Untypical MRI imaging for prostate cancer is
Case 303
【Progress】
All twelve specimen of biopsy in Case 1 revealed prostate cancer (Gleason 7 in 5 specimen, Gleason 8 in 5 specimen, Gleason 9 in 2 specimen)
【Discussion】
Prostate gland is pure-anatomically categorized into internal gland and external gland (1). Internal gland is composed of three zones: periurethral zone, transitional zone and central zone. Transitional zone surrounds periurethral zone from urinary bladder to confluence of ejaculatory duct. Central zone surrounds ejaculatory duct from seminar vesicle to confluence of ejaculatory duct. Meanwhile, external glans composes of peripheral zone. Peripheral zone surrounds the urethra after confluence of ejaculatory duct.
Prostate cancer can emerge from each zone; prostate cancer from central zone tends to invade to seminar vesicle (T3b); prostate cancer from peripheral zone tends to invade to capsule (T3a): prostate cancer from transitional cancer tends to become more larger and higher in PSA value with less incidence of T3a and T3b (1).
Prostate cancer aggressiveness is evaluated by Gleason score that is pathologically made by cancer cell atypical degree and growth pattern. It says that Gleason score 6 or less indicates low risk, Gleason score 7 indicates intermediate risk and Gleason score 8 or greater indicates high risk (1).
Diffusion weighted image (DWI) signals are acquired by giving motion probe gradient (MPG) before and after 180 degrees pulse in T2WI imaging. The signal intensity of T2WI associated with MPG becomes weaker than without MPG. The factor b indicates degree of motion probe gradient. The greater b factor induces more diffusion of water molecule, leading weaker T2WI signal in areas with potency of water molecule diffusion, while remaining T2WI signal in those with low potency of water molecule diffusion that appears as high signal intensity on DWI. ADC values imply slopes: - [loge signal intensities before giving MPG (b0)/ loge signal intensity after giving MPG (b500, b800, b10000, or b2000)]. Namely, the lower ADC values implies the more restricted water molecules.
ADC values of prostate parenchyma or hyperplastic nodule are reported to be 1.1 to 1.3 while those of prostate cancer to be 1.0 or less (2-6). Interestingly, the higher Gleason score is reported to be lower ADC values. In short, ADC values of 0.7 or less indicates prostate cancer whose Gleason score 7 or greater that imply more malignant or more aggressive, while those of 0.8 to 1.0 indicate prostate cancer whose Gleason score 6 or less (2-6).
In our cases, prostate cancer of Case 2 is demonstrated low signal intensity on MRIT2WI arisen from transitional zone and high signal intensity on DWI and low ADC values (mean 0.590) indicative of typical prostate cancer. Meanwhile, prostate cancer of Case 1 is demonstrated no low signal intensity on T2WI and fat suppression T2WI, whereas high signal intensity on DWI and low ADC vales of 0.567-0.659. ADC values of both cases were less than 0.7 indicative of Gleason 7 or greater. In fact, histologic examination revealed 12 biopsy specimen of Case 1 showed grade group 5 (highest Gleason score of 4 + 5 = 9). It is imperative to check DWI and measure ADC values irrespective of typical or untypical images of prostate cancer on T2WI or fat suppression T2WI.
【Summary】
We presented two cases with prostate cancer whose MRI images with T2WI are typical in one and atypical in another. However, Diffusion WI images depicted high signal intensity on whole prostate gland in Case 1 and corresponded to a lesion with low signal intensity in Case 2 whose ADC values in both cases were lowering of less than 0.6. It is borne in mind that ADC values reflect Clason score; ADC values of prostate nodule are 0.7 or less indicating that Gleason score 7 or greater indicative of aggressive prostate cancer. Further, internal gland includes transitional zone, central zone and periurethral zone, while external gland includes peripheral zone. Prostate cancer from central zone tends to develop to T3b, prostate cancer from peripheral zone tends to develop to T3a and prostate cancer from transitional zone tends to be greater in size and higher in PSA values.
【References】
1.Prostate Cancer, http://www.cancer.gov/cancertopics/types/prostate
2.Ragheb SR, et al. Can mean ADC value and ADC ratio of benign prostate tissue to prostate cancer assist in the prediction of clinically significant prostate cancer within the PI-RADSv2 scoring system? Egyptian Journal of Radiology and Nuclear Medicine. 2020;51:1-12
3.Kim CK, et al. Diffusion-weighted imaging of the prostate at 3 T for differentiation of malignant and benign tissue in transition and peripheral zones: preliminary results. Journal of Computer Assisted Tomography. 2007; 31: 449–454.
4.Pickles M, et al. Diffusion-weighted imaging of normal and malignant prostate tissue at 3.0 T,” Journal of Magnetic Resonance Imaging. 2006; 23:130–134.
5.Zelhof B, et al. Correlation of diffusion-weighted magnetic resonance data with cellularity in prostate cancer. BJU International. 2009; 103: 883–888.
6.Tamada T, et al. Apparent diffusion coefficient values in peripheral and transition zones of the prostate: comparison between normal and malignant prostatic tissues and correlation with histologic grade,” Journal of Magnetic Resonance Imaging. 2008;28: 720–726.
2023.7.3