MRIs improved diagnosis of severe endometriosis

* New type of MRI scan helps avoid more serious surgery

* Diagnosed 26 of 27 cases of deep endometriosis

CHICAGO, July 7 (Reuters) - An advanced type of MRI scan may help doctors more accurately diagnose a severe form of endometriosis, researchers said on Tuesday, potentially allowing some women to avoid invasive pelvic surgery.

They said a powerful new kind of magnetic resonance imaging scan called 3 Tesla, or 3T MRI, helped doctors rule out deep endometriosis in 93 percent of young women studied.

Endometriosis is a chronic disease that results when uterine tissue, called endometrium, grows outside the uterus, causing pain in the pelvis and lower back, painful menstrual cramps, fatigue and infertility. It affects 5 million American women.

In most cases, doctors can remove excess tissue using laparoscopic surgery, in which a lighted instrument is inserted through a small incision.

But in women with deep endometriosis, in which uterine tissue attaches itself to other organs such as the ovaries, Fallopian tubes and colon, excess tissue must be removed through a large incision in the abdomen, a riskier procedure that requires longer follow up.

A team lead by Dr. Nathalie Hottat of the Universite Libre de Bruxelles in Brussels, Belgium, wanted to see if the high-tech MRI scanners could help surgeons better predict which women needed more invasive surgery.

General Electric's (GE.N) GE Medical Systems, Philips (PHG.AS) and Siemens AG (SIEGn.DE) all make 3T MRI machines, which use more powerful magnets to produce high-resolution images.

Hottat's team performed MRI scans on 41 women aged 20 to 46 with suspected endometriosis prior to surgery.

They found MRI accurately diagnosed 26 of 27 cases of deep endometriosis, helping doctors to plan their surgery, the team reported in the journal Radiology.

The scans were highly accurate at determining which women would benefit from less-invasive surgery, ruling out deep endometriosis in 93 percent of cases and allowing surgeons to perform a less-invasive laparoscopic procedure. (Editing by Maggie Fox and Cynthia Osterman)