Online Learning and the Tree-in-bud Sign

Working in a Tuberculosis (TB) clinic I saw a patient who had a history of active TB and received a full course of treatment several years ago. She was presenting with new onset hemoptysis. Her CT scan showed abnormalities in the right middle lobe and the report described evidence of the "Tree-in-bud" sign. I had never heard of this before. It presented an opportunity to learn something new. There is usually a few minutes between cases to look things up before reviewing with the preceptor. I did a quick online search and discovered a blog called Radiopaedia, a wiki type resource that provides well cited explanations around radiographic signs with corresponding images. It contained an excellent article on the tree-in-bud sign. I learned that the sign refers to a pattern on CT of multiple areas of centrilobular nodules with a linear branching pattern, resulting in the appearance of a small budding tree. This sign can occur in many different conditions, but the physiologic principles underlying the presentation are usually endobronchial spread of infection or infiltration of the pulmonary arteries and interstitium. Some etiologies include: infective bronchiolitis (ie. from TB), cystic fibrosis, connective tissue disorders (rheumatoid arthritis and Sjogrens syndrome), obstruction/bronchiolitis, and neoplasms (bronchioalveolar carcinoma, lymphoma). One possible cause is atypical mycobacterial infections such as Mycobacterium avium complex. This was our main suspicion, as it fit with continued CT abnormalities and symptoms despite a full treatment for TB. This experience taught me the value of online medical blogs as learning resources. Certainly they are no substitute for peer-reviewed literature. However they are excellent starting points for a trainee to develop a basic understanding of a concept in the middle of a busy day. Radiopaedia was very useful as it gave me a brief overview of the concepts with images to solidify my understanding of the radiographic features. Additionally, it provided detailed references. This allowed me to use the online article as a jumping off point for my own studying of the primary literature.  I believe that when used correctly, community built medical wikis and blogs like Radiopaedia occupy a vital place in the heirarchy of medical literature. As the body of medical knowledge increases, I believe these resources will have a bigger and bigger role in shaping medical education.

- MH