The dark lymph node sign on magnetic resonance imaging: a novel finding in patients with sarcoidosis

The purpose of this study was to describe a characteristic magnetic resonance imaging (MRI) appearance of lymphadenopathy in sarcoidosis--the dark lymph node sign (DLNS)--and to determine its prevalence in a retrospective review of cardiopulmonary MRI examinations obtained in patients with sarcoidosis.

Fifty-one adult patients with a clinical history of sarcoidosis were evaluated with thoracic MRI during a 15-month span; 29 patients were men, and 22 patients were women. The average age of patients was 53.7±11.2 years. Patients were considered to have the DLNS on MRI if mediastinal or hilar lymph nodes demonstrated internal low intensity with a peripheral circumferential rim of hyperintensity (relative to paraspinal muscle) on post-gadolinium volume-interpolated 3-dimensional gradient echo (3D-GRE/VIBE) and fat-saturated T2-weighted fast spin echo (T2-FSE/BLADE) sequences. Univariate analyses and a logistic regression were used to determine how variables of interest related to the DLNS.

Of the 51 patients with sarcoidosis, 49% (25 patients) demonstrated the DLNS. Nodal calcification was present on computed tomography in 45.7% (16/35) of patients with computed tomography scans obtained within 90 days of MRI. The DLNS sign was not more common in those with nodal calcification. When the DLNS occurred in conjunction with calcified nodes, the extent of hypointensity on MRI was not strictly limited to the calcified portions of the lymph node in 71.4% (5/7) of such cases.

The DLNS is commonly present on MRI examinations of patients with sarcoidosis, occurring in approximately half of the participants in our study.