Fleischner sign | Radiology Signs

Answer:

The Fleischner sign is enlargement of a central pulmonary artery, usually the right descending branch, with an abrupt change in calibre distal to it, on the chest radiograph of a patient with acute pulmonary embolism. It reflects the distension of the artery by impacted thrombus together with the raised pulmonary arterial pressure that results from occlusion. Its practical importance is almost entirely historical and conceptual: the PIOPED data showed that the classical radiographic signs of embolism, the Fleischner sign, Westermark sign of regional oligaemia, Hampton hump of a peripheral wedge-shaped opacity and an elevated hemidiaphragm, are individually insensitive and non-specific, and that a normal chest radiograph is common in proven embolism. The radiograph therefore cannot exclude pulmonary embolism and its main value is to identify an alternative explanation for the presentation such as pneumothorax, consolidation or a rib fracture, and to allow interpretation of a ventilation-perfusion study. Current diagnosis follows a validated pathway of clinical probability scoring, D-dimer where probability is low, and CT pulmonary angiography, with ventilation-perfusion or perfusion-only scintigraphy where contrast is contraindicated or in pregnancy. Chronic enlargement of the central arteries with peripheral pruning instead suggests pulmonary hypertension, including chronic thromboembolic disease.

Why is it called so?

The sign is named after Felix Fleischner, who described the enlarged central artery in pulmonary embolism.

Pathophysiology

An embolus impacting in a lobar or main pulmonary artery physically distends the vessel proximal to and at the site of impaction. In addition, the mechanical obstruction and the release of vasoactive mediators such as serotonin and thromboxane from activated platelets raise pulmonary vascular resistance, so pressure and calibre rise in the arteries proximal to the occlusion. Distal to the clot, flow ceases and the vessels collapse, which produces the abrupt cut-off in calibre and, when the affected territory is large enough, the regional lucency of the Westermark sign. If infarction follows, which happens in a minority because of the dual bronchial and pulmonary blood supply, the peripheral wedge of haemorrhagic consolidation appears as the Hampton hump.

Alternative names: Knuckle sign; sausage sign of the pulmonary artery

Other associated named signs: Westermark sign, Hampton hump and the Palla sign of a prominent right descending pulmonary artery

References

1. Worsley DF, Alavi A, Aronchick JM, Chen JT, Greenspan RH, Ravin CE. Chest radiographic findings in patients with acute pulmonary embolism: observations from the PIOPED Study. Radiology. 1993;189(1):133-6. PMID: 8372182.