MR keeps breaking ground in pelvic imaging

Diffusion-weighted MR imaging could one day become a routine exam for noninvasive characterization and staging of uterine tumors, replacing unnecessary catheter or surgical biopsies, according to several studies released Sunday at the RSNA meeting.

Endometrial cancer is the most common gynecologic malignancy and the fourth most common cancer among U.S. women. Incidence of the disease is higher among white women, but it kills almost twice as many black women. About a fifth of the approximately 40,000 new cases diagnosed in 2007 will be lethal.

Carcinoma of the cervix is less common and carries low mortality rates in the U.S. compared with those in the rest of the world, mostly thanks to Pap smear screening. It hits minorities in disproportionately high numbers, though.

Both cancer types are hard to characterize, thus making biopsies necessary in many patients.

DWI will help physicians to distinguish benign from malignant lesions and reduce the number of patients who undergo these invasive procedures, said Dr. Nagaraj S. Holalkere, a radiologist at Massachusetts General Hospital.

Holalkere and colleagues retrospectively evaluated 65 women with 80 lesions who underwent DWI on a 1.5T scanner with a phased-array coil between August 2006 and March 2007. Two independent radiologists, reading blindly, characterized lesions using qualitative and quantitative parameters.

Qualitative analysis entailed comparing lesions to myometrium. Lesions were considered malignant if they appeared hyperintense on DWI and hypo- or isointense on apparent diffusion coefficient maps. Quantitative analysis involved measuring lesions' ADC values on axial and sagittal maps. ADC values below 1 were considered an indicator of malignancy.

The investigators found qualitative and quantitative analyses were reproducible tests that accurately differentiated benign from malignant lesions. Qualitative analysis yielded sensitivity, specificity, and accuracy rates of 79%, 94%, and 91%, respectively. The quantitative analysis produced mean ADC values of 0.6 for malignant lesions and 1 for benign ones. The correlation between axial and sagittal maps was statistically significant (r = 0.98, <0.0001).

MR-based characterization of benign and malignant pelvic masses should include both qualitative and quantitative DWI assessments, Holalkere said. He is using the technique routinely to gather a larger population sample and more conclusive data.

"A lower number of patients would be subjected to surgical biopsies if this technique is proven useful," he said.

Another study by Italian investigators weighed DWI's value in the assessment of myometrial tumor invasion. Dr. Sandro Sironi and colleagues at the University of Milan enrolled 37 consecutive patients with early-stage endometrial carcinoma and compared DWI data against conventional MRI and biopsy. They found the combination of conventional and diffusion-weighted MR imaging yielded diagnostic information.

Korean investigators tested DWI to characterize metastatic from nonmetastatic lymph nodes in patients with cervical cancer. The team was led by Dr Kyoung Ah Kim, a radiologist at the Pochon University College of Medicine in Sungnam. The investigators evaluated DWI data from 108 patients who underwent radical hysterectomy and lymph node dissection for uterine cervical cancer. They found DWI useful for differentiating metastatic from nonmetastatic lymph nodes in these patient populations.

Cervical lesion with restricted diffusion suggestive of malignancy on DWI. (Provided by N. S. Holalkere)