Bladder outlet obstruction: a common side effect of HIFU

The occurrence of bladder outlet obstruction (BOO) as a complication following the use of high-intensity focused ultrasound (HIFU) in the treatment of prostate cancer has been widely recognized since the early, investigational use of HIFU in the 1990s. On the basis of available data, the problem appears to occur with greater frequency in patients treated using Ablatherm technology than in those treated using the Sonoblate equipment. However, rigorous data on the complications associated with the use of both types of equipment is limited.

Relatively soon after the Ablatherm equipment became commercially available in Europe, it became common practice at some centers to require men receiving HIFU treatment for prostate cancer with the Ablatherm equipment to receive a transurethral resection of the prostate (a TURP) prior to the actual HIFU treatment for prostate cancer in order to limit the risk of BOO. (Post-HIFU BOO normally results in a limited ability to empty the bladder, increased  frequency of urination, and — in extreme cases — inability to urinate because of complete blockage of the bladder neck or the urethra.) Additional treatment to resolve this clinical problem is not usually difficult, but the risk of this side effect should be well understood by any patient contemplating HIFU as a treatment for localized prostate cancer. (Of course HIFU is still not an approved technology for the treatment of prostate cancer in the USA.)

Netsch et al. have recently published data on the occurrence of BOO in a series of 226 consecutive patients who received a single HIFU treatment between 2002 and 2007 and who were followed for at least 2 years. All patients were treated using the Ablatherm Maxis and associated Integrated Imaging devices.

The results of this study are reported by the authors as follows:

  • Median follow-up post-HIFU was 52 months (range, 24-80 months).
  • BOO was observed in 58/226 patients (25.7 percent).
  • Repeated episodes of BOO were observed in 27/226 patients (11.9 percent), and 13 of these patients had between three and seven episodes of BOO.
  • Patients who suffered repeated episodes of BOO were older than patients with a single episode of BOO (71.75 ± 4.97 vs 68.18 ± 5.03 years).
  • In patients having a primary BOO, multiple sites of obstruction were more commonly involved than in patients with repeated BOOs (25/58 vs 8/27).
  • Isolated bladder neck stenosis was predominantly found in patients who had two or more episodes of BOO.
  • A primary BOO occurred nearly twice as often in patients who had a TURP on the same day as HIFU or within 2 days of HIFU (33/96; 34.4 percent) than it did in patients who had a TURP more than 1 month before HIFU (16/89; 18.0 percent).
  • A primary BOO occurred in 9/41 patients (22.0 percent) of the patients who were treated with HIFU only (i.e., they received no TURP at all).

The authors make three points in drawing their conclusions:

  • BOO after HIFU (using the Ablatherm technology) remains common, and affects the bladder neck in particular, even when patients receive a TURP prior to HIFU treatment.
  • Risk of repeated BOOs is associated with greater patient age.
  • Regular introduction of a significant interval between TURP and HIFU (> 1 month) might reduce the risk for development of BOO as a complication of HIFU.

Data from this study does not necessarily apply to the use of Sonoblate technology, and in fact the use of a TURP as a pre-treatment for men receiving HIFU using the Sonoblate equipment is not normally required (as far as we are aware). On the other hand, we have certainly heard of patients who had problems with urinary tract blackage post-HIFU when their treatment was conducted using Sonoblate equipment, so this problem is not unique to the Ablatherm technology.

One of the more interesting findings of this study is that the basic risk for BOO was little different for the men who had no TURP (at 22 percent) than it was in the entire series (25.7 percent). One is tempted to wonder just how important the pre-HIFU TURP really is in younger patients as compared to the older ones, and whether we need better ways to determine who actually needs a TURP prior to HIFU (always assuming that HIFU is, in fact, an appropriate form of treatment for those individual patients).

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