Umbilical venous flow in the physiological situation comprises of a monophasic non-pulsatile flow pattern with a mean velocity of 10-15 cm/s. The presence of pulsatility implies a pathological state unless in the following situations:
early in pregnancy: up to ~13 weeks gestation
Uncal herniation is a subtype of transtentorial downward brain herniation, usually related to cerebral mass effect increasing the intracranial pressure.
Abnormal posture and poor GCS. There may be pupillary dilation and loss of light reflex due to direct compression of th...
The uncinate process of the ethmoid bone is a thin hook-like osseous structure of the wall of the lateral nasal cavity.
Together with the ethmoid bulla, it forms the boundaries of the hiatus semilunaris and ethmoid infundibulum.
The course of the free edge of the uncinate proces...
The uncinate process of the cervical spine is a hook-shaped process found bilaterally on the superolateral margin of the cervical vertebral bodies of C3-C7.
The uncinate processes are more anteriorly positioned in the upper cervical spine and more posteriorly location in the lower cervical spin...
Unclassified cerebellar dysplasia is defined as focal or diffuse dysplasia of cerebellar hemispheres or vermis not associated with other known malformations or syndromes.
Can present with hypotonia, microcephaly or speech delay.
Uncovertebral joints, also called Luschka’s joints, are seen bilaterally between adjacent cervical vertebrae, identified by the cat ear shaped uncinate processes of the C3-7 vertebrae (C1 and C2 have no uncinate processes).
The articulation forms between the uncina...
The uncus is the innermost part of the anterior parahippocampal gyrus, part of mesial temporal lobe.
The uncus is the most anterior portion of the medial parahippocampal gyrus. It belongs to the limbic system. Housing the primary olfactory cortex, it is part of the olfactory sys...
Undifferentiated carcinoma of the endometrium is rare histological subtype of endometrial cancer. It is considered a high grade carcinoma, carries a poor prognosis and is often under-recognised 1.
It is thought to represent approximately 1-9% of endometrial cancers 1,6.
An undifferentiated carcinoma of the ovary is a rare type of ovarian epithelial tumour. They account for ~ 4% of ovarian cancer 2.
With these tumours, cellular differentiation is not sufficient for the tumour to be categorised into serous, mucinous or other specified subtypes. Pure u...
Undifferentiated embryonal sarcomas of the liver are rare, aggressive, and malignant liver tumours encountered in the paediatric population.
Approximately 90% of cases occur in patients under 15 years of age, most commonly between 6 and 10 years of age, but some cases have been r...
Undifferentiated spondyloarthritis (uSpA), also known as undifferentiated arthritis, is a non-specific mono- or polyarthropathy that lacks the clinical, serological and radiological features that would allow specific diagnosis. It often turns out to be an early presentation of a more well known ...
The term unfolded aorta refers to the widened and 'opened up' appearance of the aortic arch on a frontal chest radiograph. It is one of the more common causes for apparent mediastinal widening and is seen with increasing age.
It occurs due to the discrepancy in the growth of the ascending aorta...
Unfused spinous process, which is really failure of fusion of the neural arch, is a relatively common anatomical variant and is part of the spectrum of spina bifida occulta.
This should be differentiated from accessory ossicles of the spinous process, which appear after non-fusion of the secon...
Fusion of sternal body segments is usually complete by 25 years of age. But non-fusion of sternal body segments can be seen in older age group.
Unicameral bone cysts (UBC), also known as simple bone cysts, are common benign non-neoplastic lucent bony lesions that are seen mainly in childhood and typically remain asymptomatic. They account for the S (simple bone cyst) in FEGNOMASHIC, the commonly used mnemonic for lytic bone lesions.
A unicornuate uterus or unicornis unicollis is a type of Müllerian duct anomaly (class II) characterised by a banana shaped uterus usually draining into a single Fallopian tube.
This type can account for ~10% (range 6-13%) of uterine anomalies and infertility is seen in ~12.5% (ra...
A unifocalisation procedure is a corrective surgical technique used in patients with complete pulmonary artery atresia with major aortopulmonary collateral arteries (MAPCAs). In this technique, the collateral vessels supplying blood from the aorta directly to the lungs are brought into continuit...
Unilateral axillary lymphadenopathy while being more concerning than bilateral axillary lymphadenopathy can still arise from a various benign as well as malignant causes.
other regional infective causes
ipsilateral arm infection, e.g. cellulitis
Unilateral facet dislocation is a relatively stable type of facet dislocation.
Flexion/distraction associated with rotation. The inferior articular facet of vertebral above moves over the superior facet of the vertebral below and becomes locked. It usually affects C4-C5 or...
Mnemonics for a unilateral hyperlucent hemithorax include:
C: contralateral lung increased density, e.g. supine pleural effusion
A: air, e.g. pneumothorax
W: wall, e.g. chest wall mass, mastectomy, polio, Poland syndrome, surgical re...
Unilateral hypertranslucent hemithorax has many potential causes. It may be the result of rotation away from an optimal position or because of pathology.
A unilateral hypertranslucent hemithorax may be caused by the positioning of the patient. Rotation away from the radiation beam alt...
Unilateral pulmonary artery atresia (UPAA) or unilateral absence of the pulmonary artery (UAPA) is a variant of pulmonary artery atresia.
The estimated prevalence is around 1 in 200,000 young adults. The reported frequency on the right side is slightly greater for some reason 10....
Unilateral pulmonary oedema represents only 2% of cardiogenic pulmonary oedema with predilection for the right upper lobe and is strongly associated with severe mitral regurgitation 1, 2. It is hypothesised that the regurgitation jet is directed towards the right superior pulmonary vein thus pre...
Unilateral pulmonary vein atresia is a type of pulmonary vein atresia.
The condition usually present in infancy or childhood with recurrent episodes of pneumonia and/or haemoptysis. Presentation in adulthood does occur but is uncommon.
It results from failure ...
The differential diagnosis for unilateral testicular lesions is wide-ranging.
seminoma (40-50% of tumours)
non seminomatous germ cell tumours:
testicular epidermoid (teratoma with ectodermal elements only)
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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 upper GI bleeding is ~100 per 100,000 adults per year. Upper GI bleeding is twice as common in men as in women and increases in prevalence with age 5. The demog...
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.
This anatomy section promotes the use of the Terminologia Anatomica, the global standard for correct gross anatomical nomenclature.
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 a frontal chest x-ray.
The normal left atrial pressure is 5-10 mmHg. An elevation of left atrial pressure to 10-15 mmHg will re...
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 of the cerebral cortex 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 sulc...
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...
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, ...
The urogenital triangle forms the anterior half of the diamond-shaped perineum. The triangle's corners are defined by the pubis symphysis anteriorly and the ischial tuberosities anterolaterally. The anterolateral borders are the ischiopubic rami and the posterior border is the transverse perinea...
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/kidney stones are used interchangeably, although some authors have slightly varying definitions of each.
See main ar...
This is a basic article for medical students and other non-radiologists
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.
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...
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 the histopathological diagnosis of usual interstitial pneumonia (UIP) are as follows:
advanced subpleural or paraseptal fibrosis +/- honeycombing
patchy temporally heterogeneous fibrosis
the absence of features against UIP