Diagnosing BPH: Ultrasound vs. Multiparametric MRI
Benign prostatic hyperplasia (BPH, also called benign prostatic hypertrophy) is a noncancerous enlargement of the prostate that occurs as men age. Global statistical estimates based on autopsies range from 20% for men in their 40s, 50-60% for men in their 60s, and 80-90% for men in their 70s and 80s. This normal age-related condition may or may not result in urinary symptoms such as difficult urination, sense of urgency, more frequent urination, interrupted night sleep, etc. In fact, many men will never need to see a doctor. For those who do, treatments range from medication to minimally invasive procedures. According to Roerhborn (2005), “…tissue ablative surgical treatment options are superior to both minimally invasive and medical therapy.”[i]
Diagnosing BPH is usually a process of ruling in and ruling out, since many conditions can cause lower urinary tract symptoms (LUTS). Blood and urine tests are used to check for infection, kidney function and prostate cancer. Evaluation of urine flow/restriction can be done based on patient questionnaire and in-office testing. Cystoscopy is a visual examination of the urethra (passage of urine from the bladder out of the body) using a very small scope with a tiny camera on the end. Digital rectal exam will give some clues to the size and shape of the prostate, but can be unreliable in diagnosing BPH.
Urologists generally use in-office ultrasound (US) to assess the size, volume and shape of the prostate, which is clearly depicted on a monitor. Most US imaging is gray-scale on the monitor (shades of black, gray and white) and, unlike multiparametric MRI, does not reveal functional differences that define distinct tissue differences. However, prostate enlargement depicted on US can give enough information to rule BPH in. A special type of US called power Doppler ultrasound (pDUS) can reveal the blood flow of the arteries that feed blood to the prostate, called the urethral (interior at the urethra) and capsular (exterior at the capsule edge) prostatic arteries. pDUS has high sensitivity for slow blood flow, so it is a clue that the added density of the prostate gland is putting pressure on the flow of blood as well as urine, so the cause is likely BPH. The measure of blood flow restriction is called the resistive index (RI). The greater the obstruction, the higher the RI value. Two studies demonstrate how RI can be used to validate a diagnosis of BPH.
The earlier of the two studies appeared in a 2012 issue of the International Brazilian Journal of Urology by authors Abdelwahab et al.[ii] They correlated other BPH factors with the RI to determine how reliably they match up. They included 82 patients with BPH who had thorough diagnostic records: International Prostate Symptoms Score (IPSS), physical exams, neurologic exams, uroflow metrics, lab tests and PSA. Their prostate volumes were measured by US, and pDUS measured the RI values of the capsular and urethral arteries.
Transrectal Power Doppler Ultrasound (PUD) was used to identify the capsular and urethral arteries of the prostate and to measures the RI value. They found a significant correlation between the RI values of all arteries and the degree of urinary obstruction, prostate volume, and severity of LUTS. They concluded that RI is a useful way to evaluate BPH urine obstruction.
The second study was recently published (April 2015) in the Kaohsiung Journal of Medical Science.[iii] This is an interesting paper because it not only correlates RI values with BPH, but it also examines the connection with cardiovascular risk factors. The authors studied 120 patients with LUTS due to BPH. Patients were thoroughly evaluated for their LUTS (physical and lab tests) as well as cardiovascular risk factors (high blood pressure, diabetes, smoking, history of cardiac events, and metabolic syndrome. pDUS was used to measure the RI values of the men, and the data subjected to statistical analysis. The authors report that “… there were statistically significant relationships between prostatic RI levels and the patients’ age, International Prostate Symptom Score, hip circumference, fasting blood glucose, prostate specific antigen, triglycerides, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, total prostate volume, uroflowmetric maximal flow rate, and all investigated CVS risk factors…” They concluded that prostate RI values are highly linked to overall metabolic syndrome and smoking in addition to BPH. Although BPH is observed in every nationality—though some ethnic groups appear to have lower incidence—this paper suggests that BPH patients with cardiovascular risk factors and who smoke are placing further burdens on their prostatic blood flow.
The above studies are aimed at urologists, whose primary imaging tool is ultrasound because the equipment is small, relatively inexpensive and able to be placed in urology practices. However, multiparametric MRI (mpMRI) which is used by interventional radiologists for detection, diagnosis and image-guided procedures can provide important information about a wide range of prostate tissue conditions. Some of these conditions may resemble prostate cancer. This is the topic of a paper by Yu et al. (2014) that describes key features of several prostate conditions that can mimic prostate cancer.[iv] The article is well illustrated with mpMRI scans, and is available at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4075530/. The authors give example of hypertrophic nodules (focal BPH) in the peripheral and central zones of the gland. They point out how hypertrophic tissue might show up on one or more of the MRI functional parameters, and describe which specific MRI parameters can be revisited to distinguish the nodules from suspicion of prostate cancer tumors.
While pDUS and RI values may offer meaningful clues regarding BPH, it does not have the capacity of mpMRI to discriminate BPH from prostate cancer. For diagnosing BPH, mpMRI not only identifies benign conditions but it can also detect other prostate conditions while they are still asymptomatic, including BPH and prostate cancer.
[i] Roehrborn, C. Benign Prostatic Hyperplasia: An Overview. Rev Urol v.7(Suppl 9); 2005. PMC1477638
[ii] Abdelwahab O, El-Barky E, Khalil M, Kamar A. Evaluation of the resistive index of prostatic blood flow in benign prostatic hyperplasia. Int Braz J Urol. 2012 Mar-Apr;38(2):250-5; discussion 255-7.
[iii] Baykam MM, Aktas BK, Bulut S et al. Association between prostatic resistive index and cardiovascular risk factors in patients with benign prostatic hyperplasia. Kaohsiung J Med Sci. 2015 Apr;31(4):194-8.
[iv] Yu J, Fulcher AS, Turner MA et al. Prostate cancer and its mimics at multiparametric MRI. BR J Radiol. 2014 May;87(1037):20130659.