Is there a role for transrectal ultrasound in the diagnosis of prostate cancer nowadays? This question was our starting point when we designed this study.
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We carried out a prospective study during one-year, which included all patients with suspicion of prostatic cancer, for whom biopsy was indicated by our Urologists.
Previously to the biopsy and without knowing PSA levels and previous US findings, the patients underwent ultrasonography by two experienced radiologists in order to look for suspicious nodules. Only solid and hypoechogenic lesions were considered to be suspicious, provided there was agreement between the two observers.
Traditionally, as we all know, literature underestimates the role of transrectal prostate ultrasonography in the detection of suspicious lesions. Some publications even indicate that ultrasonography is only useful to guide the biopsy.
On the other hand, sonographic characteristics of nodules considered suspicious have been studied and defined, and hypoechogenic solid nodules located in the peripheral region have high predictive value for cancer. In addition, with the technological development of US apparatus and intracavitary transducers with increasingly higher frequencies, the number of sonographically detected suspicious nodules has been increasing.
Should we look for suspicious nodules previously to the biopsy? Can we find suspicious nodules with the sensitivity required for a screening program? Are they a specific finding? How can we improve our cancer detection rate with US-guided biopsy? These were some questions we intended to answer with this study.
Our most important conclusion was that the high positive predictive value for the biopsied suspicious nodules, in association with the great representation of tumour in those specimens (significantly greater than in the random specimens) justifies that a systematic sonographic evaluation with particular attention to the peripheral region where most prostate tumors are found, should be performed before the biopsy. When in the presence of a suspicious nodule a combined biopsy strategy should be adopted by collecting samples from all prostate sextants, supplemented by targeted biopsy of the sonographically suspicious lesions detected. Such an approach neither increases the rate of complications nor increases significantly the cost and examination time, with the already proved advantage of allowing for greater tumor representation, and detecting some cases which otherwise would not be detected in random samples.
The low sensitivity to detect nodular lesions in malignant cases remains the biggest drawback of sonographic evaluation. It is important to keep in mind that a prostate US considered normal cannot rule out biopsy in cases where it is indicated. The low rate of suspicious nodules detection by ultrasonography, as compared with the neoplasms detected by the double sextant method, does not allow for the adoption of only targeted biopsy of nodular lesions rather than the established approach to all prostate sextants.
A lot of work still needs to be done. It is important to further investigate strategies to increase its diagnostic accuracy with methods such as Doppler, contrast-enhanced ultrasonography and elastography. On the other hand, with the increase of prostatic MRI, more suspicious nodules will be found. It will be paramount to study how we can also use MRI findings to improve ultrasound guided biopsy accuracy.
Pedro Marinho Lopes
Intern Physician, Unit of Radiology, Hospital Distrital de Santarém, Santarém, Portugal.