The renal arterial resistive index (RI) is a sonographic index of intrarenal arteries defined as (peak systolic velocity - end-diastolic velocity) / peak systolic velocity. The normal range is 0.50-0.70. Elevated values are associated with poorer prognosis in various renal disorders and renal tr...
Renal arteriovenous fistulae (AVFs) are anomalous direct communications between arteries and veins in the kidney, which may be confused with a renal arteriovenous malformation (rAVM).
The incidence of renal AVF is variable, estimated at 0.3-19% in native kidneys and 6-8% in re...
Renal arteriovenous malformations (renal AVMs) are an uncommon vascular anomaly, which may be confused with a renal arteriovenous fistula (renal AVF).
Like arteriovenous malformations elsewhere in the body, a renal AVM is formed by a connection between the arterial and venous structu...
The renal arteries originate from the abdominal aorta and enter the renal hila to supply the kidneys. Any variant in arterial supply is important to clinicians undertaking surgery or other interventional renal procedures.
They arise from the abdominal aorta at the L1-2 v...
Renal artery aneurysms (RAA) are considered the second most common visceral aneurysm (15-22%), most common being splenic artery aneurysm (60%).
RAAs occur in ~0.1% of the population 6,8. They are more common in females 6 with a median age of diagnosis of 50 years 8.
Renal artery dissection may occur as a result of the following processes 1:
aortic dissection extending to involve the renal artery
iatrogenic (e.g. catheterization)
connective tissue diseases (e.g. Marfan syndrome)
Renal artery occlusion can happen acutely due to in-situ thrombus, embolism, or dissection. Unless immediately treated, it can lead to renal infarction 1.
The condition is more common in the elderly, however, it may be seen in a younger age group if they have risk factors (describ...
Renal artery pseudoaneurysms are uncommon vascular finding, with the majority occuring after a renal intervention.
A renal artery pseudoaneurysm differs from a renal artery true aneurysm (as might occur in fibromuscular dysplasia) in that it does not involve all three layers of the a...
Renal artery stenosis (RAS) (plural: stenoses) refers to a narrowing of a renal artery. When the process occurs slowly, it leads to secondary hypertension. Acute renal artery stenosis does not lead to hypersecretion of renin.
When the stenosis occurs slowly, collateral vessels form a...
Renal cell carcinomas (RCC) (historically also known as hypernephroma or Grawitz tumor) are primary malignant adenocarcinomas derived from the renal tubular epithelium and are the most common malignant renal tumor. They usually occur in 50-70-year old patients and macroscopic hematuria occurs in...
Renal cell carcinoma staging using the TNM staging system for renal cell carcinoma. Older but still widely used system in some practices is the Robson staging system.
TNM staging (7th edition)
T1a: tumor confined to kidney, <4 cm
T1b: tumor confined to kidney, >4 cm but <7 cm
Renal colic (also known as ureteric colic) refers to a pattern of abdominal pain most commonly caused by ureteric calculi. The pain (usually unilateral) is felt in the loin radiating down to the groin and is typically colicky (i.e. coming in waves) corresponding to peristalsis or spasm of the ur...
Renal coloboma syndrome (also known as papillorenal syndrome) is a rare condition that primarily affects kidney and eye development.
Affected individuals typically have hypoplastic kidneys, which can lead to end-stage renal disease. Approximately 10% of children with hypodysplastic kidneys have...
Renal cortical defects have a variety of causes, and present on imaging as an area of focal cortical thinning or absence of renal cortex, sometimes accompanied by focal caliectasis.
The differential diagnosis for a renal cortical defect includes 1,2:
Renal cortical necrosis occurs as a result of severe systemic illness in a variety of settings and can result in permanent renal impairment.
severe hemodynamic shock
traumatic blood loss
Renal cyst is a generic term commonly used in description of any predominantly cystic renal lesion. The majority of parenchymal cystic lesions represent benign epithelial cysts; however, malignancy such as renal cell carcinoma may also present as a cystic lesion 8.
Renal cysts are usually evalu...
Renal cysts and diabetes syndrome (RCAD), also known as maturity-onset diabetes of the young, type 5 (MODY5), refers to the combination of renal cortical cysts and diabetes mellitus in patients with mutations in the HNF1B gene. When renal cysts are associated with these mutations without disturb...
Renal dysgenesis is a very broad term which can include any form underdevelopment of the kidneys. The spectrum includes:
renal agenesis: complete lack of formation
renal hypoplasia: partial lack of formation
Some authors also classify any form of renal maldevelopment affecting size, shape of ...
Renal emphysema, or intrarenal gas, refers to the presence of gas within the kidney, with or without extension to the urinary tract.It is a rare finding and only a few differentials need to be considered 1:
emphysematous pyelonephritis 1
Renal epithelial cysts, also known as simple renal cysts, are common benign lesions of the renal parenchyma. Since they are uncommon in children and progressively more common with age, they are considered acquired lesions.
overall high prevalence
increasingly common with age 1,2
Renal forniceal or calyceal rupture is the radiographic finding of a perirenal urine leak as a result of ureteric obstruction.
The renal fornices are the thin pointed projections, arising from the lateral aspects of each minor calyx, and extending a short distance into the renal column...
Renal hemosiderosis results from accumulation of hemosiderin in the kidneys. It is usually considered a benign and incidental radiologic finding and rarely results in clinically apparent renal dysfunction.
Renal hemosiderosis is a known complication of the following conditions:
A renal hilar lip is a developmental anomaly of the kidney. It is an infolding of the cortex at the level of the renal sinus and in this region the renal cortex appears thicker.
On imaging it appears as supra- or infra-hilar cortical bulges. At certain levels of cross-se...
Renal hydatid infection is a very rare manifestation of hydatid disease.
For a general discussion, and for links to other system specific manifestations, please refer to the article on hydatid disease.
Renal hydatid infection is seen in less than 5% of patients with hydatid dise...
Renal hypoplasia refers to a congenitally small kidney where there is essentially normal residual parenchyma but smaller calyces, lobules and papillae. This is in contrast to renal atrophy where renal development was initially normal but the kidney has become smaller secondary to various other p...
Renal infarction results from interruption of the normal blood supply to part of, or to the whole kidney. The main imaging differential diagnosis includes pyelonephritis and renal tumors.
The demographics of affected patients will depend on the underlying cause, although as most c...
Renal intraparenchymal acceleration time is a parameter used in assessing renal arterial stenosis on Doppler ultrasound. It is the time taken from the start of systole to peak systole.
normal range: a value of usually < 0.07 seconds is taken as being within normal limits 1.
Renal lymphangiomas, also known as renal lymphangiectasia, are a rare disorder, where there is dilatation of perirenal, parapelvic, and intrarenal lymphatics. The diagnosis can be suggested by imaging, and aspiration of chylous fluid is usually confirmatory.
For a broader discussion, please re...
Renal lymphoma is usually a part component of multi-systemic lymphoma. Primary renal lymphoma, which is defined as lymphoma involving the kidney exclusively without any manifestation of extra-renal lymphatic disease 3-5. Typical imaging findings are multiple bilateral hypodense or infiltrative r...
A renal mass can be broadly divided into two broad categories:
Renal medullary carcinoma is a rare and highly aggressive variant of renal cell cancer centered in the renal medulla.
Renal medullary carcinoma occurs almost exclusively in adolescent and young adult blacks with sickle cell trait or hemoglobin SC disease but not with homozygous h...
Renal milk of calcium cysts refer to the appearance of a calcium precipitate found either within a calyceal diverticulum, that has lost communication with the collecting system, or within a simple renal cyst.
Renal milk of calcium cysts are typically asymptomatic.
The RENAL nephrometry scoring system was developed to categorize renal masses into low, intermediate and high complexity, based on cross-sectional imaging findings. Its purpose is to aid in decision making, patient counseling, surgical planning, and patient follow-up, as well as academic reporti...
Renal oncocytomas are relatively benign renal tumors. The main clinical importance of this lesion is the difficulty in pre-operatively distinguishing it from renal cell carcinomas, as epidemiology, presentation, imaging and even histology can be very similar.
Renal oncocytomas ac...
Renal oncocytosis, also known as renal oncocytomatosis, is the presence of many concurrent renal oncocytomas with or without renal cell carcinomas. Typically a dominant larger tumor is present, with bilateral innumerable smaller tumors. Sometimes renal failure may develop 1.
Renal osteodystrophy (ROD), also known as uremic osteopathy, is a constellation of musculoskeletal abnormalities that occur in patients with chronic renal failure, due to concurrent and superimposed:
osteomalacia (adults)/rickets (children)
secondary hyperparathyroidism: abnormal calcium and p...
Papillary adenomas of the kidney are benign renal neoplasms arising from the renal tubular epithelium and almost always located within the cortex. They fall under the general category of renal adenomas, and are considered one of the commonest of renal epithelial neoplasms.
Renal papillary necrosis refers to ischemic necrosis of the renal papillae. Necrosis also occurs in the medullary pyramids.
Patients can present with both acute episodes or chronic renal papillary necrosis. Calyceal or ureteral obstruction by sloughed papillae manifests w...
Mnemonics for the causes of renal papillary necrosis are plentiful and include:
AD SPORT C: a list of causes in decreasing order of incidence
Most common causes:
N: non-steroidal anti-inflammatory drugs (NSAIDs)
S: sickle cell disease
The renal pelvis (or, more rarely, the renal infundibulum) forms part of the pelvicalyceal system of the kidney and is the connection between the calyces and the ureter.
The renal pelvis is triangular in shape, lies posteriorly in the renal hilum surrounded by fat and vessels and...
A renal pseudotumor is a mass that will simulate a tumor on imaging but is composed of non-neoplastic tissue. There are many examples 1:
prominent column of Bertin
persistent fetal lobulation
cross-fused renal ectopia
renal hilar lip
Renal replacement lipomatosis is a rare condition characterized by fatty tissue proliferation in the renal sinus and perinephric space with marked destruction/atrophy of renal parenchyma (due to chronic inflammation).
Patients usually present with non-specific complaints ...
Renal replacement therapy (RRT) (also called renal dialysis or just dialysis) is used to supplement renal function in patients with either end-stage chronic kidney disease or medically-refractory acute renal impairment.
Haemodialysis refers to the diffusion of solutes in solution across...
The renal sinus is a fat-filled compartment of the kidney.
The renal sinus is a fatty compartment located within the medial aspect of the kidney. It communicates with the perinephric space. It contains the renal hilum and is bordered by renal parenchyma laterally.
Renal sinus cysts are simple renal cysts that lie within the renal sinus.
It is worth noting that some authors 5,6 use the term renal lymphangiectasia interchangeably. It is likely that true renal lymphangiectasia is a separate and rare disorder, and is thus discussed separately.
Renal sinus lipomatosis refers to a condition where there is excessive renal sinus fat replacement.
It results from renal parenchymal atrophy, inflammation, calculous disease, aging, or exogenous or endogenous steroids.
There is usually no or rarely little mass effect on the collect...
Renal sympathetic denervation (RSDN), also known as renal denervation, is an interventional procedure that uses radiofrequency ablation to destroy the nerve endings in the wall of the renal arteries. Endovascular (trans-catheter) techniques are an alternative to surgical sympathectomy.
This is a basic article for medical students and other non-radiologists
Renal tract calculi, also known as urolithiasis, refer to renal stone formation at any point along the renal tract (from kidneys to bladder and urethra).
This is a summary article; read more in our artic...
Renal transplantation is one, if not the most, common transplant procedures undertaken worldwide. Consequently, purposeful and incidental imaging of renal transplants and renal transplant-related complications are increasingly common. These include acute renal transplant rejection and chronic re...
Renal transplant rejection is one of the feared complications of renal transplantation.
In terms of onset, this can be broadly divided into two groups:
acute renal transplant rejection
chronic renal transplant rejection: usually after one-year post-transplantation (at least after 3 months)
The recipients of renal transplants are susceptible to a number of complications. Incidence of each is variable and partially subject to specific surgical transplantation techniques and management patterns.
Renal transplant complications
These can be broadly categorized as perirena...
Renal transplant torsion is a very rare complication of renal transplant, occurring mostly in intraperitoneal transplants because of the increased mobility compared to extraperitoneal transplants, which are less mobile.
Non-specific clinical symptoms such as nausea, abdo...
The central approach of renal transplant ultrasound is to evaluate for possibly treatable surgical or medical complications arising in the transplanted kidney.
Institutions vary in the exact schedule of renal transplant ultrasound assessment, but it is common to obtain an initial ultrasound 24-...
Renal trauma can result from direct, blunt, penetrating, and iatrogenic injury.
Renal injuries account for ~10% of abdominal trauma, and thus the demographic of affected individuals reflect that population. The incidence of renal injuries increases in pre-existing congenital or ac...
Renal tuberculosis, a subset of genitourinary tuberculosis, accounts for 15-20% of extra-pulmonary tuberculosis and can result in varied and striking radiographic appearances.
Tuberculosis can involve both the renal parenchyma and the collecting system (calyces, renal pelvis, ureter, bladder a...
Renal tubular acidosis (RTA) refers to defects in the renal tubular transport of hydrogen ions, bicarbonate ions, or both, in the kidneys resulting in a normal anion gap metabolic acidosis.
The exact prevalence of renal tubular acidosis is unknown but the entity is probably u...
Renal tubular ectasia is an incidental finding that is seen more commonly on intravenous pyelography (IVP), but which can also occasionally be seen on CT urography (CTU).
Renal tubular ectasia is also known as benign renal tubular ectasia. The term "benign" was used to differentiat...
Renal tumors (for the purposes of this article taken to broadly mean neoplastic lesions) should be distinguished from renal pseudotumors.
Whilst renal tumors can be broadly divided into primary and secondary (metastatic), benign and malignant, or adult and pediatric tumors, they are more formal...
Renal vascular pedicle injury is a severe form of renal trauma, which if not recognized and treated expediently with lead to the loss of the kidney.
Contrast enhanced CT is the Imaging modality of choice. On CT it is recognized as a non-enhaning kidney. Perirenal he...
The renal veins are asymmetric paired veins that drain the kidneys.
The renal vein is formed by the union of two-to-three renal parenchymal veins in the renal sinus. It emerges from the renal hilum anterior to the renal artery and drains into the inferior vena cava at th...
There are several variations in renal venous anatomy. Some of these are specific to the left renal vein.
Left renal vein anomalies are generally classified into four types 2:
the ventral preaortic limb of the left renal vein is obliterated, but the dorsal retroaortic limb persists and...
Renal vein thrombosis (plural: renal vein thromboses) can be either from "bland" thrombus or tumor thrombus (extension of tumor into the vein). There are numerous etiologies for bland thrombus, but it most commonly occurs in the hypercoagulable nephrotic syndrome. Renal vein thrombus is commoner...
Renal vein varices develop for various reasons and are usually asymptomatic.
Renal vein varices are usually asymptomatic. Some patients may present with flank pain and/or hematuria.
chronic renal vein thrombosis
Renovascular hypertension (RVH) is a type of secondary hypertension, where high blood pressure develops secondary to renal artery disease.
Approximately 2.5% (range 0.5-5%) of hypertensive patients will have RVH as a cause 2,3.
There are a number of conditi...
Retroaortic left renal vein (RLRV) is a normal anatomical variant where the left renal vein is located between the aorta and the vertebra and drains into the inferior vena cava.
Its recognition is important in order to avoid complications during retroperitoneal surgery or interventional procedu...
Retrograde pyelography (also known as retrograde pyeloureterography) is a method of imaging the upper urinary collecting system. After IVU and CTU were developed, it has been rarely performed as a primary study, but it still has a few potential indications as a secondary study.
Retroperitoneal fibrosis (RPF), is a condition that has previously been described as chronic periaortitis. It is an uncommon fibrotic reaction in the retroperitoneum that typically presents with ureteric obstruction.
The disease is part of a spectrum of entities that have a common pathogenic pr...
Retroperitoneal hemorrhage can be a source of significant yet occult blood loss.
Some articles conflate and/or confuse retroperitoneal hemorrhage and Wunderlich syndrome 5. However Wunderlich syndrome refers primarily to bleeding around the kidney, not the retroperitoneum in genera...
The retropubic space (also known as the prevesical space, cave of Retzius or cavum Retzii) is an extraperitoneal space located posterior to the pubic symphysis and anterior to the urinary bladder. It is separated from the anterior abdominal wall by the transversalis fascia and extends to the lev...
The reverse rim sign describes relative hypoenhancement of the renal cortex and normal enhancement of the renal medulla on contrast-enhanced CT and MRI. This enhancement pattern can also be visualized using CEUS 2.
It is a typical finding of renal cortical necrosis that may occur in the setting...
Rhabdoid tumor of the kidney is a rare, highly aggressive malignancy of early childhood, closely related to atypical teratoid/rhabdoid tumors (AT/RT) of the brain (see rhabdoid tumors).
Rhabdoid tumors occur exclusively in children, with 60% occurring before the age of 1 year of a...
Rhabdomyosarcomas of the genitourinary tract are uncommon tumors occurring in pelvic organs. It is a disease nearly exclusive to the pediatric population.
For a general discussion of this type of tumor, please refer to the article on rhabdomyosarcomas.
The peak incidence of tum...
Right iliac fossa mass is a common clinical presentation and has a range of differentials that need to be excluded. Radiology plays an important role in this differentiation.
The rim sign can be seen in association with chronic hydronephrosis.
In patients with chronic hydronephrosis, in all forms of contrast-enhanced imaging of the obstructed kidney, enhancement may occur in the residual, but markedly atrophic, renal parenchyma, surrounding the dilated calyces and ...
Risk factors for testicular germ cell tumors (GCT) include:
Caucasians at higher risk than African Americans (9:1)
10-40x increased risk
around 10% of all tumors are associated with undescended testis
higher risk if intra-abdominal testis compared with intra-inguinal
Robson staging of renal cell carcinoma (RCC) is simple but has largely been replaced by the TNM system (see renal cell cancer staging article). Robson staging revolves around the relationship to Gerota's fascia, involvement of renal vein and regional nodes.
stage I: limited to kidney
Wilms tumor classically follows a "rule of 10s" 1,2:
up to 10% may have unfavorable histology
10% are bilateral
10% have vascular invasion
10% have calcifications on CT
10% have pulmonary metastases at presentation
Sacral nerve stimulators are a form of neuromodulation therapy. They are used for urogenital disorders such as urge urinary incontinence and detrusor hyperactivity, and colorectal disorders such as chronic constipation refractory to conventional medical therapy, and fecal incontinence. There is ...
The saddlebag bladder sign refers to the appearance caused on axial pelvic MR images by posterior drooping of the posterolateral wall(s) of the urinary bladder, due to loss of integrity of the lateral level 2 endopelvic fascia. If combined with a defect of the puborectalis muscle on the ipsilate...
The salt and pepper sign is used to refer to a speckled appearance of tissue. It is used in many instances, but most commonly on MRI. NB: pathologists also use the term.
Used to describe some highly vascular tumors which contain foci of hemorrhage, typic...
Sarcoidosis is a systemic inflammatory disease of unknown origin characterized by the formation of non-caseating granulomas. Virtually any organ system may be involved. Although less common than pulmonary and mediastinal disease, abdominal sarcoidosis can mimic more common infectious or neoplast...
Sarcomatoid carcinoma of the prostate is a rare malignant prostatic tumor variant usually composed of both malignant glandular cells and spindle cells.
Sarcomatoid carcinoma of the prostate is also known as carcinosarcoma, metaplastic carcinoma or spindle cell carcinoma of the pros...
Sarcomatoid renal cell carcinomas (sRCC) may develop when one of the more common histologic subtypes of renal cell carcinoma degenerates into a sarcoma.
On imaging, they are generally large masses, with irregular contours, and malignant-appearing, but do not have specific imaging features.
Schiller-Duval body is a perivascular structure that can be found in 50% of testicular yolk sac tumors also known as endodermal sinus tumors. If present it is considered pathognomonic.
A central vessel is surrounded by tumor cells, and the cell-vessel complex is contained in a cysti...
Schistosomiasis (also referred to as bilharzia or snail fever) is the result of infection by blood fluke (trematode worm) of the Schistosoma species.
Schistosomiasis is very common, affecting over 200 million people, with the vast majority (85%) in Africa. It is prevalent in tropi...
Bladder schistosomiasis, also known as bilharzia of the bladder, is an infection by the Schistosoma flukeworm and is a major health problem in developing parts of the world predisposing individuals to bladder squamous cell carcinoma.
Schistosomiasis is very common, affecting over ...
Sciatic hernias (alternative plural: herniae) are a rare type of pelvic floor hernia, which occur through either the greater or lesser sciatic foramina. The hernias can contain variable structures.
curlicue ureter sign
Scleroderma, also known as systemic sclerosis, is an autoimmune connective tissue disorder characterized by multisystem fibrosis and soft tissue calcification. As such, it affects many separate organ systems, which are discussed separately:
musculoskeletal manifestations of scleroderma
Renal manifestations of scleroderma are common, affecting up to 25% of patients. Some patients (5-10%) can present with a scleroderma renal crisis (SRC). These patients have an abrupt onset of hypertension and acute renal failure 4.
For a general discussion of scleroderma, please refer to the ...
Scrotal cystoceles are a type of urinary bladder hernia, where the bladder herniates into the scrotum.
Scrotal sac will contain fluid. Emptying of a scrotal cystocele with voiding is an i...
Scrotal filariasis is a manifestation of filariasis and refers to scrotal involvement from parasitic nematodes of the superfamily Filarioidea.
Known disease of the tropics and subtropics and a cause of morbidity in Asia, Africa and the Western Pacific regions 2.
Scrotal hematoceles are collections of blood within the scrotal sac, but outside of the testis.
A hematocele normally results from trauma to the scrotum, or on occasion following surgery. Some think that a varicocele is a risk factor for developing a hematocele 4.
The scrotum and its content are subject to a number of infective processes including: