Mon022414 - Renal Ultrasound

Anatomy, Variants, and Pathology
John C. Feldman, M.D.
Clinical Associate Professor, University of
South Florida College of Medicine.
Radiology Associates of Florida
• University South Florida College of Medicine
• University of Florida Internal Medicine (Intern) and Diagnostic Radiology
• Mayo Clinic Cross Sectional Imaging Fellowship
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Renal Anatomy by Ultrasound
Anatomic Variants
Medical Renal Disease
Renal Cysts
Solid Renal Masses
Nephrolithiasis
• Utilizes sound waves (acoustics) to generate
an image
• No radiation
• Operator dependent
• Body habitus limitations
• Findings may be described as hyperechoic
(bright), isoechoic, hypoechoic (dark), and
anechoic.
• Central renal sinus is composed of fibrofatty
tissue and is hyperechoic.
• Typically, there are eleven pyramids and nine
calices.
• Renal pyramids are hypoechoic, cortex is
slightly more echogenic.
• Cortical echogenicity should be equal to or
slightly less than the liver and much less than
the spleen.
• Renal contour is typically smooth however,
lobulations are common.
Figure 25. Drawings illustrate a variety of pseudomasses that can be created by normal renal
tissue:
Fetal
Lobulation
Dromedary
Hump
Cortical
Column
Prominent Hilar
Lips
Dyer R B et al. Radiographics 2004;24:S247-S280
©2004 by Radiological Society of North America
• Fetal kidneys are subdivided into lobes that may
be separated by grooves.
• Lobulation usually diminishes by the end of the
fetal period. Sometimes these lobulations persist
into adulthood.
• Lobulation is characterized on sonography by the
presence of renal surface indentations that
overlie the space between the pyramids.
• True renal scars are positioned over medullary
pyramids.
• Wedge shaped hyperechoic defect in the
anterior aspect of the kidney near the upper
and middle third
• Junctional parenchymal defect, caused by
incomplete fusion of the upper and lower
poles
• Triangular shape and location is diagnostic
• No associated pathology or risk of disease
• A prominent column of cortical tissue can
protrude into the renal sinus and simulate a
mass
• Column of Bertin located in the mid kidney
(interpolar region)
• Echogenicity is identical to renal cortex
• Occasionally, CT or MRI with contrast may be
required to exclude a mass
• Often mistaken for a tumor
• Look for renal pyramids, if you see them, it is a
dromedary hump
• Usually on the left kidney
• Normally hypo to isoechoic to the liver and
spleen.
• Medical renal disease is reported when cortical
echogenicity is greater than the liver or equal to
the spleen.
• Medical renal disease is a purposeful, non specific
designation.
• Most common causes includes diabetic or
hypertensive nephropathy.
• Renal echogenicity is usually normal in patients
with acute renal failure. *
• Thinning of renal cortex, usually seen in
elderly patients (greater than 70 yo).
• If seen in younger patients, can indicate
chronic kidney disease, most commonly
hypertension or diabetes.
• Comparative measurements have been
reported to be better at estimating renal
function than calculations of total kidney
volume.
Normal 36 year old patient
Creatinine 1.1
76 year old male
Creatinine 1.6
• In an otherwise healthy patient, may be
normal
• Performed to exclude a reversible cause
(obstruction)
• Non specific findings of perinephric fluid,
increased echogenicity, increased size
Right Kidney
Left Kidney
34 year old with creatinine of 5.1
Large kidneys (>14 cm)
Loss of Cortical Medullary Differentiation
Small perirenal Effusion
• Most common renal mass is a simple cortical
cyst
• Present in 50% of people over the age of 50
years old
• Most cysts are asymptomatic
• Microscopic hematuria may occasionally be
attributed to a renal cyst
• Rarely, large cysts may obstruct a collecting
system or cause hypertension
• Simple cysts require no follow up*
• Often incidental findings
• “Does not meet the criteria for classification as a
simple cyst, and malignancy cannot be excluded” can
lead to unnecessary surgery
• Dr. Morton Bosniak devised a classification system
based on imaging (CT with and without contrast)
features to determine the risk of malignancy
• Can be extrapolated to ultrasound, however, the
presence of enhancement within a solid lesion cannot
be evaluated with conventional ultrasound, requiring
cross sectional imaging for complete characterization.
• Category I lesions are simple
benign cysts showing
homogeneity, water content,
and a sharp interface with
adjacent renal parenchyma,
with no wall thickening,
calcification, or enhancement.
• Key terms: Anechoic (not
hypoechoic), sharp, smooth.
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One or two thin (≤1 mm thick)
septations or thin, fine
calcification in their walls or septa
(wall thickening > 1 mm advances
the lesion into surgical category
III)
Hyperdense benign cysts with all
the features of category I cysts
except for homogeneously high
attenuation.
A benign category II lesion must
– 3 cm or less in diameter
– Have one quarter of its wall
extending outside the kidney so the
wall can be assessed
– Nonenhancing after contrast
material is administered.
• This category consists of
minimally complicated cysts
that need follow-up. This is a
group not well defined by
Bosniak but consists of lesions
that do not neatly fall into
category II. These lesions have
some suspicious features that
deserve follow-up to detect
any change in character.
• “F” stands for follow up.
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True indeterminate cystic masses
that need surgical evaluation,
although many prove to be
benign. They may show:
– Uniform wall thickening
– Nodularity
– Thick or irregular peripheral
calcification
– Multilocular nature with
multiple enhancing septa.
Hyperdense lesions that do not
fulfill category II criteria are
included in this group.
• These are lesions with a
nonuniform or enhancing
thick wall, enhancing or
large nodules in the wall, or
clearly solid components in
the cystic lesion.
• Most common hereditary renal cystic disease
• One of 400–1000 live births and affects
approximately 300,000 to 600,000 Americans,
showing no predilection for a particular sex or
race
• 5%–10% of patients undergoing dialysis
• Mutations in two genes, which are known as
PKD1 and PKD2
• Most patients with this disease develop renal cysts by
the age of 30
• Cysts, most greater than 3cm in diameter, are
distributed diffusely throughout both kidneys
• Cyst-associated complications can be identified by
cross-sectional imaging
• Extrarenal manifestations of the disease include
hepatic, pancreatic, seminal vesicle, and splenic cysts;
intracranial arterial aneurysms; aortic aneurysms;
abdominal wall hernias; colonic diverticula; and aortic
and mitral valve abnormalities
• Several subtypes with different appearances and
prognosis
• More common in older patients but younger patients
are not uncommon
• Usually asymptomatic until large
• Ultrasound may be the initial modality of detection
• Some RCCs are indolent and may be monitored in
elderly patients or poor surgical candidates.
• Basic subtypes: Clear cell, Papillary, Chromophobe,
Cystic.
• Rarer subtypes are highly aggressive
• Most common, accounting for 70% of all RCCs
• Solid, heterogenous, hyper, iso, hypoechoic mass
which may be well or poorly defined
• Renal vein involvement
• Highly Vascular
• Can be confused with a large angiomyolipoma
• Well defined, typically indolent lesion
• Can be mistaken for a complex cyst
(hypoechoic, not anechoic)
• 2nd most common.
• Commonly involves end stage kidneys.
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3rd most common subtype
Well circumscribed, solid tumors
Hyperechoic on ultrasound
Cannot be reliably be distinguished from an
oncocytoma by biopsy or imaging
• Complex cystic masses with thickened
septations and multiloculated features
• Bosniak III and IV lesions
• Strong female predilection
• Often found incidentally
• Symptomatic presentation is most frequently associated
with spontaneous retroperitoneal hemorrhage; the risk of
bleeding being proportional to the size of the lesion (> 5 cm
diameter)
• Located in the cortex and without posterior acoustic
shadowing
• May be indiscernible from a RCC by ultrasound requiring
additional imaging
• Hyperechoic renal pyramids
• Differential considerations would include
hyperparathyroidism, medullary sponge
kidney, RTA, and sarcoidosis.
Nephrocalcinosis
Normal
• Common
• Southeastern US is the known as the “Stone
Belt”
• Many etiologies
• Most common presenting symptom is renal
colic
• 3X more common in men
• Peak between 30-60 years
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