The pattern and distribution of calcified mediastinal lymph nodes in sarcoidosis and tuberculosis: a CT study

Following granulomatous involvement, calcification of hilar and mediastinal lymph nodes is common and calcified nodes are frequently identified on computed tomography (CT). The aim of this study was to establish whether there is any difference in the pattern and distribution of such calcifications in tuberculosis (TB) and sarcoidosis.

The thoracic CT scans of 77 patients with proven TB (n=28) or sarcoidosis (n=49) were studied retrospectively. Lymph nodes were categorized by size and pattern of calcification: diffuse/homogeneous, focal deposits, eggshell, and complete nodal replacement by calcification. The position of hilar or mediastinal calcified nodes was recorded.

Nodal calcification was present in 26 fo 49 (53%) sarcoidosis patients and 13 of 28 (46%) TB patients. The mean short axis diameter of calcified nodes was significantly larger in sarcoidosis patients (sarcoidosis 12 mm, TB 7 mm, P < 0.003). A focal pattern of calcification was commoner in sarcoidosis (58% sarcoidosis nodes, 23% TB nodes) and complete calcification in TB (62% TB nodes, 27% sarcoidosis nodes). When hilar node calcification was present it was more likely to be bilateral in sarcoidosis than in TB (65% and 8%, respectively, P < 0.001).

CT of the mediastinum shows significant differences in distribution and pattern of calcification in lymph nodes in TB and sarcoidosis. Possible explanations for these differences include the route of lymphatic drainage of pulmonary TB and the caseating nature of tuberculous granulomas.