Shading sign

Shading sign is an MRI finding typically seen in an endometrioma. It may also be seen with some endometrioid tumours (e.g endometrioid carcinoma of the ovary)

It helps to distinguish endometriomas from other blood containing lesions (e.g. haemorrhagic corpus luteum cysts), with a sensitivity of 90-92%, a specificity of 91-98% and a diagnostic accuracy of 91-96% 1.

The sign is seen on T2 weighted sequences of lesions that are hyper-intense on T1, and consists of low signal (T2 shortening) affecting variable portions of the cyst. It may involve only a small portion of the cysts, typically layering dependently. Alternatively it may involve the entire cyst. The signal is due to high concentration of protein and iron within the endometrioma from recurrent haemorrhage. The degree of shading can vary from faint to complete signal loss.

Hemorrhagic adnexal cyst (most commonly, a corpus luteum cyst) may be bright on T1-weighted images, they are usually solitary and thin walled and are brighter on T2-weighted images than are endometriomas. Marked loss of signal intensity on T2-weighted images is not usually seen with hemorrhagic cysts, since they do not repeatedly bleed. Without recurrent hemorrhage and concentration of contents, viscosity of the cyst remains lower, and shading is unlikely to be present.1 

When noted with endometriosis,  lesions demonstrating a shading sign may be less likely to respond to medical treatment 2.

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Article Information

rID: 6701
Section: Signs
Tag: rewrite
Synonyms or Alternate Spellings:
  • Shading in pelvic MRI imaging

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