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1
Radiological Center of Campinas, Av. Andrade Neves, 707, Campinas-S.P.-Brazil
13013-161.
2
Department of Diagnostic Radiology, Box 57, The University of Texas M. D.
Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX 77030.
Received November 1, 1999;
accepted after revision January 4, 2000.
Address correspondence to A. Prando
Abstract
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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 in 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 and 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 three in the transitional zone in these 25 patients. Helical CT accurately 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 appears 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 determine the accuracy, sensitivity, and specificity.
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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 3.5-mm intervals. No breath-holding by the patient was necessary. Scans were obtained at 240 mAs and 120 kVp and imaged at a narrow window 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.
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Helical CT revealed malignancy in 22 (88%) of 25 patients with proven prostate cancer. Transrectal 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 in the peripheral zone (Figs. 2 3). Multifocal 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 prostatitis, and four with benign nodular hyperplasia). In this group 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. 5A,5B). Complementary studies with transrectal MR imaging were possible in eight 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 had negative findings on helical CT.
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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.
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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 [11,12,13,14,15]. In some patients, a third and perhaps a fourth or fifth biopsy set may be necessary to confirm the presence or absence of disease.
Conventional CT does not allow direct visualization of prostate cancer 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 areas with cancer in 88% of patients, corroborating the data of color Doppler sonography that define cancer as hypervascular in 50-85% of cases [7,8,9,10]. Our results suggest that helical CT of the prostate may be useful in the following 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 which 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 progress and at least 100 patients will be enrolled in the next 12 months. In patients with suspected prostatic cancer after an 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 percutaneous approach (Fig. 7).
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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.
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Peripheral zone prostate cancer detected at transrectal sonographically guided biopsy appears as a focal or 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 an 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.
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