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AJR Am J Roentgenol. 2012 Jul;199(1):W142-5. doi: 10.2214/AJR.11.7868.

Incidental pleural effusions detected on screening breast MRI.

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  • 1Department of Radiology, Tufts Medical Center, Boston, MA, USA.



Pleural effusions are a common complication of malignancy that must be differentiated from physiologic effusions identified on breast MRI. This study aimed to determine the incidence and reference range of physiologic pleural effusions observed in healthy women undergoing screening breast MRI.


A retrospective analysis of 200 consecutive women who underwent screening breast MRI between December 2007 and December 2008 was performed. Medical records were reviewed; patients with abnormal MRI findings resulting in a diagnosis of breast cancer, a prior malignancy, or cardiac or pulmonary disease were excluded. Patient age, the presence of pleural effusions, and, if present, the laterality were recorded. The largest size of effusions was measured at the anterior chest wall. A nonparametric Wilcoxon test was used to compare the sizes of right- and left-sided pleural effusions.


Of the 200 patients, 174 (87%) had a pleural effusion; 124 (62%) were bilateral and 50 (25%) were unilateral. Compared with the left side, right-sided pleural effusions were more frequent (81.5% vs 67.5%, respectively; p < 0.001) and were slightly larger (mean, 3.3 vs 2.8 mm; p = 0.019). Effusions ranged from 1 to 12 mm on the right and from 1 to 8 mm on the left. The reference range for pleural effusions on breast MRI based on this healthy population is up to 7 mm on the right side and 5 mm on the left side.


Small pleural effusions are a common physiologic finding in women undergoing screening breast MRI and should not prompt further testing.

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