MRI Is Changing Prostate Biopsy

A couple of years ago I saw a patient who previously had three negative TRUS-guided prostate biopsies. Because his PSA had been slowly rising from 4 to 10, the number of biopsy needles had increased from 10 to 12 to 14. “Doc,” he said, “they tried to numb me up for the last biopsy, but by about the 9th needle, every time I heard that sound like a mousetrap I felt like I was being hit in the bottom with a baseball bat. And the worst of it is, it came back negative and I figured I didn’t even care anymore if I have prostate cancer, I’m never going through that again.” I assured him if he had prostate cancer, we would see it on imaging, numb him up, and use the fewest number of needles.

 

It’s no wonder such personal accounts inspire dread. At the Sperling Prostate Center, we are leaders in changing the prostate biopsy procedure so it is more accurate and far less fearsome. In general terms, here are the types of prostate biopsy methods currently being done:

 

Ultrasound guided biopsies

 

  1. TRUS-guided biopsy –TRUS stands for TransRectal UltraSound, meaning that the biopsy needle gun is inserted in the rectum and the needles are guided through the rectal wall into the prostate by ultrasound (US) imaging. US reveals the size and shape of the prostate, and each needle shows up so a doctor can “see” which area of the prostate it’s hitting. Since US is “blind” to differences in tissue, it does not show a doctor exactly where to target the needle. This is why most TRUS biopsies entail 10-14 needles, with half that number going to each side of the gland. It is called a systematic blind random biopsy. ADVANTAGE: It can be done in the doctor’s office using local anesthetic for numbing. DISADVANTAGES: It tends to miss cancers in the anterior region of the gland, leading to repeat biopsies. The small risk of infection from rectal bacteria increases with the number of needles used.
  2. Transperineal or 3D-mapping biopsy – The perineum is the outer skin area between the scrotum and anus, so “transperineal” means the needles are directed into the prostate through this skin area instead of through the rectum. However, an US wand is inserted rectally to provide image guidance, but cannot show tissue differences. Rather than using a biopsy gun, the doctor positions a rigid plastic grid against the perineum, and directs needles through grid holes marked by coordinates. In this way, a doctor can sample tissue systematically every 5mm throughout the gland, watching the needle insertion on the ultrasound monitor. ADVANTAGE: Transperineal biopsies are very thorough, taking anywhere from 40-60 samples. There is no risk of infection from rectal bacteria. DISADVANTAGES: It must be done in an outpatient surgical setting due to general anesthesia. It is the most expensive type of biopsy, both because of the need for anesthesia and also the number of samples a lab must analyze. US does not show tissue differences.

 

MRI guided biopsies

  1. MRI/US guided cognitive biopsy –An MRI of the prostate is obtained prior to the biopsy, and any suspicious areas will be the doctor’s reference for placing needles using US guidance. Whether the doctor doing the biopsy is a radiologist or a urologist, he/she must be experienced at reading prostate MRIs. As the word “cognitive” suggests, the doctor mentally calculates where to place the ultrasound-guided needles based on the images. Thus, it is considered more targeted than random. ADVANTAGES: By utilizing MRI scans, the biopsy may require fewer needles since the MRI images act as a guide. When done by someone experienced in reading MRI, it has better accuracy rates than conventional TRUS biopsy (as high as 80+%[i]). It can be done in a doctor’s office. DISADVANTAGE: The images are not real time so a certain amount of educated guessing goes into the procedure.
  2. Fusion-guided biopsy – The image guidance is provided by co-registering or “fusing” an earlier MRI prostate scan with real-time transrectal ultrasound. This requires special software that recognizes and matches, point by point, the shape of the prostate and projects a 3-dimensional synthetic prostate image onto a monitor. Because a very good MRI result reveals the suspicious lesion(s), the computer can highlight that “region of interest” within the fusion image. The software “plans” the number and trajectory of the biopsy needles, and the doctor can confirm placement with the real-time ultrasound. ADVANTAGE: By incorporating MRI, the monitor reveals the area with abnormal tissue, allowing the doctor to target that area. DISADVANTAGES: Co-registering the images has room for error due to the MRI having been done at a different time with the patient in a different position, so targeting may be somewhat off; patient breathing and movement can affect the real-time ultrasound and distort the co-registration.
  3. Real time MRI-guided targeted biopsy – This is the type of biopsy we offer at the Sperling Prostate Center. It is performed transrectally under real time MRI guidance. This ensures that we can target the minimum number of needles directly into the suspicious area(s); if necessary, we can also selectively sample other areas of the gland, again with a minimum number of needles. ADVANTAGES: Targeting directly into the core of an abnormal area seen on the MRI means we have the greatest chance of an accurate diagnosis of aggression. Our diagnosis will have the greatest accuracy and the least risk of underdiagnosing prostate cancer. DISADVANTAGES: None.

As you can see, MRI has already started to change the kind of biopsy that urologists can offer. They can incorporate MRI either cognitively, or with fusion software; they do so because they recognize that MRI information makes for a better biopsy. However, nothing can compare with an MRI-guided targeted biopsy done under real time imaging. We are proud that the Sperling Prostate Center is in the vanguard of prostate biopsy change.

 


[i] Garcia Bennett J, Conejero Olesti A, Hurtado Salom C et al. Usefulness of cognitive targeting in multiparametric MRI-guided biopsy to diagnose the dominant lesion in prostate cancer. Radiologia. 2014 Nov 22. pii: S0033-8338(14)00166-0. doi: 10.1016/j.rx.2014.06.008. [Epub ahead of print]

 

 

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