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...
Uhl anomaly is an unusual cardiac disorder which affects the right ventricle where there is almost complete absence of right ventricular myocardium, normal tricuspid valve, and preserved septal and left ventricular myocardium.
History and etymology
It is named after Henry S D Uhl, who first de...
There are numerous differences between United Kingdom (UK) and United States (US) English spelling and, as stated elsewhere, we accept having a mix of UK and US spelling on the site while preferring the UK spelling for articles titles and content in our continuous aim for uniformity. The choice ...
Ulcerative colitis is an inflammatory bowel disease that not only predominantly affects the colon, but also has extraintestinal manifestations.
Typically ulcerative colitis manifests in young adults (15-40 years of age) and is more prevalent in males but the onset of disease after...
Ulegyria refers to a shrunken and flattened cortex due to global hypoxic ischaemic injury in term infants, centering on the deepest portion of gyri, usually in the parasagittal region. It is here that perfusion is most tenuous and, therefore, most susceptible to ischaemic damage.
It is one of t...
The ulna (plural: ulnae) is one of the two long bones of the forearm. It is located medially in the supinated anatomic position. It has a larger proximal end and tapers to a smaller distal end (opposite to the radius).
Prominent features of the ulna include:
The ulnar artery is a terminal branch of the brachial artery, arising at the proximal aspect of the forearm. Along with the radial artery, it is one of the main arteries of the forearm.
origin: terminal branch of the brachial artery
location: inferior aspect of the cubital fossa
Ulnar dimelia or mirror hand syndrome is a rare congenital anomaly of the upper limb characterized by absence of the radial ray (including thumb), duplication of the ulna and duplication of the ulnar halves of the carpals, metacarpals and phalanges 1.
The embryology of mi...
Ulnar hemimelia is a rare congenital upper limb anomaly characterized by complete or partial absence of the ulna bone.
Incidence is estimated at 1/100,000-150,000 live births, with a male to female ratio of 3:2.
Ulnar hemimelia may be associated with other skeletal ...
Ulnar impaction syndrome, also known as ulnar abutment or ulnocarpal loading, is a degenerative wrist condition caused by the ulnar head impacting upon the ulnar-sided carpus with the injury to the triangular fibrocartilage complex (TFCC).
Ulnar impaction syndrome most commonly pr...
Ulnar impingement syndrome is a wrist condition caused by a shortened distal ulna impinging on the distal radius proximal to the sigmoid notch. The syndrome is distinct from ulnar impaction syndrome, which typically occurs due to a long ulna (positive ulnar variance) impacting upon the triangula...
The ulnar nerve is one of the terminal branches of the brachial plexus and has motor and sensory supply to the forearm and hand.
The ulnar nerve originates as a terminal branch of the medial cord of the brachial plexus with nerve root fibres from C8-T1.
Ulnar nerve dislocation is an uncommon cause of pain and paresthesias in the ulnar nerve distribution. It occurs if the ulnar nerve subluxates and then dislocates over the anterior aspect of the medial epicondyle during flexion and extension of the elbow.
Ulnar nerve dislocation occ...
Ulnar styloid fractures occur in association with ~60% of distal radius fractures. Most of these are small avulsion fractures involving the tip of the ulnar styloid.
Usually these kind of fractures occur as the result of a fall on an outstretched arm and are often associated with a d...
Ulnar styloid impaction syndrome refers to wrist pain due to a long ulnar styloid process impacting upon the triquetral bone.
An unlar styloid >6mm in length is commonly regarded as being long. Impaction results in chondromalacia of the opposing articular surfaces, i.e. the proximal ...
Ulnar variance (also known as Hulten variance) refers to the relative lengths of the distal articular surfaces of the radius and ulna.
Ulnar variance may be:
neutral (both the ulnar and radial articular surfaces at the same level)
positive (ulna projects more distally)
negative (ulna projec...
The ulnar vein is one of the two major deep veins of the forearm, along with the radial vein. As is usual in the upper and lower limbs, there are often two veins (venae comitantes) that run on either side of the ulnar artery and anastomose freely with each other.
It forms in the hand from the d...
There are several distinct ulnar-sided wrist impaction and impingement syndromes. Underlying anatomical causes exist for each syndrome, however, repetitive or excessive use of the forearm and wrist can also contribute.
ulnar impaction syndrome: positive ulnar variance
ulnar impingement syndrom...
The ulnomeniscal homologue (UMH) is an obliquely oriented, fibrocartilaginous structure, that forms part of the ulnar collateral ligament complex (ULC).
The UMH is located between the ulnar styloid process and the triquetrum. It adheres to the ulnar joint capsule and merges with ...
Ultrasound (US) is an imaging technology that uses high-frequency sound waves to characterize tissue. It is a useful and flexible modality in medical imaging, and often provides an additional or unique characterization of tissues, compared with other modalities such as conventional radiography o...
The ultrasound "U" classification of thyroid nodules has been developed by the British Thyroid Association as part of their 2014 guidelines on the management of thyroid cancer.
It allows for stratifying thyroid nodules as benign, suspicious or malignant based on ultrasound appearances termed U1...
Ultrasound appearance of liver metastases can have bewildering variation.
Patterns do exist between ultrasound appearance of the liver metastases and the likely primary, which is sometimes helpful in directing a search for an unknown primary, as well as helping distinguish between benign lesion...
Ultrasound artifacts are commonly encountered and familiarity is necessary to avoid false diagnosis.
beam width artifact
comet tail artifact
colour comet tail artifact
mirror image artifact
ring down artifact
Ultrasound assessment of carotid arterial atherosclerotic disease has become the first choice for carotid artery stenosis screening, permitting the evaluation of both the macroscopic appearance of plaques as well as flow characteristics in the carotid artery.
This article focus on internal caro...
Ultrasound evaluation of breast cysts is the modality of choice. Obstruction of the ducts, often appearing as the result of epithelial hyperplastic processes or the stromal fibrosis, or both processes lead to the formation of cysts, disabling the drainage of the terminal ducts of the lobules.
Ultrasound frequencies in diagnostic radiology range from 2 MHz to approximately 15 MHz.
It is important to remember that higher frequencies of ultrasound have shorter wavelengths and are absorbed/attenuated more easily. Therefore, higher frequencies are not as penetrating. This explains why h...
Ultrasound guided biopsy is one form of image guided biopsy, typically performed by a radiologist. It is the most common form of image guided biopsy, offering convenience and real time dynamic observation with echogenic markers on cannulae allowing for precise placement.
It can potentially be ...
Ultrasound guided percutaneous breast biopsy is a widely used technique for an accurate histopathological assessment of suspected breast pathology. It is a fast, safe and economical procedure.
Ultrasound guidance is limited to lesions visible on ultrasound study, such as:
Ultrasound guided percutaneous drainage is one form of image guided procedure, allowing minimally invasive treatment of collections that are accessible by ultrasound study.
It has several advantages and disadvantages over CT, which include:
is a dynamic study, allowing greater prec...
Ultrasound (US) guided peripheral intravenous cannulation (IVC) is the placement of a cannula into a peripherally located vein under the direct vision of ultrasound. This process allows the cannulation of veins that are unable to be visualised or palpated without ultrasound. In trained individua...
Ultrasound of the elbow allows high-resolution imaging of elbow anatomy while simultaneously allowing dynamic evaluation of the joint, tendons, and ligaments.
There are multiple possible approaches to imaging the elbow with ultrasound. A typical protocol is as follows 1:
There are several approaches to ultrasound examination of the adult hip.
supine with the hip in mild external rotation
sagittal oblique plane parallel to the long axis of the femoral neck to assess femoral head and neck and for any joint effusio...
Ultrasound of the knee allows high-resolution imaging of superficial knee anatomy while simultaneously allowing dynamic evaluation of some of the tendons and ligaments. Knee ultrasound is somewhat limited compared with ultrasound examinations of other joints because the cruciate ligaments and th...
Ultrasound of the shoulder is a fast, relatively cheap and dynamic way to examine the rotator cuff and is particularity useful in diagnosing:
rotator cuff disorders
The examination requires attention to technique and appropriate patient positioning. ...
Ultrasound is a useful imaging modality for evaluation of the wrist, allowing high-resolution imaging of anatomy while simultaneously allowing dynamic evaluation of the joint, tendons, and ligaments.
There are multiple possible approaches to imaging the wrist with ultrasound. The exam...
An ultrasound transducer converts electrical energy into mechanical (sound) energy and back again, based on the piezoelectric effect. It is the hand-held part of the ultrasound machine that is responsible for the production and detection of ultrasound waves.
It consists of five main components:...
Ultrasound-guided fine needle aspiration (FNA) of the thyroid refers to a minimally invasive procedure where in which tissue samples are collected from a thyroid nodule or other suspicious thyroid lesion. It is usually done on a outpatient basis and generally complications are very minimal.
An umbilical arterial aneurysm (UAA) is an extremely rare but potentially lethal vascular anomaly which is usually detected in utero.
If tends to favour the placental end of the umbilical artery in the cord.
Concurrent associated anomalies are thought to be ...
Umbilical arterial catheters are used in neonatal care and need to be carefully assessed on all neonatal films.
The catheter should pass through the umbilicus, travel inferiorly through the umbilical artery, then in the anterior division of the internal iliac artery, into the common ...
Umbilical arterial (UA) Doppler assessment is used in surveillance of fetal well-being in the third trimester of pregnancy. Abnormal umbilical artery Doppler is a marker of uteroplacental insufficiency and consequent intrauterine growth restriction (IUGR) or suspected pre-eclampsia.
The umbilical artery gives rise to both a nonfunctional remnant of the fetal circulation, and an active vessel giving supply to the bladder. In the adult the obliterated area of the vessel is identifiable as the medial umbilical ligament and the patent segment is the superior vesical artery.
The umbilical cord is a fetal organ and connects the placenta to the uterus and is a vital passage for nutrients, oxygen and waste products to and from the fetus.
The umbilical cord inserts into the centre of the placental bulk and into the fetus at the umbilicus. Variations in insertion can o...
Umbilical cord coiling index is defined as number of coils per one centimeter of length of the cord . Normal index is one coil for a length of five centimeters. If number of coils are more per centimeter it is called as hypercoiled and less than it is called as hypocoiled umbilical cord. This in...
Umbilical cord cyst can refer to any cystic lesion associated with the umbilical cord. They can be single (commoner) or multiple.
They may be seen in ~3% of pregnancies in the first trimester 8.
Umbilical cord cysts can represent either true or false cysts
Umbilical cord entanglement is a feature which can mean either one of more loops of cord being encircled around any part of the any part of body 3 or two umbilical cord getting entangled with each other. In the latter situation it is a classical feature of a monochorionic-monoamniotic twin pregn...
Umbilical cord haematoma is formation of a haematoma secondary to bleeding from the umbilical cord.
The haematomas can be either spontaneous or iatrogenic. Spontaneous bleeding is very rare and documented to be around 0.02% of pregnancies. Majority of the cases are iatrogenic related...
Umbilical cord knot is a term given to denote either
true umbilical cord knot: often the term "umbilical cord knot" is used to describe this entity 1
false umbilical cord knot: usually of no clinical significance
umbilical cord entanglement
Umbilical cord prolapse is a situation where the umbilical cord protrudes into the cervical canal.
The estimated incidence is at ~ 0.2-0.5% of all pregnancies 4,5.
Recognised associations include
multifetal pregnancy: twin gestation
Umbilical cord pseudocysts are a type of cystic lesion occurring in relation to the umbilical cord.
Although the true incidence not accurately known, they are comparatively much more common than true umbilical cord cysts.
The pseudocyst basically comprises of mucoid de...
Umbilical cord thrombosis is a potentially fatal complication and can mean either a thrombosis of the umbilical vein or either or both the umbilical arteries. Umbilical vein thrombosis occurs more frequently than thrombosis of one or both umbilical arteries (umbilical arterial thrombosis)
Umbilical hernias are the most common ventral hernia and occur in the midline.
Ten times more common in females 2 and represent ~5% of all abdominal hernias 4.
Umbilical hernias present in the midline as painless or painful mass.
Umbilical vein varix (UVV) refers to a focal dilatation of the umbilical vein.
It tends to favour the intra-abdominal portion of the cord (typically between the abdominal wall and the liver) which is then termed a fetal intra-abdominal umbilical vein varix (FIUVV) or the in...
Umbilical venous catheters are commonly used in the neonatal period for vascular access, and should be carefully assessed for position on all neonatal films.
An umbilical venous catheter generally passes directly superiorly and remains relatively anterior in the abdomen. It passes th...
Umbilical venous dilatation is a rare entity and often tends to occur as an isolated finding 4.
It can arise from a number of patholgies
umbilical venous varix (UVV): particularly if focal
fetal hydrops: a focal dilatation due to an umbilical venous varix with an ensuing thrombosis can also ...
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
An umbilical-urachal sinus belongs to the spectrum of congenital urachal anomalies and represents a non-communicating dilatation of the urachus at the umbilical end.
Presentation is commoner in children and rare in adult.
An umbilical-urachal sinus...
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...
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 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...
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 Mullerian duct anomaly (class II) that is the second most commonly associated with miscarriages.
This type can account for ~10% (range 6-13%) of uterine anomalies and infertility is seen in ~12.5% (range 5-20%) of cases.
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
L: lungs, e.g. airwa...
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.
It results from failure of incorporation of the common pulmonary vein into the left atrium. There is no recognised right or left predilection.
The condition usually present in infancy or ch...
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.
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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Many pulmonary disease are described as upper or lower lobe predominant. The following mnemonics can aid recall of these differential diagnosis.
upper lobe or apical predominance: SET CAP
lower lobe or bibasilar predominance: BAD RASH
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...