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, including 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 Miami Beach.
Researchers compared rectal wall layer definition, tumor visibility, and staging ability in 20 women who received both transvaginal and transrectal ultrasound for rectal cancer staging. They used an HDI 5000 system and color Doppler to confirm neovascularity and to exclude pseudomasses due to fecal matter. Surgical pathology and biopsy were used to correlate final interpretations. Out of 40 rectal carcinomas, seven were T1, nine were T2, 21 were T3, and three were T4. (Four tubulovillous adenomas and one gastrointestinal stromal tumor also were found.)
Transvaginal sonography accurately staged 90% of tumors. Transrectal ultrasound 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 technique contribute to a higher accuracy in staging. Fluid introduced into the rectum from the enema outlines the tumor and the rectal wall, thereby providing a better view of the intraluminal tumor. Also, the balloon used in the transrectal ultrasound tends to compress polypoid tumors, obscuring their view.
"In most cases, transvaginal sonography can replace transrectal ultrasound. We now routinely prefer the modality to transrectal ultrasound for rectal tumor assessment in women," Dhamanaskar said.