**5.3 Solid deep lesions**

Solid deep lesions display low to intermediate signal intensity with punctuate areas of high signal intensity on T1 weighted images. Uniform low signal intensity is seen on T2 weighted images. The punctuate foci of high intensity are due to the zone of haemorrhage surrounded by abundant solid fibrous tissues. These may actually mimic metastatic lesions arising from intraperitoneal malignancies such as ovarian carcinomas. The two entities can be differentiated on T2 weighted images by the low signal intensity imparted by solid endometriomas often in combination with the presence of endometrial cyst.

Masses situated in the pouch of Douglas, posterior vaginal fornix and uterosacral ligaments may comprise of large fraction of glandular material with little fibrotic reaction, imparting hyperintense signals on T2 weighted images. Administration of contrast material will enhance such solid lesions, making it possible to distinguish it from necrosis or intramural hemorrhage.

Frequently the signal intensity may not be able to pick up the deep endometriosis of the uterosacral ligaments, especially if the punctuate foci of haemorrhage are missing in the lesion. In such case, the diagnosis is often made by correlating the thickening of the ligaments. Thickening more than 9mm in size or nodularity within the ligaments either bilateral or asymmetrical often give clue to the diagnosis.

#### **5.4 Bladder endometriosis**

Bladder endometriosis can be identified on MRI by deviation in signal intensity and gross anatomical anomalies in bladder wall thickness which can be localized or diffuse. Most of the times there are foci of high signal intensity in abnormally thickened bladder wall. Such findings may exist even if patients have normal cystoscopy result or without urinary symptoms. Bladder endometriosis infact infrequently infilterates the mucosa. Thus it is difficult to make out the lesions on cystoscopy. Advanced disease may present as ureteral obstruction and hydronephrosis.

#### **5.5 Rectal endometriosis**

Deep rectal involvement is less obvious on MRimaging due to the rectal contents which impart artifacts. Conventional MRI has infact sensitivity of only 33%. Results can be improved with the use of phased array coils, endovaginal coils and rectal contrast enema. MRI features that can be helpful in diagnosis include thickening of the rectal wall correlated with specific symptoms clinically, low signal intensity on T2 weighted images, and occasionally the presence of punctuate hyperintense foci of haemorrhage.

Endorectal sonography as dicussed earlier is superior to MR imaging for diagnosis of this entity. The deposits on bowel are seen as rounded hypoechoic areas.
