Tuesday, January 25, 2011

Endometrioma - MRI

32 year old female underwent MRI for pain in the lower abdomen a) T2 weighted fat saturated axial image showing bilateral ovarian cysts and one of the cyst in the right ovary (arrow) shows hemosiderin fluid levels (T2 shading). b) The same cyst in the T1 WI showing hyperintese fluid with hypointense hemosiderin. The features are consistent with endometrioma.

Endometriosis is defined as the presence of endometrial glandular tissue outside of the uterus. Endometriomas are frequently present in the premenopausal stage. It is present in 32% of women with infertility and/or pelvic pain between the ages of 20 and 45 years. Incidence is 29 - 54%.

The spectrum of findings on transabdominal sonography (TAS) is wide due to difficulty in accurately characterising the lesion. On TVS, the endometrioma is seen as a round homogeneous hypoechoic 'tissue', of low-level echoes, with a clear demarcation from the parenchyma and without papillary proliferation is present in at least 80% of cases of endometriomas.
Endometrioma do not shows acoustic streaming where as other cysts shows the same. 'Acoustic streaming' is a useful tool for differentiating endometriomas from other benign cystic lesions. 'Acoustic streaming' is defined as the bulk movement of fluid due to a sound field caused by energy transfer from an US wave to a fluid. The presence of hyperechoic wall foci (punctate peripheral echogenic foci) on ultrasonographic examination is very specific to endometriomas.
The diagnostic points described for endometrioma by different authors as follows:
  • A round-shaped homogeneous hypoechoic 'tissue' of low-level echoes without papillary proliferations associated with 'poor' vascularization (defined by Aleem et al. in 1995);
  • A round-shaped homogeneous hypoechoic 'tissue' of low-level echoes with an echogenic portion in which no flow is detected (atypical findings).
MRI demonstrates these endometriomas as cystic masses with very high signal intensity on T1-weighted images and very low signal intensity on T2-weighted images with layering of blood products termed as "T2 shading". Another common finding is a very dark peripheral rim (arrowhead), due to hemosiderin deposition, which is also the result of blood degradation.
Recently susceptibility-weighted imaging (SWI) has shown to contribute to the diagnosis of endometrioma by depicting hemosiderin deposition in the cyst wall.

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