Transrectal ultrasonography (TRUS), shown in the images below, plays a central role in the contemporary diagnosis of prostate cancer because it enables accurate, image-guided biopsy of the gland. Patients are usually referred for TRUS because an abnormality is found during DRE or because the serum PSA level is elevated.
Axial transrectal ultrasonographic (TRUS) scan shows extensive hypoechoic area (arrows) in the right peripheral zone. Biopsy revealed prostatic adenocarcinoma.
Axial transrectal ultrasonographic (TRUS) scan shows a hypoechoic area in left peripheral zone and a small hypoechoic area in right peripheral zone (arrows). Biopsy revealed an adenocarcinoma (Gleason grade 6).
Axial transrectal sonogram in a patient with normal results during digital rectal examination and a prostate-specific antigen (PSA) level of 9ng/mL. Image shows extensive bilateral, but predominantly left-sided, hypoechoic areas in the peripheral zone (arrows). Biopsy confirmed a Gleason grade 8 prostate cancer. Minor capsular irregularity is present on the left; this is consistent with a T3 tumor.
Axial transrectal ultrasonographic (TRUS) power Doppler scan in the same patient as in previous image. The patient had normal results with digital rectal examination and a prostate-specific antigen (PSA) level of 9ng/mL. A generalized increase in vascularity was noted in the posterior aspect of the prostate (arrows). However, this finding is not specific to the hypoechoic area in the left peripheral zone, illustrating the difficulty of using Doppler techniques in the assessment of prostate cancer.
Axial transrectal ultrasonographic (TRUS) scan in a patient with clinical benign prostatic hyperplasia (BPH) and a serum prostate-specific antigen (PSA) level of 11ng/mL. Enlargement of the transition zone is present, but no focal abnormality is observed in the peripheral zone. Systematic, 6-core biopsy revealed adenocarcinoma from both lobes of the prostate (ie, this is an isoechoic tumor in the peripheral zone of both prostatic lobes).
TRUS is widely available, well tolerated by patients, and relatively inexpensive. It currently offers the best opportunity to demonstrate a prostate cancer, but because many prostatic tumors are both isoechoic and multifocal, TRUS has major limitations in fully demonstrating prostate cancers. Furthermore, TRUS has a low specificity because many pathologic conditions may appear as similarly hypoechoic areas in the PZ of the prostate. For this reason, diagnostic assessment of cancer in the prostate must be made by means of histologic interpretation of biopsy samples. TRUS provides the opportunity for accurate and comprehensive biopsy of the prostate gland while providing an imaging examination.
Many pathologic processes can appear as a hypoechoic area in the PZ of the prostate or as a hypervascular area on color or power Doppler sonograms. The differential diagnoses of a hypoechoic area in the PZ include prostatitis, tuberculous prostatitis, granulomatous prostatitis, PIN, and prostatic atrophy and infarction. These are accurately differentiated only by using biopsy of the focal ultrasonographic abnormality. Furthermore, because many prostate cancers are isoechoic, these can be identified only by using systematic biopsy techniques.
With TRUS, the prostate is shown to be divided into an outer gland (PZ and CZ) and an inner gland (TZ). Calcification in the corpora amylacea in the surgical capsule between the outer and inner parts of the prostate is common. Particular attention should be paid to the PZ in prostate cancer diagnosis. The most frequently noted abnormality caused by prostate cancer is a hypoechoic area in the PZ. Rarely, cancer may appear as a hyperechoic area.
Prostate cancer and prostatitis each may have increased vascularity, as shown on color and power Doppler sonograms. This focal alteration in the prostatic vasculature is most commonly found in hypoechoic areas in the PZ, as depicted on gray-scale images. No cancer-specific flow pattern has been identified, and some cancers that are demonstrated clearly on gray-scale Doppler imaging show no focal hypervascularity.
Lymphoma of the prostate tends to present in younger men, and large hypoechoic masses in the TZ and PZ have been reported.
Prostate cancers frequently demonstrate isoechoic findings. This observation is the basis for the systematic biopsy approach in which multiple cores are taken from both lobes in a standardized manner. Color and power Doppler study results have been disappointing, and they have not been significantly helpful in detecting cancers that are isoechoic on gray-scale examination.
Few reports in the published literature describe the detailed sonographic appearances of the rarer histologic variants of prostate cancer. In comedocarcinoma—the most malignant form of prostate cancer—stippled, multiple, small, hyperechoic foci within the hypoechoic area of the cancer have been reported. In one study, multiple small cysts in the prostate were identified in 2 patients with adenoid cystic carcinoma of the prostate.
TRUS may be used for local staging of prostate cancer because it can demonstrate bulges of the prostate capsular outline or overt extracapsular extension. TRUS findings have been found to be inaccurate in the staging of localized prostate cancer, but PZ tumors longer than 2.3cm that contact the fibromuscular rim surrounding the prostate may be associated with extracapsular invasion.
The original systematic approach to biopsy included the acquisition of 6 cores, with 1 core taken bilaterally from each of the prostate lobes at the base, mid-gland, and apex in a parasagittal plane (ie, a "sextant" biopsy). Current practice is to obtain an increased number of cores (ie, lateral PZ cores, midgland cores, or TZ cores) in addition to the standard 6 cores. A 10-core biopsy that incorporates the traditional 6 parasagittal samples plus 2 lateral samples from the right and left prostatic lobes is now a standard technique for systematic biopsy.
Systematic biopsy may be supplemented with cores obtained through hypoechoic PZ lesions. Focal areas of hypervascularity in the PZ of the isoechoic prostate, as shown on color Doppler examination, may also be targeted.
Opinions differ regarding whether TZ cores should be routinely obtained during an initial biopsy procedure or whether the samples may be obtained during repeat biopsy in a patient with an elevated PSA level after the initial systematic biopsy results are negative for malignancy.
Most TZ cancers are found by analyzing systematic biopsy cores specifically obtained from the TZ. Little attention has been paid to assessing hypoechoic areas in the TZ, because of the lower frequency of cancer in the TZ and the perceived lower potential for metastatic spread of primarily TZ cancer. No specific studies in the literature report the biopsy results in focal TZ hypoechoic areas or in areas of specific focal alterations of TZ vascularity, as identified by use of color or power Doppler imaging.
Some authors describe a saturation biopsy approach in which as many as 40 cores are obtained under general anesthesia or sedation. The precise biopsy approach must be individually tailored on the basis of the patient's clinical features (eg, DRE and PSA levels).
Currently, research studies are under way to investigate whether ultrasonographic contrast agents have a role in the identification of cancer in the prostate and whether, by demonstrating tumor vascularity, they have a role in establishing prognosis of a patient with biopsy-detected prostate cancer.
However, the use of ultrasonographic contrast agents increases the time and cost of ultrasonography-guided prostate biopsy procedures. No marked improvement has been found in the accuracy of prostate cancer diagnosis with contrast agents. These agents remain experimental, and they have not been adopted into standard uroradiologic practice.
Nonetheless, the impact of ultrasonographic contrast agents on radiologic practice could be considerable if future research proves that they enable the quantitative preoperative assessment of microvascular density or that they provide prognostic information in an individual patient.
Research studies are also being conducted to assess the value of elastography in the diagnosis of prostate cancer; however, the role of this technique is still unclear.
In other research, Onik et al found that 3-D prostate mapping biopsy (3-D–PMB; carried out transperineally using a brachytherapy grid under TRUS guidance) can safely and accurately stage prostate cancer patients. The investigators compared 3-D–PMB with traditional TRUS biopsy in 180 patients with unilateral prostate cancer on TRUS biopsy. A median of 50 cores were obtained with 3-D–PMB. In 110 patients (61.1%), biopsies were positive bilaterally, and in 41 patients (22.7%), Gleason scores were increased to 7 or higher.