Teaching file: X-ray Anatomy of the lung

Standard exams


Lung parenchyma

Heart and vessels






Index (in German)

Textbook (in German)


Standard exams

Normal exam 1 with lateral projection

Chest p.a. and lateral (radiological meditation):
The domes of the diaphragms are evenly shaped and positioned in proper height.
The sinuses are not obliterated.
The pleura shows no thickening.
Both lungfields have the same transparency and no geographic or rounded densities.
There is a harmonic bronchovascular branching right into the periphery of the lungs.
The upper mediastinal shadow is not enlarged.
The tracheal band is not narrowed.
The hili are not enlarged.
There is no pathologic transformation of the cardiac silhouette.
The visualized parts of the skeleton are normal
The soft tissue of the chest wall is not conspicuous.
Standard exam of the chest.

Chest x-ray (normal as well - now it is your turn).



Synopsis of bronchial anatomy of the lung in Computed Tomography. Printed in full size DIN A4 it can be used as a working aid at the view box (93k).


Right upper lobe bronchi (cuts starting from the level of the Pulmonary Artery upwards):
The rULB is visible directly below the level of the Carina and above the level of the right pulmonary artery. Before it branches off into the anterior and posterior segmental bronchi, it runs horizontally.
The 3. segmental bronchus (B3) originates caudal of level of the Carina and is depicted in its length. Right and left B3 are situated the most caudal of all upper lobe bronchi.
The right 2. segmental bronchus (B2) originates from the upper lobe bronchus at nearly the same level as B3 but runs in laterodorsal direction.
The 1. segmental bronchus runs straight upwards. His position is ventral to the concurrent vessel.

Bronchus intermedius
The dorsal wall of the bronchus contacts the apical lower lobe segment (S6).


Middle lobe bronchus
The middle lobe bronchus either originates at the same level as the lower lobe bronchus or a little bit above. Because of its oblique and ventral direction it is cut longitudinal, ventral of the oval shaped lower lobe bronchus which points in a caudal direction.
The medial segmental bronchus (B5) runs more obliquely than the lateroventral segmental bronchus (B4).
The apex of the middle lobe separates middle and lower lobe bronchi.

Right lower lobe bronchus (craniocaudal direction):
The lower lobe bronchus either originates at the same level as the middle lobe bronchus or a little bit below. It is situated more dorsally. Because of its steep running it is visualized in an oval or round shape. The apex of the middle lobe separates middle and lower lobe bronchi. The lower lobe bronchus lies medially of the lower lobe artery.
The 6. segmental bronchus (B6) is the first that originates from the lower lobe bronchus, for a short distance in a horizontal direction, than for another short distance upwards, dorsal of the lower lobe artery.
The remaining lower lobe bronchi B7-10 originate from the lower lobe bronchus at the level of the left atrium ventrally (B7), laterally (B8), laterodorsal (B9), or dorsally (B10).


Left upper lobe bronchus (cuts starting from the level of the pulmonary artery upwards):
The first cuts show a smooth posterior wall which maybe slightly concave because of the posterocranial attached upper lobe artery.
The anterior upper lobe bronchus (B3) usually originates from the posterior segmental bronchus ("B1+2") and runs in ventral direction. Therefor it is depicted longitudinally. Sometimes the upper lobe bronchus three folds itself. The anterior segmental bronchus than originates between the posterior segmental bronchus (B1+2) and the bronchus of the lingula.
The posterior segmental bronchus (B1+2) runs straight upwards. It abuts the artery of the 3. segment first laterally, then ventrally.

Bronchus of the lingula:
The bronchus of the lingula originates near the upper lobe bronchus. Because it runs obliquely and ventrally, it is visualized longitudinally. It is departed from the ascending B6 by the descending lower lobe artery.

Lower lobe bronchus:
As on the right side the apical lower lobe bronchus (B6) originates from the lower lobe bronchus as the first segmental offspring in horizontal direction for a short distance. For a short way it runs upward and dorsal of the descending lower lobe artery.
The 7. segmental bronchus rarely exists individually. In its absence the responding segment is ventilated by B8. Mostly the medial and anterior lower lobe bronchi originate from a common segmental bronchus. The lower lobe bronchi B8-10 leave the lower lobe bronchus at the level of the left atrium into ventral and lateral (B8), laterodorsal (B9) or dorsal direction.

Bronchography on both (!) sides with deformed, dilated bronchi of the lingula. This exam is only of historic significance - and esthetic, as far as the image is concerned.


Lung parenchyma

Scheme that helps to localize consolidations to lobes and segments of the right and the left lung. Each is a half page, as a print out well suited as help at the view box. 32k each.

The secondary lobule, anatomical scheme at left, scheme of appropriate HRCT image at right (Webb, modified): Az: acinus; bv: central brochovascular ("core") structures; S: interlobular septae; Pl: pleura; V: venes; A: lobular artery; Br: lobular bronchiole

The concept of the secondary lobule is important for understanding the pathomorphology of HRCT of the lung.

The secondary lobule in CT, with magnification

The secondary lobule in the periphery of the lung

The visualization of the secondary lobule is enhanced by fluid accumulation in the interlobular septae in the course of cardiac insufficiency. ©Prof. Reuter, Kiel

Accessory lobus cardiacus


Heart and vessels

X-ray of cardiac dimensions in a.p. projection. The maximal diameters of the heard measured from the midline to the left border plus the diameter to the right border should not exceed the maximum transverse diameter of the thorax (some locate this diameter at the apex of the diaphragm which is not correct). The right border of the heart should neither project more than 5 cm from the middling nor exceed one third of the total diameter of the heart.

X-ray of the heart in lateral projection. Dorsal border of the left ventricle, vena cava, and diaphragm form the so called "cava triangle". It diminishes with enlargement of the left heart. The left ventricle forms the lower part of the dorsal contour of the heart. This contour should not pass a landmark that is situated 2 cm cranial and dorsal the crossing of the vena cava superior with the dorsal contour of the left ventricle. The line of measurement should be parallel to the nearest intervertebral space (a). Question: is there an enlargement of the left heart?

Cardiac changes in lateral projection. With enlargement the left ventricle diminishes the retrocardial space (1). The left atrium (A) also projects dorsally and compresses the esophagus. Esophageal marking by barium swallow is not practiced any longer routinely. The contrast medium might degrade computed tomograms of the abdomen for several days.
Enlargement of the right outflow (rA) comprises the retrosternal space (2). A right heart enlargement is diagnosed when the heart touches more than one third of the inner anterior chest wall (back of the sternum, retrosternal clear space).

Cardiac valves in p.a. and lateral projection. P: pulmonary valve; A: aortic valve; M: mitral valve; T: tricuspid valve.

A pericardial fat pad obliterates the cardiac border and mimics an area of density (notice lateral projection).

Arcus aortae dexter.

Magnetic Resonance Imaging of the big intrathoracic vessels (left) and of the pulmonary arteries (right). In the future, MRI will be the method of choice for visualization of thoracic vessels.

Transposition of Aorta.

Arcus aortae dexter duplex. Chest film and CT at the level of aortic arch and aortopulmonary window. At the level of the aortic arch there is an anterior and a posterior aortic ring visible. The ascending aorta is on the right, the descending on the left. The chest film shows an aortic knuckle on both sides.

Arcus aortae dexter (secondary finding). Control x-ray after transthoracic puncture with consecutive strong parenchyma bleeding.

Conventional pulmonary angiography with arterial (right side) and venous phase (left side). Note the different directions, outflow and inflow of pulmonary arteries and veins.



With the concept of the "vascular pedicle" of Milne a reproducible measurement of the width of the mediastinum and an estimation of the systemic blood volume is possible. Taken the identical position of the patient in consecutive bedside x-ray examinations, 1 cm broadening of the vascular pedicle indicates an increase of the circulating blood volume of 2 liters. According to Milne, changes of the extracellular fluid volume can be estimated by the thickness of the thoracic soft tissue shadow.

The crescent shaped density at the back of the ascending aorta is formed by a plica of the pericardium. This should not be mistaken for a lymphnode.



Usually the diaphragm is not discernible. This patient had an abdominal film in left-sided position with the central beam directing horizontally. Because of massive intraperitoneal air the liver has neither contact to the right lateral chestwall nor to the diaphragm. Therefore the diaphragm gets visible.

Ventilation induced blurring of the diaphragm. With prolonged exposure times (as with low powered mobile x-ray units for bedside exams on the ward) there may be blurring. A blurred diaphragmal contour may be misinterpreted as a fluid collection. This situation has become rare with better equipment. Another cause may be a misdirected central beam from caudal. Fat in the ventral recesses is than superimposed on the diaphragmal contour and blurs its shape.

Diaphragms: differentiation on the lateral view. The shape of the right diaphragm (white arrow) can be completely traced from ventral to dorsal. The left heart obliterates the shape of the left diaphragm (black arrow). M: Magenblase. It is situated below the left diaphragm.



The pulmonary ligament is formed by a pleural fold that does not fit closely around the pulmonary radix but reaches like an oversized sleeve caudal, dorsally and usually on the diaphragm laterally. In the opening of the sleeve the pulmonary tissue is attached with the mediastinum and the diaphragm. This series of axial computed tomograms shows the insertion of the ligament in a collapsed lung that floats in a large fluid accumulation.

The pleura is usually not seen in CT. It may be recognized as a dense line when, with a pneumothorax, the lung retracts from the thoracic wall, as seen in this case.



Lordotic view of the apex of the lung. For different view of the apices of the lungs the central beam is tilted either caudal or cranial.

Problems with wide window setting in CT. With a wide window setting (left upper image) the pronounced density due to fibrosis is hardly visible. With a narrow window setting (right upper image) the marked density is better perceptible. The heightened density is proven by the measured values (image below). The flat white curve shows the shift of the peak to lower values.

Wide and narrow window settings in CT: Small nodules of sarcoidosis with wide (right) and narrow window settings (left).

High Resolution Mode of Computed Tomography. Left: CT with 8 mm slices thickness and low kernel that does not enhance edges. Right: 2-mm thin slice reconstructed with an edge-enhancing kernel ("HRCT").

Visualization of vessels in thick (at right) and thin slices (at left) in CT. As a thick slice captures more of an obliquely running vessel, the vessel is depicted more longitudinally than in a thin slice, where only a point shaped cut of the vessel is to be seen.

Rapid measurement of minute densities in a nodule: window width is reduced to 2 HU, i.e. black and white image results. The center value is changed to a value where a first pixel in the area of interest bright up or the last disappears. This center value represents the maximal density value in the nodule.

The so-called "double window technique" should not be utilized as the blurred borders of the two windows may obliterate small pathologies.



Externally situated materials on the chest may mimic pathologies. This may happen with hair knots the proper positioning of which may be missed in veiled women.

Pericardial fat may blur the cardiac shape or even mimic a mass.

Misinterpreted round shadow. On the lateral projection there is a round shadow which can not be verified on the other projection. As the nodule is supposed to be situated close to the mediastinum, a fluoroscopy is recommended, but the nodule can not be localized. The keen radiologist performs an extreme procedure: he switches the room light on and stares at the patient who stands in front of him, arms up. In the left arm pit there is a big wart.

Misinterpreted round shadow in the right upper lung field. It is a pearl in knotted hair. I learned of this nice case from ©Dr. Brauer when we met in the Casamance, Senegal.

Supposed metastases. In the p.a. projection of the left chest there are 2 rounded shadows. They could be localized outside the lung (right, arrow) by fluoroscopy.

Supposedly right paramediastinal space occupying lesion. A Medical doctor who sports radiology (one stop shop!) did the x-ray of this lady. Duly he transferred his patient for further investigations by CT. Instead, the chest x-ray was repeated with hairs up and revealed a normal x-ray.

Accessory cervical rib at right side (arrowhead). Usually, an accessory cervical rib can be diagnosed and discerned from the usual ribs by its straight caudal direction. Lifting of the arm may result in compression of vessels by the accessory rib. In the preoperative phase it may compromise intubation.

Inspiration and expiration: differences in the chest x-ray. In expiration a normal heart may look as if the left heart is enlarged. The hili may turn enlarged and blurred, as if there is cardiac congestion. The lung is compressed which may result in misinterpretation of reduced ventilation or consolidation.

Film adjacent object. The nearer the depicted object is to the film (or detector, in CR), the sharper it is delineated. In the right x-ray the patient stands his right side to the film, on the left x-ray with his left side. Question: on which side of the lung do you localize the pulmonary lesion?

Silhouette sign: "An intrathoracic lesion touching a border of the heart or aorta will obliterate that border on the roentgenogram; an intrathoracic lesion not anatomical contiguous with a border of the heart or aorta will not obliterate the border" (Felson, 1973).
Thus if a consolidadation can not be distinguished from the heart, it must be situated in the ventral lower thorax space, probably in the middle lobe or in the lingula. If the consolidation is definable in the heart shadow however, it is situated (anterior or) posterior to the heart (most probably in the lower lobe, as anterior to the heart usually there is few space).
This space-occupying lesion in the right lower lobe dorsal to the heart has no contact to the heart. Therefore the right cardiac border is well delineated.

Cervical lymphomas can be seen as soft tissue masses on the chest x-ray.

Normal variants of the thoracic skeleton that may mimic pathologies (from Remy, modified):

1: synostosis of procc. transversariae
2: calcification at the insertion of the first rib
3: medial border of scapula - no pleural line
4: costosternal articulation
5: superposition of rib and proc. transversaria
6: indentations at the lower border of the dorsal parts of the ribs
7: chondral part of the rib
8: persistent apophysis of clavicle
9: marked indentation at medial border of clavicle
10: accessory cervical rib
11: indentation at lower margin of clavicle, medially, caused by the lig. rhomboideum
12: ossification of the insertion of the first rib
13: superposition of apophysis of rib and the sternum
14: lamina shaped lower border of rib
15: bridging of anterior parts of ribs
16: apex of scapula mimics intraparenchymal calcification

Normal variants of the soft tissue of the chest that may mimic pathologies (from Remy, modified):

1: hair knots may show up like cervical or paramediastinal masses
2: dense margin of the 2. rib
3: density by folds of clothes
4: margin of breasts
5: shadows of mammillae (more cranial situated in men)
6: lobulated contour of diaphragm
7: jugulum
8: lateral margin of m. sternocleidomastoideus
9: fossa supraclavicularis
10: skin wart
11: axillary fold
12: superposed inner margins of ribs
13: shadow of pectoral muscle in man
14: bulging intercostal fat mimics pleural thickening
15: diaphragmal insertions

Index Teaching File

The Lung in the Web


Diary (in German)

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