Prostate Volume, BPH & PSA Glossary: Terms on Your Report Explained

July 19, 2026

A prostate imaging or PSA report can pack in a dozen abbreviations most patients never encounter anywhere else. Here’s what the terms that feed into the prostate volume calculator — and the ones commonly printed alongside them — actually mean.

Imaging & Measurement Terms

TRUS (Transrectal Ultrasound) — An ultrasound probe inserted transrectally to image the prostate directly. It’s the most common way length, width, and height measurements are captured for the ellipsoid volume formula.

MRI (Magnetic Resonance Imaging) — A non-invasive imaging alternative to TRUS, increasingly used both for volume measurement and for detecting suspicious lesions via PI-RADS scoring (below). MRI-derived dimensions can be plugged into the same ellipsoid formula as TRUS measurements.

Ellipsoid (Prolate Spheroid) Method — The standard volume estimation approach: Volume = 0.52 × Length × Width × Height. It treats the gland as a symmetric oval solid, which is a good approximation for most glands but less accurate for irregularly shaped ones.

Transition Zone — The region of the prostate surrounding the urethra, and the part that enlarges in benign prostatic hyperplasia (BPH). Some reports separately calculate “transition zone volume” and a corresponding “PSA density of the transition zone (PSAD-TZ),” a more refined variant of standard PSAD used in some research and specialist settings.

PSA & Risk Terms

PSA (Prostate-Specific Antigen) — A protein produced by prostate tissue that leaks into the bloodstream in larger amounts as the gland grows, whether from BPH, inflammation, or cancer.

PSAD (PSA Density) — Serum PSA divided by prostate volume (PSA ÷ Volume), correcting a raw PSA number for gland size. See the prostate volume calculator for the 0.15 and 0.20 threshold reference.

PSA Velocity — The rate of change in PSA over time (measured across multiple tests, usually a year or more apart). A rapidly rising PSA is a separate risk signal from an elevated single reading.

Free/Total PSA Ratio — PSA circulates in blood either bound to proteins or “free.” A lower percentage of free PSA relative to total PSA is statistically associated with a higher likelihood of cancer, used as another supporting data point alongside PSAD.

Cancer Risk & Symptom Scoring

PI-RADS (Prostate Imaging Reporting and Data System) — A standardized 1-to-5 scoring system radiologists use to rate how suspicious an MRI-detected lesion looks for clinically significant cancer, with 1 being very unlikely and 5 being highly suspicious. PI-RADS and PSAD are different tools — PI-RADS scores a specific lesion seen on MRI, while PSAD is a whole-gland size-adjusted PSA calculation — and both are typically weighed together, not used interchangeably.

IPSS (International Prostate Symptom Score) — A separate 7-question, 0-35 point patient questionnaire measuring urinary symptom severity (weak stream, frequency, nighttime urination, etc.), unrelated to cancer risk. Scores group into mild (0-7), moderate (8-19), and severe (20-35) categories, and this score often drives BPH treatment decisions independently of PSA or PSAD.

BPH & Management Terms

BPH (Benign Prostatic Hyperplasia) — Non-cancerous enlargement of the prostate gland, extremely common with age, and the main reason prostate volume increases over a lifetime even in men who never develop prostate cancer.

Watchful Waiting / Active Surveillance — A monitoring-only approach (repeat PSA, imaging, sometimes repeat biopsy) used instead of immediate treatment, for low-risk findings where the statistical odds favor observation over intervention.

5-Alpha Reductase Inhibitor — A class of BPH medication (finasteride, dutasteride) that shrinks prostate volume over months of use — worth knowing because it also lowers PSA by roughly half, which needs to be accounted for when interpreting PSA or PSAD trends in someone taking one of these drugs.

Using This Glossary With Your Own Report

Match the abbreviations on an actual TRUS or MRI report against the definitions above, then enter the length, width, and height figures into the prostate volume calculator to get volume and PSAD instantly. For a walkthrough of exactly where these numbers typically appear on a real report, see understanding your prostate MRI or TRUS report: a patient’s guide. For these terms applied to real volume and PSA density calculations, see prostate volume and PSA density worked examples.