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Renal - Pathology





Evaluating a Renal Mass:

Is the mass

-small, med, large?

-well-defined/ ill-defined?

-USA- cystic, solid, complex?

  • Cystic
  • Solid
  • Complex

-Congenital or non-congenital?


Congenital Renal Cystic Disease:


Infant Polycystic Disease (IPKD)

-Rarer than adult

-Generally fatal



  • Hyperechoic
  • Bilateral  renomegaly
  • Cannot see cysts!!!


Adult Polycystic Disease (APKD)


-Presents later in life

-Hypertension/ renal failure


  • Bilateral enlarged kidneys
  • Multiple cysts, vary in size, bilateral
  • Cysts may bleed causing flank pain
  • Check liver & pancreas

Multicystic (MCDK)


-Usually uni lateral


-Lack of renal function of affected side


  • Multiple cysts, varying size
  • No normal renal parenchyma

Multicystic Dysplastic Kidney Disease:


Simple Cyst

-Solitary or multiple

-Corticle bulge through capsule

-May be multiloculated

-May cause obstruction


  • Simple cyst criteria

-Covers a wide range of disease processes

-May be

  • Typical
  • Complicated
  • Atypical


Renal Cystic Disease (non-congenital):


Simple Cyst

-Benign, asymptomatic

-May cause partial obstruction of collecting system

-Etiology unknown

-More common in older patients

-Can be found anywhere in kidney


  • Simple cyst criteria
  • Tadpole sign- narrow bands of posterior enhancement
  • May spread calyces apart & extend beyond outer border of capsule
  • Can become complicated


Para Pelvic Cyst

-AKA renal sinus cyst

-Found in hilum but does not communicate with the collecting system

-Can cause:

  • Pain
  • Hypertension
  • Obstruction


  • Well defined w/o septations
  • Can have irregular borders due to compression of adjacent structures


Medullary Sponge Kidney

-Cystic dilation of collecting tubules

-Affects medulla & papillary portions

-Usually bilateral

-Stone formation common

-Typically asymptomatic unless

  • Infection
  • Nephrolithiasis


  • Echogenic medullary pyramids
  • Shadowing if stones are present



-Dilation of collecting system

-Clinical Symptoms

  • Complaints vary
  • Ranges from severe colicky pain to vague flank discomfort- depends on degree of obstruction
  • Acute urinary retention
  • ↑BUN & Creatinine

-USA- 3 grades

  • Grade I –Mild
    • Splaying of calyceals
    • Do not confuse with peri pelvic cysts
  • Grade II-Moderate
    • Bear claw effect
    • Fluid extends into major & minor calyces
  • Grade III-Severe
    • Massive dilatation
    • Loss of renal parenchyma


-Miscellaneous patterns

  • Blown out sac
    • Long standing hydronephrosis
    • Dilated pelvis seen w/o calyces
  • Dumbbell – UPJ Obstruction
    • Extra renal pelvis larger than dilated infundibulum
  • Cauliflower
    • Less severe form of dilatation


Solid Renal Tumors:



-May appear anywhere

-Irregular  borders

-Internal echoes

-Attenuates sound






-Can have calcifications

-Alveolar type

  • Predispose to adenoca


Connective Tissue Tumors






Angiomyolipoma (AML)

-AKA Renal Hamartoma

-Fat, smooth muscle & blood vessels

-USA- round, hyperechoic mass



-Solid epithelial neoplasm, benign

-Difficult to diagnose- initially thought to be malignant

-Asymptomatic, sometime pain & hematuria


  • Non specific
  • Well defined, thin walled, homogeneous mass




Renal Adenocarcinoma, Hypernephroma, Renal Cell Carcinoma (RCC)

-In Cortex, Cortical cancer


-85% of all renal tumors

-More common in males (60-70 years-peak)


  • Solid parenchymal mass
  • Encapsulated
  • Firm, w/areas of hemorrhage & necrosis
  • May present as a cystic/complex mass


-Renal Cell Ca Staging

  • Stage I
    • Confined to kidney
  • Stage II
    • Spread to fat but within Gerota’s fascia
  • Stage III
    • Spread to renal vein, IVC and lymph nodes
  • Stage IV
    • Distant metastasis

-Clinical Symptoms

  • Microscopic or gross hematuria
  • Pain is uncommon
  • Fever
  • Palpable mass, flank area in later stages
  • Weight loss (sudden, unexplained)


Transitional Cell Ca

-In Renal Sinus


  • Mass in renal pelvis
  • Hypoechoic, low level echoes
  • Widening of central sinus



-Pediatric Carcinoma

-AKA Wilm’s Tumor

-Most common solid renal tumor in children

-90% occur before age 5

-50% occur before age 3

-May reoccur- follow up is a must

-Contains epithelial & connective tissue

-Clinical Symptoms

  • Palpable abdominal mass
  • General malaise, weakness, failure to thrive
  • May have pain
  • Advanced cases
    • Fever, weight loss, anemia, hypertenstion


  • Solid, complex mass w/ mixed echogenicity




Image of a renal abscess:

Renal Abscess

-AKA Renal Carbuncle

  • Abscess in the renal cortex
  • Usually resulting from union of smaller abscesses

-Perirenal abscess

  • Primary abscess
  • Surrounds kidney

-Results from

  • Straphylococcus infection
  • Complication of acute pyelonephritis

-Clinical Symptoms

  • Flank pain
  • Fever & chills
  • Increase leukocyte count


  • Irregular outlined cyst
  • Thickened walls
  • Debris may be present



-Inflammation of the renal collecting system and renal parenchyma

-Results from a bacterial infection

-Acute or chronic


  • Flank pain
  • Fever, chills, vomiting


  • May appear normal
  • Renomegaly
  • Decrease cortical USA


  • May have calculi
  • Increase echogenicity of cortex & medulla
  • Calyx clubbing
  • Distortion of borders


Xanthogranulomatous Pyelonephritis (XP)

-Long term debilitating disease

-Infectious renal inflammation

-Characterized by a mass in the parenchyma


-Non-functioning kidney


  • Moderately enlarged
  • Focal abscesses
  • May be difficult to distinguish from RCC
  • Calculi often present
  • Heterogeneous mass with through transmission
  • Hydro may accompany


Renal Failure:


  • Abrupt decrease in renal function
  • Retention of nitrogenous waste
  • USA
    • Normal or enlarged kidneys
    • Increased parenchymal echogenicity


  • End stage renal disease
  • Dialysis or transplant needed
  • Many causes
  • USA
    • Initially enlarged
    • Non existent over time
    • Increase echogenicity



-Renal stones

  • Cystine & uric acid stones may be dissolved chemically
  • Calcium stones are removed surgically- Staghorn calculi (2-3cm)


  • Echogenic
  • Will produce a posterior acoustic shadow if large enough

 Image showing Nephrolithiasis:


Congenital Anomalies:




  • Unilateral – 1 kidney & ureter
  • Bilateral – Potter’s Syndrome (fatal)


  • Complete duplication of kidney & ureter


  • Single functioning kidney
  • Other non- functioning (atrophied)



-Renal hypoplasia

  • Small underdeveloped kidneys
  • Renal insufficiency
  • Can be uni or bilateral

-Renal dysplasia

  • Small malformed kidneys
  • Little or no function

-Renal Ectopia

  • If during the course of development the kidney(s) fail to ascend to usual site, 3 possible anomalies can be found
    • Pelvic Kidney
      • Only reaches pelvic in its ascension
      • Anterior to sacrum
    • Crossed Renal Ectopia
      • Both kidneys fused together on one side
    • Horseshoe Kidney
      • Kidneys fused
      • Lie close to spine w/ inferior poles lying medial rather than lateral to upper pole
      • Isthmus- anterior to Aorta & IVC

Horseshoe Kidney:

-Renal Lobulation

  • Present in children till age 4 or 5
  • May be a normal variant in adults

-Bifid Renal Pelvis

  • Rarely produces symptoms
  • May become stenotic w/ obstruction