Us Urinary System and Prostate

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Ultrasound of the Urinary System

and ProstateAlain Giroux, DVM, MSc, DACVR

Introduction

Ultrasound is an excellent imaging modality to evaluate the urinary tract. With ultrasonographicexamination the entire urinary tract can be evaluated at one time and usually without the aid of anesthesia.

The kidneys can be imaged using a 5.0-megahertz transducer; however, for small dogs and cats, a 7.5-megahertz transducer is ideal.

Normal Renal Anatomy

The kidneys are located in the retroperitoneal space, usually between the caudal thoracic and 3rd lumbar

vertebrae. The kidneys are bean-shaped and are composed of the renal capsule, renal cortex, renal medullaand the diverticuli. The renal pelvis is located in the central portion of the kidneys and is usually

surrounded by renal fat (Fig. 1K and Fig. 2K). Renal arteries and veins can be identified at the hilus of the

kidneys. The ureter leaves the renal pelvis through the hilus of the kidney. The normal ureter is not

usually identified ultrasonographically.

The left kidney is located caudal to the fundus of the stomach and medial to the spleen. The right kidney is

caudal to the liver and is located in the renal fossa of the caudate lobe of the liver. The right kidney is

further cranial than the left kidney, which makes visualizing the right kidney more difficult.

The size of the kidneys varies depending on the size of the dog. A normal canine kidney can vary from 4 to

9 cm in length and feline kidneys are usually 3.8 to 4.4 cm in length.

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Figure 1K: Kidney Anatomy Figure 2K: Kidney Anatomy at the Pelvis


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Ultrasonographic Renal Anatomy

The capsule of the kidney is a hyperechoic structure which is identified surrounding the kidney. The renal

cortex is hyperechoic in relation to the medulla. There is good distinction between the renal cortex and

renal medulla in the normal kidney (Fig. 3Ka,b and Fig. 4K). The renal sinus (Fig.4K) usually contains fat

which can be seen as bright echoes and in some cases can result in acoustic shadowing. The medulla of the

kidney is separated into sections by the diverticuli. The renal cortex of the kidneys is usually lessechogenic than the spleen but more echogenic than the renal medulla. The renal cortex can be isoechoic tohypoechoic in relationship to the liver.

The renal artery and vein can usually be visualized entering the kidney at the renal sinus. Renal vessels can

be recognized in the medulla. The arcuate and interlobar arteries can sometimes be visualized at the

cortical medullary junction.

When evaluating the kidneys ultrasonographically, the patient is usuallyplaced in dorsal recumbency. Thekidneys should be scanned in both sagittal and transverse planes. The appearance of the renal cortex and

renal medulla will depend on where the sagittal and transverse images are obtained in relation to the

midline of the kidney. Renal pelvic dilatation may be best visualized in the transverse plane (Fig. 5K andFig. 6K).

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Figure 3Ka: Sagital View of Kidney:Centered on Hilus

Figure 4K: Transverse View of Kidney

Figure 3Kb: Sagital View of Kidney:Centered Off Hilus


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Renal AbnormalitiesAs with other organs, diseases of the kidneys are usually divided into focal and diffuse. The table 1K lists

examples of ultrasonographic changes in the kidney with possible causes.

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Ultrasonographic Appearance Diseases

Anechoic to hypoechoic lesions Renal cysts

Polycystic renal disease

Lymphosarcoma

Increased echogenecity Renal infarcts

InfectionNephrolithiasis

Renal calculi

Lymphosarcoma

Various echogenic appearances HematomasAbscesses

Neoplasia

Dilation of the renal pelvis Pyelonephritis

Hydronephrosis

Diuresis

Altered renal architecture Renal dysplasia

Neoplasia

End-stage renal disease

Anechoic fluid surrounding the kidneys Perinephrotic cyst

Perirenal hemorrhageExtravasation ofurine

Table 1K: Ultrasonographic Appearance of Common Renal Diseases

Figure 5K:Renal pelvis Dilatation:

Sagital View

Figure 6K:Renal Pelvis Dilatation:

Transverse View


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Urinary Bladder and Prostate Anatomy

The urinary bladder is a hollow organ which stores urine. The size and location of the bladder is

divided into the neck and body with the neck directly toward the pelvic canal and connected to the

urethra (Fig. 7K). The ureters enter the bladder on the dorsocaudal aspect of the bladder just proximal tothe neck of the bladder. The urinary bladder wall is composed of the serosa, muscular layer and mucosa.

The prostate gland is located caudal to the urinary bladder. The prostate gland in a castrated patient may

not be visualized. The prostate gland surrounds the pelvic urethra beginning at the trigone region of the

urinary bladder. The prostate gland is a bi-lobe structure and is surrounded by a capsule. The size and

position of the normal prostate gland varies with age, body size and perhaps the breed of dog.

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Figure 7K: Urinary Bladder and Prostate Anatomy:

Dorsal View


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Ultrasonographic Urinary Bladder and Prostate Anatomy

The urinary bladder is identified as an anechoic structure in the caudal aspect of the abdomen. The urinary

bladder is best evaluated when it is filled with urine. The urinary bladder wall should be uniform in

thickness and the mucosal lining smooth in contour. Its wall contains layers that can be seen in ideal

conditions as a double wall appearance (Fig. 9K).

The normal prostate gland has a homogeneous parenchymal pattern with a medium to fine texture. Theechogenicity is variable from hyperechoic to hypoechoic but should be uniform in echogenicity.

Ultrasonographically, the individual lobes of the prostate gland can be visualized in the transverse plane.

Ultrasonographic evaluation of the urinary bladder and prostate gland is usually performed with the patient

in dorsal recumbency. A 7.5-megahertz transducer is ideal for evaluating the urinarybladder andprostategland; however, in large dogs, a 5-megahertz transducer can be used to evaluate the prostate gland.

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Figure 8K: Normal Urinary Bladder Figure 9K: Normal Urinary Bladder:

Double Wall Appearance

Figure 10K: Normal Prostate:

Neutered Male


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Urinary Bladder Abnormalities

Ultrasonographic abnormalities involving the urinary bladder usually include thickening of the urinary

bladder wall which can be seen with cystitis or an infiltrative process such as neoplasia. Neoplastic lesions

are most commonly identified in the trigone region and are usually due to a transitional cell carcinoma (Fig.11K and 12K) but can be present anywhere. Severe thickening of the urinary bladder wall, especially in

cats, has been associated with neoplasia, such as lymphosarcoma. The mucosal lining of the urinarybladder wall becomes irregular with cystitis (Fig. 13K). Cystitis usually involves the cranioventral aspect

of the urinary bladder. Cystic calculi (Fig. 14K) or blood clots can be identified in the urinary bladder

lumen and usually gravitate to the dependent portion of the urinary bladder wall. Evaluating the urinary

bladder with the patient in various positions would be necessary to document that calculi or blood clots are

free floating within the lumen. Cystic calculi are usually hyperechoic and result in acoustic shadowing

(Fig. 14K).

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Figure 14K: Calculus and Cystitis

Figure 11K: Transitional Cell Carcinoma

Figure 13K: Severe Cystitis

Figure 12K: Transitional Cell Carcinoma


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Prostate Abnormalities

Most of the disease processes involving the prostate gland result in enlargement of the prostate gland.

Prostatic cysts appear as anechoic regions within the prostate gland with acoustic enhancement and can be

of various sizes. Prostatic cysts (Fig 15K) must be separated from prostatic abscesses (Fig 16K). Prostatic

abscesses usually contain echogenic material and are surrounded by a capsule. Periprostatic cysts are also

associated with the prostate gland. Prostatic cysts or periprostatic cysts may be congenital or developsecondary prostatic hypertrophy or squamous metaplasia. Benign prostatic hyperplasia or prostaticinfections can have a very similar appearance. Benign prostate hyperplasia and infection usually result in

generalized enlargement of the prostate gland. Scattered hyperechoic foci and small cysts can be

associated with prostatic hyperplasia; however, with prostatic inflammation, the parenchyma is usually

heterogeneous with a mixed pattern of echogenicity. The prostate gland may become hypoechoic with

infection. Mineralization is not usually associated with benign prostatic hyperplasia; however, with

infection, hyperechoic areas secondary to fibrosis, gas or mineralization can be visualized. The prostatic

capsule usually remains intact with both benign hyperplasia and infection.

With prostatic neoplasia, the prostatic parenchyma has no specific ultrasonographic changes to differentiate

neoplasia from infection or hyperplasia. Hyperechoic areas can be present throughout the parenchymasuggesting mineralization; however, caviar or cyst-like lesions can also be present. Differentiation of

benign prostatic hyperplasia, prostatitis, or prostatic adenocarcinoma can be difficult based on the

ultrasonographic appearance. A biopsy of the prostate gland may be necessary to establish a definitive

diagnosis. With prostatic neoplasia, evaluation of the sublumbar lymph nodes for changes to suggest

metastasis is recommended.

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Figure 15K: Prostatic Cysts and HyperplasiaFigure 16K: Prostatic Abscess

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