An 82-year-old Caucasian male with a history of prostate cancer underwent robotic assisted laparoscopic radical prostatectomy in 2007 with Gleason Grade Group 3 surgical pathology (T1C, N0, M0) and later underwent salvage radiation in 2009 due to prostate specific antigen (PSA) recurrence with negative metastatic workup. The patient was then lost to followup and was referred to our institution with a PSA of 6.62. A positron emitting tomography (PET)/computerized tomography (CT) Axumin scan demonstrated focal Axumin uptake in the region of the left prostatectomy bed posteriorly, seen in the region of surgical clips, highly suspicious for recurrent malignancy. A magnetic resonance imaging (MRI) of the pelvis showed a 2.4 cm × 1.1 cm ill-defined signal of soft tissue thickening and enhancement appearing to be left seminal vesicle remnant (fig. 1). A CT guided percutaneous biopsy was deemed challenging due to its location adjacent to the prostatectomy bed deep within the pelvis. The patient agreed to proceed with a MRI/ultrasound (US) transperineal biopsy to obtain a tissue diagnosis of this suspicious area.

Figure 1. Axial T2 weighted MRI and PET/CT Axumin scan of suspicious ill-defined soft tissue mass appearing to be left seminal vesicle remnant in left posterior prostatectomy bed.

Pelvic MRI segmentation was performed using a DynaCAD® workstation. The MRI/US fusion systems need a central point of reference to align both 3D datasets, which is typically the prostate. We segmented the prostate as the external urinary sphincter, the pubic bone as a second point of reference and suspicious MRI lesion as the target (fig. 2). This was performed using the new Philips UroNav 4.0 system, which can be used to perform prostate biopsies and focal ablations.

Figure 2. UroNav cartoon of urinary sphincter (red), lesion (green), bladder (yellow), rectum (orange) and left pubic ramus (turquoise) segmentation.

A hypoechoic lesion in the left posterior prostatectomy bed surrounded by hyperechoic clips was visualized using live transrectal ultrasound, once colocalized by fusion imaging. This hypoechoic lesion correlated well with the MRI segmentation. Multiple cores were obtained from this lesion (fig. 3). The live ultrasound imaging was particularly useful to visualize needle deflection from the lesion’s rigidity, which would not have been appreciated during a CT guided biopsy.

Figure 3. Core needle biopsy of hypoechoic lesion using MRI/US fusion technology.

The pathology was Gleason 4+3 prostate adenocarcinoma, extensively involving fibromuscular and adipose tissue. Large nerve invasion was present, with tumor permeating around ganglion cells. The patient has started a planned 6-month course of luteinizing hormone releasing hormone agonist with radiation, since the prior treatment field did not treat the area of recurrence due to the location.

To our knowledge, this is the first use of MRI/US fusion technology to diagnose prostate cancer recurrence in the postprostatectomy bed. Although this technology was first designed to better target clinically significant prostate cancer within a prostate gland, we used stationary fiducials as landmarks to localize the region of interest in 3D. Lesions suspicious for prostate cancer recurrence after radical prostatectomy are typically percutaneously biopsied using CT guidance, which can be used for histologic confirmation and molecular analyses for treatment planning.¹ The overall success rate of obtaining a histologic diagnosis of prostate cancer from CT guided bone biopsies is 69% to 77% but can decrease to 42% for lesions that are ˜8.8 cm³ in size, such as ours.^1,2 A mobile soft tissue mass is also technically more challenging to biopsy than a fixed bony lesion. We obtained a tissue diagnosis through the perineum with the same sterility as a CT guided biopsy but without any ionizing radiation. MRI/US fusion technology holds significant potential and will continue to be used for new applications in the future.