Ebook Point of care - Ultrasound: Part 2

C H A P T E R

20

Kidneys
Behzad Hassani

K E Y

POIN TS

• The primary indication to perform a point-of-care ultrasound exam of the kidney is to
evaluate for hydronephrosis.
• Any suspicious mass detected by point-of-care ultrasound warrants further investigation
and expert consultation.
• A bladder ultrasound exam should accompany every renal ultrasound exam. A distended
bladder due to bladder outlet obstruction is a common cause of hydronephrosis.

Background
Renal ultrasound provides a fast, radiationfree, and cost-effective alternative to computed
tomography (CT) for the initial workup of
low-risk patients who present with acute symptoms ranging from undifferentiated abdominal
pain to painless hematuria.1 Ultrasound is the
imaging modality of choice for investigating
obstructive uropathy in pregnant and pediatric
populations, given the adverse effects of ionizing radiation.
Focused renal ultrasound can accurately
detect and grade hydronephrosis in the context
of obstructive uropathy,2 directly visualize large
obstructing calculi,3 and characterize renal
cysts or solid masses.4 Renal ultrasound can be

incorporated into the assessment of any patient
with undifferentiated flank or abdominal pain.
When clinical suspicion for renal calculus is
high, the presence of hydronephrosis on the
side of pain can be considered as de facto
evidence of obstructive uropathy. Sensitivity
of ultrasound for detecting a calcified stone
can be improved with the addition of a single
plain film of the abdomen (kidneys, ureter, and
bladder, or KUB).5 Severity of hydronephrosis
observed may correlate with the duration of
obstruction6 and possibly with the size of the
obstructing calculus.7 When stone disease is
clinically less likely or an alternate pathology

such as abdominal aortic aneurysm, gallbladder
disease, ovarian torsion, or ectopic pregnancy is
being considered, the absence of hydronephrosis effectively guides investigations elsewhere.

Normal Anatomy
Kidneys are retroperitoneal organs that lie in
an oblique longitudinal plane with the inferior
pole of each kidney more anterior and lateral
compared to its superior pole (Figure 20.1).
Therefore, the transducer must be positioned
obliquely to image the kidney along its long
axis. The left kidney is located more superiorly
and posteriorly compared to the right kidney.
The left kidney is usually visualized through
the acoustic window provided by the spleen

due to interference by bowel and stomach gas
anteriorly, and the right kidney is often visualized through the acoustic window provided by
the liver. The right kidney is slightly larger than
the left kidney, but both kidneys are normally
within 2 cm of each other in any dimension.
Normal kidneys are 9–12 cm long, 4–6 cm
wide, and 2.5–3.5 cm thick.
Kidneys are divided into two distinct anatomic parts: renal parenchyma and renal sinus
(Figure 20.2). Renal parenchyma is further
subdivided into renal cortex and medulla.
The medulla consists of cone-shaped medullary pyramids. Renal parenchyma surrounds
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4—ABDOMEN AND PELVIS

Liver

Spleen

Right
kidney

Left
kidney
Renal
pelvis
Aorta

Inferior
vena cava

Ureter

Bladder
Urethra
Figure 20.1  Anatomy of the urinary
system.

the sinus on all sides except at the hilum. The
hilum is where the renal artery, renal vein, and
proximal ureter enter the renal sinus. Prominent fatty deposits within the renal sinus give
it a hyperechoic appearance and distinguish it
from the hypoechoic, grainy renal parenchyma.
This difference in echogenicity is known as the
sonographic double density of the kidney.4,8

Image Acquisition
A low-frequency transducer with deep penetration, either phased-array or curvilinear type, is
used to image the kidneys. The narrower beam
width of a phased-array transducer is ideal for
imaging between the ribs, but the wider beam
width of a curvilinear transducer allows visualization of the entire kidney longitudinally in a
single view.
When scanning a patient with a suspected
renal pathology, scan the unaffected side first
to obtain a baseline image to compare with
the affected side. To image the right kidney,

place the patient in a supine position with the
transducer in a coronal plane in the midaxillary to anterior axillary line at the level of the
xiphoid process. Center the kidney on the
screen and rotate the transducer 15-30 degrees
counterclockwise to aim the transducer marker
slightly posteriorly to capture a true long-axis
view of the right the kidney. While holding
the transducer in the same location on the skin
surface, tilt or fan the transducer anteriorly and
posteriorly to assess the entire kidney from its
most anterior to posterior surface. Rotate the

transducer 90 degrees counterclockwise from
the long-axis view to obtain a transverse cross
section of the kidney. Tilt or fan the transducer
superiorly and inferiorly to assess the superior
and inferior poles of the kidney. Figure 20.3
illustrates transducer positions to obtain longand short-axis views of the kidney.
The left kidney is more posterior and
superior than the right kidney. Placing the
patient in a right lateral decubitus position
facilitates visualization of the left kidney and
reduces interference from the ribs and bowel
gas. Requesting the patient to hold his breath
in maximal inspiration will shift the kidney
caudally to further reduce interference from
rib shadows. Identify the left kidney with the
transducer in a coronal plane on the posterior
axillary line and then rotate the transducer
15-30 degrees clockwise aiming the transducer

marker posteriorly to acquire a true long-axis
view (Figure 20.4). Transverse or short-axis
views are obtained by rotating the transducer
90 degrees counterclockwise from the long axis
(Figure 20.5).4,8
Sagittal and transverse views of the bladder
should be obtained for a complete evaluation of
the urinary system (see Chapter 21, Bladder).

Image Interpretation
Perinephric fat and Gerota’s fascia appear as
a hyperechoic stripe around the kidneys, and
the fibrous capsule gives each kidney a hyperechoic outline. Normally, the renal cortex has
a homogeneous appearance on ultrasound


155

20—KIDNEYS
Superior
pole
Medial
border
Renal
artery
Renal
vein

Lateral
border

Renal
pelvis
Ureter
Inferior
pole
Anterior surface of right kidney
Pyramid
in renal
medulla
Renal
papilla
Major
calyx

Fibrous
capsule
Renal
cortex
Renal
sinus
Minor
calyx

Hilum of
kidney

Renal
column

Renal
pelvis

Ureter
Internal structure of right kidney
Figure 20.2  Cross-sectional anatomy of the kidney.

that is less echogenic than the adjacent liver
or spleen. Fluid-filled medullary pyramids
are seen as hypoechoic or anechoic triangular
prominences in a semicircular arrangement
around the sinus. As a result, the renal medulla
is significantly less echogenic compared to the
surrounding cortex.
The renal sinus normally appears hyperechoic due to fat content, and in the absence
of urinary tract obstruction, the sinus appears
homogenously hyperechoic with small
anechoic pockets of urine. The ureter is usually
obscured by bowel gas but may be visible with
ultrasound when dilated. When distended, the

ureter appears as a tubular structure extending
inferiorly from the renal pelvis.4,8

Pathologic Findings
OBSTRUCTIVE UROPATHY AND
HYDRONEPHROSIS
Progressively enlarging anechoic areas within
the hyperechoic sinus develop with distal urinary tract obstruction and indicates hydronephrosis. The severity of hydronephrosis is
classified as mild, moderate, or severe (Figure

20.6)9 and may correlate with the size of the


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4—ABDOMEN AND PELVIS

B Short
axis

A
B

A Long
axis

A

B

Figure 20.3  Transducer position for kidney ultrasound in long-axis (A) and short-axis (B) planes.

distal renal stone. Most algorithms incorporate
the degree of hydronephrosis into a clinical
decision-making pathway.1,7,9
Mild hydronephrosis is defined as enlargement of the calices with preservation of renal
papillae. The renal sinus is normally hyperechoic but becomes anechoic due to mild central dilation in mild hydronephrosis (Figure
20.7). As mild hydronephrosis progresses, the
degree of central dilation of the renal sinus
increases, but the structure of the medullary pyramids is preserved (Figure 20.8). It is

preservation of medullary pyramidal architecture, not the degree of renal pelvic dilation, that
characterizes mild hydronephrosis and differentiates mild from moderate hydronephrosis
(Video 20.1 ).
Moderate hydronephrosis is characterized
by rounding of the calices, obliteration of renal
papillae, and blunting of medullary pyramids.
Progressive dilation of the calyces leads to
glovelike splaying of the renal sinus and ballooning of the medullary pyramids that has
been called the classic bear-claw appearance


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20—KIDNEYS

Pocket of
urine
Cortex

Medullary
pyramid

Sinus

Figure 20.4  Normal long-axis view of the kidney. Note the prominent medullary pyramids and the hyperechoic renal sinus in the absence of hydronephrosis.

Cortex
Sinus

Figure 20.5  Normal short-axis view of the kidney.

Normal

Mild

Moderate

Severe

Figure 20.6  Severity of hydronephrosis is graded by the degree of distortion of normal architecture. Mild
hydronephrosis: enlarged calices with preservation of renal papillae and pyramids. Moderate hydronephrosis: dilated calices with obliterated papillae and blunted pyramids. Severe hydronephrosis: calyceal ballooning, complete obliteration of papillae and pyramids, cortical thinning.


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4—ABDOMEN AND PELVIS

Mild
hydronephrosis

Cortex

Sinus

Cortex

Renal sinus replaced by
severe hydronephrosis

Figure 20.10  Severe hydronephrosis.
Figure 20.7  Mild hydronephrosis.

Perinephric fluid
Cortex

Preserved
pyramid

Mild
hydronephrosis

Sinus

Figure 20.11  Longitudinal view of the right kidney.
Note the small amount of perinephric fluid, indicative of calyceal rupture and urinary extravasation.
Figure 20.8  Mild hydronephrosis.

Cortex
Sinus
Moderate
hydronephrosis

Figure 20.9  Moderate hydronephrosis.

of moderate hydronephrosis (Figure 20.9 and
Video 20.2). Preservation of the outer cortex
is the distinguishing feature between moderate
and severe hydronephrosis.
Severe hydronephrosis is defined as calyceal

ballooning with variable degrees of cortical
thinning (Figure 20.10). Fingerlike projections
that characterize moderate hydronephrosis
coalesce into one large anechoic collection of
urine that completely obliterates the sinus and
medullary pyramids. All that remains of the
normal renal architecture is a rim of outer cortex. Total distortion of normal renal architecture is the key distinguishing feature of severe
hydronephrosis (Video 20.3)
A small amount of perinephric fluid due to
calyceal rupture and urinary extravasation may
be seen with hydronephrosis (Figure 20.11).
Perinephric fluid is associated with significant


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20—KIDNEYS

Parapelvic
cysts

Cortical cyst
Cortex

Sinus

Figure 20.12  Large cortical cyst.
Figure 20.13  Parapelvic cysts.

risk of infection or perinephric abscess formation and requires close follow-up.1

Several conditions can mimic the ultrasound appearance of hydronephrosis. Two
general guiding principles should be followed
to distinguish between true hydronephrosis
and its mimics: (1) trace the anechoic areas
of suspected hydronephrosis to the renal pelvis where the areas should coalesce; and (2)
scan the kidney in both the longitudinal and
transverse planes to thoroughly delineate the
architecture of the area of suspected hydronephrosis. Medullary pyramids may appear
anechoic and can be mistaken for collections
of urine; however, the triangular pyramids are
separated from each other by cortical tissue
and should be seen as distinct entities from
the hyperechoic renal sinus. Cortical and parapelvic cysts can also mimic hydronephrosis,
but they are distinguished by their smoothwalled, spherical shape that is not contiguous with the renal pelvis (Figures 20-12 and
20-13). Renal hilar vessels are also anechoic
and can be mistaken for hydronephrosis.
Color-flow Doppler can differentiate vasculature from hydronephrosis.8

Renal Calculus
Ultrasound has low sensitivity for detecting
ureteral calculi.3 Stones may be seen within the
renal parenchyma, at the ureteropelvic junction proximally or at the ureterovesicular junction distally. In general, ureters are obscured
by bowel gas and are difficult to assess as
they travel from kidney to bladder. Stones are
hyperechoic and exhibit acoustic shadowing
(Figure 20.14 and Video 20.4).

Renal calculus

Acoustic

shadowing

Figure 20.14  Large renal calculus in the right kidney
seen in along-axis view Note the associated prominent acoustic shadowing.

Severity of hydronephrosis may correlate
with stone size.7 Patients with renal colic and
moderate or severe hydronephrosis are significantly more likely to have stones >5 mm than
patients with mild or no hydronephrosis.7
Stones <5 mm generally pass without intervention and stones 5–9 mm in size may pass spontaneously, but stones >10 mm are unlikely to pass
and will likely require urologic intervention.10

Renal Cyst
Renal cysts are common and usually benign,
but renal malignancies may present as cystic
structures on ultrasound. A benign cyst must
fulfill all of the following criteria8:
1.
Thin-walled and smooth, with no
septations, internal echoes, or solid
elements


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4—ABDOMEN AND PELVIS

Septations

Heterogeneous mass

Debris

Renal sinus
Figure 20.15  Large complex cyst with internal septations seen in a transverse view of the right kidney.
Figure 20.17  Irregularly shaped renal mass with
heterogeneous echogenicity.

Hypertrophied
column of Bertin
Multiple cysts

Figure 20.16  Polycystic kidney disease.

2.
Round or oval shape that is well demarcated from the adjacent parenchyma
and appears homogeneous in all imaging planes
3.
Posterior acoustic enhancement must be
evident behind the cyst.
If the above criteria are not fulfilled, the
presence of a complex cyst (Figure 20.15),
renal abscess, or malignancy must be considered and warrants further workup.
Multiple renal cysts are seen in polycystic
kidney disease (PCKD) and acquired renal
cystic disease (ARCD). PCKD represents
an extreme example on the spectrum of renal
cystic disease (Figure 20.16 and Video 20.5).
PCKD is characterized by an abundance of
irregular cysts of varying size that distort the

normal renal architecture bilaterally. These
patients often present to acute care settings
with flank pain, hematuria, hypertension,
and renal failure. ARCD is another condition
associated with multiple renal cysts that is
present in patients with end-stage renal disease on hemodialysis and is associated with
higher risk of renal malignancy. While most
patients with chronic kidney disease have

Figure 20.18  Hypertrophied column of Bertin.

bilaterally shrunken and hyperechoic kidneys
(Video 20.6), those with ARCD have numerous cysts.

Renal Mass
Renal malignancies detected incidentally during abdominal imaging are associated with
lower morbidity and mortality rates.11 Any
suspicious mass detected by point-of-care
ultrasound warrants further investigation and
expert consultation (Figure 20.17).11 Normal
variants that can mimic renal malignancies
include prominent columns of Bertin, which
are hypertrophied cortical tissue that distort
the calyces in the renal sinus (Figure 20.18).
Renal cell carcinoma is the most common type
of renal malignancy in adults. These tumors are


20—KIDNEYS

notoriously heterogeneous in their sonographic
appearance. They can be isoechoic, hypoechoic,
or hyperechoic relative to adjacent parenchyma,
and they may have a partial cystic appearance that
can be mistaken for benign cysts.4 Angiomyolipoma is the most common type of benign tumor
of the kidney. The tumors are well-demarcated
hyperechoic masses located within the renal cortex. There is significant overlap in the appearance
of angiomyolipomas and echogenic renal cell
carcinoma.4 Therefore, providers using point-ofcare ultrasound should obtain additional radiographic imaging and seek expert consultation
when incidental masses are detected.

PEARLS AND PITFALLS
•Hydronephrosis may be underrecognized in hypovolemic patients due to
transient collapse of calyces. Sensitivity
of ultrasound in detecting hydronephrosis is increased after fluid resuscitation
in patients with volume depletion.
•A bladder ultrasound exam should accompany a renal ultrasound exam. A distended
bladder due to bladder outlet obstruction
may cause bilateral hydronephrosis, and

161
a repeat renal ultrasound exam should be
performed after bladder decompression.
•Varying degrees of hydronephrosis, most
often on the right side, is common in
pregnancy and may not be pathologic.
•Renal calculi are common and detection
of a nonobstructing parenchymal stone
may be unrelated to the patient’s clinical
presentation.

•Unilateral hydronephrosis may be due
to external ureteral compression by a
mass lesion or retroperitoneal lymphadenopathy, and these pathologies
should be considered.
•Absence of hydronephrosis does not rule
out ureterolithiasis because small calculi
may not create significant obstruction.
•High-risk patients (age >50) who present
with flank pain and hydronephrosis on
bedside ultrasound exam may have a
ruptured abdominal aortic aneurysm, and
any abnormal ultrasound findings in these
patients warrants additional workup.
•All renal masses are malignant until proven otherwise. Detection of a renal mass
by point-of-care ultrasound requires further workup with additional radiographic
imaging and expert consultation.


Case Studies
Case 1
Case Presentation
A 20-year-old man presents to the emergency department after 4 hours of severe left lower quadrant
abdominal pain. The pain began on his left flank, migrated to the left lower quadrant, and is associated
with nausea. He denies prior history of similar pain. His vital signs are normal but he appears uncomfortable. Physical exam reveals moderate tenderness to deep palpation of the left lower quadrant without
peritoneal signs, and mild left costovertebral angle tenderness. White blood cell count is 23,000 with
a left shift. Your primary differential diagnosis includes pyelonephritis, diverticulitis, and kidney stone.
Ultrasound Findings
A focused bedside ultrasound exam of the abdomen is performed. No free fluid is seen, but mild hydronephrosis of the left kidney is detected (Video 20.7), suggesting renal colic as a possible etiology. A
comprehensive abdominal ultrasound confirms the presence of left-sided hydronephrosis (Figure 20.19)
and reveals a 6 mm partially obstructing calculus in the distal left ureter (Figure 20.20). Bilateral ureteral

jets are seen on the posterior bladder wall using color flow Doppler ultrasound (Figure 20.21).
Case Resolution
The patient is discharged with oral analgesics and a trial of medical expulsion therapy. He is
given outpatient urology follow-up. He spontaneously passes the stone after days and recovers without
complications.
Providers can accurately detect and grade hydronephrosis using bedside ultrasound. When
clinical suspicion of renal calculus is high, unilateral hydronephrosis serves as indirect evidence of
obstructive uropathy due to a stone. Moderate to severe hydronephrosis correlates with a stone
size >5 mm, even though the actual stone may not be visualized. Stones <5 mm usually pass
spontaneously without any intervention.

Mild hydronephrosis

Figure 20.19  Longitudinal view of the left kidney
with mild hydronephrosis.

Ureteral stone with
acoustic shadowing

Figure 20.20  Left distal ureter with an obstructing
calculus measuring approximately 6 mm. Note the
anechoic bladder on the right side of the screen.

161.e1


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4—ABDOMEN AND PELVIS

Ureteral jet

Figure 20.21  Moderately filled bladder at the level
of trigone in a transverse view. A left ureteral jet is
visualized using color flow Doppler ultrasound.

Case 2
Case Presentation
A 62-year-old woman presents to the emergency department with a 2-hour history of right flank and
lower quadrant abdominal pain. She has a known history of renal colic but has been otherwise healthy
without any previous hospitalizations or surgeries. This episode is similar to her past renal colic episodes, and she insists that she will be fine at home with oral analgesics and antiemetics. She is afebrile,
and her vital signs are remarkable only for mild tachycardia of 105 beats per minute, attributed to her
pain. Her exam is remarkable only for right costovertebral angle tenderness. Urinalysis shows microscopic hematuria. WBC count, hemoglobin, and creatinine are normal.
The patient is discharged home with oral analgesics and antiemetics. Over the ensuing hours, her
condition deteriorates. She develops worsening right-sided flank pain, refractory vomiting, and progressive confusion. She is brought to the hospital by ambulance, and she is febrile (40º C), tachycardic at
120 beats per minute, and confused.
Ultrasound Findings
A focused bedside ultrasound exam of the abdomen is performed. The renal papillae and medullary
pyramids of the right kidney are blunted consistent with moderate hydronephrosis. A 2 cm renal calculus
is seen impacted in the renal pelvis (Figure 20.22 and Video 20.8).
Case Resolution
Intravenous fluids and antibiotics are initiated. The urology service is consulted, and an urgent cystoscopy is performed with ureteral stent placement. The patient’s condition improves after stent placement
and antibiotics. After a few weeks of antibiotic treatment, she undergoes successful extracorporeal
shock wave lithotripsy.
Hydronephrosis is graded by the degree of distortion of renal architecture. Moderate hydronephrosis is distinguished from mild hydronephrosis by rounding of the calices, obliteration of renal
papillae, and blunting of medullary pyramids. Severe hydronephrosis is characterized by cortical
thinning. Presence of moderate to severe hydronephrosis in a patient with renal calculus disease
correlates with a stone size >5 mm. Stones 5–9 mm might pass spontaneously, but stones
>1 cm are unlikely to pass without intervention.

161.e3

20—KIDNEYS

Stone within
renal pelvis

Figure 20.22  Obstructing calculus in the renal pelvis
with associated moderate hydronephrosis.

References
1. Swadron S, Mandavia D. Renal. In: Ma OJ, Mateer JR, Blaivas M, eds. Emergency Ultrasound. 2nd ed.
New York, NY: McGraw-Hill; 2008.
2. Dalziel PJ, Noble VE. Bedside ultrasound and the assessment of renal colic: a review. Emerg Med J.
2013;30(1):3–8.
3. Fowler KA, Locken JA, Duchesne JH, et al. US for detecting renal calculi with nonenhanced CT as a
reference standard. Radiology. 2002;222:109–113.
4. Tublin M, Thurston W, Wilson SR. The kidney and urinary tract. In: Rumack CM, Wilson SR,
Charboneau JW, Levine D, eds. Diagnostic Ultrasound. 4th ed. New York, NY: Elsevier; 2011.
5. Dalla Palma L, Stacul F, Bazzocchi M, Pagnan L, Festini G, Marega D. Ultrasonography and plain
film versus intravenous urography in ureteric colic. Clin Radiol. 1993;47:333–336.
6. Brown DFM, Rosen CL, Wolfe RE. Renal ultrasonography. Emerg Med Clin North Am. 1997;15:
877–893.
7. Goertz JK, Lotterman S. Can the degree of hydronephrosis on ultrasound predict kidney stone size?
Am J Emerg Med. 2010;28:813–816.
8. Bates JA. Abdominal Ultrasound: How, Why and When. 3rd ed. New York, NY: Churchill Livingstone;
2010.
9. Nobel V, Brown DF. Renal ultrasound. Emerg Med Clin North Am. 2004;22:641–659.
10. Coll D, Varanelli MJ, Smith RC. Relationship of spontaneous passage of ureteral calculi to stone size

and location as revealed by unenhanced helical CT. Am J Roentgenol. 2002;178:101–103.
11. Sweeney JP, Thornhill JA, Graiger R, McDermott TE, Butler MR. Incidentally detected renal cell
carcinoma: pathological features, survival trends and implications for treatment. Br J Urol. 1996;78:
351–353.


C H A P T E R

21

Bladder
Behzad Hassani

K E Y

POIN TS

• The primary indications for performing bladder ultrasound at the bedside are estimation of
bladder volume, confirmation of proper urinary catheter placement, detection of stones,
and assessment of ureteral jets in suspected obstructive uropathy.
• Bladder volume can be calculated using the following formula:
Volume = (0.75 × width × length × height).
• Detection of a bladder mass during a point-of-care ultrasound exam warrants further
workup, including additional imaging and expert consultation.

Background
Bedside ultrasound evaluation of the bladder has several clinical applications. Estimation of bladder volume, confirmation of
proper urinary catheter placement, detection of stones, and assessment of ureteral
jets in suspected obstructive uropathy are the
core indications for point-of-care bladder

ultrasound.
Many patients who present with a complaint of “urinary retention” do not truly have
urinary retention.1 Evaluation of bladder volume based on physical exam is inaccurate due
to body habitus in a significant percentage
of patients. Bladder ultrasound can precisely
determine bladder volume and avoid unnecessary urinary catheterizations. When urinary
catheterization is necessary, bedside ultrasound
can confirm proper placement and functioning
of the catheter. In pediatric patients, bladder
volume estimation can eliminate unnecessary
catheterizations,2 and real-time ultrasound
guidance can substantially reduce complications associated with suprapubic bladder
aspirations.3

Normal Anatomy
The bladder is a triangular organ positioned
in the pelvic cavity that is located inferior and
162

anterior to the peritoneal cavity and directly
posterior to the pubic symphysis (Figure 21.1).
Ureters enter the trigone of the bladder posteriorly and inferiorly (Figure 21.2). In males,
the prostate encircles the bladder neck caudally
and normally measures <5 cm in transverse
diameter.

Image Acquisition
The curvilinear transducer (3.0–5.0 MHz) is
ideal for imaging the bladder. Its mid-range
frequency allows for optimal resolution, and

its wider footprint permits visualization of
the entire bladder. A fluid-filled bladder
readily propagates sound waves resulting in
posterior acoustic enhancement, or hyperechogenicity, posterior to the bladder. This
artifact can obscure the far field of the image,
and certain findings, such as pelvic free fluid,
may be missed. The far-field gain should be
decreased to better visualize hypoechoic or
anechoic entities posterior to the bladder.5
The bladder is located posterior and inferior to the pubic symphysis and is best visualized from a suprapubic approach. With the
patient in a supine position, place the transducer in a transverse plane at the superior
edge of the pubic symphysis and aim the ultrasound beam posteroinferiorly (Figure 21.3A).


163

21—BLADDER

Uterus

Vesicouterine
pouch
Rectouterine
(Pouch of
Douglas)
Bladder
Pubic
symphysis

Rectum

Vagina

A

Ureter

Sigmoid
colon

Bladder
Pubic
symphysis
Prostate

Urethra

Rectovesicular
pouch
Seminal vesicles
Rectum
Anus

B
Figure 21.1  Normal anatomy of the bladder in the female (A) and male (B) pelvis in a sagittal plane.

Tilt the transducer superiorly and inferiorly
to visualize the entire bladder in a transverse
plane. Assess the bladder for its degree of
distention and for the presence of stones or
masses. If the bladder is not filled, the transducer often has to be pointed caudally into the

pelvic cavity to identify the bladder. The prostate gland is hyperechoic and can be visualized
in a transverse plane adjacent to the inferior
bladder wall. Rotate the transducer 90 degrees
clockwise to obtain longitudinal views of the
bladder in a sagittal plane (Figure 21.3B). Scan
the bladder thoroughly in a sagittal plane by

tilting the transducer to visualize the leftmost
and rightmost walls.
In patients with renal colic, visualization of
ureteral jets, or intermittent expression of urine
into the bladder, rules out complete obstruction of the ureter. To visualize ureteral jets,
scan slowly through the bladder in a transverse
plane and focus over the trigone.4–6 Ureteral
jets can be detected using two-dimensional
gray-scale sonography, but they are best visualized with power Doppler on a low-flow setting (i.e., low PRF setting). Power Doppler
demonstrates flow regardless of direction and


164

4—ABDOMEN AND PELVIS

Ureter

Urothelium
Lamina
propria
Opening
of ureter

Bladder

Trigone
Bladder
neck
Urethra

Prostate
Urethral
sphincter

Urethral
sphincter

Female
Male
Figure 21.2  Normal anatomy of the male and female bladder in a transverse plane.

A

B
Figure 21.3  A, Transducer position to visualize the bladder in a transverse plane. Caudal tilting of the
transducer helps visualize the bladder in the pelvic cavity. B, Transducer position to visualize the bladder in a
sagittal plane. The transducer is rocked inferiorly to visualize the bladder in the pelvic cavity.


165

21—BLADDER

Right ureteral jet

Iliac vessels

A

Bladder
length (A)
& width (B)

Figure 21.4  Transverse view of the female bladder
revealing a prominent right-sided ureteral jet on
color power Doppler originating in the trigone area.

is particularly suited for detecting low-flow
states, such as ureteral jets. The jets appear as
colorful emissions streaming from the base of
the bladder toward its center (Figure 21.4). In
well-hydrated patients, they appear at regular
intervals every 15–20 sec and last <1 sec.7
The presence of bilateral ureteral jets in a wellhydrated patient rules out significant obstructive uropathy with high specificity.8,9 Ureteral
obstruction is suspected when a jet is not
­visualized on the affected side but is visualized
­unilaterally on the unaffected side.

Pathologic Findings
DISTENDED BLADDER AND URINARY
RETENTION
Bladder volume can be calculated using the
following formula10:

Bladder volume = (0.75 × width × length × height)

The width and anteroposterior dimension
(i.e., length) are measured in a transverse plane
(Figure 21.5A). The superior-inferior dimension (i.e., height) is measured in a sagittal plane
(Figure 21.5B). Past research10 has demonstrated
close correlation between the estimated bladder
volume using the formula above and the actual
catheterized volume (correlation factor = 0.983).
A qualitative assessment of bladder distention can be performed by noting the location
of the bladder dome relative to the umbilicus.1
Center the bladder dome on the screen in a
sagittal plane. The center of the transducer on
the skin identifies the location of the dome
relative to the umbilicus. The bladder dome
extends at least halfway to the umbilicus in

Bladder
height (A)

B
Figure 21.5  A, Measurement of the width (W) and
length (L) of the bladder is performed in a transverse
plane. B, Measurement of the height (H) of the
bladder is performed in a sagittal plane. Bladder
volume is calculated using the following formula:
Volume = 0.75 × W × L × H.

the majority of patients with urinary retention (Video 21.1 ).1 The presence of urinary
retention should prompt a scan of the kidneys

to rule out bilateral hydronephrosis, a finding
that has prognostic implications in the setting
of chronic outlet obstruction.
Although bedside transabdominal ultrasound can readily detect prostatic hypertrophy
(transverse diameter >5 cm), it cannot distinguish benign hypertrophy from malignancy
(Figure 21.6). If clinically indicated, urology
consultation and additional imaging and/or
biopsy should be pursued.
BLADDER STONES
Bladder calculi are most often seen after successful passage of renal calculi from the ureters
into the bladder. Bladder stones may also form
de novo secondary to bladder stasis in patients
with chronic retention.4 Bladder stones appear
as hyperechoic, mobile entities that demonstrate
posterior acoustic shadowing (Figure 21.7).


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4—ABDOMEN AND PELVIS

Foley
balloon
Bladder
calculus
Enlarged
prostate

Figure 21.6  Transverse view of a male bladder with
a urinary catheter balloon and an enlarged prostate

in the far field.

Figure 21.7  Transverse view of the bladder revealing
a hyperechoic calculus in the far field. Note the prominent posterior shadowing associated with the stone.

BLADDER MASS4–6
Bladder masses typically appear either as irregular, echogenic projections from the bladder
wall or as foci of increased bladder wall thickness (Figure 21.8). The bladder wall is normally 3–6 mm thick but varies depending on
the degree of bladder filling. Transitional cell
carcinoma accounts for the majority of bladder
masses. The differential diagnosis of a bladder
mass includes malignancy, bladder diverticula,
congenital outpouchings of the bladder wall,
and bladder wall thickening due to chronic
or recurrent cystitis. Blood clots can be mistaken for a bladder mass, and repeat ultrasound
should be performed after adequate continuous
bladder irrigation. Additional workup, including imaging and expert consultation, is always
warranted to further evaluate bladder masses.

PEARLS AND PITFALLS
•Maximal dimensions should be used to
calculate bladder volume accurately. The
maximal dimensions should be captured
by freezing the image while tilting or
fanning the transducer through the bladder. Use the following formula: Bladder
volume = (0.75 × width × length × height).
•When conducting a qualitative assessment of bladder volume for urinary
retention, recall that in the majority of
patients with urinary retention, the bladder dome extends at least halfway to the
umbilicus.

Bladder
mass

Figure 21.8  Sagittal view of the bladder revealing
bladder cancer.

•Ureteral jets may be infrequent or not visualized in many patients. Although their
presence rules out obstruction with high
specificity, their absence by ultrasound
imaging does not rule in obstructive
uropathy.
•Free fluid in the pelvis can easily be
mistaken for the bladder. Always scan
the bladder and surrounding tissues
thoroughly in transverse and longitudinal
planes. Filling the bladder or identifying
an inflated urinary catheter balloon can
help distinguish the bladder from pelvic
free fluid.
•Blood clots may appear as a bladder mass
on ultrasound. Continuous bladder irrigation often resolves blood clots and helps
distinguish blood clots from a true mass.


Case Studies
Case 1
Case Presentation
A 60-year-old man presents with a 4-week history of nausea, vomiting, and decreased oral intake. He
reports increased urinary frequency, weak urine stream, and decreased total urine output. He denies

flank pain, dysuria, or hematuria. He has a history of benign prostatic hypertrophy treated with medications. He is afebrile with normal vital signs. He is obese and assessment of bladder size by physical
exam is difficult. Rectal exam confirms an enlarged prostate. Lab findings are notable for an elevated
creatinine.
Ultrasound Findings
Bedside ultrasound reveals a grossly distended bladder with the dome at the level of the umbilicus
(Video 21.2). A Foley catheter is inserted and its correct placement is confirmed by ultrasound (Video
21.3). The prostate is grossly enlarged, and bilateral moderate hydronephrosis is evident on renal ultrasound (Videos 21.4 and 21.5).
Case Resolution
The Foley catheter drains 2 L of urine with minimal clots. The urology service is consulted and the patient is admitted for observation. His hospital course is complicated by post-decompression hematuria
requiring blood transfusion. He also suffers from post-obstructive diuresis (urine output of 4000 mL in
24 h) requiring intravenous fluids. His creatinine returns to baseline, and he is discharged home with
an indwelling urinary catheter. He undergoes a transurethral resection of the prostate as an outpatient
several weeks later.
A bladder ultrasound exam can be performed easily at the bedside. In patients with decreased
urine output, a bladder ultrasound exam can readily differentiate urinary retention or urinary
catheter blockage from decreased urine production. The bladder volume can be quantitatively
assessed using the formula:
Bladder volume = (0.75 × width × length × height)

Case 2
Case Presentation
A 47-year-old woman presents with a 3-week history of lower urinary tract symptoms. She received
numerous courses of antibiotics for presumed urinary tract infection by her primary care provider and
urgent care clinics. She admits to bilateral flank pain, dysuria, frequency, urgency, and occasional episodes of gross hematuria. She also complains of straining, hesitancy, and incomplete voiding. She
denies prior history of renal colic or hematuria and is otherwise healthy. She has a 20 pack-year smoking
history. Vital signs are normal, and her physical exam is unremarkable. Lab results reveal mild anemia
with slight elevation in creatinine. Urinalysis shows leukocytes and blood.
Ultrasound Findings
A bedside bladder ultrasound exam is performed. The bladder is distended with a postvoid residual of
700 mL. Additionally, several bladder masses are noted (Video 21.6).

Case Resolution
Because blood clots and bladder masses have a similar appearance by ultrasound, the physician initiated continuous bladder irrigation through the Foley catheter. The bladder masses persisted on followup ultrasound exam. The urology service was consulted, and bladder cancer was diagnosed by cystoscopy. She eventually underwent transurethral resection of the bladder tumor.
Blood clots in the bladder can be easily mistaken for a bladder mass, and a trial of continuous
bladder irrigation is warranted when a mass is suspected. A suspected bladder mass warrants
further workup and consultation with a urologist.

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References
1. Skinner A. Bladder EDE. In: Socransky S, Wiss R, eds. Point-of-Care Ultrasound for Emergency
Physicians—“The EDE Book”. Sudbury, ON: The EDE 2 Course Inc.; 2012.
2. Gochman RF, Karasic RB, Heller MB. Use of portable ultrasound to assist urine collection by suprapubic aspiration. Ann Emerg Med. 1991;20:631–635.
3. Kiernan SC, Pinckert TL, Keszler M. Ultrasound guidance of suprapubic bladder aspiration in neonates. J Pediatr. 1993;123:789–791.
4. Tublin M, Thurston W, Wilson SR. The kidney and urinary tract. In: Rumack CM, Wilson SR, Charboneau JW, Levine D, eds. Diagnostic Ultrasound. 4th ed. New York, NY: Elsevier; 2011.
5. Hwang JQ, Poffenberger CM. Renal and urinary system ultrasound. In: Carmody KA, Moore CL,
Feller-Kopman D, eds. Handbook of Critical Care & Emergency Ultrasound. New York, NY: McGrawHill; 2011.
6. Hagen-Ansert SL. Textbook of Diagnostic Sonography. 7th ed. New York, NY: Mosby; 2011.
7. Bates JA. Abdominal Ultrasound: How, Why and When. 3rd ed. New York, NY: Churchill Livingstone;
2010.
8. Burge HJ, Middleton WD, McClennan BL, et al. Ureteral jets in healthy subjects and in patients with
unilateral ureteral calculi: comparison with color Doppler US. Radiology. 1991;180:437–442.
9. Strehlau J, Winkler P, De La Roche J. The uretero-vesical jet as a functional diagnostic tool in childhood hydronephrosis. Pediatr Nephrol. 1997;11:460–467.
10. Chan H. Noninvasive bladder volume measurement. J Neurosci Nurs. 1993;25:309–312.

C H A P T E R

22

Abdominal Aorta
Christopher R. Tainter

K E Y

POIN TS

• Ultrasound is the preferred initial screening modality for abdominal aortic aneurysm.
• The entire abdominal aorta should be imaged in two perpendicular planes (transverse and
longitudinal) to avoid missing subtle abnormalities.
• Oblique imaging planes may underestimate or overestimate aortic diameter and should be
avoided.

Background
The abdominal aorta is a vital retroperitoneal
structure with the potential for catastrophic
pathology that is often difficult to diagnose.
In the words of Sir William Osler, “There is
no disease more conducive to clinical humility
than aneurysm of the aorta.” When a diagnosis
of aortic pathology is identified, appropriate
interventions may improve outcomes for this
often time-sensitive presentation.1
Abdominal aortic aneurysms are the most
commonly identified aortic abnormality. They
may be complicated by thrombosis, dissection

of the intimal layer, or rupture, which carries
a particularly high mortality of approximately
90%.2 The incidence of abdominal aortic
aneurysm increases with age, family history,
male gender, and a history of smoking. The
overall prevalence is approximately 4.7% and
3.0% in men and women, respectively.3 This
peaks around 5.9% in men 80–85 years old
and 4.5% for women over age 90.4
Aortic pathology should be considered in
any patient presenting with abdominal discomfort, especially in patients with known
risk factors and those that present with
classic histories or exam findings (hypotension, back pain, pulsatile abdominal mass).
In addition, various recommendations have
been made for screening asymptomatic
patients, including a grade B recommendation by the U.S. Preventive Services Task
Force, which recommends screening all men

between the ages of 65–75 with a history of
smoking.5
Use of point-of-care ultrasound saves time,
reduces cost, and avoids ionizing radiation and
exposure to intravenous contrast when compared to other imaging modalities.1 Pointof-care ultrasound has demonstrated high
sensitivity (97.5–100%) and specificity (94.1–
100%) for detection of abdominal aortic aneurysm.6,7 It has high correlation with computed
tomography (CT) and magnetic resonance
imaging in diagnosing aortic dilation, but may
slightly underestimate the exact diameter.8

Normal Anatomy

The abdominal aorta is the section of aorta that
extends from the posterior diaphragm where
it exits from the thoracic cavity and continues
until its division into the common iliac arteries. Through the abdomen, its major branches
include the left and right renal arteries, celiac
artery, superior and inferior mesenteric arteries,
and gonadal arteries. In addition, it has branches
to supply the diaphragm, adrenal glands, abdominal wall, and spinal cord. Figure 22.1 illustrates
the major branches of the abdominal aorta.

Image Acquisition
Sonographic visualization of the abdominal
aorta is achieved through a transabdominal approach. The proximal aorta can be
viewed in the transverse (short-axis) plane by
167


168

4—ABDOMEN AND PELVIS

Diaphragm

Splenic artery

Celiac artery

Common
hepatic artery

Left gastric
artery
Right renal
artery and vein

Left renal
artery and vein

Superior
mesenteric
artery

Gonadal
arteries
Inferior
mesenteric
artery
Common iliac
arteries
Internal iliac
arteries
External iliac
arteries
Figure 22.1  Anatomy of abdominal aorta.

placing a phased-array or curvilinear transducer (3.5–5 MHz) just below the costal
margin in the center of the abdomen with the
transducer marker pointing to the patient’s
right. Commonly, the celiac artery and superior mesenteric artery are seen in this position, and occasionally left and right renal
arteries may be identified (Figure 22.2 and

Video 22.1). Evaluation of these structures is
typically less important when assessing for the
simple presence or absence of an abdominal
aortic aneurysm, but their identification provides useful landmarks. A particularly useful
sonographic reference point is the vertebral
body and its characteristic shadow, which lies
immediately posterior and slightly to the right
of the aorta.
Once the aorta is identified in a transverse plane, slide the transducer inferiorly on
the abdominal wall, allowing for contiguous
imaging of the aorta. With the transducer in
a transverse position just above the umbilicus
with the ultrasound beam directed posteriorly, the distal aorta is visualized as it divides
into the left and right common iliac arteries
(Figure 22.3 and Video 22.2 ).

After evaluating the aorta in short axis,
longitudinal views should be acquired to accurately assess the size of the aorta. Place the
transducer over the proximal abdominal aorta
and rotate the transducer clockwise 90 degrees
so that the transducer marker is pointed toward
the patient’s head. Again, it may be possible to
visualize the celiac and superior mesenteric
arteries if the plane of the ultrasound transducer is aligned with these vessels (Figure 22.4
and Video 22.3).
Measurements of the aortic diameter should
be obtained in both transverse and longitudinal
planes. It is important to measure the aortic
diameter with the transducer perpendicular
to the aorta to capture a true cross-sectional

image because oblique images can underestimate or overestimate the diameter. Calipers
should be placed on the outer edges of the aortic walls. The diameter of the aorta should be
measured proximally and distally with calipers
placed on the outer edges of the aortic walls.
If interpretable images cannot be obtained
in the anterior mid-abdomen, usually due
to bowel gas or scarring, then an alternate
approach is to image the aorta laterally from the


169

22—ABDOMINAL AORTA

A
LOGIQ
E9

HA

SPL

B

Splenic vein

SMA

Ao
IVC

Vertebral
body

Renal
arteries

C
Figure 22.2  A, Transducer position for transverse (short-axis) views of the proximal abdominal aorta.
B, Celiac artery is seen branching into the common hepatic artery (HA) and splenic artery (SPL). C, Superior
mesenteric artery (SMA) is seen along with the left and right renal arteries, splenic vein, aorta (Ao), and
inferior vena cava (IVC). Note the position of the vertebral body posterior to the aorta.

right or left flank. With the transducer marker
pointing toward the patient’s head, place the
transducer in the right or left midaxillary line
just below the costal margin to capture longitudinal views of the aorta. From the right flank,
a longitudinal view of two tubular, anechoic
structures is seen posterior to the liver at the

bottom of the image; the near-field structure is
the inferior vena cava, and the deeper structure
is the abdominal aorta. The transducer can be
rotated 90 degrees clockwise to obtain transverse views of the aorta, but acquiring transverse images laterally can be challenging due
to the depth of the aorta. The same technique


170

4—ABDOMEN AND PELVIS

A
Right and left common iliac arteries

B
Figure 22.3  A, Transducer position for transverse views of the distal abdominal aorta. B, Distal aorta in a
transverse plane showing division into the right and left common iliac arteries.

can be used to obtain longitudinal views of the
abdominal aorta from the left flank (Figure
22.5 and Video 22.4).

Image Interpretation
An arterial aneurysm is defined as a permanently localized dilation of an artery having at
least 50% increase in diameter compared to the
expected normal diameter of the artery in question.9 For the abdominal aorta, this means that
an aneurysm is present whenever the diameter
exceeds 3.0 cm. This provides a useful threshold, though it may exclude some more subtle
aneurysms. Fortunately, the complication rate
is directly related to the size of the aneurysm,
and smaller dilations are of less immediate clinical significance. Identification remains important, as these aneurysms should be monitored.1
Point-of-care ultrasound can detect abdominal aortic aneurysm with high sensitivity
(97.5–100%) and specificity (94.1–100%).6,7

Detection of an abdominal aortic aneurysm
with a diameter of 3.0 to 4.5 cm should be
followed with serial ultrasound examinations
at least annually, whereas an aneurysm with a
diameter >4.5 cm warrants consultation with a
vascular surgeon.
Transesophageal echocardiography is the

preferred ultrasound modality to evaluate for
thoracic aortic dissection, but the sensitivity and specificity of transthoracic ultrasound
imaging of thoracic aortic dissection is less well
established. Estimates of sensitivity of transthoracic ultrasound to diagnose thoracic aortic
dissection ranges from 67% to 80%.10,11 The
presence of an undulating intimal flap portends
a very high specificity, approaching 100%.

Pathologic Findings
ABDOMINAL AORTIC ANEURYSM
A distal abdominal aortic aneurysm is shown
in transverse and longitudinal planes where it


171

22—ABDOMINAL AORTA

A

Splenic vein

Celiac trunk
SMA
Aorta

B
Figure 22.4  A, Transducer position for longitudinal views of the proximal abdominal aorta. B, Proximal aorta
is seen in a longitudinal plane branching into the celiac artery and superior mesenteric artery (SMA). The
splenic vein is seen in cross section as is crosses over the SMA.

Spleen

Aorta

Figure 22.5  Longitudinal view of the abdominal aorta as typically seen when imaging from the left flank.


172

4—ABDOMEN AND PELVIS

divides into the common iliac arteries (Figure
22.6 and Videos 22.5 and 22.6). An abdominal aortic dissection is shown in transverse
and longitudinal planes exhibiting an intimal

A

Figure 22.6  Distal abdominal aortic
aneurysm seen in transverse (A) and
longitudinal (B) planes.

B

flap (Figure 22.7 and Videos 22.7 and 22.8).
Color flow Doppler ultrasound can be used to
evaluate a suspected intimal flap (Videos 22.9
and 22.10)