MRI of the female pelvis: a possible pitfall in the differentiation of haemorrhagic vs. fatty lesions using fat saturated sequences with inversion recovery.

The use of fat-saturated techniques should be an integral part of the work-up of any T1-hyperintense structure in the female pelvis for tissue characterization and for differentiation of a fat-containing ovarian mature teratoma from a haemorrhagic lesion. Two cases with haematocolpos and haematometra are presented, respectively. The haemorrhagic content showed high signal both on T1- and T2-weighted images, whereas an unexpected signal decrease in the fat-saturated T2-weighted inversion-recovery sequence was encountered. This unspecific suppression of signal in tissues with similar T1 relaxation times as fat can lead to a diagnostic pitfall both in T1- and T2-weighted STIR pulse sequences. Furthermore, a loss of signal on T2-weighting may also be due to the phenomenon of "T2-shading" in T1-bright ovarian endometrioma. Therefore, the fat-specific spectral fat-saturation of T1-weighted images is strongly recommended for tissue characterization in gynaecological disease.