Plain Film Signs in Pulmonary Embolism (with CT correlate)

Clinical History

This 43 year old male patient presented with shortness of breath (SOB) and cough.

Imaging Findings

This 43 year old male patient presented to the accident and emergency unit with SOB and cough. Significant past medical history included a deep vein thrombosis (DVT) 7 years ago. On examination, he was tachycardic and the arterial blood gas analysis demonstrated marked hypoxia. A chest radiograph was performed followed by a CT Pulmonary Angiogram (CTPA). Apart from mild neutrophilia the rest of the admission blood tests were normal.
On the PA chest radiograph the right inferior pulmonary artery was enlarged (Fleischner sign) with an abrupt change in its calibre giving it an amputated appearance (Chang’s or Knuckle sign). Subpleural wedge shape consolidation was also apparent within the right upper lobe (Hampton hump). In view of the symptoms, past history of DVT, tachycardia and hypoxia along with signs on the chest radiograph there was high index of suspicion of Pulmonary Embolism (PE). Hence the patient had an urgent CTPA performed. The CTPA showed multiple PE's involving both main pulmonary arteries extending into the lobar divisions of all the lobes bilaterally. The diameter of the pulmonary trunk was greater than that of ascending aorta. There was also straightening of the inter-ventricular septum indicating right ventricular strain. Subpleural wedge shape consolidation, due to infarction, was confirmed within the right upper lobe and the left lower lobe (Hampton's hump).
Following the initiation of warfarin therapy the patient was discharged home with anticoagulation clinic follow-up for monitoring of the INR levels following a period of inpatient care.

Discussion

CT is the first line imaging modality for PE. However, there are a number of interesting signs historically described on plain radiograph in pulmonary embolism (PE).

A prospective observational study at 52 hospitals in 7 countries which included 2,454 patients showed that the most common chest radiographic interpretations were cardiac enlargement (27%), normal (24%), pleural effusion (23%), elevated hemi diaphragm (20%), pulmonary artery enlargement (19%), atelectasis (18%) and parenchymal pulmonary infiltrates (17%)(1). An elevated diaphragm, atelectasis or enlargement of descending pulmonary artery has been reported as being the most common finding in other studies. In our case, there was cardiomegaly, an elevated hemi diaphragm, but more specifically pulmonary artery enlargement and wedge shaped atelectasis were present on the plain radiograph.

Hampton's hump appears as a well-defined pleural-based area of increased opacity with a convex medial border; this finding aids in the differentiation of pulmonary infarction from pleural thickening or free pleural fluid.

Westermark sign is an area of oligemia distal to a large vessel that is occluded by PE.

Fleischner sign is a prominent central artery that can be caused either by pulmonary hypertension that develops secondary to peripheral embolization or by distension of the vessel by a large clot (Figure 1). Chang’s sign is dilatation and abrupt change in calibre of the right descending pulmonary artery (Figure 4).

The earliest consistent sign in pulmonary infarction is widening of a previously normal descending pulmonary artery [2]. This sign usually appears within 24 hours of the onset of symptoms and shows its maximal measurements within two to three days. Serial chest radiographs can be used to monitor the resolution of the pulmonary infarcts by observing the reduction in the size of the descending pulmonary artery.
However, neither the cardiomegaly or the pulmonary artery enlargement a appears sensitive or specific indicator for right heart strain which is an important predictor of mortality associated with acute pulmonary embolism [1].

CTPA is now the standard of care for the evaluation of patients with suspected PE. The above mentioned findings on a plain radiographs can help raise the index of suspicion and may provide clues to unrecognised PE. The main value of the chest radiograph is to exclude diagnoses that may clinically mimic PE such as pulmonary oedema, pneumonia or pneumothorax, however it cannot alone exclude PE [3].

Eventhough there may be findings on a plain radiograph in patients with PE, a negative plain chest radiograph cannot rule out a PE. Hence, CTPA is the investigation of choice in patients with high probability for PE.

Differential Diagnosis List

Final Diagnosis

Pulmonary Embolism

URL:	https://www.eurorad.org/case/7735
DOI:	10.1594/EURORAD/CASE.7735
ISSN:	1563-4086