TRUS: Transrectal Ultrasound Procedure and Prostate Biopsy

Transrectal ultrasound, commonly called TRUS, is an imaging technique that uses a small probe inserted into the rectum to produce detailed pictures of the prostate gland and surrounding structures. Developed in the 1970s, it became the standard way urologists visualize the prostate, measure its size, and guide biopsy needles into suspicious tissue. While TRUS remains one of the most widely used tools in prostate care, its limitations in detecting cancer on its own have driven a wave of innovations, from MRI fusion to artificial intelligence, that are reshaping how the technology fits into modern urology.

What TRUS Actually Shows

The probe emits high-frequency sound waves that bounce off tissues at different rates depending on their density. The returning echoes are converted into a real-time image on a monitor. On a standard grayscale TRUS image, the prostate appears as a walnut-shaped organ with distinct zones. The peripheral zone, where most cancers arise, sits closest to the rectal wall and shows up as a relatively bright band. Cancers in this zone often appear as darker (hypoechoic) spots, but the appearances are variable and overlap considerably with benign conditions like inflammation or benign prostatic hyperplasia.

This overlap is the central weakness of conventional TRUS as a cancer-detection tool. The sensitivity and specificity of standard grayscale TRUS for spotting prostate cancer each hover around 40 to 50 percent, meaning it misses roughly half of cancers and flags many areas that turn out to be harmless.¹ An early study found a sensitivity of 52% and specificity of 68% in detecting unsuspected cancers.² Because the images alone are unreliable for pinpointing cancer, TRUS evolved into something arguably more important: a guidance system for taking biopsies from standardized locations across the gland, regardless of what the image looks like.

How TRUS Measures the Prostate and Why It Matters

Beyond cancer detection, TRUS is routinely used to measure prostate volume. Knowing the size of the gland helps clinicians calculate PSA density (the PSA blood level divided by prostate volume), which is a better predictor of significant cancer than PSA alone. It also guides decisions about whether a man with low-risk cancer can safely go on active surveillance rather than pursuing immediate treatment.

TRUS volumes correlate well with MRI-derived measurements. One study comparing the two found a strong linear relationship, with volumes differing by an average of only about 1.7 ml. That said, the gap widened in larger prostates: glands measured above 60 ml on TRUS differed from MRI by roughly 5 ml on average.³ For most clinical decisions, that difference is small enough that TRUS remains a practical, widely available option. But in borderline cases where PSA density is teetering near a decision threshold, the slight volume discrepancy could tip the calculation one way or another.

The TRUS-Guided Biopsy

When a man has an elevated PSA or an abnormal digital rectal exam, the next step is usually a biopsy. The most common approach has been a TRUS-guided systematic biopsy, in which the urologist uses the ultrasound image to direct a spring-loaded needle into predetermined locations across the prostate. The current accepted minimum is 10 to 12 cores, taken from both sides of the gland in a pattern designed to sample as broadly as possible.⁴

Detection rates from 12-core biopsies vary. One study of 60 patients found cancer in 40 percent.⁵ A larger study of over 2,700 men reported an overall cancer detection rate of about 28 percent, with roughly 21 percent of those being clinically significant cancers. That study also found that biopsy cores taken from the apex of the prostate were more likely to catch significant disease, suggesting that where you sample within the gland matters as much as how many cores you take.⁶

MRI/TRUS Fusion Biopsy

The biggest shift in prostate biopsy practice over the past decade has been combining MRI with TRUS. In an MRI/TRUS fusion biopsy, a man first undergoes a multiparametric MRI that highlights suspicious areas. Those MRI images are then overlaid onto the real-time TRUS display during the biopsy, allowing the urologist to steer needles directly into the targets the MRI flagged, in addition to taking standard systematic cores.

Fusion biopsy consistently outperforms systematic biopsy alone for catching aggressive cancers. In one study, adding MRI-targeted cores upgraded the cancer grade in about a third of cases and detected 67 percent more high-grade tumors compared with 12-core biopsy alone.⁷ At the same time, the targeted approach missed more low-grade disease, which many clinicians consider a feature rather than a bug: finding fewer slow-growing cancers means fewer men are pushed toward treatment they may not need.

Another study found that MRI/TRUS fusion detected clinically significant cancer at a rate of about 31 percent compared with 25 percent for systematic biopsy, with the biggest advantage appearing in men whose MRI showed highly suspicious lesions.⁸ The evidence has been strong enough that many guidelines now recommend MRI before biopsy in men with elevated PSA, with fusion biopsy for those whose MRI reveals a target.⁹

Does It Hurt?

The honest answer is that it depends on the technique used. The probe insertion itself causes pressure and mild discomfort. The biopsy needles produce a brief snapping sensation with each core, and most men describe it as a sharp sting that fades quickly. The real variable is whether you receive a nerve block.

Without local anesthesia, average pain scores on a 0-to-10 scale tend to land around 3 to 5 during the procedure. A periprostatic nerve block, in which the doctor injects lidocaine near the nerve bundles that supply the prostate, roughly halves those scores. One randomized trial found average pain dropped from about 4.7 with saline placebo to 2.7 with lidocaine, with no adverse effects from the injection.¹⁰ Another trial showed an even wider gap in men who had previously undergone biopsy without a nerve block and then received one for a repeat procedure: pain scores fell from about 4.6 to 1.7.¹¹ Pain relief held regardless of how many cores were taken. Multiple studies confirm the nerve block as the standard pain-management approach, with mean scores during biopsy hovering around 2.5 to 3 on the pain scale.¹²

If you are scheduled for a TRUS biopsy and the doctor does not mention a nerve block, it is reasonable to ask about one. The evidence overwhelmingly supports it, and the injection itself adds only seconds to the procedure.

Risks and Infection Concerns

Because the biopsy needle passes through the rectal wall, a transrectal approach carries an inherent risk of introducing gut bacteria into the prostate and bloodstream. The most common post-procedure symptoms are blood in the urine, semen, or stool, and these typically resolve on their own within a few days to weeks. The more serious concern is infection.

A population-based study in Calgary found that about 6 percent of patients visited the emergency department within 30 days of their biopsy. Sepsis occurred in roughly 2 percent, urinary tract infection in about 1 percent, and prostatitis in under half a percent. More than 80 percent of septic episodes were caused by ciprofloxacin-resistant E. coli.¹³ A single-center study in Lebanon reported a higher urosepsis rate of about 9 percent, with hypertension as a significant independent predictor.¹⁴ While the absolute numbers differ across institutions and populations, the trend of rising antibiotic resistance in rectal flora is consistent and concerning.

In rare cases, complications can be severe. Case reports describe near-fatal septic shock from multi-resistant E. coli and hemorrhage requiring emergency surgery.¹⁵ These outcomes are uncommon, but they underscore why the field has been searching for ways to reduce infection risk.

One promising approach is targeted antibiotic prophylaxis based on a rectal swab taken before the biopsy. Instead of giving everyone the same fluoroquinolone, a culture identifies which bacteria are present and which drugs they are resistant to, so the antibiotic choice can be tailored. Studies of this strategy show dramatic drops in post-biopsy infection. One found that only about 1 percent of men developed a fever after swab-directed prophylaxis, with no cases of sepsis.¹⁶ A randomized study comparing targeted prophylaxis to standard treatment found febrile urinary infection rates of about 4 percent versus 13 percent.¹⁷

Transperineal Biopsy as an Alternative Route

An increasingly popular way to sidestep the infection problem entirely is the transperineal approach. Instead of going through the rectum, the needle enters through the skin of the perineum, the area between the scrotum and the anus. Because the needle never crosses the rectal wall, the risk of introducing gut bacteria drops sharply.

A meta-analysis comparing the two routes found that infection rates were significantly lower with the transperineal approach, and the risk of severe (grade 3 or higher) infections fell by about 65 percent. Clinically significant cancer detection rates were comparable overall, though the transperineal route showed a modest edge in settings that did not use MRI targeting.¹⁸ Another pooled analysis similarly showed significantly lower sepsis rates and slightly higher cancer detection for the transperineal method.¹⁹

The trade-off is pain. The transperineal approach was associated with about double the odds of procedural discomfort in randomized comparisons, often requiring more robust local anesthesia or even brief sedation. Many centers are now shifting to transperineal as the default, viewing the infection reduction as worth the extra anesthesia logistics.

The Psychological Side

Pain scores do not capture the full experience. Waiting for a biopsy, and then waiting for results, generates real anxiety. One study found that about 64 percent of men reported anxiety before the procedure, and pre-biopsy anxiety was itself a predictor of how much pain they felt during it.²⁰ About 7 percent reported erectile dysfunction that they attributed to anxiety around the biopsy.

Among men who received a negative result (no cancer found), those who experienced bothersome physical symptoms like blood in the urine or pain reported higher anxiety at one week. By five weeks, anxiety had improved even though the physical symptoms had not fully resolved, suggesting the psychological distress was driven more by uncertainty about the diagnosis than by the symptoms themselves.²¹ For men who did receive a cancer diagnosis, anxiety predictably spiked around the time results were delivered. These findings argue for clear communication before and after the procedure: knowing what symptoms to expect, and getting results quickly, can make a meaningful difference in how men cope.

Newer Ultrasound Technologies

Researchers have been trying to make TRUS itself smarter rather than simply relying on MRI to compensate for its weaknesses. Several approaches show promise.

Contrast-enhanced TRUS uses microbubble agents injected into the bloodstream. Tumors tend to have more blood vessels than normal tissue, and microbubbles highlight this abnormal blood flow in real time. One study found that combining contrast-enhanced power Doppler with a technique called flash replenishment imaging improved diagnostic accuracy compared with standard grayscale imaging.²²

Elastography measures tissue stiffness. Cancerous tissue tends to be stiffer than surrounding healthy prostate. One form, shear-wave elastography, showed a sensitivity of 96 percent and specificity of 85 percent for distinguishing cancerous from benign tissue at a specific stiffness cutoff.²³ Combining elastography with contrast-enhanced ultrasound may improve accuracy further.²⁴

Micro-ultrasound is a newer platform that operates at 29 MHz, roughly three times the frequency of conventional TRUS. This produces much finer-resolution images that can visualize tissue architecture previously only visible under a microscope. Early reports suggested sensitivity for clinically significant cancer could reach 94 to 100 percent.²⁵ However, a recent meta-analysis of prospective studies found more tempered numbers: pooled sensitivity of about 84 percent and specificity of 41 percent, suggesting that micro-ultrasound works better as a rule-out or triage tool than as a standalone diagnostic.²⁶ The technology is still relatively new, and where it will settle in the diagnostic pathway remains an active area of research.

TRUS Beyond Prostate Cancer

Though prostate cancer screening and biopsy get most of the attention, TRUS is used for several other conditions. One important application is in evaluating male infertility. When a man has no sperm in his ejaculate (azoospermia) or very low semen volume, TRUS can reveal structural reasons why. A study of 276 infertile men found anatomic abnormalities in about three-quarters of them, including absent vas deferens, duct obstruction from calcification or fibrosis, and obstructing cysts.²⁷ TRUS can pinpoint the level of obstruction, helping surgeons decide whether to attempt duct reconstruction or proceed to sperm retrieval.

TRUS also performs well in identifying seminal vesicle abnormalities. One study of over 1,200 men with obstructive azoospermia found that seminal vesicle defects accounted for nearly 29 percent of cases, with congenital absence or underdevelopment making up the majority. TRUS showed high agreement with MRI for diagnosing these structural problems, making it a reliable first-line imaging choice.²⁸ For men with low ejaculate volume and azoospermia, TRUS can confirm or rule out ejaculatory duct obstruction without the need for more invasive procedures.²⁹

TRUS in Treatment Planning

TRUS plays an active role in treating prostate cancer, not just diagnosing it. In brachytherapy, radioactive seeds or high-dose-rate catheters are placed directly into the prostate to deliver targeted radiation. TRUS provides the real-time imaging that guides needle placement during these procedures, ensuring the radiation sources land where they are needed.

More recently, clinicians have explored fusing MRI data with real-time TRUS to improve brachytherapy planning. The MRI provides superior soft-tissue contrast, making it easier to delineate the tumor and surrounding structures, while TRUS gives live needle visualization during the implant.³⁰ This same fusion concept has been applied to focal brachytherapy, where only the tumor itself is treated rather than the entire gland. Phantom studies have demonstrated that it is feasible to deliver ablative radiation doses precisely to the tumor while protecting the rectum with a spacer.³¹

Artificial Intelligence and the Future of TRUS

Perhaps the most exciting frontier is applying artificial intelligence to TRUS images. The core limitation of conventional TRUS, its inability to reliably distinguish cancer from benign tissue on sight, is precisely the kind of pattern-recognition problem that deep learning excels at.

One AI model trained on images of biopsy needle-tract tissues achieved an accuracy of about 89 percent and detected more cancers than senior radiologists, with a false-positive rate that was over 60 percent lower than what the physicians achieved on their own.³² Another study using transfer learning with convolutional neural networks reported near-perfect accuracy in classifying TRUS images as cancerous or benign, though these results come from a controlled research setting and real-world performance would likely be lower.³³

AI integration could eventually bring TRUS full circle. The technology’s original promise was to visualize prostate cancer directly. That promise was never fulfilled by grayscale imaging alone, leading to the era of systematic “blind” sampling and then MRI-guided targeting. If AI can reliably flag suspicious regions on a live TRUS feed, it would allow real-time, image-directed biopsies without requiring a separate MRI session. For patients in settings where MRI access is limited or wait times are long, that could be a meaningful practical advance. The technology is still in relatively early validation, but the direction of travel is clear: TRUS is becoming less of a dumb guidance tool and more of an intelligent imaging partner.