This 28 year old lady presented with swollen right cervical lymph nodes. CT neck showed enlarged lymph nodes in the right deep cervical chain with low density centres (arrows). CT chest (click image) showed centrilobular nodules in the apical segment of the left lower lobe (arrows). Tuberculosis was thought to be the most likely diagnosis. Biopsy and culture of the cervical lymph nodes was positive for Mycobacterium tuberculosis.

Lymph nodes with low density are typically seen with TB, fungal infections, pyogenic infection, necrotic metastases and occasionally lymphoma. The high resolution CT appearance of pulmonary TB can include centrilobular nodules and branching linear opacities (tree-in-bud appearance). The centrilobular nodules reflect intra- and peribronchiolar inflammatory exudate, whereas tree-in-bud reflects solid caseous material filling or surrounding terminal or respiratory bronchioles or alveolar ducts. These appearances are not pathognomonic. Tree-in-bud pattern is seen in: other endobronchial infections such as atypical mycobacteria, bronchopneumonia; bronchiectasis; cystic fibrosis; ABPA; panbronchiolitis; bronchiolitis obliterans; asthma; bronchioloalveloar carcinoma. Centrilobular nodules without tree-in-bud appearance can be seen in the same conditions, as well as hypersensitivity pneumonitis, respiratory bronchiolitis, BOOP, pneumoconioses, Langerhans cell histiocytosis, pulmonary edema and vasculitis.

1. Weisslander et al. Primer of Diagnostic Imaging. 3rd edition. Mosby 2003.
2. Webb et al. High-Resolution CT of the Lung. 3rd edition. LWW 2001.

Credit: Dr Bernard Ng