Pulmonary sarcoidosis: atypical HRTC features and differential diagnostic problems. 
The aim of this paper is to present atypical or unusual appearances of pulmonary sarcoidosis, assessed at HRCT, and to suggest some elements for the differential diagnosis.  The HRCT scans of 31 patients were retrospectively reviewed.  The final diagnosis of sarcoidosis was established on the basis of clinical and laboratory data alone in one patient, of clinical and laboratory data supported by bronchoalveolar lavage (BAL) findings in 14 patients, lung biopsy in 15, and liver biopsy in one patient.  Fifteen patients presented with the main aspects of atypical manifestations.  In the 15 patients who presented with less frequent or atypical manifestations of pulmonary sarcoidosis, the following patterns were identified: 2 cases of large opacities with ill-defined margins, 8 of peripheral "pseudo-plaque" opacities, 2 of punctuate lymph node calcifications, 8 of ground-glass opacities with fine reticulation, and 5 of isolated opacities with dimensions not consistent with the surrounding background, with or without cavitation.  Besides the typical manifestations of pulmonary sarcoidosis, there may be several atypical or nonspecific presentations: it is not by chance that the literature often describes this disease as the "great masquerader".  Mediastinal lymphadenopathies and perilymphatic, subpleural or peribronchovascular nodules represent the typical patterns of pulmonary sarcoidosis; interstitial streaks and bilateral para-hilar thickening are also frequently observed.  The presence of peripheral "pseudo-plaque" opacities and of ground-glass opacities with fine reticulation is the key to a diagnosis of "atypical" sarcoidosis.  Calcifications within hilar and mediastinal lymph nodes, 1 cm or larger in dimensions, with a focal rather than diffuse distribution, should raise a suspicion of sarcoidosis rather than tuberculosis.  Upper lobe localisation is rather infrequent in bronchioloalveolar carcinoma.  Not all that excavates is tuberculosis: therefore, a differential diagnosis with tuberculosis may prove difficult, and the two diseases may coexist.  Pseudoalveolar pulmonary thickening that eventually resolves and disappears does not exclusively entail an inflammatory thickening.