[The "sarcoid cluster sign". A new sign in high resolution chest CT]

To evaluate the presence of clusters of multiple small punctiform nodules in the peripheral regions of the lung in patients with sarcoidosis, and to report this finding as a new sign "the sarcoid cluster sign" in high-resolution chest CT (HRCT).

This is a retrospective study of the HRCT findings in 91 patients diagnosed with lung sarcoidosis at our hospital. We evaluated the presence of clusters of multiple small punctiform nodules in the periphery of the lungs (the "sarcoid cluster sign"), whether these were rounded or long in shape, and their distribution in the lung fields. We used reconstructions of maximum intensity projections (MIP). We correlated the imaging and histopathological results in three patients. Afterward, we evaluated the presence of the "sarcoid cluster sign" on high resolution CT findings in 120 consecutive patients studied for suspected diffuse lung disease.

The "sarcoid cluster sign" was present at HRCT in 9 of the 91 patients with sarcoidosis (6 men and 3 women; mean age 29 years). Most clusters were rounded and most were located in the non-subpleural peripheral regions of the upper and middle fields of the lungs. When the clusters were located in the subpleural peripheral regions, the clusters contained small subpleural nodules. The correlation between the imaging and histopathological results revealed that the clusters corresponded to noncaseous, noncoalescing granulomas with a predominance of CD4+ lymphocytes, without fibrosis, that were distributed in the lymph vessels. Only 2 of the 120 patients with suspected diffuse lung disease had peripheral clusters of multiple small punctiform nodules (the "sarcoid cluster sign"); these two patients had sarcoidosis, and a total of 21 cases of sarcoidosis were diagnosed in this group.

The "sarcoid cluster sign" on HRCT has been observed only in young patients with lung sarcoidosis. This finding could be useful in the diagnosis in the diagnosis of this disease.