In staging rectal cancer, transrectal ultrasound is good for the gander, but it may not be good for the goose. Transvaginal sonography, with its superior ability to resolve rectal wall layers, was the imaging modality of choice for female patients in a study performed at Toronto General Hospital in Canada.
Men represent the majority of rectal cancer patients, and transrectal ultrasound is the accepted standard for staging the disease. However, transvaginal sonography is routinely used in gynecological applications for women, according to lead author Dr. Kavita Dhamanaskar, a staff radiologist at the Hamilton Health Sciences Corporation in Hamilton, ON.
"This same modality and technique can be used in diagnosing nongynecologic pathology. The present study was done specifically to assess its role in detecting and staging rectal tumors," Dhamanaskar said.
Transvaginal ultrasound has also helped the researchers diagnose other bowel disease, anorectal fistulas and fissures, and tumors and metastases in the rectovaginal pouch, said Dr. Stephanie Wilson, supervising author of the study and head of the ultrasound division at Toronto General. The study was presented at the American Roentgen Ray Society meeting in May.
Forty-five women who had been referred for endoluminal sonography of a rectal tumor underwent transvaginal sonography following an enema. Researchers used a Philips HDI 5000 system with color Doppler to confirm neovascularity and to exclude pseudomasses due to fecal matter.
Twenty of the women were also scanned with transrectal ultrasound. Forty rectal cancers, four tubulovillous adenomas, and one gastrointestinal stromal tumor were found in the study subjects.
The researchers determined that of the 40 rectal carcinomas, seven were T1, nine were T2, 21 were T3, and three were T4. The group used surgical pathology and biopsy to correlate final interpretations.
Dhamanaskar and colleagues compared rectal wall layer definition, tumor visibility, and staging ability in the 20 patients who had undergone both transvaginal sonography and transrectal ultrasound.
Transvaginal sonography accurately staged tumors in 90% of the 40 rectal cancers. Transrectal ultrasound, on the other hand, was suboptimal for determining stenotic tumors in three patients, for staging large tumors in two patients, and for staging tumors that were high at the rectosigmoid junction in four patients. Transvaginal sonography revealed the lesion and correctly predicted the stage of tumor in all nine cases.
The particular mechanics of the transvaginal modality also made for a higher accuracy in imaging. Fluid introduced into the rectum from the enema outlined the tumor and the rectal wall, providing a better view of the intraluminal tumor, the authors said. The balloon used in the transrectal ultrasound compressed polypoid tumors, obscuring their view.
Not only was transvaginal ultrasound more accurate, it was also preferred by the patients because it caused less discomfort, Dhamanaskar said.
"In most cases, transvaginal sonography can replace transrectal ultrasound. We now routinely prefer the modality to transrectal ultrasound for rectal tumor assessment in women," she said.