BOSTON--Transrectal ultrasound is not a reliable method for detecting residual or recurrent tumor in prostate cancer patients after cryosurgical ablation, due to the altered appearance of the gland on ultrasound after freezing, Caryl Salomon, MD, said at the 42nd Annual American Institute of Ultrasound in Medicine (AIUM) conference.
Transrectal ultrasound examination has been used after cryosurgery to localize the prostate and guide the biopsy procedure when post-therapy monitoring (via digital rectal examination and measurement of PSA levels) indicates the possible presence of residual or locally recurrent tumor.
The goal of the study by Dr. Salomon and her colleagues at Loyola University Medical Center, Chicago, was to characterize the transrectal ultrasound appearance of the prostate after cryosurgical therapy and correlate the findings with detection of tumor in biopsy specimens.
The authors reviewed the images and reports of 24 transrectal ultrasound exams performed in 15 postcryosurgical prostate cancer patients. These exams had been performed for various reasons, including postoperative follow-up, abnormal digital rectal exam, or elevated or rising PSA levels.
Ultrasound findings were then correlated with the results of pathologic analysis of biopsy specimens, on an individual basis as well as for the entire gland.
The retrospective evaluation of the ultrasound images for morphologic characteristics of the postcryosurgical prostate glands showed a sensitivity of 6%, specificity of 95%, positive predictive value of 14%, and negative predictive value of 88% for detection of residual or recurrent prostate cancer.
It was not possible for the researchers to reliably distinguish viable tumor tissue from surrounding scarred prostate tissue, necrotic tumor, and viable benign prostate gland tissue using transrectal ultrasound.
In an interview, Dr. Salomon explained that freezing generally does not destroy all of the prostate gland. In the destroyed cells, the cellular protein is denatured; the cells take on more water and are destroyed. An inflammatory process follows, leading to the development of fibrosis and eventually scarring.
These alterations lead to a distorted appearance of the prostate from the typical pretherapy ultrasound appearance, she said. Pretherapy, the central portion of the prostate gland appears darker than the periphery. After cryosurgery, the usually homogenous tissue appears more variable. Both the central portion and the periphery may appear variably dark or bright on ultrasound imaging.
"It is difficult to predict what the prostate will look like after cryosurgery," Dr. Salomon said. "The alterations from normal that would identify a tumor mass on ultrasound pretherapy are no longer distinguishable," she said.
Based on this study, Dr. Salomon said that "transrectal identification of focal lesions is not a reliable criteria for detection of residual tumor in the postcryo-surgical ablation prostate. Distorted sonographic prostate morphology is identified in the majority of patients after cryosurgical ablation."
Thus, Dr. Salomon and her colleagues at Loyola cautioned that systematic biopsy should not be deferred due to lack of transrectal ultrasound identification of focal abnormalities in patients with appropriate clinical indications.
Dr. Salomon holds out the hope for improvements in the accuracy of trans-rectal ultrasound in this setting in the future with the use of color Doppler and contrast-enhancing agents.