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
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.