Chest Imaging

Interlobular septal thickening

thickening of the interlobular septa, commonly seen in patients with interstitial lung disease. On plain radiographs, this results in visible Kerley lines. On HRCT, numerous clearly visible interlobular septa almost always indicate the presence of an interstitial abnormality; only a few septa are visible in normal patients. Interlobular septal thickening can be seen in the presence of interstitial fluid, infiltration or fibrosis.

Interlobular septal thickening can be smooth, nodular, or irregular in contour in different pathological processes. Smooth septal thickening is seen in patients with pulmonary oedema (Fig.1) associated with elevated left atrial pressure and has also been reported in pulmonary venoocclusive disease, lymphangitic carcinomatosis or lymphoma, alveolar proteinosis, interstitial infiltration associated with amyloidosis thoracic, and in a small percentage of patients with pulmonary fibrosis. Nodular or "beaded" septal thickening occurs in lymphangitic carcinomatosis or lymphoma, sarcoidosis, and silicosis or coal workers pneumoconiosis. In patients who have interstitial fibrosis, interlobular septal thickening visible on HRCT is often irregular in appearance.

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Fig.1

Prone HRCT scan showing interlobular septal thickening in a patient with interstitial pulmonary oedema.
Interlobular septal thickening, Fig.1