12-year-old female Shih Tzu

( M=Major m=Minor)

• M – Soft tissue opacity mass in the left caudal lung lobe. This mass has a well-defined cranial margin that causes cranioventral displacement of the left caudal lobar bronchus and lateral displacement of left caudal lobar vessels. The diaphragm remains well defined. The mass is best seen on the right lateral and dorsoventral projections. It is very difficult to appreciate on the left lateral projection.
• M – Moderate-to-marked diffuse unstructured interstitial pattern that partially obscures the margins of the pulmonary vessels, the heart and the left caudal lung lobe mass.
• M – Mild pleural effusion, characterized by multiple thin pleural fissure lines, border effacement of the cardiac silhouette caudoventrally and mild lung lobe retraction.
• m – Mild hepatomegaly, characterized by caudal extension of the liver with rounding of the margins.
• m – Small foci of amorphous granular mineralization: one adjacent to the left scapula and another ventral to the sternum.

Examiner Comments:

The main difficulty with this case was in identifying the caudal left lung lobe mass. Indeed, the accompanying interstitial pattern causes partial border effacement that makes the mass more difficult to see than in normally aerated lung. A few candidates were confident that it was present, and others suspected it. Remaining candidates either did not see it, or thought that it was a more severe area of interstitial/alveolar disease. The mass effect on the bronchus/vessels and well-defined cranial border were either not seen or ignored as distinguishing features.

The opacity of the mass was mistakenly thought to be fat by a few candidates. An impression of fat opacity may be explained either because 1) the mass is partially superimposed with air in the lungs on all projections, giving it an intermediate opacity, or 2) the surrounding interstitial opacity in the lungs reduces the opacity differential between the mass and the lungs.

A few candidates thought the mass could be in the caudal mediastinum; these candidates usually also thought the mass was of fat opacity. The effect of the mass on the pulmonary structures makes this unlikely. Also, the mass is centered neither around the aorta, nor the esophagus, but rather between the two on the lateral projections. Finally, there is no history that supports an esophageal mass. In this case, as well as others in the thoracic section, there was the perception that candidates ignored the history or did not trust it as they would during routine clinical duty.

The unstructured interstitial pattern was generally identified. A few candidates attributed it to the overlying pleural effusion or pulmonary underinflation. However, it was more severe than could be explained by artifact alone; this is particularly appreciable on the dorsoventral projection.

A few candidates mistakenly interpreted the fat in the cranial abdomen on the right lateral projection as a mass (either soft tissue or a lipoma) or as peritoneal effusion.

Some candidates mentioned mild left atrial enlargement. This was not considered to be an accurate finding in this case, but it was not penalized.

• Left caudal pulmonary mass, pleural effusion and interstitial pulmonary disease. Together these could be explained by 1) a neoplastic mass with diffuse pulmonary involvement and malignant effusion, such as could be seen with lymphoma or a carcinoma 2) a granuloma with diffuse pneumonitis and inflammatory effusion, such as could be seen with fungal disease. This second possibility is considered less likely and is less compatible with the patient history. A pulmonary hematoma, contusions and hemothorax are also not considered, due to the duration of clinical signs and lack of trauma.
• The interstitial pulmonary disease can also be a separate entity from the mass, possibly representing severe interstitial fibrosis or pulmonary mineralization from hyperadrenocorticism. More acute explanations such as ARDS or other causes of pulmonary edema are unlikely due to the 1-month duration of the cough and the absence of acute respiratory distress.
• Hepatomegaly may be an unrelated endocrinopathy/vacuolar hepatopathy or related to the same differentials as the caudal lung lobe mass.
• Soft tissue dystrophic mineralization is considered incidental (i.e. post injection granuloma, calcinosis cutis from hyperadrenocorticism).

Examiner Comments:

When the mass was seen, synthesis usually included appropriate differential diagnoses. It was expected that the candidate would try to tie together all of the main radiographic findings. However, additional separate considerations for the interstitial pattern (i.e. pulmonary fibrosis) were often made and considered appropriate.

When the mass was not seen, appropriate case synthesis became more difficult. Candidates received partial credit for tying together the diffuse unstructured interstitial pattern with the pleural effusion, as long as these differentials were appropriate for the history of the animal. Inappropriate differentials were those that implied an acute history, such as cardiogenic or non-cardiogenic edema/ARDS.

• Obtaining a definitive diagnosis of the nature of the left caudal lung lobe mass is the priority. Ultrasound-guided FNA for cytology is the best method to obtain this.
• The volume of pleural effusion is likely too scant to obtain a sample.
• CT-scan is not considered necessary for diagnostic purposes, unless the mass cannot be seen via ultrasound for sampling.
• Airway sampling (BAL, TTW) may be low yield as the pulmonary disease is interstitial rather than bronchial.

Examiner Comments:

Case management suffered when the pulmonary mass was not seen, as many candidates then developed a “shotgun” approach that could include bloodwork, thoracic CT, airway sampling, cardiac ultrasound and abdominal ultrasound/radiographs. Partial credit was given when this was very clearly prioritized and justified.

When the mass was seen, candidates usually recommended ultrasound-guided FNA over CT. Ultrasound was considered a much more appropriate next step as it is a less costly and less invasive method to obtain the diagnosis. Candidates were penalized for recommending CT first and/or for recommending CT with no justification or “to better define pulmonary/intrathoracic disease.”