Transcript
UNDERSTANDING HRCT THORAX
LUNG ANATOMY
• Right lung is divided by major and minor fissure into 3 lobes and 10 bronchopulmonary segments
• Left lung is divided by major fissure into 2 lobes with a lingular lobe and 8 bronchopulmonary segments
ANATOMY• The trachea (windpipe) divides into left and the right
mainstem bronchi, at the level of the sternal angle (carina).
• The right main bronchus is wider, shorter, and more vertical than the left main bronchus.
• The right main bronchus subdivides into three lobar bronchi, while the left main bronchus divides into two.
• The lobar bronchi divide into tertiary bronchi, also known as segmentalinic bronchi, each of which supplies a bronchopulmonary segment.
ANATOMY• The segmental bronchi divide into many
primary bronchioles which divide into terminal bronchioles, each of which then gives rise to several respiratory bronchioles, which go on to divide into two to 11 alveolar ducts. There are five or six alveolar sacs associated with each alveolar duct. The alveolus is the basic anatomical unit of gas exchange in the lung.
TRACHEAL ANATOMY• 10-12 cm in length• Extrathoracic (2-4cm) and Intrathoracic(6-9cm beyond
manubrium)• In men, tracheal diameter averages 19.5 mm and in women,
tracheal diameter is slightly less, averaging 17.5 mm• The posterior portion of the tracheal wall is a thin
fibromuscular membrane termed the posterior tracheal membrane
• There is marked variability in the cross-sectional appearance of the trachea, which may appear convex posteriorly, flat, or convex anteriorly
The membranous posterior membrane allows esophageal expansion during expiration
Contains glands, small arteries, nerves, lymph vessels and elastic fibers
Trachealis muscle overlies esophageal muscle and epithelium
BRONCHIAL ANATOMY• Airways divide by dichotomous branching, with
approximately 23 generations of branches from the trachea to the alveoli.
• The wall thickness of conducting bronchi and bronchioles is approximately proportional to their diameter.
• Bronchi with a wall thickness of less than 300 um is not visible on CT or HRCT.
• As a consequence, normal bronchi less than 2 mm in diameter or closer than 2 cm from pleural surfaces equivalent to seventh to ninth order airways are generally below the resolution even of high-resolution CT
BRONCHUS• BLOOD SUPPLY Bronchial Arteries( 2 on left side i.e. superior
and inferior and 1 on right side) Left arises from thoracic aorta Right from either thoracic aorta, sup. lt. bronchial or right 3rd
intercostal artery
• VENOUS DRAINAGE on right- azygous vein on left- left superior
intercostal or accessory hemiazygous vein
• NERVE SUPPLY Pulmonary plexus at hilum (vagus and sympathetic)
BRONCHOARTERIAL RATIO (B/A)
• Internal diameter of both bronchus and accompanying arterial diameter calculated and ratio measured.
• If obliquely cut section seen, then the LEAST diameter is considered.
• Normal ratio is 0.65-0.70
BRONCHIAL WALL THICKNESS (T/D)
• Wall thickness proportionately decreases as the airway divides further as according to the diameter of the airway.
• T/D ratio approximates to 20% at any generation of airway.
The Nomenclature Adopted by the Ad HOC lnternational Committee Meeting at the Time of the lnternational Congress of Otorhinolaryngology in 1949 [I]"
International Nomenclature
Brock Jackson and Huber
Right upper lobe bronchusApical (RB1)Posterior (RB2)Anterior (RB3)Middle lobe bronchusLateral (RB4)Medial (RB5)Right lower lobe bronchusApical (RB6)Medial basal (cardiac) (RB7)Anterior basal (RB8)Lateral basal (RB9)Posterior basal (RB10)
PectoralSubapical
Apical
LateralMedial
ApicalCardiac
Anterior basalMiddle basal
Posterior basal
AnteriorPostenor
Apical
LateralMedial
SuperiorMedial basal
Anterior basalLateral basal
Posterior basal
The Nomenclature Adopted by the Ad HOC lnternational Committee Meeting at the Time of the lnternational Congress of Otorhinolaryngology in 1949 [I]"
International Nomenclature
Brock Jackson and Huber
Left upper lobe bronchusUpper divisionApical (LB1)Apicoposterior LB1 and LB2Posterior (LB2)Anterior (LB3)LingulaSuperior (LB4)Inferior (LB5)Left lower lobe bronchusApical (LB6)Anterior basal (LB8)Lateral basal (LB9)Posterior basal (LB10)
ApicopectoralApical
SubapicalPectoral
UpperLower
ApicalAnterior basalMiddle basal
Posterior basal
ApicalApical-posterior
PosteriorAnterior
SuperiorInferior
SuperiorAnterior medial basal
Lateral basalPosterior basal
MEDIASTINUM
• Broad central portion that separate the two laterally placed pleural cavities.
• Imaginary plane passes through T4 divides it into Superior & Inferior mediastinum
• Inferior mediastinum is further divided-Heart enclosed in pericardium (M)Sternum to anterior pericardium (A)Posterior pericardium to vertebrae (P)
INTERSTITIAL ANATOMY
• Lung is supported by a network of connective tissue called interstitium
• Interstitium not visible on normal HRCT but visible once thickened.
• Interstitium is constituted by AXIAL fibre system (peribronchovascular & centrilobular), PERIPHERAL fibre system (subpleural & interlobular septa) and SEPTAL fibre system (intralobular septa)
Secondary Lobule
• It is the smallest lung unit that is surrounded by connective tissue septa.
• It measures about 1-2 cm and is made up of 5-15 pulmonary acini, that contain the alveoli for gas exchange.
• The secondary lobule is supplied by a small bronchiole (terminal bronchiole) in the center, that is parallelled by the centrilobular artery.
• Pulmonary veins and lymphatics run in the periphery of the lobule within the interlobular septa.
• Every CT scan starts with a scout view, a projection image that looks like a second rate X-ray.
• A line on scout view tells you the level of axial cut.
HOUNSFIELD UNIT (HU)
• HU scale is a linear transformation of the original linear attenuation coefficient measurement into one in which radiodensity of distilled water at STP is defined as zero HU, while radiodensity of air at STP is defined as -1000 HU.
• Fat -50 to -100 HU• Blood +30 to 45 HU• Bone >+400 HU• Muscle +40HU• Contrast +130 HU
APPEARANCE ON CT SCAN
• AIR JET BLACK• FAT MODERATELY BLACK• WATER GRAY• MUSCLES SLIGHT WHITE• BONES WHITE• CALICIFICATION DENSE WHITE
LUNG WINDOW
MEDIASTINAL WINDOW
BONE WINDOW
LOBAR AND BRONCHIAL ANATOMY ON HRCT THORAX
RIGHT APICAL SEGMENT
LEFT APICAL SEGMENT
TRACHEA
ESOPHAGUS
RB1 LB1
CARINA
LEFT MAIN BRONCHUSRIGHT MAIN
BRONCHUS
RB2 RB1
RB3LB3
LB1,2
BRONCHUS INTERMEDIUS LEFT UL
BRONCHUS
RIGHT ML BRONCHUS
RB5
LUL
LLLRLL
RML
RB5 LB4
LB5
RLL BRONCHUS
LLL BRONCHUS
LB6
LINGULAR BRONCHUS
RB6
RB7LB6
RLL BRONCHUS LLL BRONCHUS
MAJOR FISSURE
RB8
RB9RB10 LB10
LB9
LB8
RLL
LML
LLL
RML
LB2
LB6
LB10
RB7
RB10
RB9
RB6
RB2
RB1
RB2
LB9
LB1,2
UL
LL
UL
LLML
RB1 joining RUL bronchus LB1,2 joining LUL bronchus
LB8RB8
CARINA
RC2
LC2
RB1
RB3
RB8
ML Bronchus
LB4
LB3
RB3
RB5RB4
LB5
LB3
VASCULAR ANATOMY ON CT THORAX
Rt. CCA
Rt. IJV
Rt. EJV
Lt. IJV
Lt. EJV
Lt. CCA
Rt. BCVRt. SCV joining Rt. BCV
Rt. CCA
Lt. CCALt. SCV
Rt. SCALt. SCA
Lt. BCV joining Rt. BCVRt. BCV
Rt. BCA
Lt. CCA Lt. SCA
SUPRA AORTIC LEVEL
Formation of SVC
Branching from Aortic Arch
AORTIC ARCH
SVC
AORTIC ARCH LEVEL
Ascending AORTA
Main Pulmonary TrunkSVC
Right Pulmonary Trunk Left Pulmonary Trunk
Descending AORTA
Aorta arising from Left Ventricle
Pulmonary Trunk arising from Right Ventricle
SVC draining into Right Atrium
Pulmonary Veins draining into Left Atrium
Pulmonary Veins
RV
LV
LA
RA
RV
LVIVS
DA
IVC
RV
LV
DA
LYMPH NODE STATIONS ON CT THORAX
LYMPH NODES STATION IN THORAX
1. SUPRACLAVICULAR NODES
• LOW CERVICAL • SUPRACLAVICULAR• STERNAL NOTCH
Extends from the lower margin of the cricoid cartilage to the clavicles and the upper border of the manubrium.
The midline of the trachea serves as border between 1R and 1L.
2. UPPER PARATRACHEAL NODES
2R. Upper Right ParatrachealExtends to the left lateral border of the trachea. From upper border of manubrium to the intersection of caudal margin of innominate (left brachiocephalic) vein with the trachea.2L. Upper Left ParatrachealFrom the upper border of manubrium to the superior border of aortic arch.2L nodes are located to the left of the left lateral border of the trachea.
3A. Pre-vascularThese nodes are not adjacent to the trachea like the nodes in station 2, but they are anterior to the vessels.
3P. Pre-vertebralThese nodes are not adjacent to the trachea like the nodes in station 2, but behind the esophagus, which is prevertebral.
4. LOWER PARATRACHEAL NODES
4R. Lower Right Paratracheal From the intersection of the caudal margin of innominate (left brachiocephalic) vein with the trachea to the lower border of the azygos vein.4R nodes extend from the right to the left lateral border of the trachea.
4L. Lower Left Paratracheal From the upper margin of the aortic arch to the upper rim of the left main pulmonary artery.
5-6. AORTIC NODES
5. Subaortic nodesThese nodes are located in the AP window lateral to the ligamentum arteriosum. These nodes are not located between the aorta and the pulmonary trunk but lateral to these vessels.
6. Para-aortic nodesThese are ascending aorta or phrenic nodes lying anterior and lateral to the ascending aorta and the aortic arch.
Inferior Mediastinal Nodes 7-9
7. Subcarinal nodes Nodes below carina
8. Paraesophageal nodes Nodes lateral to esophagus
9. Pulmonary Ligament nodes Nodes lying within the pulmonary ligaments.
Hilar, Lobar and (sub)segmental Nodes 10-14
These are all N1-nodes.10. Hilar nodesThese include nodes adjacent to the main stem bronchus and hilar vessels.
On the right they extend from the lower rim of the azygos vein to the interlobar region. On the left from the upper rim of the pulmonary artery to the interlobar region.
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