Received: 18 July 2001 / Accepted: 25 September 2001 / Published online: 13 November 2001© Springer-Verlag 2001

Abstract Organizing pneumonia isa non-specific response to variousforms of lung injury and is thepathological hallmark of the distinctclinical entity termed cryptogenic organizing pneumonia. The typicalimaging features of this syndromehave been widely documented andconsist of patchy air-space consoli-dation, often subpleural, with orwithout ground-glass opacities. Thepurpose of this article is to highlight

the less familiar imaging patterns of organizing pneumonia which in-clude focal organizing pneumonia, avariety of nodular patterns, a bron-chocentric distribution, band-likeopacities, a perilobular pattern and aprogressive fibrotic form of organiz-ing pneumonia.

Keywords Organizing pneumonia ·Computed tomography · Patterns

Eur Radiol (2002) 12:1486–1496DOI 10.1007/s00330-001-1211-3 C H E S T

Anastasia OikonomouDavid M. Hansell

Organizing pneumonia: the many morphological faces

Introduction

Organizing pneumonia is one of the main reparative re-actions to acute injury by the lung and reflects the in-complete resolution of inflammation within the alveoli,and to a lesser extent the distal bronchioles [1, 2, 3]. Al-though this pathological pattern is non-specific, giventhat it can be incited by many different types of “injury”,it is the particular hallmark of a more or less distinctclinicopathological syndrome which has been given thename cryptogenic organizing pneumonia (COP) [4].Since the first description of COP in 1983 by Davison et al. [5], and the later report on bronchiolitis obliteransorganizing pneumonia (BOOP) by Epler et al. [6], muchhas been written about the terminology. There have alsobeen numerous reports about the typical radiographicfindings that characterize this entity. The purpose of thisarticle is to highlight the variable and sometimes idio-syncratic imaging appearances of organizing pneumonia.

Terminology

The competing terms, i.e. COP vs BOOP, have generatedmuch discussion over the years. “BOOP” was first

coined as a term by Epler et al. [6] to emphasise to thepathological distribution of the pneumonic process inboth alveoli and terminal bronchioles; however, the useof bronchiolitis obliterans in this term was a majorsource of confusion because of the semantic similaritythat “BOOP” shared with bronchiolitis obliterans (oblit-erative bronchiolitis) which is a completely different entity [2, 3, 4, 7, 8]: obliterative bronchiolitis is an ob-structive small airways disease with poor response totreatment, without intraluminal exudate, in which bron-chioles are cicatrized and replaced by scanty fibroticremnants. BOOP, on the other hand, is predominantly anair-space process in which terminal bronchioles may befilled with granulation tissue; but the airways are notobliterated in the true sense of the word. The cardinalcomponent of “BOOP” is the organizing pneumonia, andthis is reflected by a restrictive, not obstructive, func-tional deficit [3, 4, 8, 9, 10]. To overcome this confusion“COP” has been suggested as the preferred term for theclinicopathological syndrome as it conveys the essentialfeatures of the entity [2, 3, 4, 9, 10].

Although it seems likely that some authors will per-sist with the usage of BOOP, a working group sponsoredby the American Thoracic Society and the EuropeanRespiratory Society has abandoned the term BOOP alto-

A. Oikonomou · D.M. Hansell (✉ )Department of Radiology, Royal BromptonHospital, Sydney Street, London SW36NP, Englande-mail: d.hansell@rbh.nthames.nhs.ukTel.: +44-20-73518034Fax: +44-20-73518098

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gether and has put its authority behind the terms organiz-ing pneumonia and COP to describe the pathological andclinical entities, respectively [11].

Histology

Histologically, organizing pneumonia is characterized by the presence of buds of granulation tissue in the distalair spaces comprising fibrin exudates and collagen-containing fibroblasts. The fibroblasts are embedded in amyxoid matrix with a variable infiltrate of lymphocytes,macrophages, plasma cells, neutrophils and eosinophilsforming characteristic elongated polypoidal masses(Masson bodies or bourgeons conjonctifs; Fig. 1); theseare located predominantly in the alveolar spaces but of-ten extend into bronchiolar lumens. The buds of connec-tive tissue frequently extend directly from one alveolusto the next, through the pores of Kohn, producing a char-acteristic “butterfly” pattern. There is no disturbance ofthe lung architecture. Other histological features includechronic inflammation in the walls of the surrounding alveoli with minor infiltration of the interstitium bymononuclear cells [1, 4, 6, 9, 10]. In a few cases the in-flammatory infiltrate is more intense with the incorpora-tion of fibrosis in the alveolar walls [2, 10, 12].

Association of OP with other conditions

It is worth emphasizing that there can be overlap be-tween organizing pneumonia and other pneumonic enti-ties such as chronic eosinophilic pneumonia and extrin-sic allergic alveolitis. In these conditions the presence ofclusters of eosinophils or occasional granulomas, in what

Fig. 1 An open-lung biopsy specimen showing polypoidal massesof organized granulation tissue (Masson bodies) within the alveoli.The intervening alveolar walls show mild thickening by an inflam-matory infiltrate, but the lung architecture is otherwise preserved.There are no features of established fibrosis. (Courtesy of A.G.Nicholson)

Table 1 Causes of organizing pneumonia and associations withother conditions

InfectionBacterial– Streptococcus pneumonia [15]– Legionella pneumophila [16]– Mycoplasma pneumonia [17]– Coxiella burnetti [18]– Nocardia asteroides [19]– Chlamydia pneumonia [20]Viral– Adenovirus [21]– Cytomegalovirus [14]– Influenza [22] and parainfluenza [3, 23]– Human immunodeficiency virus [24]

DrugsAntibiotics– Amphotericin B [14]– Cephalosporins [25]– Minocycline [26]– Nitrofurantoin [27]Others– Sulfasalazine [28]– Bleomycin [29]– Amiodarone [30]– Acebutolol [31]– Busulfan [32]– Barbiturates [33]– Paraquat [34]– Cocaine [35]– Gold [36]– Phenytoin [37]

Connective tissue disorders– Systemic lupus erythematosus [38]– Rheumatoid arthritis [39]– Sjogren syndrome [40]– Polymyositis [40]– Dermatomyositis [41]– Polymyalgia rheumatica [42]

Immunological disorders– Common variable immunodeficiency syndrome [43]– Essential mixed cryoglobulinaemia [44]

Organ transplantation– Bone marrow [45]– Lung [46]– Renal [47]

Miscellaneous– Inflammatory bowel disease [48]– Primary biliary cirrhosis [49]– Polyarteritis nodosa [50]– Haematological malignancies– Myelodysplastic syndrome [51]– T-cell leukaemia [52]– Lymphoma [53]– Seasonal syndrome with cholestasis [54]– Radiotherapy [55, 56]– Environmental exposure (textile printing dye) [57]– Penicillium mould dust [58]

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chogram and bronchial dilatation may be present in con-solidated areas. Response to corticosteroid treatment isprompt in most cases and relapse does not occur if suffi-cient therapy is given.

Serial radiographic and clinical features are regardedas sufficiently characteristic in some cases, as to obviatethe need for biopsy confirmation. Nevertheless, there isincreasing awareness that imaging patterns of OP maydeviate from this typical picture. What follows is a de-scription of the less commonly encountered and atypicalCT manifestations of organizing pneumonia.

CT variants of organizing pneumonia

Focal lesion

Focal organizing pneumonia can closely resemble lungcancer on a chest radiograph and the exclusion of malig-nancy cannot be made on the basis of the radiographicappearances alone. In most cases resection or biopsy ismandatory.

In a study by Cordier et al., COP was stratified intoone of three clinical profiles with “focal COP” being one of them (Fig. 3) [69]. This category accounted forone-third of the study group and is noteworthy that the lo-cation in 4 of 5 patients was in the upper lobes, the com-monest site for lung cancer. The patient’s symptoms mayalso suggest the diagnosis of lung cancer as focal orga-nizing pneumonia may present with haemoptysis [70, 71,72]. Occasional cavitation of focal organizing pneumoniaraises the question of whether such lesions are in factsterile post-infective or post-infarctive abscesses. The CTcharacteristics of 18 cases of focal solitary OP were eval-

Fig. 2 A 58-year-old woman from Kuwait with a 6-month historyof lethargy, night sweats and increasing breathlessness on exer-tion. A standard CT shows the typical CT features of cryptogenicorganizing pneumonia. There are several basal and peripheral ar-eas of air-space consolidation. A lung biopsy confirmed the diag-nosis of organizing pneumonia

would otherwise be regarded as organizing pneumonia,suggest the diagnosis of eosinophilic pneumonia or ex-trinsic allergic alveolitis, respectively [12]. Similarly,diffuse alveolar damage in the organizing phase is simi-lar to OP in that there is extensive cellular fibroblasticproliferation associated with a myxoid-appearing matrix.Diffuse alveolar damage differs in that the changes tendto be more diffuse and uniform, with the characteristicformation of hyaline membranes [9]. An organizingpneumonia-like reaction can also be a major histologicalfeature in Wegener’s or bronchocentric granulomatosisand other inflammatory lesions including lung abscesses,pulmonary infarcts and lung cancer [12, 13, 14]. Indeed,a component of organizing pneumonia is identifiable in a huge variety of different contexts, including resolvinginfection, as a drug reaction, in association with connec-tive tissue disorders, and many other conditions. A sam-ple of the many causes and association of organizingpneumonia are given in Table 1.

Classical COP: clinical and imaging presentation

The “typical” COP syndrome is characterized by an in-dolent onset of a flu-like illness accompanied with fever,non-productive cough, malaise, anorexia and weightloss. Dyspnoea is common but usually mild and evidentonly on exertion. Less common symptoms are bronch-orrhoea, haemoptysis (but severe haemoptysis is exceed-ingly rare), chest pain, arthralgia and night sweats. It affects men and women equally and occurs in middle-aged adults with a peak incidence in the sixth decade. Nocause has been identified, although there is the suspicionthat infection, viral or otherwise, may be the trigger insome cases; in particular, COP is not related to smoking.The mean duration of symptoms at presentation varies,but in most cases it is less than 3 months. Patients are often prescribed antibiotics (without obvious effect) inthe belief that the clinical picture is of a community-acquired pneumonia. Pulmonary function tests show amild to moderate restrictive defect and the total gastransfer (Dlco) is reduced, although the Kco (gas transferadjusted for alveolar volume) is preserved. Arterial hypoxaemia is occasionally severe and probably reflectsright-to-left shunting through consolidated lung. Airflowobstruction is not a feature [4, 5, 6, 10, 59, 60].

The imaging in classical COP has been thoroughlydescribed [4, 5, 6, 10, 59, 61, 62, 63, 64, 65, 66, 67, 68].The most usual radiographic appearance is of bilateralpatchy areas of air-space consolidation with a tendencyto progress and change location over time. Spontaneousregression of some focal areas of consolidation is a strik-ing feature. The CT findings mirror the radiographic ap-pearances, but there is often associated ground-glassopacification, and the distribution of disease is predomi-nantly peripheral and lower zone (Fig. 2). An air bron-

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uated and a trend towards location of the lesion in thelung periphery (outer third of the lung parenchyma) wasreported [73]. Helpful, but not definitive, differentiatingCT features from lung cancer include:

1. Location of the lesion in contact with the pleura (i.e.relatively broad pleural-based lesion) or along thebronchovascular bundle with some contraction andconvergence of vessels

2. The presence of flat, oval or trapezoidal-shaped mass-es instead of a rounded lesion

3. The presence of satellite lesions [73]

Fig. 3a, b Two examples of focal organizing pneumonia. a Themass-like lesion in the lingula was thought, at radiographic pre-sentation, to represent a lung cancer. Note ground-glass opacity inthe contralateral right lower lobe. b Patient with ulcerative colitisand focal cavitating lesion in the right upper lobe, shown to be afocus of organizing pneumonia on surgical resection

Fig. 4 A 59-year-old man with ulcerative colitis and insulin-de-pendent diabetes mellitus. The CT shows multiple focal mass-likelesions, some of which contain an air bronchogram. On biopsythese lesions proved to be areas of organizing pneumonia

Focal OP can also present as multiple mass-like opacities(Fig. 4) [74, 75, 76]. This was the most frequent findingin one study in which the majority of cases were periph-erally located and demonstrated a pulmonary vesselleading to a nodular opacity or a small bronchus enteringthe centre of the nodular opacity [77]. In a series of Akira et al., in which COP manifested as focal multiplelarge nodules or masses, the most prominent feature wasthe irregular and spiculated margin [78]. It is noteworthythat bleomycin-induced lung organizing pneumonia canpresent as pseudometastatic pulmonary nodules, occa-sionally with cavitation [29].

Nodular pattern

Organizing pneumonia can present as one of two nodularpatterns:

1. A well-defined “acinar” pattern with nodules of ap-proximately 8 mm in diameter (Fig. 5)

2. A more subtle poorly defined (micro)nodular pattern(Fig. 6).

In two early CT series describing COP, nodules were re-ported to be one of the more prevalent features. InMüller et al.’s study, well-defined nodules of up to 5 mmdiameter and situated predominantly along the broncho-vascular bundles were described [65]. The authors alsonoted the presence of nodules up to 10 mm in diameter(“acinar” nodules). Pathological correlation showed thatthese represented focal areas of organizing pneumoniaaround plugged bronchioles. This type of lesion was sep-arated from others by a zone of relatively normal aeratedlung, which explained the nodular appearance. In thestudy by Lee et al., nodules were present in one-third ofpatients [66]. They were the sole finding in 9% of pa-

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Bronchocentric pattern

The bronchocentric pattern was first identified in thefirst two CT series by Müller et al. [65] and Lee et al.[66] (Figs. 7, 8). In Müller et al.’s study one-third of pa-tients showed a combination of subpleural and peribron-chovascular consolidation [65]. In Lee et al.’s study, ap-proximately one-third of cases also had a predominantlyperibronchovascular pattern [66].

There have been subsequent reports about pulmonarydisease associated with polymyositis and dermatomyosi-tis that have emphasized the association with predomi-nantly bronchocentric organizing pneumonia. In a studyof patients with poly- or dermatomyositis the consolida-tion on CT had a predominantly peribronchovasculardistribution which corresponded pathologically to OP[83]. The authors concluded that although air-space con-solidation is a nonspecific finding, in the context of

Fig. 5 A CT of the right upper lobe of a patient with a 10-day his-tory of dyspnoea and suspected community acquired pneumonia.Combined pattern of peripheral “acinar” nodules and smaller nod-ules, some of which resemble a tree-in-bud pattern. Biopsy-provenorganizing pneumonia. (Courtesy of S. Diederich, Muenster)

Fig. 6 a A 23-year-old bodybuilder gradually became severelydyspnoeic and ultimately required mechanical ventilation. The diagnosis of organizing pneumonia was confirmed on lung biopsyand he responded slowly to prolonged treatment with steroids (nospecific cause was found). On CT there is a micronodular patterncharacterized by small ill-defined centrilobular nodules of lessthan 5 mm. b Lung biopsy specimen showing discrete small fociof organizing pneumonia, surrounded by normal aerated lung

tients and part of a mixed pattern in the remaining cases.Most of the nodules had well-defined margins and wererandomly distributed. Nishimura and Itoh reported anodular pattern (nodules of approximately 1 cm in diam-eter) superimposed on an overall increase in lung densityor ground-glass opacification [67]. In a recent study thepresence of parenchymal nodules with ill-defined mar-gins and a predominantly peripheral distribution was themost important discriminating CT feature between orga-nizing pneumonia and chronic eosinophilic pneumonia[79].

A micronodular pattern (nodules ≤4 mm) in which themicronodules are poorly defined and of relatively low attenuation is an uncommon CT appearance of organiz-ing pneumonia (Fig. 6) [64, 80] and is more frequentlyencountered in subacute extrinisic allergic alveolitis. In a study of the CT and histopathological characteristics of bronchiolar diseases, the authors mention that in occasional cases of organizing pneumonia the CT ap-pearances resemble an infectious bronchiolitis with atree-in-bud pattern [81].

Cordier describes in a recent review article, a distinctbronchiolocentric distribution in which organizing pneu-monia is limited to the alveoli immediately adjacent tothe involved bronchioles, thus giving a miliary pattern[4]. Although organizing pneumonia is not mentioned asa differential diagnosis in a survey of cases characterizedby tree-in-bud appearance [82], it is reasonable to assumethat in order to have any kind of “nodular” pattern the af-fected bronchioles and adjacent alveoli occupied by OPmust be surrounded by normally aerated parenchyma.

Linear and band-like pattern

A linear or band-like pattern of OP is unusual and strik-ing and has been described in isolation or in combinationwith other patterns. It is seen on CT as lines or bands longer than 2 cm, smooth or irregular sometimes formingarcades and/or containing air bronchograms. These linesor bands are usually at least 8 mm in width (Fig. 9) [85].

Murphy et al. reported two distinct types of linear opac-ity [86]: (a) those extending in a radial manner along theline of the bronchi towards the pleura, usually intimatelyrelated to bronchi; and (b) those occurring in a peripherallocation bearing no relationship to the bronchi [86]

These linear opacities are usually associated withmultifocal areas of consolidation, but in 2 of 11 patientsthey were the sole HRCT abnormality. Organizing pneu-monia may present on CT with extraordinary crescenticand ring-shaped opacities surrounding areas of ground-glass opacification (Fig. 10) [87]. These features may beaccompanied by a more typical nodular or a consolida-tion pattern. The CT pathological correlation has shownthat the central areas of ground-glass opacification in CTreflect alveolar septal inflammation and cellular debris.In an HRCT study of patients with polymyositis or der-matomyositis, subpleural band-like opacities have beendescribed which lie in the lung periphery parallel to thechest wall [83]. This may be regarded as bronchocentricdistribution of organizing pneumonia around adjacentsubpleural bronchi that gives the impression of a band asbronchi are “joined” together by intervening organizingpneumonia (Fig. 11).

Perilobular pattern

A “perilobular” distribution was a term first coined byMurata et al. in their description of the localization ofparenchymal disease at the level of the secondary pulmo-nary lobule [88]. They reserved this term for lesions thatmainly involved the structures bordering the lobule, no-tably the interlobular septa and the pleura. In a more re-cent study the authors added in the definition of the peri-lobular region the peribronchovascular interstitium ofthe larger bronchi and accompanying pulmonary arterieswhich are too large to be located within the centre of thesecondary lobules and therefore are located in the pe-riphery of the lobule [89]. In this context, interstitial andair-space disease involving these perilobular (paraseptal)alveoli may mimic abnormalities of the interlobular sep-ta on HRCT. Accumulation of organizing exudate (i.e.organizing pneumonia) or the infiltration of the alveolarwalls, even if they are not associated with thickening ofthe interlobular septa histologically, may be seen as “ap-parent” septal thickening contributing to a coarse reticu-lar pattern on HRCT. In terms of anatomical distributionthere is some congruence between the perilobular pattern

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known polymyositis/dermatomyositis, dense broncho-centric opacification on CT is likely to represent organiz-ing pneumonia.

In a study that assessed the diagnostic accuracy ofthin-section CT in patients with idiopathic interstitialpneumonias, although a peripheral distribution wasfound in the majority of OP cases, 17% had a predomi-nantly peribronchovascular pattern [80]. Furthermore, abronchocentric location of air-space and ground-glassconsolidation was found to be a more frequent feature in organizing pneumonia when compared with chroniceosinophilic pneumonia [79].

Fig. 7 Bronchocentric pattern of organizing pneumonia: areas ofconsolidation surround the bronchovascular bundles in a patientadmitted to intensive care

Fig. 8 Bronchocentric pattern of organizing pneumonia: a strik-ingly peribronchovascular distribution in a diabetic patient with bi-opsy proven organizing pneumonia. (Courtesy of A. Vathi, Bolatti,Milan)

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and the grosser distribution of “typical” OP: a subpleuraldistribution is the dominant feature in COP and, at amuch smaller or microscopic level, a perilobular disposi-tion of OP can also be regarded as “subpleural”(Fig. 12). One of the secondary changes that accompa-nies OP is a mild inflammatory infiltrate [9] which prob-ably contributes to the perilobular disease. It can bespeculated that this pattern of OP is responsible for thereported resolution of an apparently irreversible (fibrot-

Fig. 9 A 41-year-old man developed cryptogenic organizingpneumonia concurrent with an episode of pericarditis. On CTthere are bilateral band-like opacities, both of which contain anair-bronchogram. Biopsy of one of these lesions confirmed orga-nizing pneumonia

Fig. 10a, b A CT scan of a 14-year-old boy not responding totreatment for suspected tuberculosis (later excluded). A strikingpattern of ring-like opacities surrounding areas of ground-glassopacification is seen in the a upper and b lower lobes. Open-lungbiopsy revealed organizing pneumonia

Fig. 11 A bronchocentric distribution of organizing pneumoniaaround adjacent bronchi resembling a band as bronchi are “joinedtogether” by the intervening organizing pneumonia

Fig. 12 A perilobular pattern of organizing pneumonia. There isopacification around the periphery of individual secondary lobulesresembling poorly defined thickened interlobular septa

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ic) pattern in nitrofurantoin-induced lung disease, inwhich there is an OP-like reaction [27, 90].

In some CT studies of OP, thickening of the interlobu-lar septa is described and is usually associated with areasof consolidation or near nodules and masses [65, 78, 86,91]; however, it remains uncertain how often this is“real” thickening of the interlobular septa, as opposed to“apparent” thickening caused by perilobular disease, asdescribed above.

Progressive fibrotic pattern

A less distinct pattern (unlike the previous relativelywell-defined morphological patterns) encompasses thosecases of “aggressive” OP in which there is superveningirreversible fibrosis. This pattern, if it can be called that,was initially described as a separate clinical–radiologicprofile of COP having an overlap with usual interstitialpneumonia and consequently a worse prognosis thantypical COP [69]. In a recent study, 10 patients with aninitial histological diagnosis of OP had a fulminantcourse leading to death. Post-mortem examination re-vealed OP associated with alveolar septal inflammation,established fibrosis and honeycombing [92]. The authorssuggested that OP can, on occasion, be the precursor ofinterstitial fibrosis and end-stage honeycomb lung.

One of the main objectives of the defining series byEpler et al. was the differentiation between UIP and OP,particularly given the much better prognosis of OP [6].As background to this apparent overlap, it may be usefulto consider the following histopathological concepts [93, 94, 95, 96, 97, 98, 99]. Alveolar epithelial damage isan early event in both UIP and OP. In OP the necrosis ofbronchiolar and alveolar epithelium is followed by migration of fibroblasts from the interstitial compart-ment into the airways and air-spaces through gaps in thedamaged basal membrane; organization begins with theformation of fibro-inflammatory buds with deposition of a loose connective tissue matrix (intraluminal organi-zation) [4, 9, 10]. The alveolar architecture is remarkablypreserved and there is a variable inflammatory cellularinfiltration of the interstitium. On the other hand, whenorganization is predominantly interstitial the epithelialbasal lamina is disrupted and fibrosis is incorporatedwithin the alveolar interstitium [61, 93]. In UIP small fi-broblastic foci are usually restricted to interstitium, andintraluminal fibrosis is much less extensive than in OP[9]. After a seemingly similar initial alveolar injury, it isnot clear what determines whether organization will pro-ceed intraluminally (OP) or in the interstitium (UIP) [61,93, 94, 95]. One determinant may be that significant fi-broblastic proliferation occurs where the continuity ofbasal lamina is disrupted [96, 97], whereas the integrityof the lung parenchyma can be restored after injury ifbasal lamina remains relatively intact [98, 99].

The radiographic pattern of organizing pneumonia admixed with interstitial fibrosis probably first appearedin the literature in 1973 when Gosink et al. [100] report-ed five patients with organizing pneumonia and linear/reticular opacities on chest radiography; however, it wasnot until 1989 that Cordier et al. formally suggested aseparate group, characterized by more interstitial in-volvement [69]. On CT a bibasal reticular pattern may besuperimposed on a background of areas of frank consoli-dation or acinar nodules (Fig. 13) [10]. It is the relativepaucity of consolidation and ground-glass opacificationtogether with the predominance of reticular elementswith architectural distortion that distinguishes this pat-tern from typical or “simple” OP. Other features of inter-stitial fibrosis, including traction bronchiectasis, honey-combing, with or without patchy areas of ground glass,may all be seen on CT in this “overlap” entity. This pat-tern is most frequently encountered in organizing pneu-

Fig. 13a, b A 36-year-old woman presented with the presumptivediagnosis of bronchopneumonia, with minor improvement on anti-biotics; however, exertional dyspnoea and a restrictive ventilatorydefect remained. a The initial CT showed patchy areas of consoli-dation concentrated in the lower lobes, but no obvious features established interstitial fibrosis. b The same patient 15 months laterafter prolonged steroid treatment. The areas of consolidation hadlargely resolved, but an extensive coarse reticular pattern, indicat-ing supervening fibrosis, had developed

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monia associated with connective tissue diseases, partic-ularly polymyositis/dermatomyositis, and has a poorerprognosis [84].

Conclusion

In the 20 years since cryptogenic organizing pneumoniawas first described, the terminology and pathological

concepts surrounding this entity have been clarified.The basic imaging pattern of changing multifocal air-space consolidation that characterizes cryptogenicorganizing pneumonia is widely recognized but the in-creasing number of reported variant morphologies of or-ganizing pneumonia, shown to advantage on CT, needto be borne in mind if the diagnosis is not to be over-looked.

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