What are the MRI manifestations of prostate cancer

MRI mainly relies on T2-weighted images to detect and display prostate cancer, which mainly manifests as a low-signal defect area in the peripheral band, which is significantly different from the normal high-signal peripheral band and helps with diagnosis. When the tumor is confined to the prostate, the outer edge of the prostate is intact and has a clear boundary with the surrounding venous plexus.

The capsule of the prostate is a linear low signal on T2-weighted images. When the capsule is blurred, interrupted, or discontinuous on the lesion side, it indicates that the capsule is invaded. The venous plexus around the prostate is located on the periphery of the capsule and is a thin layer of structure. It is more obvious at 4-5 o'clock and 7-8 o'clock. Under normal circumstances, it is symmetrical on both sides. Its signal on T2-weighted images is equal to or higher than the surrounding band. If the venous plexus on both sides is asymmetrical and the signal is reduced adjacent to the tumor, it is considered a sign of invasion. Tumor invasion of the peripapillary fat is manifested as a low signal area in the high signal fat, especially on the outside of the prostate, called the prostate rectal angle. The disappearance of this structure is a typical manifestation of peripapillary fat invasion.

When the seminal vesicles are normal, they are basically symmetrical on both sides. If the signals of both sides are reduced or part of the seminal vesicles are replaced by low signals, they may have been invaded by tumors.

MRI staging: MRI is very helpful in staging prostate cancer, especially in distinguishing between T2 and T3 stages:

1. MRI can directly observe whether prostate cancer has penetrated the capsule. MRI indications of prostate cancer invading the capsule include: (1) irregular bulging of the outer edge of the prostate on the affected side, with an uneven margin; (2) the tumor protrudes posterolaterally or forms an angle, and the bilateral neurovascular plexus is asymmetric; (3) the tumor directly penetrates the capsule and enters the surrounding high-signal fat, and the fat in the neurovascular plexus or the prostate rectal fossa disappears.

2. MRI is sensitive to showing invasion of the seminal vesicle, reaching more than 97%, which is an indication of prostate cancer invading the seminal vesicle: (1) showing a low-signal tumor entering and surrounding the seminal vesicle from the base of the prostate, resulting in the appearance of low-signal foci in the seminal vesicle with normal T2 high signal and disappearance of the prostate seminal vesicle angle; (2) showing the tumor invading the seminal vesicle along the ejaculatory duct and disappearance of the seminal vesicle wall; (3) focal low-signal areas in the seminal vesicle.

3. MRI is sensitive to detecting pelvic lymph node metastasis, and its accuracy is similar to CT;

4. MRI can also detect metastasis to other parts of the body due to its large display field. In recent years, various multi-parameter MRI and MRI-guided prostate biopsy have developed rapidly, providing more accurate information for the diagnosis, staging and postoperative follow-up of prostate cancer.