Common Renal Pathology

By

Godwin Agada Negedu B.sc, PgDMU

(Sonographer)

Acknowledgement

• My dear wife, Tohmoh Haruna-Godwin and my lovely kids
• Dr. Mohammed Akhter Hossain CEO- Shristy Institute Dhaka, Bangladesh
• Prof. SB Danborno, Dept of Human Anatomy. ABU zaria, Nigeria
• Mr. Andrew Mattawale Supervisor ECHP Jos, Nigeria
• Mr. Nathan Ibrahim
• Mr. Okechukwu Obi

Renal Calculus – Renal Stone – Urolithiasis/Nephrolithiasis

• Renal stone or Urolithiasis is most common in males aged 20 – 40 years.
• Stone formation may be –
• Idiopathic
• Associated with stasis of urine. Stasis also predisposes the patient to infection.
• Prolonged ingestion of stone forming substances
• Chronic urinary tract infection
• Climatic conditions associated with dehydration.

Clinical features

• Patient may be clinically silent or asymptomatic
• Patient may come with flank pain, hematuria (microscopic or gross), renal colic.
• Stones can occur in any part of the urinary system but most common in the kidneys – the renal cortex, medulla, vessels, calyces or renal pelvis.
• Most calculi arise in the collecting system.
• Ultrasound features:
• Calculi are seen as highly echogenic structures regardless of chemical composition.
• Detection of posterior acoustic shadow depends on stone size, transducer frequency and focal zone.
• Tiny calculi will not shadow if they are smaller than the focal zone.

Collecting System stones

• The reflectivity of stones in the renal sinus may be equal to that of the renal sinus itself, therefore sometime difficult to distinguish.
• If the patient is scan in a hydrated condition, the fluid in the sinus outlines the calculus and enables better visualization of the calculus versus the echogenic renal sinus.
• A staghorn calculus is a stone that completely fills the entire collecting system i.e. the pelvis and calyces.
• It is usually associated with chronic infection and obstruction.
• Sonographically, staghorn calculus appears as a curved echogenic structure in the renal sinus area with posterior acoustic shadowing (which often hides any associated Hydronephrosis).

Pitt-falls:

• False-positive Dx occurs when other structures are mistaken for calculi.
• These structures can be: arterial calcification, gas bubbles, small echogenic masses, milk of calcium in small calyceal or renal parenchymal cysts and papillary necrosis.

Nephrocalcinosis

• Nephrocalcinosis is the formation of calcium deposits in the renal parenchyma, a process that can impair the kidney function.
• Nephrocalcinosis may eventually result in acute obstructive uropathy or chronic obstructive uropathy, leading to eventual kidney failure.
• The disorder is often discovered when symptoms of renal insufficiency/renal failure, obstructive uropathy, or urinary tract stones develop.
• Calcium salts deposition occurs most commonly in the medullary pyramids.
• May also occurs in the renal cortex – either alone or in conjunction with medullary deposits.

Cortical Nephrocalcinosis:

• Sonographically, cortical Nephrocalcinosis is seen as increased cortical echogenicity which may be associated with acoustic shadowing.
• It is usually diffuse and bilateral.
• Causes:
• Chronic hypercalcemic states
• Acute cortical necrosis
• Chronic Glomerulonephritis
• Ethylene glycol poisoning
• Rejected renal transplants.

Medullary Nephrocalcinosis:

• Sonographically, medullary Nephrocalcinosis is usually seen diffusely throughout both kidneys.
• The renal pyramids appear more echogenic than the adjacent cortex.
• The hyperechoic regions may be seen throughout the entire renal pyramids or they may be seen only at the periphery of the pyramids or only at the tips.
• With time, further calcium deposition and stone formation occurs.
• Posterior acoustic shadowing is not associated with medullary Nephrocalcinosis, unless there is concurrent stone formation.

Causes in adults:

• Hyperparathyroidism (40%)
• Renal tubular acidosis (20%)
• Medullary sponge kidney
• Bone metastases
• Chronic Pyelonephritis
• Cushing’s syndrome
• Hyperthyroidism
• Malignancy
• Renal papillary necrosis
• Sarcoidosis
• Sickle cell anemia
• Gout.

Causes in infants and children:

• Furosemide therapy –most common cause in premature infants.
• it is used for Rx of heart failure or bronchopulmonary dysplasia.
• It causes hypercalciuria.
• Severe osteoporosis, steroid therapy, vitamin D excess also causes hypercalciuria.
• Idiopathic hypercalcemia.

Renal stone with posterior acoustic shadowing and associated with mild fluid collection

Staghorn calculus: The right kidney shows particularly large stones filling the collecting system in the upper and lower halves ie: the renal calyces

Renal Stone with Hydronephrosis –outlet obstruction

Small stone with twinkling artifact

Medullary Nephrocalcinosis

Renal Cortical Nephrocalcinosis – showing a thin band of echogenicity around the cortex

Anomalies of Structure and Function

Renal agenesis

• if bilateral => death
• usually unilateral but very rare,
• Large compensatory contralateral kidney,
• Often an elongated adrenal gland is visualized,
• May be assoc. with cystic seminal vesicles or unilateral seminal vesicle agenesis in male or uterine anomaly in female i.e. uterine didelphys or bicornuate uterus.
• Potters Syndrome: Bilateral agenesis of kidneys, non-visualization of urinary bladder, oligohydramnios and pulmonary hypoplasia.

Hypoplastic Kidney

• These are small, underdeveloped kidneys.
• Unilateral with compensatory hypertrophy of the opposite kidney.
• In ultrasound: the hypoplastic kidney appears small but otherwise normal kidney.
• D/D: atrophy from infarction or infection, small contracted CRF kidney

Duplicated Collecting System/Duplex Kidney/Bifid Kidney

• This is a very common renal anomaly with unilateral enlarged kidney, seen in 1% of population.
• In ultrasound:
• An enlarged kidney with a large cortical area between two separate renal sinuses & pelves.
• Two common types are seen:
• Incomplete duplication – most common and involves two complete separate renal pelves with fusion of ureters.
• So only one ureter inserts into the bladder.
• The insertion site into the bladder is normal.

• Complete duplication – consists of two separate renal pelves and two ureters.
• The upper moiety (portion) ureter will have an ectopic insertion into the bladder.
• 50% of this abnormal insertion is associated with an ectopic ureterocele with partial or total obstruction of the upper moiety and obstructive hydronephrosis.
• The lower moiety is associated with vesicoureteric reflux in majority of cases.
• Duplex kidneys may be associated with other anomalies.
• In males, agenesis or dysplastic kidney, agenesis of seminal vesicles or cysts in seminal vesicles.
• In females, uterine anomalies, duplication or atresia of the vagina.

Uncomplicated duplex kidney. There is a bridge of renal tissue separating the two renal hila.

Complicated Duplex Kidney with gross hydronephrosis of lower pole

Extrarenal Pelvis

• The renal pelvis is not within the renal sinus.
• Instead, it is located medially in the perinephric fat.
• Frequently may be associated with malrotated kidney.
• External pressure by lower surrounding tissue causes chronic dilatation of the pelvis.
• This should not be mistaken for hydronephrosis.

Malrotation of kidney

• Unusual axis of the kidney.
• can appear abnormal on an IVP.
• Frequently associated with extrarenal pelvis.

Extrarenal Pelvis of Left Kidney-A major portion of the renal pelvis lies outside the renal sinus

Malrotation of Right Kidney with large extrarenal pelvis

Persistent Fetal Lobation

• Normally fetal lobation disappears at birth or shortly after birth.
• Fetal lobation may persist after birth as an anatomic variant.
• In ultrasound: can be seen as prominent indentations on the surface of the kidneys with the reminder of the kidney appearing normal.

Junctional parenchymal defect

• Embryologically, each kidney is formed from upper and lower units of renal parenchyma that fuse along an oblique line.
• The junction points may persist as a prominent indentation of the cortical surface.
• In Ultrasound:
• The parenchymal defects is seen as a triangular echogenic focus best seen in sagittal scan.
• It commonly located anteriorly, at the junction of the upper and middle thirds of the kidney.
• The defect is more common in right kidney.

Junctional line/Inter Renicular Septum

• Junctional line is the site of fusion of two embryological renal units.
• More commonly seen in the right kidney.
• In ultrasound: In longitudinal scan, seen as an oblique echogenic linear band through the medial aspect of the kidney connecting the Junctional parenchymal defect to the renal hilum.

Junctional parenchymal defect (arrow) in the right upper pole (7-year-old child).

(A) Junctional parenchymal line (inter-renicular septum) in the right upper pole. This 6-month-old was investigated for urinary tract infection and had a normal Technetium-99m dimercaptosuccinic acid (Tc99m-DMSA) scan (B).

Fetal lobulation in a normal neonate

Junctional parenchymal defect

Dromedary Hump

• Both kidney, but more commonly the left kidney, may show a lateral bulge at its mid portion.
• The internal architecture of kidney is normal and this has no clinical significance.

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Hypertrophied Column of Bertin

• This is a common anatomic variant, can be mistaken as parenchymal solid mass.
• There is a double layer of renal cortex that is folded toward the center of the kidney, displacing a portion of the renal sinus.
• The echotexture is same as the adjacent renal cortex.
• Also known as hypertrophy of septal cortex or renal column hypertrophy.

Dromedary hump (arrow) on the lateral aspect of the left kidney in a 10-month-old.

Prominent column of Bertin in a 14-year-old (arrow) protruding towards the fat-containing renal sinus. The medullary pyramids are noticeably hypoechoic in this patient which is also normal

Renal Sinus Lipomatosis

• This is a heavy deposition of fat in the renal sinus.
• With advancing age, the renal parenchymal thickness decreases whereas the amount of renal fat increases, thus a larger highly echogenic sinus can bee seen.
• Can be mistaken as sinus neoplasm.

The renal sinus is echogenic, compatible with Renal Sinus Lipomatosis

The renal cortical parenchyma is atrophic, and the renal sinus is expanded and hyperechoic, which indicates RRSL. A large calculus is located in the pelviureteral junction

Ectopic Kidney

• An ectopic kidney is a kidney located outside the renal bed.
• An empty renal fossa aids in the Dx of ectopic kidney.
• The kidney can be located anywhere between the pelvis and upper abdomen.
• Most ectopic kidneys are located in the pelvis and known as pelvic kidney.
• Ectopic kidney receives their blood supply from regional vessels which are often common or internal iliac arteries.

• Ectopic kidney may be normal developmentally.
• However may be associated with dysplasia, duplication anomalies, short ureter, Ureteropelvic junction obstruction, vesico-ureteral reflux, and/or hydronephrosis.
• These kidneys are often small, malrotated. 50% of pelvic kidneys have decreased renal function.
• Associated anomalies, poor drainage and collecting system dilatation predisposes stone formation and infection.
• Ectopic kidney may be two types:
• 1. Congenital Ectopic Kidney: is due to failure of the kidney to ascend from its fetal location.
• 2. Ptosis of the kidney – is due to trauma which has torn the supporting attachments of the kidney and permitted the kidney to fall.
• In ultrasound: most ectopic kidney appears normal in an abnormal location. May be smaller in size.
• May be associated with vesico-ureteral reflux, and/or hydronephrosis, stone formation.

Right kidney just to the right of the uterus in the true pelvis. There was no kidney visualized in the right renal fossa

Sonography revealed an empty right renal fossa.

Right kidney was visualized in the pelvis more on the right side.

Crossed Renal Ectopia/Crossed Fused Kidney

• In this condition, both kidneys are found on the same side.
• In 85-90% of cases, the ectopic kidney will be fused to the other kidney.
• Usually the lower pole of the normally positioned kidney is fused to the upper pole of the ectopic kidney.
• The incidence is 1:1000 to 1:1500 at autopsy.
• The pelvis of the ectopic kidney is usually directed anteriorly and the ectopic ureter crosses the midline and inserts on the correct side of the bladder.

Sonographically

• Both kidneys are on the same side and are typically fused and unusually long.
• There is often a notch defect at the fusion point.
• There are two separate renal sinuses.
• The Ureteropelvic junctions are normal.
• The opposite kidney is absent.

Crossed Fused Kidney

Renal ultrasound showed a mass extending over the midline compatible with the diagnosis of a crossed fused ectopic left kidney.

Horseshoe kidney/Congenital fusion

• Most common renal fusion anomaly.
• Incidence rate is 1:400 at birth and more common in male.
• It occurs when metanephrogenic blastema fuse prior to ascent.
• 95% fusion is usually at the lower poles and the fused area is called the isthmus.
• Typically the isthmus is consists of functional renal tissue (parenchymal tissue).
• Rarely the isthmus may composed of a band of fibrous tissue connecting the lower poles.
• The horseshoe kidney sits anterior to the great vessel (aorta & IVC) and recieves blood supply from the aorta and regional vessels such as IMA, CIA, IIA and EIA.

• Hilus of each kidney looks forwards and the ureters always pass in front of the connecting piece.
• Abnormal position of the uretrs impairs drainage resulting higher incidence of infection, obstruction, stone formation.
• Horseshoe kidney may be associated with other congenital anomalies i.e., skeletal, CHD, CNS and anorectal malformation.
• Also associated with higher risk of renal tumors, i.e., wilms tumor, TCC.
• On Ultrasound:
• Horseshoe kidneys are usually lower in position than normal.
• Transverse scan of retroperitoneum shows the renal isthmus (comonly normal renal tissue or rarely fibrous tissue) crossing the midline anterior to the aorta and IVC.
• Hydronephrosis or stones are common.

D/D:

• Abdominal Aortic Aneurysm – presence of isthmus with internal collecting system (sinus) and horseshoe shape in transverse scan helps to differentiate.
• Lymphadenopathy/Lymphoma – further evidence of Paraaortic Lymphadenopathy and/or Splenomegaly.
• Retroperitoneal fibrosis.
• Bilateral Malrotation of kidneys -no isthmus will be seen.

Medullary Sponge Kidney (MSK)

• It is also called Renal Collecting Tubular Ectasia.
• MSK is the congenital defect with formation of microscopic cysts in the collecting tubules (thus 'sponge').
• The disease is present at birth but does not apparent until adulthood.
• Generally asymptomatic other than high risk of nephrolithiasis. And hematuria.
• May be normal on all other imaging.
• On ultrasound, there is increase intermedullary echogenicity which may surround the pyramids.
• This is suggestive of, but not specific to medullary sponge kidneys. In children, the sonogram is usually normal.

Medullary sponge kidney

Calyceal diverticulum

Calyceal diverticulum/Congenital megacalices

• Congenital megacalices are typically unilateral, non-obstructive cystic enlargement of the calices.
• It is usually non-progressive.
• Renal parenchymal or cortical thickness and renal functions are maintained.
• Infection and stone formation are increased.
• Commonly associated with primary megaureter.
• ultrasound: enlarged clubbed calices or a calyceal cyst is seen with normal cortical thickness .

Congenital Megaureter

• Megaureter is an anomaly where the distal ureter is abnormally dilated.
• It is an uncommon condition which is more common in males, may be bilateral, and is often associated with other congenital anomalies.
• The cause is thought to be aperistalsis of the distal ureter, leading to dilatation and functional ureteric obstruction and a tendency to infection.
• The ureteric orifice appears normal and a ureteric catheter passes easily.
• At ultrasound: Fusiform dilatation of the distal third of the ureter. Depending on severity, hydronephrosis may or may not be present.
• Calculi may form just proximal to the adynamic segment.

Congenital Megaureter

Bilateral Ureteroceles

UVJ Obstruction

Uretero-Pelvic Junction Obstruction (UPJ Obstruction)

• UPJ obstruction is common anomaly or ureter.
• Commonly occurs in male with a 2:1 male predominance.
• More commonly seen in the left kidney (Twice more common than right).
• 10 – 30 % can be bilateral.
• Most UPJ obstruction are thought to be functional.
• Rarely, intrinsic valve or luminal stenosis is the cause of obstruction.

At ultrasound:

• Hydronephrosis is present to the level of the UPJ.
• Marked ballooning of the renal pelvis is often seen with associated renal parenchymal atrophy.
• The caliber of the ureter remains normal.
• Associated renal anomaly can be seen with increased incidence of Multicystic dysplastic kidney and renal agenesis.

Uretero-Vesical junction obstruction (UVJ Obstruction)

• UVJ obstruction is located where the ureter meets the bladder.
• The obstruction impedes the flow of urine down to the bladder, causing the urine to back up in the ureters and kidney, creating dilation of the system (megaureter and hydronephrosis).
• Unilateral UVJ obstruction is the second most common prenatally detected obstructive disease, occurs during fetal development.
• Most of the time, the blockage is caused when the connection between the ureter and the bladder narrows.
• UVJ obstruction can also be due to scar tissue, infection, a benign polyp or kidney stones.
• Ultrasound may show a significant amount of dilation (megaureter and hydronephrosis.

Ureteroceles:

• An ureterocele is a cystic out-pouching of the distal ureter into the urinary bladder.
• It is resulting from a spectrum of abnormal embryogenesis associate with anomalous development from the intravesical ureter, the kidney, and the collecting system.
• Ureteroceles may be unilateral or bilateral.
• May be asymptomatic or may present with a wide range of clinical signs and symptoms, from recurrent cystitis, bladder outlet obstruction, hydronephrosis or renal failure.
• May be associated with a normal, well-functioning kidney to a nonfunctioning, dysplastic renal kidney.

Reno-vascular malformation/Aberrant Vessel

• The kidney derives its blood supply from higher levels of the aorta, as it ascends during its embryological development.
• Aberrant renal arteries will be present if the vascular supply from the lower level of aorta persists.
• Aberrant vessel may compress the ureter anywhere along their courses.

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