Medical Image Of The Week: Westermark Sign

Figure 1. Chest x-ray showing decrease pulmonary vasculature on the right upper lobe (red circle, Westermark sign).

Figure 2. Coronal section of the CT angiogram showing occlusive thrombosis on the right pulmonary artery. 

A 71 year old man was evaluated in the Emergency Department for acute onset of dyspnea. On exam he was tachypneic, tachycardic and hypoxemic requiring 6 L/min of oxygen. He had recently underwent prostatectomy for prostate cancer. Past medical history was also significant for coronary artery disease treated with coronary bypass.

The chest x-ray (Figure 1) shows unilateral oligemia concerning for a pulmonary embolus and the CT angiogram of the chest (Figure 2) confirms the diagnosis.

While the chest radiograph is normal in the majority of pulmonary emboli, the ‘Westermark sign’ may be seen in up to 2% of the cases (1). It represents a focus of oligemia seen distal to a pulmonary embolism. The finding is a result of a combination of dilation of the pulmonary artery proximal to the thrombus and the collapse of the distal vasculature. 

Muna Omar MD¹, Tammer Elaini MD² and Bhupinder Natt MD¹

¹Division of Pulmonary, Allergy , Critical Care and Sleep Medicine

²Department of Internal Medicine

University of Arizona Medical Center

Tucson, AZ

Reference

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. [CrossRef] [PubMed] 

Reference as: Omar M, Elaini T, Natt B. Medical image of the week: Westermark sign. Southwest J Pulm Crit Care. 2015;10(3):125-6. doi: http://dx.doi.org/10.13175/swjpcc015-15 PDF

March 2015 Imaging Case of the Month

Michael B. Gotway, MD

Department of Radiology

Mayo Clinic Arizona

Scottsdale, AZ

Clinical History: A 35-year-old man presented with a history of Von Hippel-Lindau syndrome, including prior right-sided renal cell carcinomas, cerebellar hemangioblastomas, and retinal hemangiomas. The patient’s renal malignancies were treated with laparoscopic radiofrequency ablations 6 and 8 years prior to presentation, and subsequently with percutaneous microwave ablations in the interim between 2008 and presentation. The latest percutaneous microwave ablation procedure (Figure 1) was performed to address two nodular enhancing foci in the posterior superior pole of the right kidney and one interpolar enhancing, septated lesion that were noted to have enlarged slightly on a recent MRI examination (Figure 2) of the abdomen compared with one year earlier.

 Figure 1. Percutaneous microwave of three right-sided renal lesions, 2 posterior-superior pole, the other lateral interpolar in location, shows two NeuWave microwave antennas inserted into suspicious lesions in the right kidney.

 

Figure 2. MRI of abdomen (A and B, axial steady-state free precession fat saturation images and, C and D, coronal subtraction contrast-enhanced images) shows three potentially solid, enhancing foci, two in the posterior and superior pole of the right kidney (arrowheads), and one in the lateral interpolar kidney, the latter with thick septations (arrow) that have shown slight enlargement from MR. performed one year previously.

A CT of the abdomen (Figure 3), performed 2 years earlier, is shown as a baseline comparison.

Figure 3.  Upper panel: selected image from the CT of the abdomen performed 2 years prior to presentation shows enlargement of the bilateral kidneys with numerous, bilateral renal cystic lesions. No pleural or lung base abnormality is evident. Lower panel: movie of CT scan performed 2 years prior to presentation.

Several days following the percutaneous microwave ablation procedure, the patient complained of right-sided chest pain, and frontal chest radiography was performed (Figure 4). 

Figure 4. Frontal and lateral chest radiography performed several days following the right-sided percutaneous microwave ablation procedure.

Which of the following statements regarding the chest radiograph is most accurate? (Click on the correct answer to proceed to the second of seven panels)

1. The frontal chest radiograph shows a large right pleural effusion
2. The frontal chest radiograph shows diffuse lung opacities suggesting diffuse alveolar damage
3. The frontal chest radiograph shows mediastinal widening
4. The frontal chest radiograph shows pneumomediastinum
5. The frontal chest radiograph shows pneumothorax 

Reference as: Gotway MB. March 2015 imaging case of the month. Southwest J Pulm Crit Care. 2015;10(3):112-24. doi: http://dx.doi.org/10.13175/swjpcc031-15 PDF