted at CT; we recorded stenosis as present only when luminal diameter narrowing greater than 25% (compared with a normal segment) was observed.
The differential diagnosis of airway wall thickening or stenosis includes tracheobronchial amyloidosis, tracheopathia osteochondroplastica, Wegener's granulomatosis, sarcoidosis, histoplasmosis, tuberculosis, and rhinoscleroma [11, 12]. Tracheobronchial amyloidosis can cause focal or diffuse airway wall thickening but usually affects the airway circumferentially [13, 14]; relapsing polychondritis, on the other hand, affects only the cartilaginous portion of the airway, with the posterior membranous portion of the airway wall usually spared. Tracheopathia osteochondroplastica manifests with multiple calcified tracheobronchial nodules that grow along the cartilaginous walls of the trachea and main bronchi; diffuse narrowing is not a typical feature of this entity [15]. In theory, nodular thickening due to relapsing polychondritis might be difficult to distinguish from tracheopathia osteochondroplastica. However, nodular thickening was an uncommon manifestation of relapsing polychondritis in our series, and most affected patients have other clinical stigmata suggestive of the correct diagnosis. Wegener's granulomatosis, sarcoidosis, histoplasmosis, and tuberculosis can also result in focal or diffuse airway wall thickening or narrowing. However, these diseases typically have other radiologic or clinical features that suggest the correct diagnosis.
We saw cylindric bronchiectasis in only three (27%) of 11 of patients in whom lung window settings were available for review. Peripheral bronchiectasis is an infrequently reported CT finding in patients with relapsing polychondritis [7]. Whether bronchiectasis is caused by cartilage inflammation or is an indirect result of recurrent pneumonia is not clear [7]. All patients with bronchiectasis in our series had a history of prior pneumonia.
Air trapping and airway wall collapse at end expiration were seen in three (50%) of six patients who had expiratory CT in our study. These findings are likely due to loss of cartilaginous support of airway walls [16] and are considered a key feature of the disease [3]. Patients having these findings may be more symptomatic than those without airway collapse at end expiration, may more frequently manifest recurrent pneumonia, and may ultimately require airway stent placement for relief of symptoms [16,17,18]. More important, expiratory CT provides this information without the associated risks of fiberoptic bronchoscopy, which may exacerbate airway inflammation [3]. For these reasons, we believe that expiratory CT should be part of the CT evaluation of any patient with relapsing polychondritis and known or suspected lower respiratory tract involvement.
CT is an important tool in the evaluation of patients with known or suspected relapsing polychondritis. In patients with known disease, CT is useful for confirming intrathoracic involvement and for routine follow-up to assess progression of disease. Tillie-Leblond et al. [3] reported that CT was better than fiberoptic bronchoscopy in identifying airway stenoses and tracheal wall alterations in the early stages of disease. In patients without a known diagnosis of relapsing polychondritis, the finding of diffuse increased airway wall attenuation and thickening at CT, with or without stenosis, suggests the diagnosis and should prompt a careful rheumatologic assessment [1, 2].
In summary, the most common CT manifestations of lower respiratory tract involvement by relapsing polychondritis in our series were increased airway wall attenuation and smooth diffuse airway wall thickening that notably spared the posterior membranous portion of the airway. Both the tracheal and bronchial walls were typically affected. Tracheal or bronchial stenosis was much less common. Airway collapse and lobar air trapping were seen in half of patients examined with expiratory CT.
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