In case you missed my previous blog, I attended the Radiological Society of North American (RSNA) meeting in Chicago. Several poster presentations were devoted to multiparametric MRI of the prostate. In my last blog, I summarized a poster on mpMRI and imaging of the anterior zone of the prostate. This time, I’m reporting on another poster out of the Ottowa Hospital/University of Ottowa.[i]
The authors identify two specific prostate cancer diagnostic problems:
- Conventional TRUS biopsy misses cancer at least 20% of the time (false negative), understages cancer 30-45% of the time, and under-samples the anterior prostate and transition zone.
- With regard to mpMRI in cases of previous negative TRUS biopsies but suspicion of cancer remains, inexperienced readers may incorrectly interpret prostate cancer that is not there (false positive).
The poster contained images that show how four parameters each give different types of functional information about healthy and diseased tissues. The parameters are
- T2 weighted images (T2-MRI)
- Diffusion weighted images (DWI-MRI)
- Dynamic contrast enhancement (DCE-MRI)
- Spectroscopy (MRI-S)
The purpose of their poster was to illustrate interpretative pitfalls related to the following conditions: normal gland anatomy (central zone and anterior zone), post-biopsy artifacts related to bleeding, benign prostatic hyperplasia (BPH or normal gland enlargement as men age), prostatitis (an inflammation of the gland), and specific problems with parametric tests. For example, chronic prostatitis can mimic prostate cancer, even on functional imaging, necessitating an MRI-guided targeted biopsy to be sure of the diagnosis.
It was clear from the poster’s illustrations how certain parameters provide better tissue information in each of the conditions listed above. In other words, comparing the results of each parameter can help less experienced readers correctly identify whether a patient on active surveillance with a history of one or more negative TRUS biopsies truly has prostate cancer.
In spite of the misinterpretations of less experienced readers, the authors stand by mpMRI as a “proven imaging modality for the detection and grading of prostatic carcinoma,” emphasizing that it has a “crucial role” in matching patients with appropriate cancer management strategies, including active surveillance. Personally, I find that such posters, showing how the same tissues show up differently depending on the functional parameter, shed a great deal of light on the need to cross-reference parameters and confer with more experienced radiologists to obtain correct interpretations.
[i] Quon J, Flood TA, Schieda N. All that glitters is not gold: Multi-parametric MRI – pathological correlation in false positive cases of prostate cancer diagnosed in the setting of active surveillance and rising PSA with negative biopsy. Poster URE003-b. RSNA 2014 (Chicago).