HELICAL CT of Prostate Cancer: Early Cinical Experience
Dr. Adilson Prando e Dr. Sidney Wallace
OBJECTIVE

This study was undertaken to determine whether helical CT can reveal carcinoma of the prostate detected at transrectal sonographically guided biopsy.

MATERIALS AND METHODS

Helical CT of the prostate was performed in 35 patients: 25 with proven prostate cancer (group I) and 10 without cancer detected at biopsy (group II). All patients in group I had cancer I the peripheral zone, and three of these showed foci of cancer in the transitional zone. All patients of group II had undergone at least two sets of biopsy before CT. In group I, areas of contrast enhancement in the peripheral zone of the prostate were defined as suggestive of cancer an correlated with the histopathologic findings.

RESULTS

Helical CT revealed cancer in 22 (88%) of 25 patients with proven prostate cancer. Transrectal sonographically guided biopsy detected 102 cancer sites in the peripheral zone and in the transitional zone in these 25 patients. Helical CT accuretely revealed 59 peripheral zone cancer sites (58%) but did not reveal 43 cancer sites (42%). Abnormal contrast enhancement in the peripheral zone that was not caused by cancer was seen in 10% of suspicious lesions. The three cancer sites in the transitional zone were indistinguishable from benign nodular changes.

CONCLUSION

Prostate cancer detected at transrectal sonographically guided biopsy appear on helical CT of the prostate as focal or diffuse areas of contrast enhancement in the peripheral zone. A prospective study has been initiated to deterrmine the accuracy, sensitivity, and specificity.
Although helical CT is the state-of-the-art technique for the evaluation of the pelvis, to our knowledge its role in the evaluation of prostate cancer has not been addressed in the radiology literature. Knowing that prostate cancer enhances earlier then healthy prostatic tissue on dynamic MR images [1, 2], the purpose of this study was to evaluate the role of halical CT in revealing prostate cancer detected at transrectal sonographically guided biopsy and to evaluate the usefulness of this technique for the detection of prostate cancer in selected groups of patients.

Materials and Methods

Between October 1998 and August 1999, helical CT of the prostate was performed in 25 patients (age range, 45-72 years) with prostate cancer proven at transrectal sonographically guided biopsy (group I) and in 10 patients (age range, 50-65 years) with prostate cancer suggested by positive digital rectal examination or elevated prostate-speciffic antigen (PSA) level (range, 4.1-30.0; mean, 14.5 ng/mL) but with negative transrectal sonographically guided biopsy (group II). All these patients underwent at least two sets of transrectal sonographically guided biopsy (10-16 core biopsy samples of peripheral zone and four core biopsy samples of both transitional zones if clinically necessary). All patients were examined with a CT scanner (HiSpeed CT; General Electric Medical Systems, Milwaukee, WI). The scans were obtained 3-5 weeks after transrectal sonographically guided biopsy.
The following technique was used to obtain all scans: The upper and lower margins of the prostate were demarcated from preliminary axial images; contiguous 7-mm-thick helical images through the prostate were obtained 50 sec after the initiation of an IV injection of contrast material. The helical images were then reconstructed at 3.5mm intervals. No breath-holding by the patient was necessary. Scans were obtained at 240 mAs and 120 kVp and imaged at a narrow windows width and a low window level. Patients were given 120 mL of contrast material (300 mg I/mL) at a rate of 3 mL/sec. All asymmetric focal or diffuse areas of contrast enhancement in the peripheral zone were considered suggestive of cancer. The location of contrast enhancement was recorded and compared with the results of transrectal sonographically guided biopsy. The transrectal sonographically guided biopsy was performed in the sagittal plane for lateral lesions and in the axial plane for the mid prostate or transitional zone.


Results

The normal peripheral zone of the prostate appears on helical CT as a homogeneous hypodense band of grandular tissue (nine patients of group II). The thickness of this hypodense band varies depending on the degree of hyerplastic nodular cjanges in the central portion of the gland, chich appear as symmetric or asymmetric focal areas of contrast enhancement. Prominent capsular branches and neurovascular bands may be seen in the lateral and posterolateral regions of the prostate and should not be misinterpreted as aras of abnormal contrast enhancement (Fig. 1).

Helical CT revealed malignancy in 22 (88%) of 25 patients with proven prostate cancer. Transretal sonographically guided biopsy detected 102 cancer sites in the peripheral zone and three in the transitional zone in these 25 patients. Helical CT correctly identified 59 (58%) of the cancer sites when correlated with the results of the transrectal sonographically guided biopsy. The cancer lesions presented as focal or diffuse areas of abnormal contrast enhancement caused by cancer were seen in 48% of patients with cancer. The degree of contrast enhancement and the size of nodular changes were more intense and larger in patients with higher levels of PSA (greater than 10.0 ng/mL; 75%) and higher Gleason scores (greater than 5; 78%) (Fig. 4). Helical CT, as a result of the small size of the lesion (microscopic) or lesion avascularity, did not reveal 43 cancer sites (42%). Almost 10% of the focal abnormal contrast enhancement was not caused by cancer (in three patients with prostatic intraepithelial neoplasia, three with prostatitism and four with benign nodular hyperplasia). In this ggroup with benign diseases, the degree of contrast enhancement and the size of the nodular changes were significantly less intense and smaller than those of the group with cancer sites. Additional signs suggesting extracapsular extension of disease were seen in 28% of patients: tumor mass extending beyond the confines of the prostate invading the periprostatic fat (three patients), abnormal enhancement of the seminal vesicles (two patients), and thickening and dense contrast enhancement of the neurovascular bundle contiguous with the suspicious areas
(two patients) (Fig. 5). Complementary studies with transrectal MR imaging were possible in eigght patients with cancer, confirming the helical CT findings in four patients and revealing the extent of disease better than helical CT in the other four patients, two of whom ad negative findings on helical CT.
In nine of 10 patients in group II, a third set of biopsies (12 core biopsy samples, of the peripheral zone) was performed, despite negative findings on helical CT, and confirmed the absence of tumor. In only one patient with a suspicious area of contrast enhancement in the peripheral zone, repeated transrectal sonographically guided biopsy oriented by these CT findings allowed the detection of cancer (Fig. 6). Findings were negative on helical CT for only two of 25 patients with cancer.

Fig. 1 - 65 year-old man with normal findings on digital rectal examination and prostate specific antigen of 7.5ng/mL. Helical CT scan of prostate shows normal appearance of peripheral zone as band of hypodense tissue (arrows). Note usual appearance of symmetric, contrast-enhanced nodules of hiperplastic tissue in central gland (H)

Fig. 2 - 68 year-old man with abnormal findings on digital rectal examination and prostate-speciffic antigen of 10.5 ng/mL. Helical CT scan shows area of focal abnormal contrast enhancement in mid portion of left peripheral zone (arrow). Note lack of findings in right peripheral zone lesion. Transrectal sonographically guided biopsy (not shown) revealed prostatic adenocarcinoma (Gleason score of 6 in mid portion of left peripheral zone) and foci of adenocarcinoma (Gleason score of 5 in right peripheral zone)

Fig. 3 - 60 year-old man with positive digital rectal examination and prostate-specific antigen of 6.5 ng/mL. Transrectal sonographically guided biopsy detected adenocarcinoma, Gleason score of 6 in left apical portion of peripheral zone. Helical CT clearly shows focal area of contrast enhancement (arrow) in same area where cancer was detectedz

Fig. 4 - 58 year-old man with abnormal findings on digital rectal examination and prostate-specific antigen of 15 ng/mL. Helical CT shows extensive area of intense abnormal contrast enhancement in posterior and left portion of peripheral zone (arrows) (adenocarcinoma of prostate with Gleason score of 8 at transrectal sonographically guided biopsy).

Fig. 5 - 68 year-old man with positive findings on digital rectal examination and prostate-specific antigen of 12 ng/mL. Transrectal sonographically guided biopsy detected adenocarcinoma, Gleason score of 8 in right peripheral zone, and Gleason score of 7 in left peripheral zone. A, Helical CT shows focal area of contrast enhancement in right peripheral zone of prostate (arrow). B, Note abnormal contrast enhancement of contiguous neurovascular bundle (arrow), suggestive of tumor involvement, which was confirmed on transrectal MR imaging

Fig. 6 - 58 year-old man with negative digital rectal examination and rising prostate-specific antigen levels in last 3 years who had undergone three sets of transrectal sonographically guided biopsies (including transitional zones) with negative results. His recent prostate-speciffic antigen level was 18 ng/mL. Helical CT scan of prostate shows small area of abnormal contrast enhancement in posterior portion of right peripheral (arrow), suggestive of cancer. Repeated transrectal sonographically guided biopsy with particular emphasis to this area (six core giopsy samples) allows detection of adenocarcinoma in 50% of only one core biopsy sample and Gleason score of 6. No other focus of tumor was found (toptal of 14 core biopsy samples)

Discussion

Digital rectal examinations, PSA levels with associated parameters (i.e., PSA density, PSA adjusted to age, excess PSA, and free-PSA transitional zone), and color Doppler transrectal sonographically guided biopsies are the main diagnostic tools for the evaluation of men at risk for carcinoma of the prostate (3-10).
A significant number of patients have a rising PSA level despite negative findings on biopsy. Transrectal sonographically guided biopsy is the best technique for detecting cancer in patients with elevated PSA or a positive digital rectal examination, but this biopsy has its limitations. Repeated biopsies are associated with a 20-40% incidence of positive findings in men with persistently elevated PSA serum levels (11-15). In some patients, a third and perhaps a fouth or fifth biopsy set may be necessary to confirm the presence or absence of disease.
Conventional CR does not allow direct visualization of prostate cacncer and is of little value in detection of this disease [16]. Dynamic contrast-enhanced MR imaging is particularly useful because prostate cancer enhances earlier than healthy prostatic tissue, especially when the images are made in the early phase of enhancement [1, 2].
Because helical CT is more frequently used for the investigation of pelvic disease, we decided to evaluate prostatic tissue in the early phase of contrast enhancement. Although our clinical experience is limited, helical CT shows contrast enhancement in aras with cancer in 88% of patients, corroborating the data of color Doppler sonography that define cancer as hypervascular in 50-85% of cases [7-10]. Our results suggest that helical CT of the prostate may be useful in the ffollowing selected groups of patients: patients with a rising PSA level and negative biopsies; patients with a rising PSA level after an abdominoperineal resection; and patients with routine helical CT pelvic examinations during wich abnormal focal contrast enhancement in the peripheral zone is observed.
In our institution in Campinas, Brazil, all patients with negative findings on biopsy undergo helical CT of the prostate for better planning of a repeated biopsy, because of the higher cost of transrectal MR imaging. If any area in the peripheral zone is suggestive of cancer, we skip the transitional zone is and obtain 12-16 core biopsy samples from the peripheral zone only, with particular emphasis on the area of abnormal contrast enhancement (3-5 core biopsy samples). If the peripheral zone appears normal on helical CT, six core biopsy samples of the peripheral zone and six of the transitional zone (three samples of each side) are obtained. This protocol is still in progbres and at least 100 patients will be enrolled in the next 12 months. In patients with suspected prostatic cancer after am abdominoperineal resection in which transrectal MR imaging and transrectal sonographically guided biopsy is impossible, helical CT of the prostate (four patients) is performed. The finding of abnormal areas of contrast enhancement in the peripheral zone in two patients led to the diagnosis of cancer on biopsy of the suspicious region using the transgluteal percutaneaous approach (Fig. 7).
Since August 1999, a protocol has been initiated by performing helical CT of the prostate in all patients who are more than 50 years old and who are examined by pelvic evaluation for a variety of clinical problems. Using these described criteria, helical CT detected areas of abnormal contrast enhancement in eight (12%) of 68 patients, allowing the incidental detection of prostate cancer in three (4%) of these patients (Fig. 8). Prostatitis [3] and benign nodular hyperplasia [2] were revealed in the remaining patients.
Peripheral zone prostate cancer detected transrectal sonographically guided biopsy appear as a focal of diffuse area of contrast enhancement on helical CT. Helical CT of the prostate can be a useful alternative to transrectal MR imaging to guide a prostatic biopsy in patients with a rising PSA level and negative findings on biopsy.
Helical CT of the prostate is especially useful in the group of patients who have undergone a abdominoperineal resection. All focal areas of contrast enhancement should be biopsied to exclude prostate cancer. A larger study is mandatory to evaluate the accuracy, sensitivity, and specificity of the finding of a focal or diffuse contrast enhancement in the peripheral zone of the prostate in men more than 50 years old who are examined by helical CT of the pelvis.

Fig. 7 - 68 year-old man with abdominoperineal resection and prostate-specific antigen level of 16 ngmL. After helical CT of prostate that showed suspicious area of agnormal contrast enhancement in mid portion of right peripheral zone, transgluteal percutaneous biopsy of this suspicious area allowed detection of adenocarcinoma with Gleason score of 6.

Fig. 8 - 63 year-old man who underwent abdominal and pelvic CT for staging non-Hodgkin´s lymphoma. Helical CT of pelvis revealed abnormal contrast enhancement in right peripheral zone of prostate with capsular bulging (arrows). Note adenopathy also in inguinal regions (asterisks). Transrectal sonographically guided biopsy revealed adenocarcinoma with Gleason score of 8 in both peripheral zones. Prostate-specific antigen level (15 ng/mL) was then obtained.

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