A 55-year-old female patient with a 60 pack-per-year smoking history, presented with a two-month history of dry cough and pleuritic chest pain. She denied febrile episodes, haemoptysis, dyspnoea or weight loss. Her sister had been diagnosed with lung cancer. Physical examination was unremarkable and blood showed elevated inflammatory markers.
Chest X-ray demonstrated a soft tissue density focal nodule with an irregular outline in the left middle lung zone (Fig. 1). This was a new finding, not present on CXR taken two years prior. Due to the presence of a raised D-dimer, a CT pulmonary angiogram was performed, which excluded pulmonary embolism. It however demonstrated a 2cmx2cm spiculated nodule in the apical segment of the left lower lung lobe (Fig. 2a) corresponding to the lesion seen on CXR. Another 1.7cmx1.6cm nodule was seen in the medial basal segment of left lower lung lobe (Fig. 2b), together with a 2.3cmx1.3cm nodule at the base of the right lower lobe (Fig. 2c). CT lung biopsy was requested on the basis that these lesions could represent malignancy. Differential diagnosis of cryptogenic organising pneumonia was suggested at multidisciplinary discussion, given the multifocality of the disease process on CT.
Background: Cryptogenic organising pneumonia (COP) is an idiopathic type of organising pneumonia resulting from an inflammatory process affecting both alveoli and distal bronchioles, with the primary area of damage being in the alveolar wall. This condition was formerly referred to as bronchiolitis obliterans organising pneumonia. However, due to the fact that bronchiolitis obliterans is a commonly absent finding, this term is no longer in use. The diagnosis of COP requires the exclusion of secondary causes, such as connective tissue disease, drug toxicity, infection, malignancy and graft-versus-host disease. [1,2]
Clinical perspective: COP predominantly occurs in the 5th to 6th decade of life, with non-smokers being affected twice as often as smokers.  Clinical manifestations are non-specific.
Imaging perspective: Imaging features vary considerably. Typical findings consist of confluent bilateral areas of peripheral parenchymal consolidation with subpleural sparing. Consolidation is accompanied by traction bronchiectasis and parenchymal distortion and is often migratory. Ground glass opacification (GGO) is also seen and is usually bilateral and random in distribution. GGO may also manifest as the classic reverse halo- or ‘atoll’-sign; an area of central ground glass opacification with a surrounding crescentic or complete ring of denser perilobular consolidation. Less commonly, COP may manifest as single or multiple pulmonary nodules that may mimic malignancy. COP nodules are mostly bilateral, often have irregular margins and may even manifest cavitation. Another described manifestation is the perilobular pattern, where thick, ill-defined linear opacities with a polygonal or arcade appearance are seen around the interlobular septa. [3,4]
Outcome: Whether a diagnosis of COP is to be accepted without histology is subject to debate; however the diagnosis of COP without a biopsy can rarely be justified.  Treatment in mild cases may be conservative with monitoring, as some cases are self-resolving. However, when symptoms are persistent, as in most cases, treatment with corticosteroids is indicated. COP responds rapidly to steroid treatment but can recur, especially in older women. [6,7] In our case, due to clinical suspicion of COP, the patient was started on prednisolone, following CT-guided biopsy. Histology confirmed this as the diagnosis. At outpatient review, the patient reported marked improvement in her symptoms. Follow-up CXR performed 8 weeks later demonstrated resolution of the left-middle lung zone nodule (Fig. 3).
Take home message/teaching points: This case serves to highlight how clinical, biochemical and imaging features of COP are rather non-specific when considered separately. However, when combined, the diagnosis becomes more evident. Multidisciplinary discussion is therefore paramount and image-guided biopsy should clinch the diagnosis.
Written informed patient consent for publication has been obtained.
 Cordier JF, Loire R, Brune J. (1989) Idiopathic bronchiolitis obliterans organizing pneumonia. Definition of characteristic clinical profiles in a series of 16 patients. Chest; 96:999–1004. (PMID: 2805873)
 Mueller-Mang C, Grosse C, Schmid K, Stiebellehner L, Bankier AA. (2007) What every radiologist should know about idiopathic interstitial pneumonias. RadioGraphics; 27: 595–615. (PMID: 17495281)
 Zare Mehrjardi M, Kahkouee S, Pourabdollah M. (2017) Radio-pathological correlation of organizing pneumonia (OP): a pictorial review. Br J Radiol; 90(101): 20160723. (PMID: 28106480)
 Flowers JR, Clunie G, Burke M, et al. (1992) Bronchiolitis obliterans organizing pneumonia: the clinical and radiological features of seven cases and a review of the literature. Clin Radiol; 45:371–377. (PMID: 1606793)
 Baha A, Yıldırım F, Köktürk N, Galata Z, Akyürek N, Demirci NY, et al. (2018) Cryptogenic and Secondary Organizing Pneumonia: Clinical Presentation, Radiological and Laboratory Findings, Treatment, and Prognosis in 56 Cases. Turk Thorac J. Sep 13. (PMID: 30322441)
 Wells AU. (2001) Cryptogenic organizing pneumonia. Semin Respir Crit Care Med;22 :449–459. (PMID: 16088692)
 Godbert B, Clement-Duchêne C, Regent D, Martinet Y. (2010) Do all cryptogenic organizing pneumonias require lung biopsy and steroid treatment? Rev Mal Respir. May;27(5): 509-14. (PMID: 20569886)