Contrast-Enhanced Transrectal Ultrasound for Follow-up After Focal HIFU Ablation for Prostate Cancer

Abstract

The optimal strategy for imaging after focal therapy for prostate cancer is evolving. This series is an initial report on the use of contrast-enhanced transrectal ultrasound (TRUS) in follow-up of patients after high-intensity focused ultrasound (HIFU) hemiablation for prostate cancer. In 7 patients who underwent HIFU hemiablation, contrast-enhanced TRUS findings were as follows: (1) contrast-enhanced TRUS clearly showed the HIFU ablation defect as a sharply marginated nonenhancing zone in all patients; (2) contrast-enhanced TRUS identified suspicious foci of recurrent enhancement within the ablation zone in 2 patients, facilitating image-guided prostate biopsy, which showed prostate cancer; and (3) contrast-enhanced TRUS findings correlated with multiparametric magnetic resonance imaging and biopsy histologic findings.

Keywords: contrast-enhanced ultrasound; focal therapy; high-intensity focused ultrasound; prostate cancer; transrectal ultrasound.

Figure 1.

Example of prostate MRI before HIFU and contrastenhanced TRUS appearance of prostate hemiablation with HIFU. A, T2-weighted (left) and ADC (right) MR images show a 1.2-cm left peripheral zone lesion in the 1- to 3-o’clock position, with low T2 and ADC signals (arrows), Prostate Imaging Reporting and Data System category 4. This appearance corresponded to Gleason 3 + 4 prostate cancer on biopsy. B, Split-screen grayscale (left) and contrast-enhanced TRUS (right) images before HIFU ablation. The left prostate lobe shows diffuse slightly increased enhancement (arrow) relative to the right. C, Split-screen grayscale (left) and contrast-enhanced TRUS (right) images immediately after HIFU ablation. The left prostate lobe shows complete absence of enhancement (arrow). The right prostate lobe enhances normally.

Figure 2.

Example of the post-HIFU appearance of the prostate on contrast-enhanced TRUS, with time-intensity curve and histologic correlates: 72-year-old man with prostate cancer (case 2 from Table 1). A, Pretreatment TRUS image shows a 1 × 0.8-cm hypoechoic lesion in the peripheral right mid lobe in the 7-o’clock position (arrow), which corresponded to Gleason 4 + 3 prostate cancer on biopsy. B, Transrectal US image 13 months after right hemigland HIFU ablation shows shrinkage of the ablated right lobe (arrow) versus the left lobe. The ablated right lobe is mildly hypoechoic diffusely relative to untreated left lobe. C, Contrast-enhanced TRUS image shows a clear and well-defined nonenhancing ablated right lobe (arrow) and a normally enhancing left lobe. Yellow and blue circles are manually selected ROIs placed for generation of time-intensity curves. D, Time-intensity curves generated from the ROIs placed in C. Time is on the x-axis (seconds), and peak intensity is on the y-axis (decibels). The untreated left lobe (blue ROI) shows gradual wash-in of contrast, peak enhancement at approximately 50 seconds, followed by gradual wash-out (blue curve). The treated right lobe (yellow ROI) shows a flat waveform (yellow curve), with no quantifiable enhancement. E, Histologic specimen (hematoxylin-eosin, original magnification × 10). Follow-up biopsy at 13 months confirmed necrosis in the ablated right lobe. F, Simultaneous biopsy of the untreated left lobe showed a normal prostate gland.

Figure 3.

Example of the post-HIFU appearance of recurrent prostate cancer on MRI and contrast-enhanced TRUS, with time-intensity curve and histologic correlates: 41-year-old man with prostate cancer who presented for follow-up with a rising PSA level 1 year after left hemigland HIFU ablation of the prostate for Gleason 3 + 4 prostate cancer in the left apex anterior (case 5 from Table 1). A, Axial T2-weighted MR image at the level of the apex shows atrophy of the treated left versus the right prostate lobe. A linear band of low T2 signal intensity (arrow) at the left anterior apex is nonspecific given the history of HIFU. B, Color map from dynamic contrast-enhanced MR images at the same level as A. There is abnormal rapid enhancement and wash-out (arrow) at the left anterior apex, in the area of low T2 intensity on A, suspicious for a recurrent tumor. C, Split-screen grayscale and contrast-enhanced TRUS transverse images at the level of the prostate apex. Contrast-enhanced TRUS matches MRI findings showing a discrete enhancing suspicious lesion at the left anterior apex, in the otherwise ablated left lobe. Time-intensity curves were created with ROIs placed on the untreated right lobe (orange ROI), ablated left lobe (yellow ROI), and discrete enhancing left anterior apex lesion (blue ROI). D, Time-intensity curves generated from the ROIs placed in C. Time is on the x-axis (seconds), and peak intensity is on the y-axis (decibels). The suspicious lesion in the left apex anterior (blue curve) shows an earlier time to peak and higher peak intensity compared with the untreated right lobe (orange curve). The ablated left lobe (yellow curve) shows a relatively flat waveform, with less enhancement than the untreated right lobe. E, One-year follow up biopsy. Histologic examination of the suspicious enhancing lesion at the left anterior apex (blue ROI) confirmed Gleason 3 + 4 prostate cancer. F, Biopsy of the ablated left lobe (yellow ROI) showed hyalinized prostatic stroma devoid of prostatic glands. G, Biopsy of the normal prostate gland in the untreated right lobe (orange ROI) showed normal prostate glandular tissue. H, Left lobe biopsy including both ablated hyalinized prostatic stoma devoid of prostatic glands (corresponding to yellow ROI) and prostate cancer (corresponding to the blue ROI) that matches the contrastenhanced TRUS findings. Note the sharp delineation (arrows) between hyalinized prostatic stoma devoid of prostatic glands (below and to the left) and prostate cancer (above and to the right).

Figure 4.

Example of echogenic cavitation during HIFU. TRUS images (A–D) show the development of cavitation, manifesting as echogenicity at the level of the red band and corresponding to the region of ablation. The cavitation, in addition to being transient and having poor anatomic resolution, is variably seen. In the final frame (D), no echogenic cavitation is seen (orange circle) to correspond to the region being treated.