The organ that has been most closely studied in urology with the 3D US device is surely the prostate. Owing to its particular anatomical position, the prostate gland is ideally suited to US studies of normal or pathological characteristics. Although the ultrasound devices in most common use can provide considerable information on the organ under study, their 2D view and impossibility of scanning the coronal plane pose limitations. These were not recognized as limits until magnetic resonance imaging with an endorectal bobbin demonstrated the far greater diagnostic and staging potential of three-dimensional study of the prostate gland.

The fact that 3D US is a novelty, and so its use in clinical practice is still limited, means that its full potential has not yet been entirely realized. Most research has been focused on understanding this novelty in terms of the images obtained with 3D US.

Scanning the coronal plane makes it possible to reveal some anatomical details that cannot otherwise be assessed. In fact, the central zone of the gland is only visible on the frontal plane. It appears as a cuneiform hypoechogenic area, surrounded by the isoechogenic peripheral gland. The transition zone is a tenuous, symmetrical hypoechogenic area lying to the sides of the proximal urethra. Moreover, it is possible to follow the complete course of the ejaculatory ducts up to their outlet in the verumontanum region (Fig. 49.3).

With increasing biological aging of the organ, the transition zone tends to become much more voluminous. This modifies the appearance of the prostate on the coronal plane; it has been shown, in fact, that the increased tissue volume in BPH occurs exclusively in this prostatic zone.

The remarkable reliability of volumetric calculations of the prostate done with the 3D US device fitted with a multiplanar transrectal probe is due to the highly precise definition of the images. The practical advantage of correct volumetric measurements of the prostate is that it allows assessment of the true efficacy of surgical treatment, as well as its feasibility in benign prostatic hyperplasia and in prostatic carcinoma. Naturally, a more accurate estimate of the disease extent allows a better assessment of the diagnostic and prognostic factors [1]. In fact, 3D US can overcome the difficulties encountered using conventional TRUS for local staging of cancer. The visualization of an additional scanning plane can clarify the anatomical relationships between the tumor and surrounding healthy prostate tissue, including the capsule. A precise view of the whole length of the ejaculatory ducts can demonstrate any invasion by the tumor, that is, the first step toward involvement of the seminal vesicles, a well-known unfavorable prognostic factor. In addition, the bladder-prostate angle is more easily visualized and investigated [2] Video 49.1.

Thus, 3D US can play a major role in the diagnostic workup of prostatic carcinoma. As is well known, the disease mostly originates in the peripheral zone of the gland, but in 20 % of tumors it arises in the transition zone. Some important studies have demonstrated a greater incidence of tumors in the transition zone if the biopsy is done under 3D rather than the usual 2D ultrasound guidance. This higher percentage of tumors identified in the TZ does not seem to be due so much to being able to visualize anomalous areas as to a better visualization of the transition zone thanks to the coronal plane scans. In short, a precise visualization of the transition zone on the coronal plane allows targeted biopsies to be performed, resulting in a demonstrated increase in the number of diagnoses of carcinoma in this prostate area. In short, 3D US allows a greater diagnostic accuracy of prostatic biopsies, reducing the number of false-negative cases [3]. In addition, the biopsy course followed can be recorded, which can be an extremely useful point if any further biopsy needs to be done.