Color Doppler Twinkling Artifact

Longitudinal images of the left kidney show a stone (arrow) in the lower pole with posterior acoustic shadowing and the color Doppler twinkling artifact (short arrows).

Facts:

• Rapidly alternating red and blue signal behind a highly reflective structure on color Doppler US
• Useful diagnostic signs especially for urinary calculi detection and improved diagnostic confidence
• Can also be seen in calcifications in various tissues, biliary stones, encrusted indwelling urinary stents, gallbladder adenomyomatosis and bile duct hamartomas
• Two proposed mechanisms:
• Phase jitter - intrinsic machine noise causing random fluctuation of acoustic waves
• Acoustic waves hitting a rough interface producing complex beam pattern with multiple reflections

Reference

Kim HC, et al. Color Doppler twinkling artifacts in various conditions during abdominal and pelvic sonography. J Ultrasound Med 2010; 29:621.

Emphysematous Cystitis

Sagittal-plane ultrasound image of the bladder shows a linear hyperechoic structure with posterior "dirty shadowing" in the anterior aspect of the urinary bladder. There is no recent bladder catheterization. Upon decubitus positioning, this abnormality is immobile, suggesting extraluminal location. 

Axial non-contrast CT of the same patient demonstrates gas within the anterior and posterior walls of the urinary bladder (arrows).

Facts:

• Rare bladder inflammation with gas in bladder wall and surrounding tissues
• Generally caused by E.coli, K.pneumoniae or anaerobic gas-forming organisms
• Pathology: numerous gas filled intramural cysts on mucosal surface
• Risk factors: diabetes, immunocompromised state, urinary tract obstruction
• Most patients have mild forms of disease and respond well to antibiotics. Some have severe inflammation, gangrene and sepsis

Imaging:

• X-ray and CT usually is diagnostic with gas in the bladder wall, surrounding tissues and in the lumen in the absence of prior catheterization
• Ultrasound may show gas in the wall as hyperechoic lesions with posterior dirty shadowing. Visualization of posterior wall of urinary bladder may be limited if gas is present in the anterior aspect of the bladder. Decubitus scan helps localizing gas, whether inside the bladder lumen or in the wall
• CT helps detecting complications such as perforation or emphysematous pyelonephritis

Reference

Gillenwater JY, et al. Adult and pediatric urology, volume 1, 2002.

Petersen RO, et al. Urologic pathology, 2009.

Silicone Granulomas

MLO mammographic view of the left breast shows diffuse, markedly increased breast density throughout from prior direct silicone injection for breast augmentation. 

Transverse view of ultrasound of the left breast shows a cystic lesion (arrow) and multiple several lesions that has ill-defined borders and posterior acoustic shadowing (short arrows), representing silicone granulomas.

Axial non contrast CT shows multiple isodense soft tissue nodules in both breasts, some with thin rim of calcifications. 

Breast Augmentation with Direct Silicone Injection

• Was done in the USA in 1950s to 1960s but later prohibited in 1970s by the US FDA
• Liquid form of silicone was directly injected into breast parenchyma
• Adverse effects include lymphadenopathy, infection, formation of granulomatous masses (siliconoma) and fibrosis
• They make cancer difficult to find on physical examination and mammography 

Imaging Appearance of Free Silicone

• Ultrasound: variable appearance including 1) classic = highly echogenic pattern of scattered and reverberating echoes or "snowstorm" appearance, 2) lesion with acoustic shadowing, 3) hypoechoic masses almost indistinguishable from cysts surrounded by echogenic noise
• Mammography: distortion of breast parenchyma with increase density of the breast
• CT: soft tissue nodules with rim calcification
• MRI: low signal intensity on T1W with fat suppression, high signal intensity on T2W with water-suppression

Reference:

Caskey CI et al. Imaging spectrum of extracapsular silicone: correlation of US, MR imaging, mammographic and histopathologic findings. RadioGraphics 1999;19:S39-S51

Renal Ultrasound for Elevated Serum Creatinine

A sagittal ultrasound image of the right kidney shows a normal-sized kidney with normal parenchymal echogenicity in a patient with acute renal failure. 

What clinicians want to know is whether elevated serum creatinine "acute or chronic" 

• This information is important to narrow differential diagnosis, urgency of investigation and treatment. 
• Chronicity of renal dysfunction can be determined with 1) a search for previous measures of renal function (i.e., old labs), 2) clinical history (i.e., recent onset of acute illness, oliguria that would suggest acute renal failure), 3) daily deterioration of renal function (suggestive of acute renal failure - ARF), 4) ultrasound
• ARF can be prerenal, renal or postrenal

Why Ultrasound?

• Ultrasound can help determining the kidney size. Small renal size (less than 8 cm in adults) is suggestive of CRF
• Demonstrate hydronephrosis, suggesting a postrenal cause. Note that to produce ARF, both kidneys must be affected (i.e., bilateral ureteric obstruction or bladder outlet obstruction, or hydronephrosis of a single functioning kidney)
• To exclude obstruction, US should be done as early as possible. But US is not necessary if there are "clear reversible causes on initial assessment + Rx instituted + clear evidence of prompt response with return to normal renal function within a few days"
• Increased echogenicity of renal cortex is not a sensitive measure of renal function. When present, it is more commonly seen in tubulointerstitial disease rather than glomerular disease

Limitations of Ultrasound

• No hydronephrosis is not equal to no obstruction. False negative study can occur 1) in the first few days of obstruction because the collecting system is relatively noncompliant, 2) if ureters and collecting systems are encased by tumor or fibrosis
• Detection of hydronephrosis can be difficult in patients with cystic kidney disease

Reference:

Baxter GM, Sidhu PS. Ultrasound of the urogenital system, 2006.

Gallbladder Cholesterolosis

Longitudinal US image of the gallbladder demonstrates multiple tiny echogenic spots within the wall with comet-tail artifacts. No evidence of gallbladder wall thickening. 

Facts:

• Other names: cholesteatosis, strawberry gallbladder
• Common, degenerative, proliferative changes of gallbladder
• Usually in females during their 4th and 5th decades
• Usually asymptomatic
• Not associated with increased risk of malignancy, cholelithiasis or cholecystitis

Differentiation from Adenomyomatosis:

• May be difficult at times because they may coexist and are believed to be a continuum of same pathology
• In cholesterolosis, the gallbladder has normal size, shape, lumen and often normal wall thickness

Reference:

Schmidt G. Differential diagnosis in  ultrasound imaging: A teaching file, 2006

Atypical Hepatic Hemangioma - Echoic Border

Ultrasound images of the liver show a round hypoechoic nodule (arrow, calipers) in the right lobe with an echoic border. Background fatty liver is noted. 

Hemangioma with Echoic Border

• Frequent atypical pattern at ultrasound
• Can have either thick echoic rind or thin echoic rim
• Internal echo is at least partially hypoechoic, which is assumed to represent previous hemorrhage, necrosis, scarring or myxomatous change

Reference:

Vilgrain V, et al. Imaging of atypical hemangiomas of the liver with pathologic correlation. Radiographics 2000; 20:379.

Focal Fat Sparing

Figure 1: US image of the liver shows focal masslike area of hypoechogenicity of the left lobe posterior to the left portal vein branch. Note high echogenicity of the background liver, suggesting fatty change.

Figure 2 & 3: In-phase and out-of-phase MR images show liver signal intensity drop in the chemical shift imaging confirming diffuse fatty liver. The abnormality in the left lobe liver does not change between the two phases, suggesting a focal area of fat sparing.

Facts: Fatty Liver

• Most common abnormality of the liver seen on cross-sectional imaging
• Common patterns: diffuse fat accumulation, diffuse fat accumulation with focal sparing, and focal fat accumulation in an otherwise normal liver
• Unusual patterns may mimick neoplasm, inflammation or vascular conditions
• Pathology: triglyceride acculation within cytoplasm of hepatocytes
• Term "fatty liver" is preferred over "fatty infiltration of the liver" because triglyceride accumulation occurs within hepatocytes but rarely other cell types. Infiltration of fat into parenchymal does not occur

Imaging Findings and Sensitivity/Specificity

• US: 1) Liver echo greater than renal cortex and spleen with attenuation of sound wave, 2) loss of definition of diaphragm, 3) poor delineation of intrahepatic architecture (to avoid false-positive diagnosis, all three findings should be fulfilled).  Sensitivity 60-100%. Specificity 77-95%.
• CT: Liver attenuation 10 HU less than that of spleen, or less than 40 HU. Sensitivity 43-95%. Specificity 90%.
• MRI: Signal intensity loss on opposed-phase images in comparison with in-phase images. Sensitivity 81%. Specificity 100%.

Patterns

1. Diffuse deposition: most common
2. Focal deposition and focal sparing: characteristically in specific areas (adjacent to falciform ligament or ligamentum venosum, porta hepatis, in GB fossa). Suggestive findings of fatty pseudolesions rather than true masses are:
1. Fat content
2. Characteristic location
3. Absence of mass effect on vessels and other liver structures
4. Geographic configuration (not round or oval)
5. Poorly delineated margin
6. Contrast enhancement similar to or less than that or normal liver parenchyma
3. Multifocal deposition
4. Perivascular deposition
5. Subcapsular deposition

Reference:


Hamer OW, Aguirre DA, Casola G, et al. Fatty liver: imaging patterns and pitfalls. Radiographics 2006;26: 1637-1653.

ESWL-induced Perinephric Hematoma

Ultrasound image of the kidney shows a crescentic heterogeneous hypoechoic lesion in the perinephric space (arrows). The kidney is marked by the calipers. 

Axial unenhanced CT images confirm a thick left perinephric hematoma (stars) and several fragmented stones in the lower pole of the left kidney.

Facts

• ESWL (Extracorporeal Shock Wave Lithotrypsy) is a common and standard treatment for renal/proximal ureteric calculi in majority of patients
• Most common complication = microscopic hematuria
• Perinephric hematoma and infection (including pyelonephritis) can occur
• Incidence of hematoma varies depending on method of diagnosis. By US, incidence is about 0.1-0.6%. By CT/MRI, incidence rises to 20-25% of cases. 
• No clear correlation between number of shockwaves or intensity given and incidence of hematoma
• Most perinephric hematoma resolves spontaneously within 2 years and the renal function is preserved. They are mostly treated conservatively

Imaging: US and CT

• Crescent-shaped collection surrounding the affected kidney
• Hypoechoic on US, hyperattenuating on non-contrast CT and no enhancement after IV contrast
• Displacement or compression of adjacent renal parenchyma
• Differentiate from subcapsular hematoma by appearance and pressure effect to underlying kidney.
• "Page" kidney occurs when (usually) subcapsular hematoma causes chronic renal parenchymal compromise and then hypertension

Reference:
Labanaris AP, Kuhn R, Schott GE, Zugor V. Perirenal hematomas induced by extracorporeal shock wave lithotripsy (ESWL). Therapeutic management. TheScientificWorldJOURNAL 2007;7:1563-1566.

Pyonephrosis

 Longitudinal ultrasound image of the right kidney shows moderate right hydroureteronephrosis (arrows) with internal debris.

Longitudinal image of the right ureter (arrows) shows a stone (arrowhead) in the distal ureter causing proximal hydroureter. 

Facts:

• Bacterial infection of urine associated with ureteral obstruction, AKA infected hydronephrosis. Accumulation of pus in the renal pelvis and calices of the kidney
• Common causes are ureteric obstruction by stone and ureteropelvic junction (UPJ) obstruction
• Septic patients with high fever, flank pain and tenderness
• Any febrile patients with hydronephrosis should be suspected of having pyonephrosis
• Ultrasound: echogenic urine and debris in the hydronephrotic kidney
• Prompt drainage essential 

Reference:

Hodler J, Von Schulthess GK, Zollikofer ChL. Diseases of the abdomen and pelvis 2010-2013

Cesarean Section Scar Diverticulum

A sagittal US scan of the uterus shows a cystic lesion in the anterior wall of the lower uterine segment. The patient reported prior cesarean section

Facts:

• Defect within the lower uterine cavity in patients with history of cesarean section in expected location of a hysterectomy incision
• Based on a study utilizing hysterosalpingograms, 60% of women with prior C-section had this anatomic defect
• Knowledge of this anatomic defect avoids misdiagnosing it as other pathology
• Often benign clinical significance. Some reports of ectopic scar pregnancy and abnormal uterine bleeding associated with this pathology

Imaging Appearance

• Focal outpouching (most common feature) and thin linear defect
• Location: lower uterine segment (most common) > uterine isthmus, upper endocervical canal

Imaging Mimics

• Prominent cervical glands (tubular, symmetric structure from both walls of endocervical canal)
• Postmyomectomy diverticula (unilateral, from site of resection, correlated with surgical history and location of diverticula)
• Gartner's duct cyst (long, tubular structure parallel to uterine cavity)
• Adenomyosis (location of defect anywhere along uterine cavity)

Reference

Surapaneni K, Silberzweig JE. Cesarean section scar diverticulum: appearance on hysterosalpingography. AJR 2008;190:870-4

Soft Tissue Lipoma

A longitudinal ultrasound image of the back (behind the scapula) shows a well-circumscribed, oval, solid mass (arrows) with internal slight hyperechogenicity superficial to the deep muscle.

Facts: Soft Tissue Lipoma

• Very common mesenchymal tumors
  
• May be palpable, painless, soft and mobile on clinical examination
  
• May be multiple in up to 5% of cases
• Common in patients older than 50 years

US Findings

• Classic lipomas are hyperechoic and homogeneous (compared with muscle) with well-defined borders
• Sonographic appearance may depend on internal cellularity (amount of fat and water in the lesion). Lesions with pure fat are hypo- or anechoic but those with mixed fat/water are quite echogenic
• Appearance highly variable from hyper-, iso-, hypoechoic or mixed echoic and bordes can be circumscribed or poorly defined
  
• It can be difficult to confidently diagnose lipoma on US, accounting for variable US features and high interobserver variability on description of lesions.
  

Our case: soft tissue lipoma proven by histopathology

Reference:

Inampudi P, Jacobson JA, Fessell DP, et al. Soft-tissue lipomas: accuracy of sonography in diagnosis with pathologic correlation. Radiology 2004;233:763-767.

Pneumothorax on Ultrasound

M-mode ultrasound images of the lungs (right and left) show a normal "lung sliding" on the right side "Right" and absence of it on the left side "Left".

Facts:

• Ultrasound can be performed to diagnose pneumothorax with high accuracy
• Normal "lung sliding" is seen when pleura moves against the chest wall during respiration. The movement is easily seen on real-time imaging and can be captured on M-mode ultrasound
• M-mode US shows normal lung sliding as a "seashore sign", in which the motion of pleura/lung produces sand-like granular appearance on the image. The non-mobile chest wall shows several uninterrupted band or "sea"
• Some diseases may produce "loss of lung sliding", most notably pneumothorax

Pneumothorax on US

• Absence of lung sliding shown on real-time imaging
• On M-mode as "barcode sign" or "stratosphere sign" (see above image labeled "left")
• More specific sign is the "lung point sign"

Our case: left pneumothorax (confirmed with radiography)

Reference:

Lichtenstein DA, Menu Y. A bedside ultrasound sign ruling out pneumothorax in the critically ill. Chest 1995; 108:1345-48.

Scrotal Pyocele

Gray-scale and color Doppler US images of the testicle shows a complex fluid collection (stars) around the testicle and marked scrotal skin thickening. The epididymis is edematous with increased flow (image not shown).

Facts: Scrotal Pyocele

• Also known as scrotal abscess
• Can be superficial (from infected hair follicles, wound) or intrascrotal
• Causes: epididymitis, TB, instrumentation, neurogenic bladder, chronic catheter indwelling, spread from intraabdominal infection (i.e., appendicitis)
• Intrascrotal abscess requires surgical drainage

Imaging

• US is the modality of choice
• Complex-appearing fluid around the testicle
• Scrotal skin thickening with hyperemia
• Evidence of causes such as epididymitis or others
• Based on imaging, it is difficult to distinguish pyocele from hematocele

References

1. Siegel MJ. Pediatric Sonography, 2010.

2. Resnick MI, Novick AC. Urology Secrets, 3rd ed, 2003.

Renal Scarring

A longitudinal ultrasound image of the kidney shows a focal depression of the lower pole cortex (arrows) with focal parenchymal thinning and a caliceal stone (between calipers).

Facts:

• Renal scar is a common incidental finding during imaging of the GU tract
• It can occur both with and without episodes of infundibular obstruction
• Reflux is considered a major contributor in development of non-obstructive scarring, particularly in children with vesicoureteric reflux (VUR)
• In adults, renal scarring is more associated with renal stone disease, either with stone or history of stone

Imaging

• Focal cortical thinning and depression of the cortex, overlying the pyramid on any imaging modalities (IVU, US, CT, MR)
• Hyperechoic band is seen over the parenchymal thinning on US
• Mimic = normal renal lobulation. Lobulation will span the pyramids with echogenic lobular junctions into renal columns

Reference:

Newhouse JH, Amis, Jr, ES. The relationship between renal scarring and stone disease. AJR 1988; 151:1153-1156.

Unilateral Diaphragmatic Elevation

An AP chest radiograph shows elevation of the right hemidiaphragm.

Unilateral Diaphragmatic Elevation: Differentials

• Lung/pleural disease: Pneumonectomy, lobectomy, pleurisy, subpulmonic effusion
• Diaphragm disease: Phrenic nerve palsy / eventration
• Abdominal disease: Hepatomegaly / hepatic mass / abdominal neoplasm / distended stomach

US and CT images demonstrate a very large cyst in the right lobe liver as a cause of elevated right hemidiaphragm.

AFP-Negative Hepatocellular Carcinoma

An US image of the liver shows a 2 cm solid nodule in a cirrhotic liver.

CT images of the liver in arterial and portovenous phases show arterial contrast enhancement with rapid washout of the nodule.

Facts: Serum AFP & Hepatocellular Carcinoma (HCC)

• First detection of AFP in serum of HCC patients in 1970s
• Currently, it is the only widely used serologic marker for diagnosing HCC. Additional useful markers in use are AFP-L3 and DCP
• Normal range 10-20 ng/mL
• AFP greater than 400 ng/mL generally considered a point of discriminating HCC from other chronic liver disease
• Problem: about 60% of patients with HCC have AFP below 200, up to 20% have normal AFP (AFP-negative HCC; AFP below 20)

Clinical Features of AFP-negative HCC

• Less likely to be hepatitis B positive
• Tend to have a lower level of ratio of serum glutamic oxaloacetic transaminase (AST)/pyruvic transaminase (ALT)

References:

1. Law WY. Hepatocellular Carcinoma, 2007.

2. Nomura F, Ohnishi K, Tanabe Y. Clinical features and prognosis of hepatocellular carcinoma with reference to serum alpha-fetoprotein levels. Analysis of 606 patients. Cancer 1989;64:1700-1707.

Intussusception: Ultrasound

A longitudinal US image shows a "pseudokidney" sign of intussusception (arrows). Arrowheads point to enlarged mesenteric lymph nodes within the intussusceptum.

A transverse US image shows a "target" sign with a hypoechoic ring of the intussuscepiens surrouning the central echogenic area of intussusceptum. Arrowheads point to enlarged nodes.

Facts

• A segment of bowel (intussusceptum) prolapses into a more distal bowel segment (intussuscepiens)
• Most frequently seen in the first two years of life but can be seen up to 4 years. If older child has intussusception, looks for a lead point such as polyp, Meckel diverticulum, lymphoma, duplication cyst.
• Classic triad: colicky pain, vomiting and bloody (red currant jelly) stools (seen in less than 25% of cases)
• X-ray is positive in only 50% of cases, and is not reliable in diagnosing this condition

Ultrasound Findings

• Modality of choice to diagnose intussusception
• "Target" sign = hypoechoic ring with an echogenic center on transverse US image
• "Pseudokidney" sign = hypoechoic bowell wall extending along a hyperechoic mucosa
• Helpful in searching for a lead point. US can provide a specific diagnosis in one-third of these cases.

Reference:

1. Daldrup-Link HE, Gooding CA. Essentials of Pediatric Radiology: A Multimodality Approach, 2010.

2. Hodler J, Von Schulthess GK, Zollikofer CL. Diseases of the Abdomen and Pelvis 2010-2013: Diagnostic Imaging and Interventional Techniques, 2010.

Obstructing Ureteric Stone on Ultrasound

Figure 1: A gray-scale ultrasound image of the right kidney shows right hydronephrosis and hydropelvis.

Figure 2: The scan in the right pelvis demonstrates an echogenic focus (arrow) with posterior acoustic shadowing (arrowheads) at the site where the ureter abruptly changes its caliber.

Facts:

• Imaging in patients presenting with renal colic is performed to 1) confirm the suspected renal colic, 2) diagnose cause and level of obstruction, 3) detect or rule out complications of renal colic (obstruction, infection), 4) detect alternative diagnoses
• Non-contrast CT is current gold standard for diagnosis of urinary tract stone disease
• Ultrasound may be an initial imaging done although its sensitivity is limited (37% - 64%) for detecting renal calculus (lower for ureteric calculus) and acute obstruction (74% - 85%)

Imaging Appearance

• Stone (brightly echogenic focus with posterior acoustic shadowing). For renal stone less than 5 mm, ultrasound is of limited accuracy. Ureteric stone is uncommonly appreciated on US.
• Hydronephrosis
• Twinkling artifact behind the stone, and absent ureteral jet on color Doppler imaging

Reference:

Scott LM, Sawyers SR, Bokhari J, Hamper UM. Ultrasound evaluation of the acute abdomen. Ultrasound Clin 2007;2:493-523.

Bladder Stones

Transverse ultrasound image of the urinary bladder shows a 5-cm mobile hyperechoic lesion (between arrows) with posterior acoustic shadowing within the bladder lumen.

Facts:

• Risk factors: urinary stasis (voiding dysfunction i.e., urethral stricture, benign prostatic hyperplasia, bladder neck contracture, neurogenic bladder), infection, bladder diverticula, foreign body (Foley catheter balloon, suture material, etc)
• Common compositions: uric acid, ammonium urate, calcium oxalate
• Uric acid stones predominate in a setting of bladder outlet obstruction
• Magnesium ammonium phosphate and apatite stones predominate in a setting of urinary tract infection (UTI)
• Patient presentation: hematuria, suprapubic pain, interruption of urine stream

Imaging

• If sufficiently calcified, bladder stones may be visible on radiography
• Tends to locate in the midline when the patient is supine
• If calcification is located laterally, think of a stone in the diverticulum or ureterocele
• Key to confirm that the abnormality is a stone = mobility (either on radiography or ultrasound)

Reference:

1. Zagoria RJ. Genitourinary Radiology: the Requisites, 2004.

2. Tanagho EA, McAninch JW. Smith's General Urology, 2004.

Caval Index

Longitudinal ultrasound images of the IVC in an asymptomatic patient demonstrate a normal inferior vena cava (IVC) during inspiration and expiration, in which the diameters (yellow double-headed arrows) do not change significantly. In this case, the diameters of the IVC were measured 2-3 cm below the right atrial border (yellow lines).

Facts: IVC Diameter

• IVC diameter changes following total body volume (increases with increasing total body volume, and decreases with volume depletion)
• IVC normally collapses with inspiration (decreased intra-thoracic pressure) and expands with expiration (but this collapsibility should not exceed 50%)

Caval Index

• Caval Index = 100 x (diam expiration - diam inspiration)/diam expiration
• Where to measure the IVC? Several ways exist, and none is perfect yet. Easy way is to measure with a longitudinal view of the IVC - find the junction of the atrium and IVC and measure the IVC at 2-3 cm below the junction
• Interpretation: studies vary greatly as to significance of values in different patient populations. In general, if caval index is greater than 50% it suggests low central venous pressure (CVP less than 8 mmHg) and high probability of fluid responsiveness

Reference:

Nagdev AD, Merchant RC, Tirado-Gonzalez A, et al. Emergency department bedside ultrasonographic measurement of the caval index for noninvasive determination of low central venous pressure. Ann Emerg Med 2010; 55:290-295.