kidney pathlo

Simple Renal Cyst

The most common type of renal cyst, occurring in 50% of people over age 50, originating from obstructed uriniferous tubules. Sonographically, they show acoustic enhancement, absence of internal echoes, a sharply defined thin wall, and a round or oval shape. Cortical or parenchymal cysts are located in the periphery, while peripelvic cysts are in the center (renal sinus) of the kidney.

Pyelogenic Cyst

A type of renal cyst that represents a calyceal diverticula and sonographically appears as a simple cyst.

Parapelvic Cyst

Cortical cysts that bulge into the central sinus of the kidney.

Peripelvic Cyst

Lymphatic cysts located in the central sinus of the kidney.

Complex Cysts

Cysts that may contain hemorrhagic components, with a prevalence of 6% among simple renal cysts. The reported incidence of neoplasm in these lesions approaches 30%. Lesions not meeting classical criteria for a simple cyst should be investigated.

Hemorrhagic Cysts

A type of complex cyst appearing hyperdense on CT due to the presence of blood, which increases attenuation. Warrants investigation if criteria for a simple cyst are not met.

Atypical Renal Cysts

Cysts with characteristics like multiple thick septations, irregular walls, or a solid component, which may suggest a malignant cystic lesion and require histological confirmation (fine needle aspiration) for definitive diagnosis.

Milk of Calcium (MOC)

Represents small calcium carbonate crystals (or other substances) that may move within the cystic mass when the patient changes position. MOC is usually asymptomatic and requires no treatment.

Tuberous Sclerosis

A multi-system genetic disease classically presenting with seizures, mental retardation, and facial angiofibromas. The kidneys are a main focus of abdominal sonographic evaluation due to an increased incidence of renal cysts and bilateral angiomyolipomas.

Von Hippel-Lindau Disease

An autosomal dominant disorder presenting in the 3rd-5th decade, characterized by retinal and central nervous system hemangioblastomas. Tumors are often bilateral and multifocal, with concurrent findings including renal cell carcinomas, pheochromocytomas, islet cell tumors, and renal/pancreatic cysts.

Angiomyolipoma

A hyperechoic benign renal tumor with echogenicity greater than or equal to that of the renal sinus. A propagation speed artifact may result in posterior displacement of structures. CT confirmation of fat is considered diagnostic, and 80% involve the right kidney.

Renal Cell Carcinoma (RCC)

Also known as hypernephroma or adenocarcinoma, it is the most common malignant tumor of the kidney (80%-90% of adult renal malignancies). Occurs most often after age 50 (2:1 male to female ratio). Classic symptoms include costovertebral angle pain, a palpable mass, and hematuria (present in only 15% of patients). Sonographically, it is hypoechoic relative to normal adjacent renal parenchyma, and tumor extension into renal veins and IVC is common. Lungs are the most common site of distant metastases.

Renal Metastases

Secondary tumors in the renal parenchyma metastasized from primary organs (lung, breast, colon) or from malignant cells like leukemia and lymphoma. Sonographically presents as hypoechoic masses or a diffusely enlarged inhomogeneous kidney.

Wilm’s Tumor (Nephroblastoma)

The most common childhood renal tumor (mean age at diagnosis 3-4 years). Patients typically present with a large asymptomatic flank mass. Other symptoms include hypertension, fever, and hematuria. Metastasis can be seen to lungs, liver, bone, lymph nodes, and retroperitoneum. Has a 90% survival rate. Wilm's tumors destroy the renal contour, distinguishing them from adrenal neuroblastomas.

Hydronephrosis

Dilation of the renal pelvis and calyces, producing a separation of the normal sinus echogenicity by an anechoic urine collection. Occurs in 65%-85% of pregnancies (right side). If untreated, it can lead to hypertension, loss of renal function, and sepsis. Common causes include calculi, benign prostatic hypertrophy, prostate cancer, pelvic malignancies, pregnancy, and ureteropelvic junction obstruction.

Nephrolithiasis (Urolithiasis)

Development of stones/calculi anywhere in the urinary system (urolithiasis), most commonly in the kidney (nephrolithiasis). Prevalence is 0.1%-5% in industrial countries, more common in White men aged 20-50 years. Over 80% contain some form of calcium. Ureteral stones are more difficult to visualize sonographically.

Nephrocalcinosis

Renal parenchymal calcium deposition, predominantly cortical or medullary, or involving both regions, distinguishing it from nephrolithiasis (stones in the collecting system). Causes of medullary nephrocalcinosis include hyperparathyroidism, renal tubular acidosis type I, and medullary sponge kidney. Cortical nephrocalcinosis is associated with chronic glomerulonephritis, renal cortical necrosis, and chronic transplant kidney rejection. Sonographically, it may be difficult to differentiate from large renal calculi or air.

Medullary Sponge Kidney

A condition where tiny bright dots are noted in the renal pyramids, representing small calculi.

Acute Pyelonephritis (APN)

A tubulointerstitial inflammation of the kidney involving both the renal pelvis and parenchyma, usually due to an ascending bacterial infection (often E. coli) from the bladder. Most common in women aged 15-35 years. Sonographic findings can be variable, including unilateral/bilateral involvement, focal/diffuse swelling, renal enlargement, or absence of sinus echoes, but ultrasound may be normal.

Emphysematous Pyelonephritis

A life-threatening bacterial infection associated with renal ischemia, with a mortality rate as high as 30%-40%. More common in diabetics (87%-97% of patients), immunosuppressed patients, and those with urinary tract obstructions, most commonly caused by E. coli infection. Nephrectomy is usually required.

Chronic Pyelonephritis (CPN)

Renal injury induced by recurrent renal infection leading to pathologic involvement of calyces and pelvis, resulting in kidney scarring and parenchymal atrophy. A significant cause of renal failure (responsible for 25% of renal insufficiency/end-stage renal disease cases). Sonographically appears as a small hyperechoic kidney with cortical thinning.

Xanthogranulomatous Pyelonephritis (XGPN)

A rare type of CPN resulting from chronic infections due to long-term obstruction, generally from a staghorn calculus. Characterized by replacement of normal renal parenchyma with lipid-laden macrophages, plasma cells, and multinucleated giant cells. Patients typically present with renal calculi (usually staghorn), renal enlargement, and lack of renal function.

Pyonephrosis (Pyohydronephrosis)

Purulent material (pus) in the collecting system of the kidney associated with an infection secondary to renal obstruction. Percutaneous or surgical drainage is required for adequate treatment. Sonographic findings are variable depending on the stage and duration of inflammation.

Renal Fungal Infections

Most commonly Candidiasis, resulting from hematogenous seeding or ascending from the bladder. Sonographic findings are hyperechoic, nonshadowing masses. Individuals at risk include premature infants with long-term catheters, adults with diabetes, cancer (leukemia/lymphoma), indwelling foreign bodies, chronic illness, IV drug abuse, prolonged antibiotic/corticosteroid/immunosuppressive therapy, and immunocompromised patients (e.g., AIDS).

Acute Renal Failure (ARF)

An abrupt decrease in renal filtration marked by an increase in serum creatinine or blood urea nitrogen (azotemia). The three main mechanisms are Prerenal (hypotension, volume depletion), Intrinsic (Acute Tubular Necrosis, glomerular diseases), and Postrenal (bilateral renal obstruction). Ultrasound determines hydronephrosis (postrenal) or abnormal resistive index (suggests intrinsic failure).

Acute Tubular Necrosis (ATN)

The most common intrinsic (intrarenal) cause of acute renal failure, resulting from prolonged ischemia or nephrotoxins (drugs, contrast agents) causing damage to the tubular epithelium. The renal insufficiency can be reversible. Sonographic findings include renal enlargement and increased resistive index (RI).

Chronic Kidney Disease (CKD)

An irreversible loss of kidney function, affecting nephrons and causing decreased GFR, tubular function, and reabsorption. The two main causes are diabetes and hypertension. Sonographic findings include echogenic, diminished kidney size (<9 ext{ cm}), cortical thinning, and poor visualization of renal sinus and pyramid.

Papillary Necrosis

Ischemia of the medullary pyramids. Clinical diagnosis can be made by identifying sloughed papilla in the urine, which can cause pain and ureteric obstruction. Associated conditions include analgesic abuse (most common), diabetes mellitus, urinary tract obstruction/infections, renal vein thrombosis, sickle cell disease, and chronic heart failure. Sonographically, echogenic material within the collecting system or triangular cystic collections representing the absence of medullary pyramids may be seen.

Renal Vein Thrombosis

A condition associated with extrinsic compression, nephrotic syndrome (most common), renal tumors, renal transplants, or trauma. Sonographic findings include a dilated thrombosed renal vein, absent intrarenal venous flow, an enlarged hypoechoic kidney, and a high-resistance renal artery waveform (increased RI) due to urinary retention/low urine output.

Renal Artery Thrombosis

A sudden cause of prerenal failure presenting as acute flank pain, hematuria, and a sudden rise in blood pressure. Sonographic findings include focal hypoechoic areas of infarct, absence of intrarenal