ANATOMY	DESCRIPTION
Renal capsule	Fibrous capsule (true capsule) surrounding the cortex
Renal cortex	Outer portion of the kidney Bound by the renal capsule and arcuate vessels Contains glomerular capsules and convoluted tubules
Medulla	Inner portion of the renal parenchyma Within the medulla lie the renal pyramids Renal 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 kidney Contains 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 aorta May have multiple ipsilateral arteries A single ipsilateral artery may divide into multiple renal arteries at the hilum Courses posterior to the renal vein Main renal artery arises 1.0-1.5 cm inferior to the origin of the superior mesenteric artery Right renal artery is longer than the left renal artery Demonstrates low-resistance blood flow Supplies the kidney, ureter, and adrenal gland
Segmental artery	After entering the renal hilum, the artery divides into 4 to 5 segmental arteries Demonstrates low-resistance blood flow
Interlobar artery	Branch of the segmental artery Course alongside the renal pyramids Demonstrates low-resistance blood flow
Arcuate artery	Boundary between the cortex and medulla Branch of the interlobar artery located at the base of the medulla Arcuate arteries give rise to the interlobular arteries Demonstrates 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 hilum Courses anterior to the renal artery Left renal vein receives the left suprarenal and left gonadal vein Left renal vein is longer than the right renal vein Dilatation 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 muscle Primary flexor of the hip joint Lies posterior to the inferior pole of each kidney
Quadratus lumborum muscle	Muscle of the posterior abdominal wall Lies posterior and medial to each kidney
Transversus abdominis muscle	Deepest layer of flat muscles of the anterolateral wall Lies lateral to each kidney
Gerota’s fascia	Fibrous covering of tissue surrounding each kidney Also 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 kidney Demonstrated most often on the left	Asymptomatic	Lateral outward cortical bulge Echogenicity equal to the cortex	Carcinoma Hematoma Renal cyst Hypertrophied column of Bertin
Extrarenal pelvis	Renal pelvis extrudes from the renal hilum	Asymptomatic	Anechoic oval-shaped structure medial to the renal hilum No vascular flow	Hydroureter Renal cyst Renal vein
Fetal lobulation	Immature renal development	Asymptomatic	Lobulations in the renal contour	Junctional parenchymal defect Dromedary hump
Hypertrophied column of Bertin	Enlarged column of Bertin	Asymptomatic	Mass extending from the cortex into the renal pyramids Echogenicity similar to cortex	Carcinoma Renal duplication Abscess
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 factors Calcified artery Angiomyolipoma Fetal lobulation

Congenital Anomalies

ANOMALY	DESCRIPTION	CLINICAL FINDINGS	SONOGRAPHIC FINDINGS	DIFFERENTIAL CONSIDERATIONS
Agenesis	Absence of the kidney(s) Unilateral or bilateral	Asymptomatic when unilateral Fatal when bilateral Associated with genital anomalies	Empty renal fossa(e) Large, contralateral kidney	Pelvic kidney Surgical removal Crossed fused ectopia
Cake kidney	Variant of a horseshoe kidney Found in the pelvis	Asymptomatic Pelvic mass	Fusion of entire medial aspect of both kidneys Anterior rotation of the renal pelvis	Crossed fused ectopia Renal mass
Crossed fused ectopia	Both kidneys are fused in the same quadrant Two separate collecting systems Two normally located adrenal glands	Asymptomatic Abdominal mass	One single, large kidney Irregular contour Inferior pole is directed medially	Renal mass Cake kidney Sigmoid kidney
Duplication	Two distinct collecting systems May involve kidney, ureter, and/or renal pelvis May be partial or complete	Asymptomatic Flank pain	Increase in renal length Two distinct collecting systems The superior system is most likely to obstruct	Hypertrophied column of Bertin Renal mass
Horseshoe kidney	Fusion of the kidneys usually at the inferior poles Connected by an isthmus of functioning parenchyma or nonfunctioning fibrotic tissue Anterior rotation of the renal pelves and ureters Separate collecting systems Most common form of renal fusion	Asymptomatic Pulsatile abdominal mass	Bilateral low-lying medially placed kidneys with partial or complete fusion of the inferior poles “Dipping effect” of both inferior poles Isthmus of tissue demonstrated anterior to the abdominal aorta Isthmus echo texture is similar to the renal cortex	Renal mass Lymphadenopathy Bowel Retroperitoneal tumor
Pelvic kidney	Failure to ascend with development Associated with a short ureter Renal artery and vein are located more inferior Renal vein drains directly into the inferior vena cava (IVC)	Asymptomatic Pelvic pain	Elongated core of echogenic tissue surrounded by less echogenic parenchyma Located in the lower abdomen or pelvis Empty ipsilateral renal fossa Lies in an oblique plane	Bowel Pelvic mass
Renal ptosis	Unusual mobile kidney that descends from the normal position toward the pelvis Poor support structures	Asymptomatic	Abnormal mobility of a kidney	Pelvic kidney Horseshoe kidney
Sigmoid kidney	Variant of the horseshoe kidney	Asymptomatic Abdominal mass	Superior pole of one kidney is fused with the inferior pole of the contralateral kidney S-shaped	Bowel Abdominal mass
Thoracic kidney	Kidney migrates into the chest through a herniation in the diaphragm Rare finding	Chest mass	Elongated core of echogenic tissue surrounded by less echogenic parenchyma Located in the chest Not 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 echogenicity Less 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 anechoic Do 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 approach Right inferior pole with subcostal approach
Left posterior oblique (LPO)	Allows bowel to move away from right kidney Subcostal or intercostal approach
Left lateral decubitus	Liver and kidney “fall” from the rib cage Aids in obese or gassy patients
Right posterior oblique (RPO)	Left superior pole with intercostal approach Posterior subcostal approach for left inferior pole
Right lateral decubitus	Left posterior approach with deep inspiration
Prone	Demonstrates mid and inferior poles of both kidneys Great for infants and small children Superior poles may be visualized Used in renal biopsies