Editing Prostate: Transrectal Ultrasound

== General urological uses of a transrectal ultrasound (TRUS) ==

*  '''Uses: (5):'''
#'''Assess prostate volume'''
#'''Locate focal prostate abnormalities'''
#'''Assess for obstructive cause of infertility''' (dilated seminal vesicles secondary to ejaculatory duct obstruction)
#'''Guide prostate biopsies'''
#'''Guide placement of brachytherapy seeds'''
==Grayscale TRUS==
*'''Probe frequency'''
**'''Increasing the frequency increases the resolution''' and decreases the depth of penetration
**'''Decreasing the frequency increases the depth of penetration''' and decreases the resolution
**'''The commonly used 7-MHz transducer''' produces a high-resolution image with a focal range from 1-4 cm from the transducer '''(best for peripheral zone where most cancers arise)'''
**Lower frequency transducers (e.g., older 4-MHz transducers) have a focal range from 2-8 cm but at lower resolution
==TRUS Anatomy of the Prostate==
*Traditionally described based on a pathologic zonal architecture:
**Anterior fibromuscular stroma (FS), which is devoid of glandular tissue
**Transition zone (TZ)
**Central zone (CZ)
**Periurethral zone
**Peripheral zone (PZ)
**'''CZ and PZ cannot be distinguished from each other on US''', and are often collectively referred to as the PZ on TRUS
**'''The TZ is generally hyperechoic compared to the CZ and PZ'''
**Click here for image
**See video on GU Sonography of the Urinary Bladder, Scrotum & Prostate
*'''Calcifications along the surgical capsule, known as the corpora amylacea, highlight the plane between the PZ and TZ (multiple diffuse calcifications are a normal,''' often incidental finding and represents a result of age rather than a pathologic entity)

== Prostate lesions on TRUS ==
*'''The peripheral zone is used as the reference for isoechoic when describing lesions'''
*'''<span style="color:#ff0000">Most (60%) prostate cancers are hypoechoic; however, can also be iso (39%) or even hyperechoic (1%)'''§
**Images of hypoechoic lesions on TRUS
*'''A hypoechoic lesion contains cancer ≈20% of the time.'''
**While there is a need to biopsy hypoechoic lesions, these lesions are not pathognomonic for cancer and '''do not correlate with the aggressiveness of the disease as measured by Gleason score.'''
**'''<span style="color:#ff0000">Differential diagnosis of hypoechoic lesions on TRUS (5):</span>'''
**#'''<span style="color:#ff0000">Granulomatous prostatitis</span>'''
**#'''<span style="color:#ff0000">Prostatic infarct</span>'''
**#'''<span style="color:#ff0000">Lymphoma</span>'''
**#'''<span style="color:#ff0000">BPH nodules</span>'''
**#'''<span style="color:#ff0000">Normal urethra</span>'''
*'''Many cancers, including hematologic malignancies of the prostate, are isoechoic'''
**'''Prostatic cysts'''
***'''May be congenital or acquired but are rarely clinically significant, regardless of cause'''
***'''Congenital prostatic cystic lesions may arise from either müllerian (prostatic utricles and müllerian duct cysts) or wolffian (ejaculatory duct and SV cysts) structures'''
****'''Enlarged prostatic utricle'''
*****A diverticular projection from the posterior urethra at the level of the verumontanum
*****'''Appears as a midline anechoic structure'''
*****'''Associated with genital anomalies''', including hypospadias (most common), ambiguous genitalia, undescended testes, and congenital urethral polyps
****'''Müllerian duct cysts'''
*****Result from failure of the müllerian ducts to fuse with the urethra.
*****'''Appears as a midline anechoic structure;''' generally ovoid to pear shaped, with the cyst neck oriented toward the verumontanum.
*****'''Should prompt renal US to assess for unilateral renal agenesis'''
****'''SV cysts'''
*****'''Can be caused by congenital or acquired obstruction of the ejaculatory duct'''
*****'''Associated with cystic renal disease'''
*****'''Should prompt renal US to assess for unilateral renal agenesis'''
*****'''Zinner syndrome (3):'''
*****#'''Ipsilateral SV cyst'''
*****#'''Ejaculatory duct obstruction'''
*****#'''Unilateral renal agenesis'''
*'''TRUS appearance after treatment'''
**External-beam radiation monotherapy therapy usually results in decreased volume by 6 months after treatment.
**With brachytherapy, prostate volume declines significantly after treatment, with a 37% size reduction at 1 year after treatment and > 50% reduction 8 years after implantation
**'''Irradiated prostates are diffusely hypoechoic'''
**Androgen ablation with luteinizing hormone–releasing hormone analogues will cause ≈30% volume decrease with androgen deprivation in prostates with and without cancer
**'''Volume decreases by ≈21% at 6 months with 5-ARIs'''
==<span style="color:#ff0000">Estimating Prostate Volume</span>==
*'''Most formulas assume that the gland conforms to an ideal geometric shape: either an <span style="color:#ff0000">ellipse (π/6 × transverse diameter × AP diameter × longitudinal diameter)</span>,''' sphere (π/6 × transverse diameter3), or a prolate (eggshaped) spheroid (π/6 × transverse diameter2 × AP diameter).
**'''All formulas reliably estimate gland volume and weight, with correlation coefficients > 0.90 with radical prostatectomy specimen weights,''' because 1 cm3 = approximately 1 g of prostate tissue.
**'''<span style="color:#ff0000">Planimetry is the most accurate means of volume measurement by US</span>'''
***Planimetry allows for variation in shape as the area is calculated in consecutive ultrasonographic cross-sections. The area is multiplied with the distance between the cross-sections and the total volume is determined by summation of all contributions.§