Tumorsize dependent detection rate of endorectal MRI of prostate cancer—A histopathologic correlation with whole-mount sections in 70 patients with prostate cancer

Abstract

Purpose

To evaluate the value of T2w endorectal MRI (eMRI) for correct detection of tumor foci within the prostate regarding tumor size.

Materials and Methods

70 patients with histologically proven prostate cancer were examined with T2w eMRI before radical prostatectomy at a 1.5 T scanner. For evaluation of eMRI, two radiologists evaluated each tumor focus within the gland. After radical prostatectomy, the prostates were prepared as whole-mount sections, according to transversal T2w eMRI. For each slice, tumor surroundings were marked and compared with eMRI. Based on whole-mount section, 315 slices were evaluated and 533 tumor lesions were documented.

Results

Based on the T2w eMRI, 213 tumor lesions were described. In 137/213, histology could prove these lesions. EMRI was able to visualize 0/56 lesions with a maximum size of <0.3 cm (detection rate 0%), between 0.3 and 0.5 cm 4/116 (3%), between 1 and 0.5 cm 22/169 (13%), between 2 and 1 cm 61/136 (45%) and for >2 cm 50/56 (89%). False positive eMRI findings were: <0.3 cm n = 0, 0.5–0.3 cm n = 12, 0.5–1 cm n = 34, 1–2 cm n = 28 and >2 cm n = 2.

Conclusion

T2w eMRI cannot exclude prostate cancer with lesions smaller 10 mm and 0.4 cm³ respectively. The detection rate for lesions more than 20 mm (1.6 cm³) is to be considered as high.

Introduction

Prostate cancer (PCa) is the most common malignancy in men and according to the American Cancer Society the estimated new cases in the United States of America will be 192,280 men in 2009; the estimated deaths will be 27,360 [1]. The potential of MRI for imaging PCa was already recognized and evaluated in the beginning of the wide introduction of MRI into clinical practice in the early eighties [2]. Until today, the combination of T2 weighted turbo-spin-echo (T2w TSE) sequences and the application of an endorectal coil (eMRI) has to be considered as state-of-the-art for local tumor staging [3], [4], [5], in particular for high magnetic field strengths up to 3 T. At present the main indication for eMRI of the prostate in the clinical work-up is tumor staging for assignment of best therapy. But clinical demands changed during the last two decades. While PSA testing has significantly reduced the amount of advanced PCa (T4/T3; N+, M+ stages) at the time point of diagnosis, there has been also an increasing number of negative prostate biopsies [6]. Also the increased fraction of cancer with low-risk profiles (T1a-b tumors with a Gleason-scores of 5 and below in combination with a total PSA-level of <10 ng/ml) as well as clinical insignificant PCa in old men with unclear benefit from radical prostatectomy/radiotherapy introduced alternative therapy regimes, e.g. active surveillance or (focal) tumor ablation [5], [7]. MRI as method with excellent soft tissue contrast for detecting non-organ confined tumors is also a prerequisite for being a useful tool for biopsy-planning, either ultrasound- or MRI-guided [8], [9].

Additional information provided by metabolic (MR-spectroscopic imaging; MRS) and functional imaging (diffusion-weighted imaging; DWI and T1w dynamic-contrast media enhanced MRI; T1w DCE) for improving the diagnostic performance of MRI has been obtained in the meantime [10], [11]. However, it is still inevitable to use T2w TSE MRI as a robust, fast and as easily repeatable diagnostic modality.

Data about T2w TSE eMRI to identify suspicious lesions within the prostatic gland regarding exact tumor size are rare. Most of the published data do lack of exact match with histopathology (no whole-mount sections), were focussed on local tumor staging or evaluating new imaging techniques like DWI. Older studies focussed on low-filed MRI and/or low-resolution MRI. It is an important point for the further clinical development of (multimodal) MRI to evaluate the detection rate of state-of-the-art T2w TSE eMRI in special regards towards the upcoming requirements: detection and monitoring of suspicious lesions within the gland [5], [12].

Therefore, purpose of this study was to evaluate the detection rate of tumor foci of prostate cancer by T2w TSE eMRI at 1.5 T regarding tumor size.