2006 Radiology Exam - Thorax Case 1

Information Provided to Candidate
1. 9 month old male German Shepherd. Presented with acute onset of respiratory distress
2. Please ignore the subcutaneous emphysema
3. State the radiographic findings.
4. Give a concise assessment and prioritized differential diagnosis.
5. Any further imaging studies needed?
6. If not, why not? If yes, what studies are indicated and why?

Right Lateral, Left Lateral and Dorsoventral Thorax

See images below. Click to enlarge.

Findings Expected from Candidate
The candidate was expected to recognize the marked unilateral (left) pneumothorax resulting in almost complete collapse of the entire left lung. The heart is displaced to the right and the right lung compressed, indicating a tension pneumothorax. This was a critical finding in the assessment of the case. In addition to the pneumothorax, there is a large, smoothly marginated relatively mobile peanut shaped soft tissue mass within the mid left hemithorax, probably originating from the left cranial lung lobe. A smaller more irregular mass immediately adjacent to it is likely the cranial aspect of the left cranial lung lobe, and this appears to contain a gas filled bulla. There is apparent subpleural air or multiple small bullous lesions, most apparent on the left side. Scant pleural fluid is present. There is an ill defined increase in opacity in the cranial aspect of the right cranial lung lobe which may be secondary to atelectasis or infiltrate.
There is degenerative joint disease and probable radiohumeral subluxation in one elbow - radiographs are indicated.

Conclusion Expected from the Candidate
Left sided tension pneumothorax. Lobulated mass within the left hemithorax; differentials include congenital pulmonary cyst, hematocele or less likely hematoma or abscess. Possible pulmonary bullae or subpleural gas. Scant pleural fluid. Probable congenital elbow disease.

Summary of Overall Candidate Performance

• This case was more about the 'journey' and not the 'destination'. The candidate needed a systematic approach to ensure detection of the pertinent roentgen signs, but also needed to be able to think through as to the most likely explanation for the array of radiographic findings. In this case, using a logical thought process, applying the basic principles of thoracic radiographic interpretation and knowledge of thoracic physiology were more important than getting the 'correct diagnosis'. Many candidates were perplexed initially but by applying the principles of radiographic interpretation they worked through the radiographic findings and arrived at a logical list of differentials, just as you do daily on the clinic floor.
• Some candidates failed to recognize the severe unilateral tension pneumothorax and misinterpretated the heart as being the 'mass' in the left hemithorax. Failure to address the life threatening pneuomothorax in a timely fashion may have resulted in patient death. If you are unsure where the heart is, follow the trachea down to the bifurcation. Unilateral pneumothorax is rare in a dog and usually indicates either prior pleural disease or a congenitally intact mediastinum. Those that correctly identified the pneumothorax and heart position on the VD view, were able to come up with a sensible list of differentials.
• A preoperative CT after the control of the pneumothorax was considered the most appropriate next step.

Followup:
A chest drain was placed, the pleural air immediately evacuated. Subsequently a CT was done preoperatively (dorsal plane MPR movie was available). Both the left cranial and right middle lung lobes were removed. The final histologic diagnosis was lung bullae and multiple pulmonary hematomas of unknown etiology.