Transurethral convective water vapor as a treatment for lower urinary tract symptomatology due to benign prostatic hyperplasia using the Rezūm(®) system: evaluation of acute ablative capabilities in the human prostate

Abstract

Background: The purpose of this study was to assess the acute ablative characteristics of transurethral convective water vapor (steam) using the Rezūm(®) system in men with benign prostatic hyperplasia through histologic and radiographic studies.

Methods: Seven patients were treated with transurethral intraprostatic injections of sterile steam under endoscopic visualization followed by previously scheduled adenectomies. The extirpated adenomas were grossly examined followed by whole mount sectioning and staining with triphenyl-tetrazolium chloride (TTC) to evaluate thermal ablation. Histology was performed after hematoxylin and eosin staining on one prostate. After review of results from the first patient cohort, an additional 15 patients with clinical benign prostatic hyperplasia were treated followed by gadolinium-enhanced magnetic resonance imaging (MRI) at one week.

Results: In the first patient cohort, gross examination of TTC-stained tissue showed thermal ablation in the transition zone. In addition, there was a distinct interface between viable and necrotic prostatic parenchyma. Histopathologic examination revealed TTC staining-outlined necrotic versus viable tissue. Gadolinium-enhanced MRIs in the cohort of 15 patients demonstrated lesion defects in all patients at 1 week post-procedure. Coalesced lesions were noted with a mean (± standard deviation) lesion volume of 9.6±8.5 cm(3). The largest lesion volume was 35.1 cm(3). Ablation using vapor was rapid and remained confined to the transition zone, consistent with the thermodynamic principles of convective thermal energy transfer.

Conclusion: Thermal ablation was observed in all specimens. The resulting coalescing ablative lesions, as seen on MRI, were confined to the transition zone. These studies confirm the ablative capabilities of vapor, validate the thermodynamic principles of convective heating, and allow for further clinical studies.

Keywords: benign prostatic hyperplasia; lower urinary tract symptomatology; minimally invasive; steam; thermotherapy; vapor therapy.

Figures

Figure 1

(A) Adenoma removed from suprapubic prostatectomy, whole mount sectioned, and stained with triphenyl-tetrazolium chloride. Note the distinct interface between the red viable tissue and the tan nonviable tissue from the steam injections. (B) Close-up of slice 7 from Figure 1A. The red box outlines the right transition zone and is used for histology in Figure 2A–C. Note the urethra is preserved and the maximum lesion size is 2.1 cm ×2.8 cm.

Figure 2

(A) Whole mount hematoxylin and eosin section of the right lobe outlined by the red box is seen in Figure 1B. (B) Hematoxylin and eosin micrograph at 10× magnification taken at the interface between the viable (left side of the green line) and necrotic prostatic parenchyma (right side of the green line) identified by triphenyl-tetrazolium chloride-staining and confirmed by microscopic evaluation. (C) 20× magnification identifying foci of thrombosed vasculature scattered throughout the necrotic prostate.

Figure 3

(A) Whole mount hematoxylin and eosin section of the left lobe. (B) Preservation of urethral epithelium at 10× magnification.

Figure 4

(A) Gadolinium-enhanced coronal magnetic resonance imaging showing large thermal lesions contained within the transition zone bilaterally. (B) Three-dimensional volumetric renderings based on the magnetic resonance imaging data. Notes: Yellow, total prostate volume; brown, total transition zone; green, right thermal lesion; blue, left thermal lesion; total volume of necrosis =35.1 cm3.

Figure 5

Gadolinium-enhanced transverse (A) and coronal (B) magnetic resonance images showing large thermal lesions outlining the transition zone while preserving the peripheral zone and urethra.