Teaching Case

50-year-old patient who reports a sudden onset of stabbing right thoracic pain without fever, dyspnoea or cough. Previous medical history included ulcerative colitis, bladder cancer and deep venous thrombosis.

X-ray (10 days after the acute episode):
A non-specific parenchymal opacity within the right inferior lobe and blurring of the right costophrenic angle (pleural effusion). Note the enlarged inferior pulmonary artery (Palla's sign). (Fig. 1b) Following these findings, the patient started an antibiotic treatment.

X-ray (15 days):
Increasing pleural effusion with blurring of the right costophrenic angle (Ellis-Daimoseau line) and a slightly enlarged inferior pulmonary artery (Fig. 1c). After these new findings and his previous medical history, a CECT was performed to rule out other pathological conditions.

CECT:
Pulmonary embolism involving the latero-basal and postero-basal arterial branches of the right lower lobe (Fig. 2).
Triangle-shaped consolidation with peripheral air lucencies within it (which are not air bronchograms) and diminished enhancement of lung parenchyma (Fig. 3a, b). Note the absence of arterial vessels within the consolidation (Fig. 3, 4).

X-ray (before being discharged):
Persistent right lower lobe subtle opacity with a residual linear scar and pleural thickening. No pleural effusion is present (Fig. 5).

A- BACKGROUND [1]

Pulmonary infarction is due to coagulative ischaemic necrosis. The ischemic damage to the arterial endothelium and alveolar cells causes haemorrhage (early stages) or coagulative necrosis (infarction, later stages).
Peripheral emboli rather than central, tend to cause infarction (10–30% of patients with pulmonary embolism have pulmonary infarction), this is related to a dual blood supply of the lung: from pulmonary arteries and bronchial arteries. Peripheral blood flow relies mainly on pulmonary arteries, this is the reason why this area suffers the most important ischaemic changes.


B- CLINICAL PERSPECTIVE [1, 2]

Infarction and haemorrhage occur at the periphery of the lung. Small haemothorax secondary to pulmonary infarction tend to irritate the pleura and cause pain.

Pleuritic chest pain is more frequent in patients with pulmonary infarction than in patients with acute pulmonary embolism who do not have infarction.

C- IMAGING PERSPECTIVE [1, 2, 3]

X-ray:

Unspecific parenchymal opacity. A typical appearance as a wedge-shaped pleurally-based opacity ‘Hampton hump’ typically abutting the pleura, could be found.
Pleural effusion is more common in pulmonary embolism with than without infarction.
Chronic pulmonary infarcts can leave residual radiographic changes as linear scars and pleural thickening.

ULTRASOUND:

Pleurally-based hypoechoic, triangular or round lesion.
Early infarcts are often hypoechoic.

CT:

- Wedge-shaped, broad pleurally-based opacity with a truncated apex and a convex border (‘Hampton hump’).

- Central lucencies are suggestive of pulmonary infarction, although they could represent aerated non-infarcted lung. Interobserver agreement seems good for central lucencies.

- Lower frequency of air bronchograms within the infarcted lung parenchyma.

CONTRAST-ENHANCED CT:

- Thromboembolism within the pulmonary artery feeding the "opacity" could be detected.

- The vascular sign (a thickened vessel leading to the apex of the opacities) is difficult to recognize.

- Decreased enhancement is related to a diminished perfusion of the lung secondary to the vascular occlusion.

MRI:

MRI appearance changes according to signal characteristics of the aging blood present in the alveoli (haemorrhage):
- <24 h = T1 hypointense and T2 hyperintense.
- >24 h to 1 week = Subacute infarction being T1 hyperintense.

D- OUTCOME

Infarcts should diminish (‘melting sign’) with complete resolution or leaving a residual scar or pleural thickening, although this occurs over a period of weeks or months.


E- TAKE HOME MESSAGE

- Central lucencies are very specific for infarct.

- Pleural effusion is a frequent finding.

- Wedge-shaped, broad pleurally-based opacity with a truncated apex and a convex border (‘Hampton hump’) is typical.