"Tree-in-bud" can mean tumor in bronchi too...

62 year old male, history of HIV, presents with groin swelling, otherwise asymtomatic. Ultrasound shows extensive DVT in the iliac venous system. This let to a CT, which showed large pelvic mass, extending into the left iliac venous system. 

So far it was straightforward. But now the lung windows showed dreaded "tree-in-bud" opacities. As the great Dr. Webb says, this means the "answer is in the sputum", and it is usually an infectious process.

But is it? Patient does not complain of cough. Turn on spectral, and notice that the "tree-in-bud" opacities have clear iodine uptake. This is consistent with intrabronchial tumor. This is very hard to pick up on imaging, or prove histologically, as this is well beyond the range of bronchoscopy. Patient does have a large para-esophageal lymph node, as some of you will astutely note in second image below, and it has been biopsied. Results are awaited, but I think this will be a metastatic sarcoma.

With spectral, we can now resolve down to branch bronchi, and do not have to guess anymore. We might be seeing more bronchial metastasis now...

Maximum Intensity projection shows "tree-in-bud" in the both the lungs 

Iodine map shows uptake in the "tree-in-bud". Not convinced? Look at magnified views below. The large paraesophageal lymph node is great for biopsy...

Detail view shows "tree-in-bud" opacity 

Iodine uptake in the "tree-in-bud"

Large mass in left pelvis. Note extension into the left external iliac vein.

Oblique sagittal with iodine overlay nicely demonstrates the intravenous extension.