Metanephric blastema (or metanephrogenic blastema) is one of the two embryological structure that gives rise to the kidney, the other one being the ureteric bud.
Persistent metanephric blastemas after 36 weeks of gestational age are called nephrogenic rests. They are associat...
Metaplasia is a general pathology term that refers to process when one cell type is replaced by another. It usually occurs in the context of a changed cellular environment to which the new cell type is better adapted 1. Examples include 2-5:
Barrett esophagus: normal squamous epithelium replace...
Metastases to testis are a very rare cause of a testicular mass and may be bilateral in up to 15% of patients.
Metastases to the testes are apparent in ~0.04% of autopsy studies in patients with known malignancy. The average age is 57 years, much older than the primary age for pr...
Microlithiasis (rare plural: microlithiases) merely means very small stones and may refer to:
The middle adrenal (suprarenal) artery is one of the three adrenal arteries that supply the adrenal gland.
The middle suprarenal arteries arise from the aorta on each side between the inferior phrenic artery and the renal artery. They run laterally across the diaphragmati...
Milk-alkali syndrome is the combination of:
It is due to a large amount of calcium and alkali being ingested (e.g. milk and antacids for peptic ulcer disease treatment or calcium carbonate for osteoporosis). It is a cause of medullary nephrocal...
The term milk of calcium (MOC) is given to dependent, sedimented calcification within a cystic structure or hollow organ. This sort of colloidal calcium suspension layering can occur in various regions:
renal: milk of calcium in renal cyst (most common)
ureter: milk of calcium in the ureter 7
Mixed gonadal dysgenesis (MGD) is a type of gonadal dysgenesis characterized by gonadal asymmetry, and/or sex chromosomal mosaicism, as well as retained Müllerian ducts.
Depending on the chromosomal composition, patients may have testes and/or streak gonads.
Mixed epithelial and stromal tumors (MEST) are a family of uncommon renal neoplasms in adults in a spectrum ranging from predominantly cystic (adult cystic nephroma) to more solid tumors.
There is a female preponderance 10:1 1 with tumors occurring predominantly in middle-aged pe...
The abdominal molar tooth sign refers to the appearance of contrast media which has spilled out of the urinary bladder on CT cystography after extraperitoneal bladder rupture.
Contrast flows out of the ruptured bladder, occupying the preperitoneal cavum Retzii and surrounds the bladder in the s...
The molar tooth sign may refer to:
molar tooth sign (CNS)
molar tooth sign (abdomen)
Mondor disease is a rare benign breast condition characterized by thrombophlebitis of the subcutaneous veins of the breast and anterior chest wall. It can also occur in the dorsal veins of the penis.
Although Mondor disease is rarely reported in the literature, this is likely in p...
The mons pubis (plural: montes pubis) refers to the rounded protuberant skin-covered soft tissue overlying the symphysis pubis (in both sexes). It is most prominent in adult females.
In females it forms the most superior part of the vulva and it is also called the mons Veneris (plural: montes V...
Moth eaten calyx refers to the ragged, feathery calyceal outline due to irregular erosions of the calyx. It is one of the earliest excretory urographic appearance of genitourinary tuberculosis.
This appearance is due to necrotizing papillitis, which may further progress to form medu...
MR defecating proctography is a dynamic study for evaluation of the pelvic floor and pelvic organ prolapse.
There are four phases of evaluation:
Method of evaluation
Many variations in the techniques described below exist.
MRI targeted prostate biopsy refers to an imaging targeted technique rather than the traditional systematic approach of a prostate biopsy after respective imaging with multiparametric MRI (mpMRI) of the prostate.
As a consequence of the recent advances of multiparametric MRI (mpMRI) of the pros...
MR spectroscopy is a promising development in the radiological evaluation of possible prostate malignancy.
The MR spectroscopic evaluation is mainly based on the choline peak elevation and choline-creatinine ratios.
Choline/creatine to citrate ratios:
> 0.5: suspicious
> 0.8: very suspiciou...
A mulberry stone is one of the types of urinary tract stones. It is formed of calcium oxalate dihydrate. It can be considered as a subset of a jackstone calculus which has a spiked appearance. When the stone has less well-developed spikes, it may appear to have a mamillated appearance, hence it ...
A Müllerian duct cyst is a cyst that arises from remnants of the Müllerian duct and is one of the midline cystic masses in the male pelvis.
Müllerian duct cysts usually occur in the 3rd and 4th decades of life (whereas prostatic utricle cysts are most often detected in the 1st an...
Multicystic dysplastic kidney (MCDK) is a type of non-heritable pediatric cystic renal disease. It results in multiple cysts being formed in utero in the affected kidney.
Unilateral incidence is estimated at 1:2500-4000. There may be a predisposition for the left kidney, a slightl...
Multicystic mesotheliomas are a rare benign subtype of mesothelioma.
The nomenclature for this condition can be confusing due to the use of multiple interchangeable different synonyms that put it together with the peritoneal inclusion cysts. Although there is still some debate on ...
Multilocular cystic renal neoplasm of low malignant potential is a low-grade adult renal tumor composed entirely of numerous cysts. The entity was previously known as multilocular cystic renal cell carcinoma, which usually had clear cell morphology, but was redefined in the 2016 WHO classificati...
Multiple endocrine neoplasia (MEN) syndromes are a collection of syndromes characterized by the presence of, as the name would suggest, multiple endocrine tumors. They are autosomal dominant in inheritance.
MEN1 (Wermer syndrome)
MEN2 (multiple endocrine adenomatosis)
MEN2a (Sipple syndrome)
Multiple endocrine neoplasia type II (MEN2) is also known as mucosal neuroma syndrome or multiple endocrine adenomatosis. It is a collection of syndromes characterized by the presence of multiple endocrine tumors.
They are autosomal dominant in inheritance, and share medullary thyroid carcinom...
Multiple endocrine neoplasia (MEN) type IIb, also known as MEN type 3 (MEN3) 3 or mucosal neuroma syndrome 2, accounts for only 5% cases of MEN2 and is characterized by:
pheochromocytoma(s): in 50% of patients, often bilateral, and can be extra-adrenal
medullary thyroid cancer: 100% of patient...
Multiple filling defects within a ureter, as seen on conventional IVU or CT IVU, have a relatively small differential including:
spreading or multifocal transitional cell carcinoma (TCC)
multiple ureteral stones (steinstrasse)
Multiple filling defects within a ureter, as seen on conventional IVU or CT IVU, have a relatively small differential which can be learned using this mnemonic:
U: ureteritis cystica
T: transitional cell carcinoma (TCC)
S: stones, Stevens-Johnson syndrome
Mumps is a (usually) self-limited viral infection that often occurs in epidemics among children. Its incidence has markedly diminished in countries with childhood vaccination programs, but may still be seen in adult patients who have not received vaccinations or who have waning immunity. It may ...
Musculus compressor nuda is a small striated musculotendinous sling of the bulbocavernosus muscle, which extends from the anterior and lateral surfaces of the proximal bulbous urethra.
Musculus compressor nuda causes the proximal bulbous urethra to form a symmetric convex cone shape where the t...
N-acetylcysteine (NAC) if often used as a prophylaxis against contrast-induced nephropathy. Protocols for administration vary widely from institution to institution and the true efficacy is still controversial.
A typical protocol is [1-2]:
600 mg acetylcysteine twice daily on the day of the ex...
Neonatal hydronephrosis is most commonly diagnosed antenatally as fetal pylectasis, and in the majority of cases is due to pelvi-ureteric junction (PUJ) obstruction.
pelvi-ureteric junction (PUJ) obstruction (50% of cases 1,6)
vesicoureteric reflux (~20% of cases 5)
Nephroblastomatosis refers to diffuse or multifocal involvement of the kidneys with nephrogenic rests (persistent metanephric blastema).
Nephrogenic rests are found incidentally in 1% of infants.
Nephrogenic rests are foci of metanephric blastema that persist beyond 36...
Nephrocalcinosis, previous known as Anderson-Carr kidney or Albright calcinosis, refers to the deposition of calcium salts in the parenchyma of the kidney. It is divided into several types, with differing etiologies, based on the distribution:
medullary nephrocalcinosis: 95%
Nephrogenic systemic fibrosis (NSF), also known as nephrogenic fibrosing dermopathy, is a complication of gadolinium-based contrast agents used in MRI.
It is characterized by "firm, erythematous, and indurated plaques of the skin associated with subcutaneous edema" 1. Eventually, flexure contra...
Nephroptosis, also known as floating/wandering kidney or ren mobilis, refers to the descent of the kidney more than 5 cm or two vertebral bodies when the patient moves from a supine to upright position during IVU 1,2.
Displacement can also occur medially across the midline, so-called medial nep...
Nephrostomy is a common urologic or interventional radiology procedure in which a tube/catheter is introduced into the renal collecting system (usually the renal pelvis).
Nephrostomies can either be
"open" nephrostomy: after a urological surgical procedure, such as a UPJ stone removal
Nephrotic syndrome results from loss of plasma proteins in the urine and characterized by hypoalbuminemia, hyperalbuminuria, hyperlipidemia, and edema. It may be caused by primary (idiopathic) renal disease or by a variety of secondary causes.
Patients present with marked...
Neuroblastomas are tumors of neuroblastic origin. Although they may occur anywhere along the sympathetic chain, the vast majority arise from the adrenal gland.
They represent the most common extracranial solid childhood malignancy and are the third commonest childhood tumor after leukemia and b...
There are two methods of neuroblastoma staging, one that is based on post-operative patients (INSS) and one developed for pre-treatment patients (INRGSS).
International Neuroblastoma Staging System (INSS)
This staging system is for post-operative patients and mainly for prognosis 1:
Both neuroblastoma and Wilms tumor occur in early childhood and typically present as large abdominal masses closely related to the kidneys. Distinguishing between the two is important, and a number of features are helpful.
calcification very common: 90%
encases vascular structur...
Neurocristopathy syndromes encompasses a group of conditions united by abnormal migration, differentiation, division or survival of neural crest cells 1.
neurofibromatosis type I (NF1)
Neurogenic bladder is a term applied to a dysfunctional urinary bladder that results from an injury to the central or peripheral nerves that control and regulate urination. Injury to the brain, brainstem, spinal cord or peripheral nerves from various causes including infection, trauma, malignanc...
Non-seminomatous germ cell tumors (NSGCTs) are one of the main groups of germ cell tumors (the other being seminoma). Although they are made up of distinct histological entities, in general, they have similar radiographic appearances. They can, however, be found widely in the body, with variable...
This article lists examples of normal imaging of the genitourinary tract and surrounding structures, divided by modality.
KUB: example 1
abdominal x-ray: example 1
Intravenous Urogram (IVU) and Intravenous Pyelogram (IVP)
IVU: example 1, example 2
Normal kidney size in adults varies with the height of the individual. Also, in general, it decreases with age and increases with body mass index (BMI).
The size of the kidneys is measured mainly sonographically, although both CT and MRI scans also can be used to estimate renal size.
The mean ...
The normal size of kidneys in children will naturally depend on the age and size of the child. Based on the children's ages normal average renal length on ultrasound are as follows:
0 to 2 months: 5 cm (approximately 2 inches)
2 months to 6 months: 5.7 cm
6 months to 1 year: 6.2 cm (2.5 inche...
The nutcracker phenomenon, also known as nutcracker anatomy or left renal vein entrapment, refers to the anatomic or pathophysiologic entity wherein the superior mesenteric artery compresses and impedes outflow of the left renal vein into the inferior vena cava. It can be a common incidental fin...
Nutcracker syndrome is a vascular compression disorder that refers to the compression of the left renal vein most commonly between the superior mesenteric artery (SMA) and aorta, although other variations can exist 1. This can lead to renal venous hypertension, resulting in rupture of thin-walle...
Obstructive cystic renal dysplasia, or Potter type IV cystic renal disease, is a potential complication that can occur from prolonged obstruction of the bladder outlet or urethra during gestation.
Ureteric obstruction during active nephrogenesis results in cystic renal dysplasia; th...
An obstructive uropathy is a catch-all term encompassing any cause of complete or partial, congenital or acquired, and permanent or intermittent obstruction of the urinary tract. Depending on the severity of obstruction and extent, it may result in permanent change in both the collecting system ...
An oncocalyx is a dilated tumor filled renal calyx, typically seen in patients with transitional cell carcinomas of the renal pelvis.
Orchitis (plural: orchitides) is an infection of the testicle, which is rarely isolated, and when in conjunction with the epididymis is called epididymo-orchitis.
Usually, bacteria retrogradely seed into the testis from the bladder or prostate. It can also be secondary to viral infec...
Ossifying renal tumor of infancy (ORTI) is a rare renal tumor.
extremely rare, <<1% of pediatric renal neoplasms (17 cases reported)
6 days - 3 months
Histology reveals spindle cells and osteoblastic cells in a calcified osteoid matrix. It is thought...
Ovarian vein syndrome is a relatively rare condition where a dilated ovarian vein (ovarian venous varix) causes notching, dilatation, or obstruction of the ureter. This is usually secondary to varicosities of the ovarian vein or ovarian vein thrombosis and occurs at the point where the ovarian v...
Oxalosis is supersaturation of calcium oxalate in the urine (hyperoxaluria), which in turn results in nephrolithiasis and cortical nephrocalcinosis.
This article focus on the secondary oxalosis, please refer to primary oxalosis for a specific discussion on this entity.
The pediatric cystic renal diseases are a heterogeneous group of conditions defined by the presence of kidney cysts due to hereditary or non-hereditary causes:
isolated simple cyst
cystic renal dysplasia
multicystic dysplastic kidney (MCDK)
obstructive cystic renal dysplasia
The pediatric kidneys follow a growth curve. The measurements below are of the longest maximal dimension. Measurements in parentheses are one standard deviation.
0 months 1: female: 4.15 cm (0.35); male: 4.22 cm (0.32)
2 months: 5.28 cm (0.66)
6 months: 6.15 cm (0.67)
10 months: 6.23 cm (0....
Pediatric renal tumors and masses are another group of diseases (just like cystic renal diseases in both the adult and child) that are bewildering in their number, nomenclature and overlapping findings.
Wilms tumor: common in older children 1-8 years old
Pediatric urinary tract infections are common and are a source of significant imaging in young children.
Pediatric urinary tract infections affect up to 2.8% of all children every year, with approximately 2% of boys and 8% or more of girls developing a urinary tract infection at s...
The British National Institute for Health and Care Excellence (NICE) published the “Urinary tract infection in under 16s: diagnosis and management” in 2007 as a guideline for pediatric urinary tract infection (UTI) management, including imaging, prophylaxis and follow-up 1.
This article intend...
Page kidney, or Page phenomenon, refers to systemic hypertension secondary to extrinsic compression of the kidney by a subcapsular collection, e.g. hematoma, seroma, or urinoma.
Patients present with hypertension, which may be recognized acutely after an inciting event or...
A paintbrush appearance describes the streaky appearances of dilated contrast filled tubules within the renal medulla on IVP or CT-IVU. This appearance is characteristic for medullary sponge kidneys.
A similar appearance is also seen in the renal tubular ectasia; though less pronounced.
The pampiniform plexus (plural: plexuses) is the venous network of approximately 10 veins draining the testis and epididymis. The network surrounds the testicular artery in the spermatic cord and lies anterior to the ductus deferens. Each network coalesces to form the testicular (internal sperma...
Pancake kidney (also known as discoid kidney, disc kidney, lump kidney, fused pelvic kidney or cake kidney) is a rare renal fusion anomaly of the kidneys of the crossed fused variety.
Pancake kidney may be an incidental finding. However, they can present clinically becaus...
Papillary cystadenomas of the epididymis are the second most common benign tumors of the epididymis after adenomatoid tumors and are common in patients with von Hippel-Lindau disease (vHL).
Papillary cystadenomas are usually asymptomatic.
They are more comm...
Papillary renal cell carcinomas (pRCC) are the second most common histological subtype of renal cell carcinoma.
This subtype may account 13-20% of all renal cell cancer 1. There is slightly increased male predilection.
As with other types of renal cell canc...
The pararectal spaces are paired, triangular-shaped spaces in the posterior pelvis.
anterior: cardinal ligament
medial: rectal pillars
lateral: levator ani muscle, internal iliac arteries
The pelvic splanchnic nerves also known as nervi erigentes are preganglionic (presynaptic) parasympathetic nerve fibers that arise from S2, S3 and S4 nerve roots of the sacral plexus. These nerves form the parasympathetic portion of the autonomic nervous system in the pelvis.
Paratesticular lesions have a long list of differential diagnoses:
epididymal cyst (most common epididymal mass)
scrotal tunica cysts
tunica vaginalis cyst
tunica albuginea cyst
spermatic cord lipoma
scrotal hemangioma: is often hypervascular on color Doppler, unlike ot...
A paratesticular mass may derive from a number of structures that surround the testicle within the scrotum; most commonly, they derive from the spermatic cord.
The masses can be categorized as benign (70%) or malignant (30%).
spermatic cord lipoma (most common par...
The paraurethral ducts (or Skene ducts) drain the paraurethral glands of the female urethra. There is one duct, draining each gland, on each side, just proximal to the external urethral meatus.
History and etymology
Skene ducts are named after the Scottish-American gynecologist Alexander John...
Paraurethral duct cysts are retention cysts that form secondary to inflammatory obstruction of the paraurethral (Skene) ducts in females.
The cysts are lined by stratified squamous epithelium due to their origin from the urogenital sinus.
Paraurethral glands (or Skene glands) lie within the wall of the distal female urethra and secrete mucus during sexual activity. Each gland is drained by a single paraurethral (Skene) duct. They are homologous to the male prostate gland.
If the paraurethral duct becomes obstructed (inflammation...
The paravesical spaces are paired avascular spaces of the pelvis. The paravesical spaces generally contain fat, but can become filled with ascites, blood, or other substances during pathological processes.
superior: lateral umbilical folds
inferior: pubocervical fasc...
A patent urachus is one of the spectrum of congenital urachal anomalies. It has occasionally been termed "urachal fistula".
A patent urachus is often diagnosed in neonates when urine is noted leaking from the umbilicus. The umbilicus may also have an abnormal appearance o...
Pear-shaped (or teardrop-shaped) bladder is one whose normal round or ovoid shape has been extrinsically compressed to resemble a pear. The pear may be inverted or upright, depending on how the excess pelvic tissue compresses the bladder.
Causes of a pear-shaped bladder inc...
A pelvic abscess refers to a walled-off collection of pus in the pelvis.
Some of the causes include:
pelvic inflammatory disease (tubo-ovarian abscess)
iatrogenic e.g. post-surgical
inflammatory bowel disease
pelvic actinomycosis infection
Pelvic congestion syndrome (some prefer pelvic venous insufficiency 9) is a condition that results from retrograde flow through incompetent valves in ovarian veins. It is a commonly missed and potentially-treatable cause of chronic abdominopelvic pain.
It tends to be more common ...
Pelvic kidney (sometimes known as sacral kidney) is a kidney that is fixed in the bony pelvis or across the spine, and is an anatomic variant 1.
Pelvic ectopia is seen in 1 in 2,100-3,000 autopsies. It is considered the most common form of renal ectopia 4.
Pelvic lipomatosis or pelvic fibrolipomatosis represents excessive deposition of fat in pelvis due to overgrowth of adipose cells leading to compression of pelvic organs.
The condition usually presents in patients 20-50 years of age. The condition is predominantly (~66% of cases) ...
The pelvic peritoneal space is the inferior reflection of the peritoneum over the fundus of the urinary bladder and the front of the rectum at the junction of its middle and lower thirds. In females, the reflection is also over the anterior and posterior surface of the uterus and the upper poste...
Pelviureteric junction (PUJ) obstruction/stenosis, also known as ureteropelvic junction (UPJ) obstruction/stenosis, can be one of the causes of obstructive uropathy. It can be congenital or acquired with a congenital pelviureteric junction obstruction being one of the commonest causes of antenat...
Penile fracture or rupture is a rare event, however, requires emergency diagnosis and intervention. It is a rupture of penile tunica albuginea of the corpora cavernosa or spongiosum caused by trauma to an erect penis, most commonly during sexual intercourse. The urologist needs to know whether t...
A simple grading system for penile fracture has been developed but it is not widely used or validated nor recognized by relevant urological surgical societies. Regardless, this system which relies on ultrasound assessment of the tunica albugenia, corpora of the penis, urethra and other fascia 1 ...
Penile implants are a surgically placed device to assist with erectile dysfunction. The device has inflatable components inserted in the penile shaft with a reservoir typically placed in the pelvis.
Penile Doppler in erectile dysfunction
medical devices in the a...
The penis (plural: penises or, rarely, penes) is the external midline urinary and reproductive structure of the male urogenital system.
The gross anatomy of the penis can be divided into five sections:
loosely connected to the tunica albuginea
distally folded to form the...
Percutaneous ablation in the kidney is now performed as a standard therapeutic nephron-sparing option in patients who are poor candidates for resection. It can either be a radiofrequency ablation or a cryoablation.
Follow up time frame
Can vary according to center but usually includes contrast...
Percutaneous nephrolithotomy (PCNL) is a surgical procedure for the extraction of large renal calculi. It is usually performed in the operating theater either by a urologist or combined urologist-radiologist team.
PCNL is used to destroy and remove renal calculi, typically over 2 cm...
Percutaneous nephrostomy is a technique in which percutaneous access to the kidney is achieved under radiological guidance. The access is then often maintained with the use of an indwelling catheter.
Percutaneous nephrostomy is usually reserved for when retrograde approaches are un...
Percutaenous nephrostomy salvage and tube exchange are two procedures undertaken in those with long term nephrostomies. These patients are often either unsuitable or do not wish to have ureteric stenting to relieve their urinary tract obstruction.
Nephrostomy salvage is und...
Percutaneous renal biopsy, utilizing either ultrasound or CT, allows for an accurate, reliable method of acquiring renal tissue for histopathological assessment.
The biopsy may be of a native or transplant kidney. It is divided into two types:
non-focal or non-targeted
focal or targeted (i.e....
The perineal body, also known as the central tendon of the perineum, (TA: corpus perineale) is a key midline fibromuscular structure, with important muscular attachments, which acts to stabilize the structures of the pelvis and perineum. It is located between the anal canal and the bulb of the p...
The perineal membrane is a thin triangular horizontal layer of dense tough fascia in the perineum which divides the urogenital triangle into superficial (inferior) and deep (superior) perineal pouches.
It attaches to the inferior margins of the ischiopubic rami, enclosing the anterior portion o...