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An unroofed coronary sinus is a rare variant of atrial septal defect (ASD). The atrial wall between the coronary sinus and left atrium is either partially or completely absent, resulting in a left-to-right shunt.
It is associated with persistent left-sided SVC and heterotaxy syndromes.
Unsupervised learning is one of the main algorithms used in machine learning.
Unsupervised learning algorithms are used on datasets where output labels are not provided. Hence, instead of trying to predict a particular output for each input, these algorithms attempt to discover the underlying ...
Unverricht-Lundborg disease (ULD or EPM1) inherited neurodegenerative disorder which often results in myoclonic epilepsy.
It is considered the most common single cause of progressive myoclonus epilepsy worldwide.
It carries an autosomal recessive inheritanc...
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The upper and lower lobe distribution of certain bilateral pulmonary pathologies can be recalled using the following mnemonics:
upper lobe or apical predominance: SET CAP
lower lobe or bibasilar predominance: BAD RASH
E: EG/extrinsic allergic alv...
Upper extremity dislocations are relatively common on account of the great range of motion the upper limb is capable of (a general principle is that the greater the range of motion of a joint, the more prone it is to dislocation). In many instances dislocations are associated with fractures eith...
The upper limb sustains a wide variety of fractures that range significantly in demographics, treatment and functional impact.
blade of scapula fracture
coracoid process fracture
Upper gastrointestinal bleeding (UGIB) is defined as bleeding proximal to the ligament of Treitz.
The incidence of acute UGIB is ~100 per 100,000 adults per year. UGIB is twice as common in men as in women and increases in prevalence with age 5. The demographics of the affected in...
An upper gastrointestinal bleed usually refers to bleeding proximal to the ligament of Treitz.
Upper limb anatomy encompasses the anatomy of the shoulder, arm, elbow, forearm, wrist and hand.
Upper limb radiography is the radiological investigation of the shoulder girdle, humerus, ulna, radius, carpals and metacarpals of the hand. It is often utilised in the context of trauma to rule out fractures and dislocations.
Distribution of bronchiectasis can help in narrowing the differential diagnosis. Upper lobe bronchiectasis is typically seen in:
Rarely it may be seen with non tuberculous mycobacterial infection (e.g. MAC infection 2)
When in mid-upper lobes also consid...
Upper lobe predominant pulmonary fibrosis can be associated with a number of pathologies. These include
cystic fibrosis - see pulmonary manifestations of cystic fibrosis
Langerhans cell histiocytosis
Upper lobe pulmonary venous diversion (cephalisation) reflects elevation of left atrial pressure and can occur with pulmonary oedema. It produces Stag-antler's sign on frontal chest x-ray.
The normal left atrial pressure is 5-10 mmHg. An elevation of left atrial pressure to 10-15 mmHg will resu...
The upper subscapular nerve, also known as the short or superior subscapular nerve, arises from the posterior cord of the brachial plexus and supplies the subscapularis muscle.
The upper subscapular nerve branches from the posterior cord of the brachial plexus with fibres...
The upper T sign is one of the features useful in identifying the central sulcus on cross-sectional imaging.
It relies on identifying the superior frontal sulcus which intersects the precentral sulcus in a "T" junction, thus defining the precentral gyrus. The central sulcus is the next posterio...
The upper zone is one of the four chest radiograph zones. Sometimes the upper zone includes the apical zone.
on frontal chest radiographs, the upper zone extends from the inferior margin of the clavicles to the superior aspect of the hilum
Urachal cysts are one of the manifestations of the spectrum of congenital urachal remnant abnormalities.
Urachal cysts usually remain asymptomatic until complicated by infection or bleeding.
Infected urachal cyst can occur at any age.
The urachus is the fibrous vestigal remnant of the fetal allantois.
The lumen of the urachus usually obliterates after birth and it becomes the median umbilical ligament, a midline linear fibrous fold of parietal peritoneum, extending from the apex of the bladder to the umbilicus.
If the lumen...
Uraemic encephalopathy (UE) is an acquired toxic syndrome characterised by delirium in patients with untreated or inadequately treated end-stage renal disease. UE is often associated with lethargy and confusion in the acute phase, which can progress to seizures, coma, or both in the chronic phas...
Urbach-Wiethe disease, also known as lipoid proteinosis or hyalinosis cutis et mucosae, is a rare autosomal recessive genodermatosis that primarily affects the skin, upper respiratory tract, and central nervous system (CNS).
Urbach-Wiethe disease is a very rare condition, with few...
The ureter is a paired fibromuscular tube that conveys urine from the kidneys in the abdomen to the bladder in the pelvis.
The ureter is 25-30 cm long and has three parts:
abdominal ureter: from the renal pelvis to the pelvic brim
pelvic ureter: from the pelvic brim to the bla...
Ureteral duplication is the most common congenital abnormality associated with the urinary tract, and occurs in ~1% of the population.
Duplication can occur unilaterally or bilaterally, and may be partial or complete:
partially duplicated ureters fuse into a single ureter proxim...
Ureteral pseudodiverticulosis is acquired false diverticula resulting from herniation of epithelium through the muscularis layer of the ureter and characterized by the presence of multiple outpouchings smaller than 5 mm. It is more commonly bilateral and located in the upper two-thirds of the ur...
A number of tumours may affect the ureter, by far the most common histology being transitional cell carcinoma.
transitional cell carcinoma of the ureter: 95% 1
squamous cell carcinoma of the ureter: 5%
adenocarcinoma of the ureter: <1%
The ureteric bud (also known as the metanephrogenic diverticulum) is a protrusion of the mesonephric duct that appears during the embryological development of urogenital organs. It will eventually form the urinary collecting system (i.e. collecting tubes, calyces, renal pelvis, ureter) of the ki...
Ureteric calculi or stones are those lying within the ureter, at any point from the ureteropelvic junction (UPJ) to the ureterovesical junction (UVJ). They are the classic cause of renal colic-type abdominal pain. They are a subset of the broader topic of urolithiasis.
Ureteric injury is a relatively uncommon, but severe event, which may result in serious complications as a diagnosis is often delayed.
Ureteric injuries unreliably demonstrate macro- or micro-scopic haematuria as it may be absent in up to 25% of patients 5, 6. Classic cl...
Ureteric rupture is rare but has been described. It may be spontaneous or secondary to another pathology or intervention.
The most common symptoms are sudden, severe, persistent lower abdominal pain with severe peritoneal irritation. Abdominal compartment syndrome, respir...
Ureteric stents, also known as double J stents or retrograde ureteric stents, is a urological catheter that has two "J-shaped" (curled) ends, where one is anchored in the renal pelvis and the other inside the bladder.
Stents are used for the free passage of urine from the kidney to the bladder,...
Ureteritis refers to inflammation of the ureter, it is rare and is often associated with cystitis or pyelonephritis 1.
Patients may present with symptoms of cystitis or pyelonephritis with suprapubic/flank pain, dysuria, haematuria and/or fever. White cell count may also...
Ureteritis cystica or pyeloureteritis cystica is a benign condition of the ureters representing multiple small submucosal cysts.
Typically this condition is seen in diabetics, with recurrent urinary tract infection. As such is is most frequently seen in older patients and is more...
Ureterocoeles represent congenital dilatation of the distal-most portion of the ureter. The dilated portion of the ureter may herniate into the bladder secondary to the abnormal structure of vesicoureteric junction (VUJ).
Most ureterocoeles are congenital, usually associated with ...
Ureterovaginal fistulae refer to abnormal communications between the lumina of the ureter(s) and the vagina.
Patients usually present with urinary incontinence through the vagina which may be accompanied by fever and chills 1. Symptoms usually begin within 2-4 weeks foll...
The urethra is the terminal segment of the genitourinary system. Because of vastly different anatomy between the sexes, male and female urethras are discussed separately:
Urethral agenesis (or urethral atresia) refers to a situation where there is a congenital absence of the urethra. It can be a cause of fetal obstructive uropathy.
prune belly syndrome 5
bladder agenesis 2
May show a dilate...
Urethral calculi are an uncommon type of urolithiasis, accounting for ~1% of all urinary tract stones.
They almost all occur in males 2 with two peak incidences - one in childhood and the other at 40 years 3.
Most commonly acute lower urinary tract symptoms...
Various radiological and surgical instruments, including urethral clamps, have been developed to try to improve retrograde/ascending urethrogram (RUG/ASU) and voiding cystourethrogram (VCUG) technique in males. These are very rarely (if ever) used anymore.
This device has a metall...
Urethral diverticulum, or urethrocoele, is a focal outpouching of the urethra. It should not be confused with a ureterocoele of the distal ureter.
Urethral diverticula occur far more frequently in women than in men and are estimated to occur in 1-6% of women, especially those with...
Urethral diverticulum adenocarcinoma is a rare occurrence in a urethral diverticulum.
Urethral diverticulum seen in ~0.6-6% of women. In small series, only 3-6% of resected urethral diverticula show adenocarcinoma 3-4.
Urinary frequency, urgency, burning mictur...
Urethral duplication is a rare condition in which either a part or the entire urethra is duplicated. It usually occurs in the sagittal plane and the more dorsal copy is usually the duplication.
A urethral duplication may occur due to a variety of developmental miscues. In a woman, it...
Urethral injuries can result in long-term morbidity and most commonly result from trauma. The male urethra is much more commonly injured than the female urethra and is the focus of this article.
In the setting of trauma, the classic triad of blood of the external urethral...
Urethral strictures are relatively common and typically occur either in the setting of trauma or infection.
The demographics of the affected population is dictated by the aetiology, but in general, it is safe to say that adult males make up the vast majority of cases.
Urethrography refers to the radiographic study of the urethra using iodinated contrast media and is generally carried out in males.
When the urethra is studied with instillation of contrast into the distal/anterior urethra it has been referred to as
retrograde urethrography (RUG)...
The urinary bladder (more commonly just called the bladder) is a distal part of the urinary tract and is an extra-peritoneal structure located in the true pelvis.
The bladder has a triangular shape with a posterior base, an anterior apex and an inferior neck with two inferolatera...
There are numerous causes of urinary bladder diverticula:
Primary (congenital or idiopathic)
Hutch diverticulum (in paraureteral region)
Bladder outlet obstruction
bladder neck stenosis
posterior urethral valve
prostatic enlargement (hypertrophy; carcinoma)
Bladder diverticulum are outpouchings from the bladder wall, whereby mucosa herniates through the bladder wall. They may be solitary or multiple in nature and can vary considerably in size.
There are two peaks - one at 10 years and the other at 60-70 years 2.
Herniation of the urinary bladder is a relatively uncommon but not a rare condition. It occurs when the urinary bladder or ureter herniates into the inguinal canal, scrotal sac or femoral canal. Herniations through ischiorectal, obturator or abdominal wall openings have also been described. Blad...
Urinary bladder rupture is usually seen in the context of significant trauma.
Bladder rupture can be categorised into five types depending on the location and extent of the rupture.
This is commonly seen but sometimes not classed as true rupture, since it in...
Causes of urinary bladder wall or lumen calcification include:
schistosomiasis of the urinary tract
calculus in a urachal cyst or in a bladder divertic...
Urinary diversion is created after the removal of the urinary bladder (radical cystectomy or cystoprostatectomy, usually done to treat invasive bladder cancer).
There are three main varieties:
neobladder formed from a segment of ileum (i.e. ileal conduit, also known as a "Bricker conduit")
The urinary system consists of the kidneys, ureter, bladder and urethra. With the exception of the urethra, this is equitable in both males and females. It spans the abdomen and pelvis, from the upper abdomen to the extreme pelvis, being inextricably linked with the genital system.
Urinary tract infection (UTI) is a common clinical condition involving the bladder (cystitis) and kidneys (pyelonephritis). It is commonly divided into 'uncomplicated' and 'complicated' infections.
UTIs occur when there is bacterial colonisation of the uroepithelium and a subsequent...
Urinomas, or uriniferous fluid collections, are urine collections usually found in the retroperitoneum, most commonly in the perirenal space, as a consequence of renal track leakage caused by urinary obstruction, trauma, or post-instrumentation.
Although there is no definitive dis...
Urinothorax is a rare cause of pleural effusion due to the accumulation of urine within the pleural space.
Patients present with varying degrees of respiratory distress depending on the amount of fluid that has accumulated 1,3.
The aetiology of urinothorax can...
The urogenital curriculum is one of our curriculum articles and aims to be a collection of articles that represent the core genitourinary knowledge.
Topics pertaining to the urinary tract (kidneys, ureter, bladder, urethra), adrenal glands, prostate penis, scrotal content (testes, ...
Urolithiasis refers to the presence of calculi anywhere along the course of the urinary tracts. For the purpose of the article, the terms urolithiasis, nephrolithiasis and renal or kidney stones are used interchangeably, although some authors have slightly varying definitions of each.
Ultrasound abdomen is one of the tests that is commonly used in the assessment of patients with abdominal pain. It is particularly useful for the assessment of solid organs and fluid-filled structures.
This is a summary article; we do not have a more in-depth reference articl...
The ubiquitous USB flash drive (or USB stick) may be an odd article on a radiology website, but those who report a lot of chest radiographs will be aware that it can be often be confused for an implantable loop recorder device.
Whilst USB drives come in a variety of shap...
US carotids is a standard test performed in the assessment of cranial arterial blood supply.
This is a summary article; we do not have a more in-depth reference article.
assessment of carotid stenosis
This style guide article outlines the use of racial terminology on Radiopaedia.org.
Race and ethnicity is a complex topic with a history of, and potential use for, discrimination. There are many issues in the use of race in medicine, mainly centred on definition, identification and ...
The U sign denotes the characteristic "U" shaped appearance of the subcentral gyrus which surrounds the inferolateral end of the central sulcus and abuts the lateral (Sylvian) fissure. It has been found, at least in one study, to be the most reliable anatomical feature to identify the central su...
Using e.g. in Radiopaedia.org articles is common and good practice. However, it is important to use e.g. consistently across the site.
It should be remembered that when using e.g., the user is trying to give an example, not an exhaustive list.
There are many causes of m...
Usual interstitial pneumonia (UIP) is one of the morphological and pathological patterns of interstitial lung disease.
On imaging, it usually presents with a patchy craniocaudal gradient of peripheral septal thickening, bronchiectasis, and honeycombing.
In the past, the term UIP ...
American Thoracic Society (ATS) criteria for histopathological diagnosis of usual interstitial pneumonia (UIP) are as follows:
advanced subpleural or paraseptal fibrosis +/- honeycombing
patchy temporally heterogeneous fibrosis
absence of features against UIP
Uterine agenesis is the extreme of Mullerian duct anomalies (Class I) where there is a complete absence of uterine tissue above the vagina.
The uterine agenesis-hypoplasia spectrum accounts for ~10-15% of all Müllerian duct anomalies.
Uterine arteriovenous malformations (UAVM) result from formation of multiple arteriovenous fistulous communications within the uterus without an intervening capillary network.
Presentation can vary. UAVMs can cause life-threatening massive bleeding in young women. Bleedin...
The uterine artery is seen bilaterally and is a branch of the anterior division of the internal iliac artery.
It runs medially in the pelvis, within the base of the broad ligament, to the outer surface of the uterus. From lateral to medial it has a descending, transverse ...
Uterine artery embolisation (UAE) is an interventional radiological technique to occlude the arterial supply to the uterus and is performed for various reasons.
Uterine artery embolisation has been practised for more than 20 years for controlling haemorrhage following delivery / aborti...
Uterine artery embolisation (UAE) is used as an alternative to hysterectomy in selected patients and MRI assessment is key in allowing not only pre-procedure assessment but also assessing post-procedural outcome.
For a general discussion of the underlying condition refer to the article on ute...
Uterine artery flow notching refers to phenomenon observed in uterine arterial Doppler ultrasound assessment.
The presence of notching after 22 weeks is associated with several other conditions including adverse pregnancy outcomes. These include
pregnancy induced hyper...
Uterine artery pseudoaneurysm (UAP) is a rare cause of secondary postpartum haemorrhage.
UAP usually presents as delayed (secondary) postpartum haemorrhage, that is per vaginal bleeding which occurs more than 24 hours and up to 6 weeks postpartum. However, some reported ...
Uterine biophysical profile refers to assessment of uterus to produce a successful conception and implantation environment.
Uterine scoring system for reproduction (USS)
The uterine scoring system for reproduction comprises the following parameters, taken in mid-cycle:
1. endometrial thickne...
Uterine choriocarcinomas are one of the commonest choriocarcinomas and are often associated with gestational trophoblastic disease (GTD).
These tumours typically occur in women of childbearing age as a gestational choriocarcinoma. Most such cases present within one year of an ant...
Uterine dehiscence is, usually, used to refer to the process of gradual myometrial rupture without a rupture of membranes. However, the term is used synonymously with uterine rupture by some authors. It is often described in the context of C-section scar where it is also termed an incisional deh...
Uterine duplication anomalies are a group of Müllerian duct anomalies where fusion of the Müllerian duct associated structures fail to some degree:
uterus didelphys: class III
bicornuate uterus: class IV (second commonest duplication anomaly)
septate uterus: class V (commonest duplication ano...
Uterine enlargement can occur in a number of situations from both diffuse and focal processes. These include:
gestation related events
normal intrauterine pregnancy
molar pregnancy - gestational trophoblastic disease
postpartum uterus - still larger than usual
Uterine leiomyomas, also referred as uterine fibroids, are benign tumours of myometrial origin and are the most common solid benign uterine neoplasms. Commonly an incidental finding on imaging, they rarely cause a diagnostic dilemma. There are various medical, surgical and interventional treatme...
Uterine leiomyosarcomas are malignant uterine tumours that arises from the myometrium. The uterus is the commonest location for a leiomyosarcoma.
Typically present in women in the 6th decade. They account for up to one-third of uterine sarcomas but only ~8% of all uterine cancers ...
Uterine lipoleiomyomas result from degeneration of smooth muscle cells in an ordinary leiomyoma and represent a rare benign tumour of the uterus 1.
Lipoleiomyomas have a reported incidence of 0.03-0.20% and are typically found in postmenopausal patients with typical uterine leiomy...
Uterine lymphoma refers to involvement of the uterus with lymphoma. Some authors also place lymphoma of the uterine cervix under this group.
It is rare condition with initial uterine involvement occurring in only 1% of patients with lymphoma 3. However, uterine involvement is more...
Uterine perforation represents a serious complication that can occur as a result of any type of intrauterine procedure or implantation. Some authors use the term uterine rupture synonymously with the term uterine perforation.
IUCD insertion: IUCD related uterine perforation
Uterine rupture is a rare but nevertheless potentially catastrophic complication that can occur in pregnancy.
The incidence rate in pregnancy is at 0.05% 6.
Uterine rupture is usually an acute presentation with haemodynamic instability and abdominal disc...
Uterine sarcoma is a malignant uterine tumour thats is composed of part or all sarcomatous (mesodermal) elements. They however account for a minority of all uterine malignancies (1-6% 3-4).
They can be broadly classified as pure or mixed 4:
malignant mixed Mu...
Uterine smooth muscle tumours of uncertain malignant potential (STUMP) is a recently defined entity by the World Health Organisation for a heterogeneous group of uterine smooth muscle tumours that cannot be histologically diagnosed as unequivocally benign or malignant 1.
The uterine tube, also known as the fallopian tube, is a paired structure that bridges between each ovary and the uterus and functions to convey the mature ovum from the former to the latter. If conception occurs, it normally does so within the tube. It can be affected by a wide range of patholo...
Uteroplacental blood flow assessment is an important part of fetal well-being assessment and evaluates Doppler flow in the uterine arteries and rarely the ovarian arteries.
In a non-gravid state and at the very start of pregnancy the flow in the uterine artery is of high pulsatility ...
The uterus is a hollow, thick-walled, muscular organ of the female reproductive tract that lies in the lesser pelvis.
The uterus has an inverted pear shape. In the adult, it measures about 7.5 cm in length, 5 cm wide at its upper part, and nearly 2.5 cm in thickness. It weighs ...
Uterus didelphys is a type of Müllerian duct anomaly (class III) where there is a complete duplication of uterine horns as well as duplication of the cervix, with no communication between them.
Didelphic uteri account for approximately ~8% (range 5-11%) of Müllerian duct anomali...
The uvea (also called the uveal layer or vascular tunic) is the middle three layers that make up the eye. It is the pigmented layer and its main function is of nutrition and gas exchange. It sits between the retina (innermost layer) and sclera.
It is traditionally split up into three anatomica...
Vacuum-assisted therapy, also known vacuum-assisted closure (VAC) or negative pressure wound therapy, refers to a device used in the treatment of acute or chronic wounds.
foam dressing applied on the wound
covering transparent adhesive membrane
vacuum source: VAC ...