MR white lung sign: incidence and significance in pulmonary consolidations

The presence of a pulmonary consolidation with a signal intensity comparable with that of the static fluid on heavily T2-weighted MR images has been named the "MR white lung sign." This sign has been described in mucinous bronchioloalveolar carcinoma (BAC). Our purpose was to establish the frequency and significance of this sign in pulmonary consolidations of varied causes.

In this prospective study, 83 patients with pulmonary consolidation underwent MR examination between January and December 1999. Segmental or lobar consolidations were due to pneumonia without central obstruction (n = 22), pneumonitis with central obstruction (n = 21), cicatricial atelectasis (n = 8), passive atelectasis (n = 10), radiation pneumonitis (n = 8), mucinous BAC (n = 5), infarction (n = 3), bronchiolitis obliterans organizing pneumonia (n = 3), nonmucinous BAC (n = 2), and lymphoma (n = 1). The MR white lung sign was considered present when the signal intensity of a pulmonary consolidation was comparable with that of the static fluid on heavily T2-weighted images obtained with MR hydrography sequences. Interobserver agreement, sensitivity, and specificity of the white lung sign in diagnosing mucinous BAC were calculated.

The MR white lung sign was present in 7 (8%) of 83 consolidations, including 5 (100%) of 5 cases of mucinous BAC and 2 (10%) of 21 cases of obstructive pneumonitis. The frequency of the white lung sign was 100% in mucinous BAC and 2.6% in consolidations due to other causes. The difference was statistically significant (p < 0.05).

The white lung sign is an uncommon finding in pulmonary consolidations evaluated with heavily T2-weighted sequences. However, the sign is characteristic of mucinous BAC and adds specificity to the radiologic diagnosis.