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7-year-old Labrador Retriever

September 1, 2006

Presented with acute onset of respiratory distress

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  • The candidate was expected to recognize the presence of a cranial mediastinal mass, generalized megaesophagus and the presence of patchy alveolar infiltrate in the right middle lung lobe. In addition the presence of a small tube within the trachea should have been documented.
  • While there are many differentials for the radiographic findings, the presence of a cranial mediastinal mass, coupled with a generalized megaesophagus and patchy, ventrally located alveolar infiltrate should alert one to the possibility of a thymoma with secondary megaesophagus and aspiration pneumonia, – likely associated with myasthenia gravis. This was considered the most likely diagnosis. No additional radiographic studies were thought necessary. An esophogram is not necessary, and may put the patient at further risk of inhalation. Sonography and aspiration of the mass is a reasonable option.
  • This was one of the few cases where a question relating to non imaging tests was present. The candidate was expected to indicate that the most appropriate test to confirm the presence of myasthenia gravis as a paraneoplastic syndrome is an Acetyl Choline Receptor Antibody test.
  • The candidate should also confirm that the tube within the trachea is a tracheal oxygen tube and not a misplaced esophageal tube. Some comment relating to the potential moribund state of the patient (based on presence of tracheal oxygen tube) and how this might be contributing to the presence of megaesophagus was thought appropriate.
  • While most candidates correctly identified the radiographic findings, many candidates failed to make the association between the esophageal and pulmonary pathology and the cranial mediastinal mass. As radiologists, knowledge of this syndrome and the radiographic features is very important and this case tested both recognition of radiographic findings and knowledge of pathophysiology of disease. This was considered a straightforward case, where the candidate was expected to recognize compelling radiographic findings and present a primary differential diagnosis and possibly 1-2 other less likely differentials.