Computed Tomography in Chest Diseases

Dr. Rikin Hasnani

• Developmental Anomalies• Airway Diseases• Pulmonary infection & Pneumonias• Neoplastic diseases• Diffuse Lung Diseases • Disease of mediastinum , Pleura & Chest Wall

Developmental Anomalies of Lung

Tracheal bronchus• Also known as “pig bronchus” or “bronchus suis.• Incidental finding• Usually arise from lateral wall of trachea.• Other type of anomalous bronchus – pre and post eparterial

bronchus, accessory cardiac bronchus, pre and post hyparterial bronchus.• Displaced v/s supernumery bronchus

Anomalous bronchi

Etiology • Tracheobronchial development occurs during the early embryonic

period (26 days to six weeks). • Precise etiology of tracheal (and other anomalous) bronchi is not

known, • regression of anomalous bronchial buds, • migration of primitive bronchi to anomalous positions, and • induction of anomalous bronchial branches by surrounding primitive

mesenchyme have all been suggested as possible mechanisms.

Development of lung

Imaging • Visualization of anomalous bronchus originating from lateral tracheal wall or

proximal mainstem bronchus • Multiplanar reformations, shaded surface displays , volume rendering, and

virtual bronchoscopy techniques useful in anatomic characterization and classification• D/D• Tracheobronchial diverticula are blind-ending airways that often arise from

the mainstem bronchi.• Tracheal air cysts are tracheal diverticula manifesting as air-filled thin-walled

blind-ending structures at the thoracic inlet. These exhibit a normal mucosal lining and cartilage within their walls.

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Tracheal Air Cyst

Bronchial Atresia• Bronchial atresia is a rare congenital anomaly that typically affects segmental

bronchi, although lobar and subsegmental bronchi may also be involved. • The left upper lobe bronchus (apical-posterior segment) is affected in

approximately 64% of cases.• The surrounding alveoli may fail to develop normally and may overinflate

because of collateral air drift through pores of Kohn, canals of Lambert, or other communications. • Endoluminal debris accumulating distal to the atresia may form a mucocele.• Symptoms

Imaging Radiography • Focal overinflation surrounding mucocele (Rounded, tubular, or branching opacity) • Expiratory air trapping surrounding mucocele • Air-fluid level within mucocele (with superimposed infection)MDct • Rounded , branching , or tubular typically central opacity; low attenuation (–5 to 25 HU))• Absence of contrast enhancement within bronchus or mucocele • Overinflated lung surrounding mucocele Mri • Visualization of mucocele with high signal intensity on T1- and T2-weighted imagesManagement :D/D – vascular abnormalities , endobronchial growth

Pulmonary Sequesterations• It is abnormal unventilated lung tissue that has no normal communication with the

bronchial system and derives its blood supply from systemic , rather than pulmonary circulation.• Intralobar sequestrations are four times more frequent than extralobar

sequestrations and occur almost exclusively in the lower lobes, slightly more frequently on the left.• The systemic arterial supply to the lesion often courses within the pulmonary

ligament and originates from the descending aorta. The venous drainage is into the pulmonary veins.• The lesion is often heterogeneous due to acute and chronic inflammation and

bronchopneumonia with resultant bronchiectasis, fibrosis, and cystic change. • The lesion typically abuts adjacent normal (nonsequestered) lung.

• Extralobar sequestrations represent accessory pulmonary lobes that result from abnormal foregut budding and are located outside the confines of normal lung. • They may occur in the thorax, diaphragm, or abdomen; are

characteristically supplied and drained by the systemic circulation; and represent true congenital anomalies.• Affected patients are diagnosed within the first 6 months of life, but a

small number of lesions (10%) are diagnosed in asymptomatic adults.

Feature Intralobar Extralobar

Frequency More common Less common

Male : female 1:1 4:1

Most common site Within Posterior basal segment

Between lower lobe and diaphragm

Side of thorax 60% left sided 90% left sided

Arterial supply 70% thoracic aorta 45% thoracic aorta

Venous drainage Usually pulmonary vein Often systemic vein

Diagnosed in neonates Rarely Commonly

Other cong. defects Uncommon Frequent

Clinical features• Extralobar are frequently diagnosed in 1st year of life.• Intralobar may present with LRTI, recurrent pneumonic episode or

massive hemoptysis. • Extralobar sequestraaions are less liable to infections

Imaging

• Radiography • • Typical location: posterior basal segment of a lower lobe.• • Consolidation or mass; may contain air, fluid, and/or air-fluid levels and

multilocular cystic areas, irregular margins typical,• • Predominantly cystic lesions; exhibit a single cyst or multiple cysts of

variable sizes • • Rarely, branching tubular opacities representing mucoid impacted bronchi• • Surrounding lung may be hyperlucent • • May produce mass effect on adjacent structures

• MDCT • Heterogeneous enhancement • Hyperlucent or predominantly cystic lesion with single or multiple thin-walled cysts; may contain air and/or

fluid• Demonstration of anomalous systemic arterial supply (usually from descending aorta) in up to 80% of cases;

CT angiography with multiplanar reformatted images may enhance visualization of anomalous vessel• MRI• Heterogeneous intrapulmonary lower lobe lesion; may exhibit cystic areas • Gradient-echo sequences may

demonstrate systemic blood supply and pulmonary venous drainage• Angiography • Aortography for demonstration of anomalous systemic arterial supply arising from descending aorta in up to

73% of cases, or other systemic abdominal arteries • Selective angiography of anomalous systemic artery may allow demonstration of pulmonary venous

drainage

Pulmonary Arteriovenous Malformation• It is an abnormal communication between a pulmonary artery and a

pulmonary vein without an intervening capillary bed, and results in a right-to-left shunt.• It is of two types• Simple PAVMs (90%) are defined as single or multiple feeding arteries

originating from a single segmental pulmonary artery. • Complex PAVMs (10%) are characterized by feeding arteries

originating from two or more segmental pulmonary arteries.

Etiology • Congenital • Acquired • Rendu-Osler-Weber syndrome or hereditary hemorrhagic

telangiectasia (HHT) is an autosomal dominant disorder characterized by recurrent epistaxis, mucocutaneous telangiectasias, and arteriovenous malformations, with an estimated prevalence of one in 5,000 to 10,000 persons.• c/f – asymptomataic, dyspnea, paradoxical emboli

• Radiography • Lobular well-defined non-calcified nodule/mass • Typically in peripheral lower lobe; often projects below dome of diaphragm.• Associated tortuous tubular opacities coursing to and from ipsilateral hilum representing feeding and

draining vessels • Rarely, multiple pulmonary nodules/masses• CT• PAVM manifests as nodule with feeding and draining vessels • Evaluation of origin, number, length, and diameter of feeding vessels and internal structure of

vascular sac• CECT shows Enhancing mass with vascular connections, Rapid contrast enhancement and washout • Unenhanced or enhanced multidetector CT imaging for screening , characterization, and

quantification of PAVM

• Mri • Low-signal flow void in PAVM; low to intermediate signal in PAVM with internal thrombus • Three-dimensional contrast-enhanced MR angiography for non-invasive diagnosis of PAVM larger

than 3 mm in size, it shows high-signal-intensity nodule and associated vessels • Evaluation of size and number of feeding vessels prior to embolotherapy• Angiography • Opacification of feeding vessels and draining veins • It is useful in confirmation of diagnosis, documentation of multiple lesions, and evaluation of

origin, number, length, and diameter of the feeding vessel for coil embolization therapy planning.• Contrast-enhanced two-dimensional echocardiography for screening (90% sensitivity for

detection of intrapulmonary shunts) • Lung perfusion scintigraphy for determination of shunt size

Scimitar Syndrome• Scimitar syndrome, also known as pulmonary venolobar syndrome or

hypogenetic lung syndrome, is characterised by a hypoplastic lung that is drained by an anomalous vein into the systemic venous system. It is a type of partial anomalous pulmonary venous return.

Imaging • Chest radiographic findings are that of a • decreased lung volume with ipsilateral mediastinal shift, • Diminished right pulmonary vascularity • Broad retrosternal band-like opacity on lateral radiography• Blunt costophrenic angle • Vertically oriented curved tubular opacity (anomalous draining vein)

in right inferior hemithorax coursing toward right cardiophrenic angle scimitar sign.

Pulmonary stenosis

Airway Diseases

Tracheal StenosisTracheal stenosis is defined as narrowing of the tracheal lumen by more than 10% of its normal diameter. Etiology – cong, acquired Clinical features – dyspnea , wheezing , stridorImaging –Management - Surgical excision of stenotic segment and reconstruction Endoscopic mechanical dilatationTracheal stenting Laser photoablation for focal mucosal lesions

Saber sheath trachea• Saber sheath trachea is defined

as a tracheal deformity in which the transverse tracheal diameter is equal to or less than one-half the AP diameter, measured 1 cm above the superior aspect of the aortic arch.

• The deformity begins at the thoracic inlet, affects only the intrathoracic trachea, and is a manifestation of chronic obstructive pulmonary disease.

Tracheobronchomegaly; Mounier-Kuhn Syndrome• It is also known as

tracheal diverticulosis and tracheobronchiectasis.• It is diagnose when

diameter of trachea , right main bronchus or left main bronchus size greater than 3.0 cm; 2.4cm ; 2.3 cm respectively.

Tracheobronchomalacia • It is characterised by excessive expiratory collapse of the tracheal walls

and/or supporting cartilage and is an important cause of airway obstruction, chronic cough, recurrent lung infection, and other respiratory symptoms. • Percentage of luminal collapse between end inspiration and expiration is

calculated as follows: • LC = 100 · [1 – (LAee/LAei)] • LC = percentage of luminal collapse • LAee = luminal area at end expiration (mm2) • LAei = luminal area at end inspiration (mm2) • ≥70% luminal narrowing on forced expiration is the diagnostic threshold for

TM

Tracheoesophageal Fistula• TEF may occur as a complication of intrathoracic malignancy (60%),

prolonged tracheal intubation, esophageal instrumentation, infection, or trauma. • TEF occurs in 5–10% of patients with advanced esophageal cancer

and is more prevalent in those who have had prior irradiation. • The diagnosis is usually made with a fluoroscopic contrast

esophagogram. • CT may demonstrate an occult TEF in patients at risk who have a

normal esophagogram.

Chest radiography • Normal chest radiographs • Pneumomediastinum (common) • Pneumothorax • Consolidation related to aspiration • Air-distended esophagus • Airway opacification on contrast esophagography MDct/3-D.reformations • Direct visualization of fistula • Assessment of fistula size and location

Bronchiectasis • It is defined as abnormal,

irreversibly dilated and thick-walled bronchi.• It is typically graded

according to its severity as mild, moderate, and severe forms, respectively termed cylindrical, varicose, and saccular (cystic)

Imaging • Radiography Visible bronchial walls –• Single or parallel “tram track” lines (thickened airway walls seen longitudinally) ◦ • Poorly defined ring-like/curvilinear opacities (thickened airway walls seen on-end or

obliquely) Variable lung volume (atelectasis or hyperinflation) ◦ Round, oval, or tubular Y- or V-shaped opacities (dilated airways filled with secretions, mucoid impaction) Multiple thin-walled ring-like opacities in cystic bronchiectasis, often with air-fluid levels Normal chest radiograph in 7% of affected patients

• MDCT/HRCT • Absence of normal distal tapering of bronchial lumen • Internal diameter of bronchial lumen greater than that of adjacent

pulmonary artery (i.e., signet ring sign) • Visible bronchi within 1.0 cm of costal pleura or abutting mediastinal

pleura • Mucus-filled dilated bronchi • Associated bronchiolitis in 75% of patients (decreased lung attenuation

and vascularity, bronchiolectasis, and centrilobular tree-in-bud opacities)

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Emphysema • Emphysema is defined as abnormal permanent enlargement of the

airspaces distal to the terminal bronchiole accompanied by destruction of their walls with minimal or absent fibrosis. • Emphysema is categorized according to the affected part of the

pulmonary acinus. • Proximal acinar (syn. centrilobular, centriacinar) emphysema involves the proximal aspect of the acinus with distension and destruction that primarily affects the respiratory bronchioles

Imaging • Radiography • Increased lung volumes or lung height (measured ≥30 cm from right first rib

tubercle to diaphragm dome)• Diaphragmatic flattening (highest level of diaphragmatic contour is <1.5 cm above a

line connecting the costophrenic and vertebrophrenic junctions on PA view or a line connecting the sternophrenic and posterior costophrenic angles on lateral view) • Enlarged retrosternal clear space (horizontal distance between sternum and

anterior margin ascending aorta >2.5 cm on lateral view)• Abnormal lucency in the upper lung zones• Reduction in number and caliber of pulmonary vessels; vessels may be displaced by

bullae or emphysematous spaces; may exhibit widened branching angles with loss of side branches• Crowding of vessels in mid and lower lungs in moderate and severe emphysema • Normal in mild cases

MDCT • Focal areas (3–10 mm) of centrilobular low attenuation with

imperceptible walls .• Central nodular opacity (centrilobular arteriole) within an area of low

attenuation.• More severe involvement of upper lobes and superior segments of lower

lobes.• Large confluent areas of emphysema may progress to panlobular

involvement • Associated paraseptal emphysema and/or bullae

Panacinar emphysema

Panacinar (syn. panlobular) emphysema affects each acinus in its entirety and all acini within the secondary pulmonary lobule. It is the characteristic finding in patients with α-1-antiprotease deficiency. While panacinar emphysema may involve the lung diffusely, predominant lower lung involvement is characteristic.

Radiology – Large lung volumes Decreased pulmonary vascularityPredominant lower lobe involvement MDct/hrct • Extensive areas of abnormal low attenuation • Paucity of vasculature • Involvement of entire secondary pulmonary lobule • Diffuse or lower lobe predominance • Absence of focal lucencies or bullae

• Distal acinar (paraseptal) emphysema is the least common type of emphysema and, together with proximal acinar emphysema, is frequently associated with the formation of bullae. • It affects the periphery of the acinus.• Adjacent foci of paraseptal emphysema may coalesce to form bullae. • A bulla is defined as a sharply demarcated air-containing space measuring 1.0

cm in diameter or more in the distended state. Bullae are characteristically thin-walled (1 mm) and may be unilocular or compartmentalized by thin septa.• The term giant bullous emphysema refers to bullae that occupy at least one-

third of a hemithorax.

Imaging Features Chest.radiography • Thin-walled, well-defined avascular areas in lung parenchyma (bullae)• Mass effect on adjacent lung• Air-fluid levels within secondarily infected bullae • Associated pneumothorax

MDCT/HRCT• Many of the same features seen on chest radiography • Focal subpleural cystic areas near interlobular septa, large vessels, and bronchi • Frequent associated proximal acinar emphysema • Large bullae, usually between 2–8 cm in diameter (giant bullous emphysema)

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