CT features of focal organizing pneumonia: An analysis of consecutive histopathologically confirmed 45 cases

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Abstract

Objective

To study the CT characteristics of solitary focal organizing pneumonia (FOP).

Materials and methods

Chest CT of consecutive 45 patients (34 males and 11 females, median age: 56 years) with confirmed FOP were analyzed. The CT features between large FOP (>3 cm, n = 27) and small FOP (≤3 cm, n = 18) were compared.

Results

FOP lesions predominately located in peripheral lungs (86.7%), with the right lower lobe being most common lobe (44.4%). No lesion mainly located in the inner 1/3 of lungs. All large lesions were polygon in shape and had an irregular margin, while small lesions were more likely to be round or oval with an irregular or smooth border. Air bronchogram or small bubble-like lucency was present in majority of the lesions. 42.2% of lesions had incompact internal structure with inhomogeneous density besides air component. Most lesions were associated with a contraction or convergence of surrounding vessels; while no pulmonary vessel was interrupted abruptly by a small FOP lesion. Majority of large lesions had broad contact with the pleura, while only one patient had mild pleural effusion. Mild mediastinal lymph nodes enlargement was present in about 1/5 of the patients.

Conclusion

Compared with the known CT features of lung cancer, our results suggest differential diagnosis can often be made for large FOP, while small FOP may resemble lung cancer.

Introduction

Organizing pneumonia (OP), formally named bronchiolitis obliterans organizing pneumonia (BOOP), is a well-known pathological and clinical entity [1], [2], [3]. Histopathologically OP is characterized by loose plugs of granulation tissue (Masson bodies) within alveolar ducts and airspaces with varying degrees of bronchiole involvement [1], [3], [4], [5], [6], [7]. OP can be primary, i.e. cryptogenic OP, or secondary. Cryptogenic OP, which occurs without a known cause, is classified as an idiopathic interstitial pneumonia [8]. Secondary OP can be associated with various diseases, including infection, connective tissues diseases, malignancies, drugs, radiation injury, and organ transplantation [1], [3], [5], [6], [9], [10].

Focal organizing pneumonia (FOP) is a subset of OP and presents as an isolated focal lesion. It has been reported in the literatures also as a nodular BOOP [11], solitary involvement of BOOP [12], focal variant of OP [10], and localized OP [2]. OP is considered as a rare disease with an incidence of 1.96/100,000 [13]. FOP accounts for approximately 10–15% of all case of OP [4], [10], [14]. As a result of its rarity, relatively little is known of the radiological features of FOP. Only sporadic FOP cases or small case series have been reported [2], [9], [15], [16], [17]. The reports on CT features of FOP show wide variations. It is difficult to differentiate FOP from a bronchogenic carcinoma and FOP is often removed surgically. However, some patients may improve without treatment, and steroids have been reported to be effective in the treatment of OP [18]. In view of its benign nature and the efficacy of steroid therapy, the unnecessary pulmonary resection should be avoided. In this study, we sought to clarify CT features of FOP by retrospectively reviewing 45 consecutive histopathologically confirmed FOP patients. It is generally believed that solitary lunglesions larger than 3 cm tend be malignant, while nodular lesions less than 3 cm have more chance to be benign [19], [20]. Therefore in this study, the CT features of large (>3 cm) and small (≤3 cm) FOP lesions were compared.

Section snippets

Patients

With the approval by the Institutional Review Board and Ethics Committee of our hospital, we reviewed all medical files of patients admitted to our hospital from June 2005 to April 2012. From the files, we identified 45 patients who fulfilled the following inclusion criteria: (1) chest CT images showed as a solitary small nodule or a large mass lesion; (2) the lesion sample was obtained by surgical resection or CT guided percutaneous core-needle biopsy; (3) the histopathological pattern was

Results

CT features of 45 OP lesions are summarized in Table 2. The lesions ranged in size from 10 mm to 55 mm (mean: 32 mm, median: 34 mm), including 27 large lesions and 18 small lesions. Lesions predominately located in peripheral lungs (86.7%, Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5), with the right lower lobe being most common lobe (44.4%). Five large lesions involved three regions (inner, middle, and outer thirds of the lung). One small lesion located in the middle third of lung. No lesion located

Discussion

To our knowledge, the current study represents the largest series of FOP reported. Similar to previous reports of FOP [2], [4], [9], [17], [21], our results shows this disease is more common in males with smoking history; a large portion of the patients was cryptogenic. The common symptoms of FOP included cough and chest pain/discomfort, and our study further confirmed that FOP could be present in asymptomatic subjects. It is not possible to diagnose FOP based on clinical features. A definitive

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