ANATOMY	DESCRIPTION
Renal capsule	Fibrous capsule (true capsule) surrounding the cortex
Renal cortex	Outer portion of the kidneyBound by the renal capsule and arcuate vesselsContains glomerular capsules and convoluted tubules
Medulla	Inner portion of the renal parenchymaWithin the medulla lie the renal pyramidsRenal pyramids contain tubules and the loops of Henle
Column of Bertin	Inward extension of the renal cortex between the renal pyramids
Renal sinus	Central portion of the kidneyContains the major and minor calyces, peripelvic fat, fibrous tissues, arteries, veins, lymphatics, and part of the renal pelvisï»¿
Renal hilum	Contains the renal artery, renal vein, and ureter

Renal Vasculature

RENAL VESSEL	DESCRIPTION
Main Renal Artery	The right renal artery arises from the anterolateral aspect of the aorta; the left renal artery arises from the posterolateral aspect of the aortaMay have multiple ipsilateral arteriesA single ipsilateral artery may divide into multiple renal arteries at the hilumCourses posterior to the renal veinMain renal artery arises 1.0-1.5 cm inferior to the origin of the superior mesenteric arteryRight renal artery is longer than the left renal arteryDemonstrates low-resistance blood flowSupplies the kidney, ureter, and adrenal gland
Segmental artery	After entering the renal hilum, the artery divides into 4 to 5 segmental arteriesDemonstrates low-resistance blood flow
Interlobar artery	Branch of the segmental arteryCourse alongside the renal pyramidsDemonstrates low-resistance blood flow
Arcuate artery	Boundary between the cortex and medullaBranch of the interlobar artery located at the base of the medullaArcuate arteries give rise to the interlobular arteriesDemonstrates low-resistance blood flow
Interlobular artery	Branch of the arcuate arteries entering the renal glomeruli
Main Renal Vein	Formed from the junction of tributaries in the renal hilumCourses anterior to the renal arteryLeft renal vein receives the left suprarenal and left gonadal veinLeft renal vein is longer than the right renal veinDilatation of the left renal vein, caused by mesenteric compression, may be demonstrated

Ureter anatomy

• 25 to 34 cm long tubular structure connecting the renal pelvis to the urinary bladder.

• Course vertically with retroperitoneum along the psoas muscles.

• Insert posterior and inferiorly at the trigone of the bladder.

• Distal ureter at the trigone considered extraperitoneal.

Arterial supply to the ureter

• Renal artery.

• Testicular or ovarian artery.

• Superior vesical artery.

Support Structure of the Kidneys

Psoas muscle	Major groin musclePrimary flexor of the hip jointLies posterior to the inferior pole of each kidney
Quadratus lumborum muscle	Muscle of the posterior abdominal wallLies posterior and medial to each kidney
Transversus abdominis muscle	Deepest layer of flat muscles of the anterolateral wallLies lateral to each kidney
Gerota’s fascia	Fibrous covering of tissue surrounding each kidneyAlso known as Gerota’s capsule; renal fascia
Perinephric fat	Fatty tissue surrounding each kidney
Renal capsule	Protective connective tissue capsule surrounding each kidney

Location

• Paired bean-shaped structures lying in a sagittal oblique plane in the retroperitoneal cavity.

• Located between the first and third lumbar vertebrae.

• Superior poles lie more posterior and medial.

• Inferior poles lie more anterior and lateral.

• Left kidney lies superior to the right kidney.

Each kidney is located

• Anterior to the psoas and quadratus lumborum muscles.

• Medial to the transverse abdominis muscle and liver or spleen.

• Lateral to the quadratus lumborum muscle.

Renal Anatomical Variants

VARIANT	DESCRIPTIONS	CLINICAL FINDINGS	SONOGRAPHIC FINDINGS	DIFFERENTIAL CONSIDERATIONS
Dromedary hump	Cortical bulge on the lateral aspect of the kidneyDemonstrated most often on the left	Asymptomatic	Lateral outward cortical bulgeEchogenicity equal to the cortex	CarcinomaHematomaRenal cystHypertrophied column of Bertin
Extrarenal pelvis	Renal pelvis extrudes from the renal hilum	Asymptomatic	Anechoic oval-shaped structure medial to the renal hilumNo vascular flow	HydroureterRenal cystRenal vein
Fetal lobulation	Immature renal development	Asymptomatic	Lobulations in the renal contour	Junctional parenchymal defectDromedary hump
Hypertrophied column of Bertin	Enlarged column of Bertin	Asymptomatic	Mass extending from the cortex into the renal pyramidsEchogenicity similar to cortex	CarcinomaRenal duplicationAbscess
Junctional parenchymal defect	Embryonic remnant of the fusion site between the upper and lower portions of the kidney	Asymptomatic	Triangular echogenic area in the anterior aspect of the kidney	Technical factorsCalcified arteryAngiomyolipomaFetal lobulation

Congenital Anomalies

ANOMALY	DESCRIPTION	CLINICAL FINDINGS	SONOGRAPHIC FINDINGS	DIFFERENTIAL CONSIDERATIONS
Agenesis	Absence of the kidney(s)Unilateral or bilateral	Asymptomatic when unilateralFatal when bilateralAssociated with genital anomalies	Empty renal fossa(e)Large, contralateral kidney	Pelvic kidneySurgical removalCrossed fused ectopia
Cake kidney	Variant of a horseshoe kidneyFound in the pelvis	AsymptomaticPelvic mass	Fusion of entire medial aspect of both kidneysAnterior rotation of the renal pelvis	Crossed fused ectopiaRenal mass
Crossed fused ectopia	Both kidneys are fused in the same quadrantTwo separate collecting systemsTwo normally located adrenal glands	AsymptomaticAbdominal mass	One single, large kidneyIrregular contourInferior pole is directed medially	Renal massCake kidneySigmoid kidney
Duplication	Two distinct collecting systemsMay involve kidney, ureter, and/or renal pelvisMay be partial or complete	AsymptomaticFlank pain	Increase in renal lengthTwo distinct collecting systemsThe superior system is most likely to obstruct	Hypertrophied column of BertinRenal mass
Horseshoe kidney	Fusion of the kidneys usually at the inferior polesConnected by an isthmus of functioning parenchyma or nonfunctioning fibrotic tissueAnterior rotation of the renal pelves and uretersSeparate collecting systemsMost common form of renal fusion	AsymptomaticPulsatile abdominal mass	Bilateral low-lying medially placed kidneys with partial or complete fusion of the inferior poles“Dipping effect” of both inferior polesIsthmus of tissue demonstrated anterior to the abdominal aortaIsthmus echo texture is similar to the renal cortex	Renal massLymphadenopathyBowelRetroperitoneal tumor
Pelvic kidney	Failure to ascend with developmentAssociated with a short ureterRenal artery and vein are located more inferiorRenal vein drains directly into the inferior vena cava (IVC)	AsymptomaticPelvic pain	Elongated core of echogenic tissue surrounded by less echogenic parenchymaLocated in the lower abdomen or pelvisEmpty ipsilateral renal fossaLies in an oblique plane	BowelPelvic mass
Renal ptosis	Unusual mobile kidney that descends from the normal position toward the pelvisPoor support structures	Asymptomatic	Abnormal mobility of a kidney	Pelvic kidneyHorseshoe kidney
Sigmoid kidney	Variant of the horseshoe kidney	AsymptomaticAbdominal mass	Superior pole of one kidney is fused with the inferior pole of the contralateral kidneyS-shaped	BowelAbdominal mass
Thoracic kidney	Kidney migrates into the chest through a herniation in the diaphragmRare finding	Chest mass	Elongated core of echogenic tissue surrounded by less echogenic parenchymaLocated in the chestNot easily demonstrated on ultrasound	Chest mass

Size

DIVISION	SONOGRAPHIC APPEARANCE
Renal capsule	Well-defined echogenic line surrounding the kidney
Renal cortex	Fine, moderate, to low-level echogenicityLess echogenic compared to the normal liver parenchyma
Medulla	Hypoechoic; may appear anechoic
Columns of Bertin	Moderate to low-level echogenicity
Renal sinus	Hyperechoic; most echogenic
Arcuate vessels	Small echogenic foci at the corticomedullary junction
Cortical thickness	Minimum 1 cm

Normal Sonographic Appearance—Pediatric Kidney

DIVISION	SONOGRAPHIC APPEARANCE
Renal capsule	Sparse amount of perinephric fat makes it difficult to distinguish the capsule
Renal cortex	Moderate to highly echogenic
Medulla	Commonly anechoicDo not mistake for hydronephrosis
Renal sinus	Barely visible in infants

Technique

Preparation

• Kidneys—patient should be hydrated.

• Renal vessels—nothing by mouth for 6 to 8 hours before the examination.

• Bladder—drink 8 to 16 ounces of water 1 hour before the examination.

Examination technique and imaging optimization

• Use the highest-frequency abdominal transducer possible to obtain optimal resolution for penetration depth.

• Place gain settings to display the normal adult renal cortex as moderate or low-level echogenicity and the renal sinus as the most echogenic with adjustments to reduce echoes within the vessels.

• Position the focal zone(s) at or below the region of interest.

• Sufficient imaging depth to visualize structures posterior to the region of interest.

• Harmonic imaging and decreasing the compression (dynamic range) can be used to reduce artifactual echoes within anechoic structures and improve prominence of posterior acoustic shadowing.

• Spatial compounding can be used to improve visualization of structures posterior to a highly attenuating structure.

• Evaluation and documentation of the superior, inferior, medial, and lateral aspects of each kidney in the coronal or sagittal plane.

• Evaluation and documentation of the superior pole, renal hilum, and inferior pole of each kidney in the transverse plane.

• Measurements of maximum length, thickness, and width of each kidney.

• Measurement of the cortical thickness of each kidney.

• Evaluation and documentation of the bladder wall.

• Prevoid and postvoid bladder volumes may be included.

• Kidneys are best evaluated with an empty urinary bladder.

• Documentation and measurement of any abnormality in two scanning planes with and without color Doppler should be included.

Patient Positions

PATIENT POSITION	DEMONSTRATES/BENEFITS
Supine	Right superior pole with intercostal approachRight inferior pole with subcostal approach
Left posterior oblique (LPO)	Allows bowel to move away from right kidneySubcostal or intercostal approach
Left lateral decubitus	Liver and kidney “fall” from the rib cageAids in obese or gassy patients
Right posterior oblique (RPO)	Left superior pole with intercostal approachPosterior subcostal approach for left inferior pole
Right lateral decubitus	Left posterior approach with deep inspiration
Prone	Demonstrates mid and inferior poles of both kidneysGreat for infants and small childrenSuperior poles may be visualizedUsed in renal biopsies