Prostate Gland

Alok Anand MD Ashley Davidoff MD

Introduction

The size of prostate is smaller than one would imagine. It has been compared to a small kiwi fruit, small plum, an almond and a chestnut. In fact after a small experiment involving the purchase of these fine fruits and nuts it was found that the chestnut was closest in size in all dimensions.

Size of the Prostate

The diagram depicts the variety of structures that have been compared to the size of the prostate. After a shopping spree to Russo’s in Newton Massachusetts and some significant research into the true sizes of the fruits and nuts that have been compared to the prostate, it was found that the chestnut (e) is closest to the size of the prostate. The kiwi (b) and plum (c) were far larger and A-P dimensions particularly excessively large. The walnut (d) was close but A-P dimension too large, the plum tomato (f) too round, and the almond (g) too thin in the A-P dimension.

By virtue of its small size, it does not allow it to store large amounts of secretions. A normal prostate gland weighs about 20g-30g in a 30 year old male. The normal volume is between 20-30ccs. The prostate normally measures 3 cm in length (height), 4 cm in width (transverse), and 2 cm in depth (anteroposterior dimension).

It remains relatively stable in size until the age of 50 when increasing weight of the gland is observed. By the age of 80, the average prostatic weight is 35-45g.

Prostate Volume Calculation

A simple prorated ellipsoid formula is commonly used to calculate prostate volume: (anterior-posterior diameter) x (transverse diameter) x (superior-inferior diameter) x Π/6 (approximately 0.52) is accurate and reproducible.

From a practical point of view in imaging the gland is usually enlarged if the transverse dimension is greater than 4cms.

Normal Prostate by Ultrasound

The volume of this gland is calculated by the formula using a simple prorated ellipsoid formula. Thus transverse diameter of 3.5cms is multiplied by A-P dimension of 3.5cms by the craniocaudad dimension of 3.9cms and then by a correction factor of .52 . This calculation reveals a volume of 25ccs which is normal.

Courtesy Ashley Davidoff MD 74897c03

Applied Biology

BPH

The 70 year old male shows an enlarged prostate 7.2cms in A-P by 6.1cms. in the axial plane. The gland is enlarged based on these measurements. Two distinct zones are identified because the gland is abnormal. The posterior zone is canoe shaped is hypodense and represents the peripheral zone. The anterior region is more hyperdense layer and is combination of zones including the central zone, transition zone and the anterior fibromuscular layer. In this patient who has benign prostatic hyperplasia (BPH) the transitional zone is enlarged due to the hyperplasia

BPH and Zonal Anatomy

The 70 year old male shows an enlarged prostate 7.2cms in A-P by 6.1cms. in the axial plane. The gland is enlarged based on these measurements. Two distinct zones are identified. . The posterior zone is canoe shaped is hypodense and represents the peripheral zone. The anterior more hyperdense layer is combination of zones. Since the prostate gland has 4 major zones and we have accounted for the peripheral zone (pz), three other zones are present. Inward of the peripheral zone is the central zone followed by the transitional zone and finally the anterior fibromuscular layer In this patient who has benign prostatic hypertrophy (BPH) the transitional zone is enlarged due to hyperplasia. Note that BPH is a misnomer because the enlargement is due to hyperplasia and not hypertrophy.

Image (c) illustrates the enlarged transitional zone which is where the hyperplasia of BPH takes place.

Large Bilobed Smooth Gland

The CTscan is from a patient with an enlarged prostate. The anterior aspect of the gland protrudes with two symmetrical homogeneous components likely representing an enlarged transitional zone and prostate hyperplasia though by the nature of the disease the combination of cancer and BPH commonly coexist. The urinary bladder wall is minimally thickened.

Large Irregular Gland

The CTscan is from a patient with an enlarged prostate. The anterior aspect of the gland protrudes into the bladder with an irregular shape (green arrow). The bladder wall is slightly thickened (orange arrow). The peripheral zone is suggested by a hypodense posterior region (maroon arrow)

Large Gland in the Sagittal Plane

The CTscan reconstructed in the sagittal plane is from a patient with an enlarged prostate. The anterior aspect of the gland protrudes with two symmetrical homogeneous components likely representing an enlarged transitional zone and prostate hyperplasia though by the nature of the disease the combination of cancer and BPH commonly coexist. The matrix of the gland is heterogeneous The bladder wall is thickened anteriorly.