A structured approach to interpretation of HRCT involves the following questions: What is the dominant HR-pattern: reticular nodular high attenuation (ground-glass, consolidation) low attenuation (emphysema, cystic) Where is it located within the secondary lobule (centrilobular, perilymphatic or random) Is there an upper versus lower zone or a central versus peripheral predominance Are there additional findings (pleural fluid, lymphadenopathy, traction bronchiectasis). Correct diagnosis of IIPs can be achieved only by means of interdisciplinary consensus and stringent correlation of clinical, imaging, and pathologic findings.
Dominant pattern Distribution in Secondary Pulmonary Lobule Distribution within lung Reticular vs Nodular High density vs Low density Centrilobular, Perilymphatic, Random Upper zones, Lower zones Central or Peripheral HRCT Basic Interpretation
Chest radiographs : collection of innumerable small linear opacities that, by summation, produce an appearance resembling a net. This finding usually represents interstitial lung disease. The constituents of a reticular pattern are more clearly seen at thin section CT, whether they are interlobular septal thickening, intralobular lines, or the cyst walls of honeycombing.
Interlobular septum 10–20-mm long forming the borders of lobules; perpendicular to the pleura in the periphery. Composed of connective tissue and contain lymphatic vessels and pulmonary venules. Thin linear opacities between lobules Not usually seen in the healthy lung (normal septa are approximately 0.1 mm thick) but are clearly visible when thickened (eg, by pulmonary edema). Intralobular lines visible as fine linear opacities in a lobule when the intralobular interstitial tissue is abnormally thickened. When numerous, they may appear as a fine reticular pattern. Intralobular lines may be seen in various conditions, including interstitial fibrosis and alveolar proteinosis.
Honeycombing UIP Septal Thickening Thickened Interlobular Septae Fibrosis Reticular Pattern Nodular/Irregular Sarcoidosis Lymphangitic spread of carcinoma or lymphoma Silicosis Smooth Interstitial pulmonary edema Lymphangitic spread of carcinoma or lymphoma Alveolar proteinosis.
Chest radiographs : innumerable small rounded opacities that are discrete and range in diameter from 2 to 10 mm. The distribution is widespread but not necessarily uniform. CT :classified as one of three anatomic distributions: centrilobular, perilymphatic, or random.
Patchy : + axial interstitium (>90% fissures or bronchovascula r) Diffuse and Uniform: Normal axial interstitium(no predominance) Tree-in-bud Tree-in-bud absent Nodules along the pleura and fissures ? NO YES Centrilobular Nodules Multiple Small Nodules: Differential Algorithm Bronchiolar/ Vascular Disease Smoker: RB-ILD Non-smoker: Subacute HP BAC,COP,Oedema, LCH,Vasculitis Bronchiolar disease Infectious Bronchiolitis Bronchopneumo nia,TB Random Distribution Metastasis Lymphangitic Ca Miliary Infection Perilymphatic Distribution Sarcoid Silicosis/CWP Lymphangitic Ca
Infection Airway disease Tuberculosis MAC (mycobacterium avium) Bacterial, Fungal Cystic Fibrosis or Bronchiectasis Tree in bud ABPA Allergic Bronchopulmonary Aspergilosis (rare)
Chest radiographs : area of hazy increased lung opacity, usually extensive, within which margins of pulmonary vessels may be indistinct. CT : hazy increased opacity of lung, with preservation of bronchial and vascular margins. It is caused by partial filling of airspaces, interstitial thickening (due to fluid, cells, and/or fibrosis),partial collapse of alveoli, increased capillary blood volume, or a combination of these, the common factor being the partial displacement of air. Ground-glass opacity is less opaque than consolidation, in which bronchovascular margins are obscured.
Nonspecific Highly significant 60-80% : active and potentially treatable lung disease % : fibrosis(associated HRCT findings of fibrosis, such as traction bronchiectasis and honeycombing ).
Patchwork of regions of differing attenuation that may represent (a) patchy interstitial disease, (b) obliterative small airways disease or (c) occlusive vascular disease. Air trapping secondary to bronchial or bronchiolar obstruction may produce focal zones of decreased attenuation, an appearance that can be enhanced by using expiratory CT. The mosaic attenuation pattern can also be produced by interstitial lung disease characterized by ground- glass opacity; in this situation, areas of higher attenuation represent the interstitial process and areas of lower attenuation represent the normal lung.
Density differences between affected and non-affected lung areas - patchy areas of black and white lung. The role of the radiologist is to determine which part is abnormal: the black or the white lung Look at expiratory scans for air trapping Look at the vessels
Permanently enlarged airspaces distal to the terminal bronchiole with destruction of alveolar walls. Areas of low attenuation without visible walls as a result of parenchymal destruction. Centrilobular emphysema Most common type Irreversible destruction of alveolar walls in the centrilobular portion of the lobule Upper lobe predominance and uneven distribution Strongly associated with smoking. Panlobular emphysema Affects the whole secondary lobule Lower lobe predominance In alpha-1-antitrypsin deficiency, but also seen in smokers with advanced emphysema Paraseptal emphysema Adjacent to the pleura and interlobar fissures Can be isolated phenomenon in young adults, or in older patients with centrilobular emphysema In young adults often associated with spontaneous pneumothorax
Lung cysts are defined as radiolucent areas with a wall thickness of less than 2mm. Cavities are defined as radiolucent areas with a wall thickness of more than 2mm and are seen in infection (TB, Staph, fungal, hydatid), septic emboli, squamous cell carcinoma and Wegener's disease.
Pathology.—A cyst is any round circumscribed space that is surrounded by an epithelial or fibrous wall of variable thickness. Radiographs/CT:Round parenchymal lucency or low- attenuating area with a well-defined interface with normal lung. Variable wall thickness but are usually thin-walled (2 mm) and occur without associated pulmonary emphysema. Usually contain air but occasionally contain fluid or solid material. Enlarged thinwalled airspaces in patients with lymphangioleiomyomatosis or Langerhans cell histiocytosis Thickerwalled honeycomb cysts are seen in patients with end- stage fibrosis.
Irreversible localized or diffuse bronchial dilatation,usually resulting from chronic infection, proximal airway obstruction, or congenital bronchial abnormality. Radiographs and CT :Signet ring sign, lack of tapering of bronchi, and identification of bronchi within 1 cm of the pleural surface. Cylindric, varicose, or cystic, depending on the appearance of the affected bronchi. Often accompanied by bronchial wall thickening, mucoid impaction, and small-airways abnormalities. May mimic cystic lung disease and bullous emphysema. Bronchiectasis caused by primary airway disease should be differentiated from tracion bronchiectasis as a result of fibrosis.
Small cystic spaces with irregularly thickened walls composed of fibrous tissue. Peripheral and subpleural lung regions regardless of the cause. Subpleural several contiguous layers. Distinguished from paraseptal emphysema in which subpleural cysts usually occur in a single layer.
Pathology.—Honeycombing represents destroyed and fibrotic lung tissue containing numerous cystic airspaces with thick fibrous walls, representing the late stage of various lung diseases, with complete loss of acinar architecture. The cysts range in size from a few millimeters to several centimeters in diameter, have variable wall thickness, and are lined by metaplastic bronchiolar epithelium. Chest radiographs : closely approximated ring shadows, typically 3–10 mm in diameter with walls 1–3 mm in thickness, that resemble a honeycomb; the finding implies end-stage lung disease. CT : the appearance is of clustered cystic air spaces, typically of comparable diameters on the order of 3–10 mm but occasionally as large as 2.5 cm. Honeycombing is usually subpleural and is characterized by well-defined walls. It is a CT feature of established pulmonary fibrosis.Because honeycombing is often considered specific for pulmonary fibrosis and is an important criterion in the diagnosis of usual interstitial pneumonia, the term should be used with care, as it may directly impact patient care.
Upper zone Sarcoid Silicosis Coalworkers Pneumoconiose Centrilobular Emphysema Langerhans Cell Histiocytosis Chron. Hypersens. Pneumonitis Lower Zone Edema Panlobular Emphysema UIP in: IPF * Collagen-vascular disease * Asbestosis Upper vs Lower zone
Central zone Sarcoid Bronchitis Pulmonary Edema Peripheral Zone COP/OP Chronic Eosinophilic Pneumonia Hematogenous Metastases UIP in: * IPF * Collagen - Vascular Disease * Asbestosis Central vs. Peripheral zone
Pleural effusion is seen in: 1. Pulmonary edema 2. Lymphangitic spread of carcinoma - often unilateral 3. Tuberculosis 4. Lymphangiomyomatosis (LAM) 5. Asbestosis
In sarcoidosis the common pattern is right paratracheal and bilateral hilar adenopathy ('1-2-3-sign'). In lung carcinoma and lymphangitic carcinomatosis adenopathy is usually unilateral. 'Eggshell calcification' in lymph nodes commonly occurs in patients with silicosis and coal-worker's pneumoconiosis and is sometimes seen in sarcoidosis, postirradiation Hodgkin disease, blastomycosis and scleroderma.
Know anatomy of secondary pulmonary lobule Identify Pattern: Reticular,Nodular, High Attenuation, Low Attenuation Distribution Additional Findings
1.http://www.radiologyassistant.nl/en/42d94cd0c326b Accessed 2/3/2012 HRCT part I &2 Robin Smithuis, Otto van Delden and Cornelia Schaefer- Prokop Radiology Department of the Rijnland Hospital, Leiderdorp and the Academical Medical Centre, Amsterdam, the Netherlands 2.Diffuse Nodular Lung Disease – A Differential Alogrith:Naidich - MDCT Congress, Sandton,RSA. 16/08/ March 2008 Radiology, 246, Fleischner Society: Glossary of Terms for Thoracic Imaging