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Anterior Fibromuscular Stroma (AFMS)- Advanced Problem Solving

4 min.
Pomeranz, Stephen
Stephen J Pomeranz, MD
Chief Medical Officer, ProScan Imaging. Founder, MRI Online
CME Eligible

Dr. P here with the AFMS, anterior fibromuscular stroma. Let's take a typical scenario. The patient has had two negative biopsies, one a year ago, one two years ago. You might say, "Well, okay, two negative biopsies, I'm not particularly worried." They already shot their gun two separate times and nothing came out on the other end. So probably the patient doesn't have cancer.

Or the AFS, which is over here, is not a particularly easy area... right there... not a particularly easy area to access with the gun from the back via the rectum. So maybe they just didn't get there. This is the area where cancer is hardest to elucidate on TRUS biopsy, on ultrasound guided biopsy. That's why you have MR mapping. And even with MR mapping, it can be a little bit challenging.

So you've got two scenarios, one where negative biopsy influences you to not call cancer, and you've got another where negative biopsy makes you a little bit worried that they didn't get there the first or second time around.

So what's a mother to do? Well, first, prostate cancer doesn't originate from the anterior fibromuscular stroma. But when you're reporting a suspicious lesion, if you can figure out, just by morphology and shape, whether the abnormality arose from here and grew in, or whether it arose from here and grew in, you can trace it back very carefully. Or the epicenter is here and secondarily involves here, epicenter here, secondarily involves here. Then you use the typical criteria for PZ, or in this case, typical criteria for TZ. That's easy. But what if you can't tell? What if it's just a morass of hypo-intensity and you cannot discern whether it came from the TZ or the PZ? Then you've got to be clever.

So the negative biopsy history may help you, may not. Things like PSA density going up. The PSA going up may make you more aggressive in reading the lesion. But in terms of visualization, shape helps me a lot. If I see my AFMS lesion and it's effacing, say, the surgical capsule, or it's effacing the anatomic capsule, or it's effacing this midline cleft so that I can't separate one side from the other, I find that useful and I tend to be more aggressive in my call. If I'm looking at the sagittal projection, let's make this a sagittal view, this would be anterior and posterior. And in the front, the area of interest looks very lentiform but very smooth, and I can see it's not violating the capsule, I'm going to be more conservative.

On the other hand, if it's a little more blobby looking or irregular in the sagittal projection... so I'm using two projections and I've lost the anterior capsule, again, I get more aggressive. So I'm looking for respect of key anatomic boundaries and zones like the surgical capsule, the anatomic capsule, and the midline.

Added to that are more typical criteria. Heavy diffusion restriction, especially on high b-value imaging. Early, very early, hyperintensity or enhancement on DCE MRI. That combined with the morphology and the tricks that I've just given you, will shove you in one direction or the other in dealing with AFMS lesions. Dr. P out.

LESSON 2, TOPIC 25

Mastery Series: PI-RADS 2.1 Update

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Content reviewed: December 29, 2021

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