Fleischner sign

Fleischner sign describes prominence or dilatation of a central or proximal pulmonary artery on chest radiography in association with pulmonary embolism. The enlarged hilar arterial contour may reflect a large central embolic obstruction, acute pulmonary hypertension with dynamic dilatation of the proximal pulmonary arteries, or a combination of both.

The affected pulmonary artery may taper or terminate abruptly distal to the obstruction; this associated vascular cutoff is better considered separately as the knuckle sign. Fleischner sign is an uncommon and non-specific radiographic clue to pulmonary embolism and cannot establish or exclude the diagnosis.

Historically, proximal pulmonary arterial enlargement in pulmonary thrombosis had been described before Fleischner. His principal contribution between 1958 and 1962 was to demonstrate that hilar arterial enlargement could be dynamic and haemodynamically mediated, and to document its development and subsequent regression during acute pulmonary embolism.

Fleischner sign 2019
The“Fleischner sign” consists of a prominent central pulmonary artery upstream of cutoff (white arrows in A, black asterisk in B). It is frequently caused by a large embolus into the central pulmonary artery, as well depicted on axial CT image of the same patient (C, white arrowhead), Chiarenza 2019

Related findings

Oligaemia with contralateral pleonemia and raised hemidiaphragm with basal atelectasis were additional findings described during Fleischner’s work on pulmonary embolism, but are not alternative definitions of the Fleischner sign. Abrupt distal pulmonary arterial termination is generally termed the knuckle sign. Fleischner lines are linear opacities produced by plate-like atelectasis and represent a separate Fleischner eponym.

Historical development

1910 – Otto von Dehn published Über röntgenologische Lungenbefunde im Vergleich zu den Ergebnissen der Sektion. His study comparing chest radiographic appearances with postmortem findings was an early report of radiographic findings in pulmonary thrombosis. Dehn noted stark ausgesprochene Hilusschatten (marked hilar shadows) in a patient with thrombosis of both pulmonary arteries and almost no hilar lymph-node enlargement at autopsy.

1931 – Clarence H. Boswell and Harold D. Palmer published Progressive thrombosis of pulmonary artery. Their case provided a strong radiographic–pathological correlation. The chest radiograph showed an increased density of the shadow of the right pulmonary artery noting that its significance was not recognized before death. An abnormal hilar/pulmonary arterial shadow was retrospectively correlated with an obstructing thrombus.

1936–1941 – In parallel with his later work on pulmonary vascular disease, Felix George Fleischner investigated plate-like atelectasis and basal linear pulmonary shadows, subsequently associated with the separate eponym Fleischner lines.

1951 – Hanelin and Eyler published Pulmonary Artery Thrombosis: Roentgen Manifestations reviewing five cases involving the main pulmonary artery or major branches. Their contribution was detailed radiographic–pathological correlation between the altered hilar contour and the morphology of the contained thrombus. They described dilatation proximal to the obstruction, enlargement or altered contour at the thrombus, and diminished distal vessels producing regional hyperlucency.

1958 – Felix George Fleischner (1893-1969) published Pulmonary embolism, integrating the vascular and parenchymal radiographic manifestations of PE. He distinguished mechanical hilar enlargement caused by thrombus from dynamic dilatation of the hilar pulmonary arteries caused by acute pulmonary hypertension. In one patient the right hilar artery enlarged serially from 11 to 14 to 22 mm, before decreasing to 15 mm as the episode resolved. At maximal pulmonary hypertension the pulmonary artery trunk was also visibly dilated. Fleischner interpreted this as the transient combination of peripheral arterial constriction and oligaemia with pulmonary hypertension and central arterial dilatation.

1959 – Fleischner published Unilateral pulmonary embolism with increased compensatory circulation through the unoccluded lung. Rather than introducing proximal pulmonary arterial enlargement, Fleischner treated the oligemic lung and plump hilar shadow as established findings. His new observation was that massive unilateral PE diverted pulmonary arterial flow to the unobstructed lung. This produced oligaemia of the embolised lung and compensatory pleonemia with dilated hilar and peripheral vessels contralaterally. These changes could resolve with recanalisation or become permanent with persistent obstruction

…an embolus had lodged in the right pulmonary artery. The mechanical obstruction and vasoconstriction of the peripheral arteries prevented blood flow to the right lung, which appeared oligemic. The right hilar shadow was increased in size, due either to the embolothrombus lodged there or to the pulmonary hypertension, or to both.

Fleischner, 1958 (in reference to a chest radiograph)

1961 – Fleischner published Roentgen diagnosis of pulmonary embolism in the Heart Bulletin, providing an overview of the radiographic physiology of acute PE. He distinguished direct hilar enlargement from embolothrombus from dynamic arterial dilatation caused by acute pulmonary hypertension. Embolic obstruction and regional arterial spasm reduced peripheral perfusion, producing oligaemia. Increased pulmonary vascular resistance caused dilatation of the hilar pulmonary arteries and when severe, the main pulmonary artery trunk.

Fleischner described the characteristic combination of plump or tumour-like hilar arterial shadows with disproportionately reduced peripheral vascular markings. He noted that the right intermediate pulmonary artery could increase from a normal 10–12 mm to 22–25 mm during acute pulmonary hypertension.

right pa Roentgen diagnosis of pulmonary embolism
Fleischner sign: dynamic pulmonary arterial dilatation. Serial radiographs during puerperal pulmonary embolism show transient enlargement of the right hilar pulmonary artery from 15 → 17 mm, followed by regression to 13 → 12 mm with recovery. Right upper-lung oligaemia and transient plate atelectasis are also demonstrated. Fleischner, 1961.

1962 – Fleischner published Pulmonary embolism and provided his synthesis of the roentgen manifestations of PE. He described a haemodynamic sequence in which embolic obstruction and vasospasm increased pulmonary vascular resistance, producing acute pulmonary hypertension and dynamic dilatation of the hilar pulmonary arteries. The affected lung could simultaneously become oligemic, while shunting produced contralateral pleonemia.

Fleischner 1958
Serial chest radiographs during acute pulmonary embolism showing dynamic enlargement of the right intermediate pulmonary artery from 11 to 14 to 22 mm, followed by regression to 15 mm. At maximal pulmonary hypertension (C), the main pulmonary artery trunk is also dilated; oligaemia is present in the right upper lung field. Fleischner, 1962.

1971 – Kerr, Simon and Sutton published The value of the plain radiograph in acute massive pulmonary embolism in which they compared plain chest radiographs with pulmonary angiograms in 25 patients with acute massive pulmonary embolism. They evaluated oligaemia, hyperaemia, infarct shadows, hilar size, elevation of the diaphragm and the configuration of the main pulmonary artery. Vascular changes were present in all 25 patients and were considered the most important radiographic feature, while the other findings helped localise the affected lung.

1972 – Murray G. Baron published Fleischner lines and pulmonary emboli, documenting that the linear shadows associated with focal plate-like atelectasis had become known as Fleischner lines. He defined their morphology and emphasised that they were an indirect, non-specific manifestation of PE caused by focal bronchial obstruction and atelectasis rather than by direct visualisation of vascular occlusion.

1992 – Stein, Athanasoulis, Greenspan and Henry studied 123 patients with acute PE and no previous cardiac or pulmonary disease. They demonstrated that a prominent central pulmonary artery on CXR correlated with higher mean pulmonary arterial pressure in patients with acute PE without prior cardiopulmonary disease. This supported Fleischner’s earlier interpretation of proximal pulmonary arterial enlargement as a haemodynamic manifestation of acute pulmonary hypertension rather than simply the silhouette of an embolus.

1993 – Worsley et al reported results from PIOPED Study. They defined Fleischner sign as a prominent central pulmonary artery. Among 1,063 patients evaluated for suspected PE, the Fleischner sign, Westermark sign and Hampton hump were all found to be poor independent predictors of PE.

2006 – Marshall et al. published Signs in thoracic imaging. They defined Fleischner sign as enlargement of the proximal pulmonary arteries on chest radiography or angiography secondary to PE, particularly massive PE. Their illustration shows an enlarged right interlobar artery on CXR with multiple embolic filling defects and distension of the same vessel at angiography.

Fleischner sign dilated central pulmonary artery
Fleischner sign. Frontal chest radiograph demonstrates enlargement of the right interlobar pulmonary artery (arrow). Pulmonary angiography confirms multiple embolic filling defects with distension of the same artery. Marshall et al., 2006.

2019 – Chiarenza et al. define Fleischner sign as a prominent central pulmonary artery upstream of cutoff, usually caused by a large central embolus or pulmonary hypertension, and place the adjacent abrupt vascular termination under the separate knuckle sign

Associated Persons
Alternative names
  • Fleischner’s sign
References

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BA MA (Oxon) MBChB (Edin) FACEM FFSEM. Emergency physician, Sir Charles Gairdner Hospital. Passion for rugby, medical history, medical education, and asynchronous learning #FOAMed evangelist. Editor-in-Chief and Webmaster of Life in the Fast lane, LITFL | On Call 4e| Eponyms | Books | Horology |

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