Articles

Articles are a collaborative effort to provide a single canonical page on all topics relevant to the practice of radiology. As such, articles are written and edited by countless contributing members over a period of time. A global group of dedicated editors oversee accuracy, consulting with expert advisers, and constantly reviewing additions.

904 results found
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Periportal free gas sign

The periportal free gas sign has been described as being strongly suggestive for upper gastrointestinal hollow viscus perforation. See also bowel perforation (summary) pneumoperitoneum
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Periportal halo (liver)

Periportal halo or periportal collar sign refers to a zone of low attenuation seen around the portal veins on contrast-enhanced CT or hypoechogenicity on liver ultrasound. It likely represents periportal edema, which is often used as a synonymous term. Periportal haloes may occur around the cent...
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Perirenal cobweb

Perirenal cobwebs are the presence of prominent perinephric septa. It is best appreciated on CT images. Pathology The cobweb is considered to be due to engorged venous collaterals or due to edema and fluid extravasation into the perirenal space 1. Perirenal cobwebs may be seen in many benign ...
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Peritoneal stripe sign (pneumoperitoneum)

The peritoneal stripe sign in abdominal ultrasonography is considered indicative of intraperitoneal free air, present in pneumoperitoneum. Free air in the abdomen will collect in an anti-dependent manner, typically the anterior prehepatic space in the supine patient, settling against the parieta...
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Periwinkle sign (supratentorial ependymoma)

The periwinkle sign has been coined to describe what has been claimed to be a characteristic appearance of intraparenchymal supratentorial ependymomas on non-enhanced CT axial images. The central solid component with centripetal calcification surrounding central necrotic area resembles a flower...
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Phantom calyx

A phantom calyx is a solitary calyx which fails to opacify with contrast amidst an otherwise well-opacified pelvicalyceal system. It is due to an intrarenal process which has infiltrated and caused obliteration of the involved collecting system element. It may be seen in: tumor: especially tra...
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Phemister triad (tuberculosis)

The triad of Phemister refers to three features seen classically with tuberculous arthropathy: juxta-articular osteopenia/osteoporosis peripheral osseous erosions gradual narrowing of joint space History and etymology Named after Dallas Burton Phemister (1882-1951), American orthopedic surg...
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Phrygian cap

Phrygian caps are the most common congenital anatomic variant of the gallbladder. It denotes folding of the fundus back upon the gallbladder body and is asymptomatic with no pathological significance. Radiographic findings A Phrygian cap may be identified on ultrasound, multiphase CT/MRI or ch...
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Picture frame vertebral body

Picture frame vertebral body is a radiologic appearance in which the cortex of the vertebral body is thickened. This sign can be seen in patients with Paget disease.  It is a result of disorganized new cortical bone formation after excessive osteoclastic activity causes the resorption of normal...
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Piece of pie sign (wrist)

The piece of pie sign refers to an abnormal triangular appearance of the lunate on a PA image of the wrist representing either lunate dislocation or perilunate dislocation 1,2. A lateral image will help differentiate whether there is lunate or perilunate dislocation, with lunate dislocation demo...
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Piglet sign (osmotic demyelination)

The piglet sign is seen in central pontine myelinolysis. It refers to the appearance of the upper pons in axial T2 and FLAIR images. The areas of coalescent T2 signal increase are reminiscent of a pigs snout, with other features on axial MR images resembling the rest of the face of a piglet with...
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Pine cone bladder

A pine cone bladder or Christmas tree bladder is a cystographic appearance in which the bladder is elongated and pointed with a thickened, trabeculated wall. It is typically seen in severe neurogenic bladder with increased sphincter tone (detrusor sphincter dyssynergia) due to suprasacral lesion...
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Pistol grip deformity (hip)

The pistol grip deformity is considered a typical radiographic sign of cam-type femoroacetabular impingement. The shape of the proximal femur is reminiscent of a flintlock pistol known from old pirate movies. History and etymology It was first described by American orthopedic surgeon S David S...
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Pitt pit

Pitt pit refers to an oval or round lucency in the anterosuperior aspect of the femoral neck, just distal to the articular surface. It represents a herniation of synovium or soft tissues into the bone through a cortical defect, hence the alternate name synovial herniation pit. They are usually a...
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Pivot shift test

The pivot shift test forms part of the orthopedic examination of a post-traumatic knee. A positive test shows high specificity for injury of the anterior cruciate ligament. Procedure The pivot shift test is performed on a supine patient.  At the start the subject's knee is permitted to droop ...
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Plankton sign (ultrasound)

The plankton sign refers to swirling, punctiform internal echoes within an otherwise anechoic pleural effusion which demonstrate slow, whirling dynamics, occasionally buffered by cardiac and respiratory impulses. When present, one may rule out a transudative effusion, and should be highly suspic...
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Pleural mouse

A pleural mouse (also known as a fibrin body), is a 1-2 cm mobile rounded clump of fibrin left over after resolution of a pleural effusion.
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Pneumolipohaemarthrosis

Pneumolipohaemarthrosis is the presence of intra-articular gas in a lipohemarthrosis. It indicates an open intra-articular fracture. 
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Pneumothorax in supine projection

A pneumothorax does not display classical signs when a patient is positioned supine for a chest radiograph. Instead, the pneumothorax may be demonstrated by looking for the following signs: relative lucency of the involved hemithorax deep, sometimes tongue-like, costophrenic sulcus: deep sulcu...
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Pneumothorax (ultrasound)

Pneumothorax is a serious potential consequence of blunt thoracic trauma and, if misdiagnosed, it may quickly become life-threatening. For a discussion on epidemiology, clinical presentation, pathology, and treatment and prognosis please see the main pneumothorax article.  Radiographic feature...
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Polka-dot sign (vertebral hemangioma)

The polka-dot sign is the result of the replacement of the normal cancellous bone by thickened vertical trabeculae surrounded by fat marrow or vascular lacunae in vertebral intraosseous hemangiomas 2. It is the axial equivalent of the corduroy sign seen on sagittal and coronal images. On CT the ...
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Polo mint sign (venous thrombosis)

The polo mint sign is a description given to a venous thrombosis on contrast-enhanced CT imaging.  When viewed in the axial plane, a thin rim of contrast persists around a central filling defect due to thrombus. This gives an appearance like that of the popular UK mint sweet, the Polo (figure 1)...
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Polycoria

Polycoria is the presence of more than one true pupil in the iris, each possessing their own fully functional sphincter pupillae muscle, which responds appropriately to light and drugs. It is a very rare entity with only a few case reports in the global literature 1,2. Pseudopolycoria occurs whe...
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Pool sign (intracranial; metastatic adenocarcinoma)

The pool sign is a recently described brain MRI appearance where an intracranial mass exhibits a T2 hyperintense rim adjacent to a solid mass surrounded by peritumoral edema. This appearance has been recently suggested to be a feature characteristic of metastatic adenocarcinoma (with various pri...
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Pooping duck sign

Pooping duck sign indicates the presence of a triquetral fracture in a lateral wrist radiograph, where an avulsed fracture fragment from the dorsal cortex of the triquetrum projects along the dorsal aspect of the osseous structures of the wrist. In this sign, the fracture fragment represents th...
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Popcorn calcification

Popcorn calcification refers to amorphous calcifications often with rings and arcs that resemble popped corn kernels. This type of calcification may be seen in many radiological settings including 1: chondroid lesions (e.g. enchondroma, chondrosarcoma) fibrous dysplasia pulmonary hamartomas ...
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Popcorn calcification within the breast

Popcorn calcification in the breast is the classical description for the calcification seen in involuting fibroadenomas which, as the name suggests, has a popcorn-like appearance.  Pathology A fibroadenoma in the long run may degenerate and calcify. Initially there are a few punctate periphera...
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Porcelain gallbladder

Porcelain gallbladder refers to extensive calcium encrustation of the gallbladder wall. The term has been used to emphasize the blue discolouration and brittle consistency of the gallbladder wall at surgery but is often an incidental finding on multiple different imaging modalities.  Clinical p...
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Porcelain left atrium

Porcelain left atrium, also known as coconut left atrium, is a term used when a large part of or the entire left atrial wall becomes calcified. It can occur as a rare consequence of endocarditis (with underlying rheumatic heart disease). It has also been described in the setting of end-stage ren...
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Positive bronchus sign

The positive bronchus sign is seen on CT chest, and refers to the presence of a bronchus leading directly to a peripheral lung lesion 1,2. In one study, four types of tumor-bronchi relationships were described 3: patent bronchus leads directly to the tumor mass bronchus is within the tumor ma...
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Positive carpal sign

The positive carpal sign is a useful radiographic sign for the diagnosis of Turner syndrome in association with the other musculoskeletal manifestations. Radiographic features Abnormality in the shape of the proximal carpal row in the dorsopalmar radiographs of the wrist and hand (taking in th...
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Positive metacarpal sign

In the metacarpal sign, a line drawn along the heads of the 4th and 5th metacarpals will intersect the head of the 3rd metacarpal if shortening is present. The shortened 4th metacarpal is the key to the sign. The sign is positive in up to 9.6% of normal individuals 3. It is however seen in a va...
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Positive PCL line sign

The positive PCL line sign is an indirect sign of anterior cruciate ligament (ACL) tear based on secondary changes of the posterior cruciate ligament (PCL) on MRI images. A line tangent to the upper border of the PCL should normally intersect the medullary cavity of the distal femur, if it does ...
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Posterior fat pad sign (elbow)

The posterior fat pad sign is the visualization of a lucent crescent of fat located in the olecranon fossa on a true lateral view of an elbow joint with the elbow flexed at a right angle indicating an elbow joint effusion. Normally, the posterior fat pad will not be seen on this view.  In the s...
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Posterior pituitary bright spot

The posterior pituitary bright spot is an MRI feature of the normal pituitary gland. It refers to the intrinsically high T1 signal of the posterior pituitary thought to be from the storage of vasopressin, which has a T1-shortening effect 2. It is important to note that a posterior pituitary bri...
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Potato nodes

Potato nodes are a classical moniker for the large nodes seen in the lung hila and mediastinum on the chest radiograph in pulmonary sarcoidosis. This name is derived from the characteristic bulky irregular morphology of the nodes which is reminiscent of large lumpy potatoes. Although this appear...
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Powers ratio

The Powers ratio is a measurement of the relationship of the foramen magnum to the atlas, used in the diagnosis of atlanto-occipital dissociation injuries. The ratio, AB/CD, is measured as the ratio of the distance in the median (midsagittal) plane between the: basion (A) and the posterior spi...
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Pretzel sign (serpentine aneurysm)

The pretzel sign is seen on DSA and is indicative of a serpentine aneurysm 1. The sign refers to the sinusoid configuration of the intra-aneurysmal vascular channel seen in serpentine aneurysms, giving it the appearance of a pretzel.
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Prévost sign (eyes)

The Prévost sign, also known as the Vulpian sign, refers to conjugate ocular deviation in patients with acute cortical hemiparetic stroke. The direction is variable, depending on the location of the stroke 3. In a hemispheric stroke, the eyes usually deviate towards the lesion (away from the h...
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Pronator quadratus sign

The pronator quadratus sign can be an indirect sign of distal forearm trauma. It relies on displacement of the fat pad that lies superficial to the pronator quadratus muscle. Pathology Displacement, anterior bowing, or obliteration of the fat plane in the setting of trauma may indicate a dista...
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PSA density

The PSA density (PSAD), is a calculation performed at diagnosis and is the serum PSA level (ng/mL) divided by the volume of the prostate gland (mL)1. Prostate volume is calculated from TRUS measurements2,3.  Alternatively, PSAD may be calculated using MRI measurements3 of prostate volumes or le...
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Pseudoboutonniere deformity

The pseudoboutonniere deformity is the result of an untreated hyperextension injury of the proximal interphalangeal joint. It is due to an uncommon avulsion of the volar plate from the proximal phalanx causing a flexion deformity of the PIP joint, while the central slip of the extensor tendon r...
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Pseudocalculus sign (common bile duct)

The pseudocalculus sign is a term coined to describe a mimic of a distally impacted common bile duct (CBD) stone on ERCP, MRCP and the various forms of cholangiography, including T-tube, CT, intraoperative, and percutaneous 1. It results from the forceful contraction of the choledochal sphincte...
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Pseudocavitation (lung)

Pseudocavitation has been described as a well recognized feature of  adenocarcinoma in situ / minimally invasive adenocarcinoma (bronchoalveolar carcinoma) of the lung. It refers to the central bubble-like low density region seen within a pulmonary nodule on CT.
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Pseudodysraphism

A pseudodysraphism refers to the splayed appearance of a normal spine created due to excessive craniocaudal angulation during sonographic evaluation. This can erroneously lead to the diagnosis of a spinal neural tube defect.
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Pseudogallbladder sign

Pseudogallbladder sign is a sonographic feature that can be seen in some children with biliary atresia. Radiographic features Ultrasound Appears as a cystic structure seen in the liver which is confused with gallbladder in a few cases of biliary atresia. In these patients it is an important f...
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Pseudogestational sac

A pseudogestational sac, also known as a pseudosac or intra-cavitary fluid, is the concept that a small amount of intrauterine fluid in the setting of a positive pregnancy test and abdominal pain could be erroneously interpreted as a true gestational sac in ectopic pregnancy. The sign was origi...
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Pseudokidney (intussusception)

The pseudokidney of intussusception is an ultrasound finding in some cases of intestinal intussusception. It refers to the longitudinal ultrasound appearance of the intussuscepted segment of bowel which mimics a kidney. The fat-containing mesentery which is dragged into the intussusception, con...
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Pseudo-omphalocele

Pseudo-omphalocele is a spurious sonographic appearance giving an impression of an anterior abdominal wall defect. Radiographic features Antenatal ultrasound Pseudo-omphalocele may be seen in: scanning errors where there is a deformation of the fetal abdomen by transducer pressure and the im...
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Pseudopneumomediastinum

Pseudopneumomediastinum is the false impression, usually on a chest x-ray, of pneumomediastinum. Correctly identifying pneumomediastinum is important, but making the diagnosis in error may lead to further unnecessary investigation and possible treatment. Causes include: Mach band superimposed...
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Pseudo-Rigler sign

The pseudo-Rigler sign is an important form of pseudopneumoperitoneum, and a mimicker of the classic Rigler (double wall) sign, that can be encountered normally on abdominal radiographs. Radiographic features The pseudo-Rigler sign can result from omental or mesenteric fat, or oral contrast me...
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Pseudosubarachnoid hemorrhage

Pseudosubarachnoid hemorrhage describes an apparent increased attenuation within the basal cisterns simulating true subarachnoid hemorrhage. It is usually due to cerebral edema. Pathology Etiology The most common cause is cerebral edema where there is a decrease in parenchymal attenuation and...
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Pseudovein sign (bowel)

The pseudovein sign can occur with active gastrointestinal bleeding where contrast extravasation during angiography may have a curvilinear appearance as it pools in the gastric rugae or mucosal folds of bowel, mimicking the appearance of a vein. However, contrast in the “pseudovein” persists bey...
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Psoas sign (abdominal x-ray)

The psoas sign is a classic non-specific finding on the abdominal radiograph, potentially representing retroperitoneal pathology. Normally on an abdominal radiograph, the lateral margins of both the psoas muscles are clearly visible due to adjacent fat. When the lateral edge of one, or both, ps...
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Ptosis

Ptosis (or blepharoptosis) is a drooping or falling of the upper eyelid. Complete ptosis is due to complete oculomotor nerve palsy. Partial ptosis is due to a dysfunction of the sympathetic pathway leading to paralysis of Muller muscle.  Note that facial nerve paralysis prevents screwing of the...
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Puff of smoke sign

The puff of smoke sign describes the characteristic angiographic appearance of tiny abnormal intracranial collateral vessel networks in moyamoya disease. Progressive narrowing of the supraclinoid internal carotid arteries and circle of Willis vessels results in extensive small collateral arteria...
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Pulmonary plethora

Pulmonary plethora is a term used to describe the appearances of increased pulmonary perfusion on chest radiographs. It is commonly used in pediatric radiology.  Pathology Usually a left-to-right shunt of 2:1 is required for pulmonary plethora to occur 2,3. Increased pulmonary perfusion occurs...
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Pulvinar sign (Creutzfeldt-Jakob disease)

The pulvinar sign refers to bilateral FLAIR hyperintensities involving the pulvinar thalamic nuclei. It is classically described in variant Creutzfeldt-Jakob disease. It is also described in other neurological conditions: Fabry disease: the hyperintense signal is seen on T1 rather than T2 bila...
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Punctate microcalcification within the breast

Punctate microcalcifications in the breast are defined as calcific opacities <0.5 mm in diameter seen within the acini of a terminal duct lobular unit. Pathology Associations fibrocystic changes skin calcification skin talc rarely in DCIS: punctate, clustered, segmentally distributed Radi...
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Putaminal rim sign

The putaminal rim sign, also known as the putaminal slit sign, is a relatively specific sign of multiple system atrophy - parkinsonism (MSA-P), and refers to a linear region of high signal surrounding the lateral aspect of the putamen at 1.5 T MRI on T2 weighted images or ADC map. Importantly th...
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Putty kidney

A putty kidney refers to a pattern of renal calcification associated with renal tuberculosis conventionally described on plain radiography. The calcification is characteristically very homogeneous and ground glass-like, representing calcified caseous tissue 3,4. Premkumar et al. labeled calcific...
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Pyrexia

Pyrexia (or fever) is a clinical sign, indicated by an abnormally elevated core body temperature, which is defined by several medical societies as ≥38.3°C (≥101°F). The temperature elevation may be persistent or episodic. The commonest cause of fever is infection, in one study of hospital inpati...
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Quad sign

The quad sign is a static sonographic sign observed in pleural effusion. It consists of four lines representing the pleura, rib, fluid, and lung. Similar to the sinusoid sign, this sign has a high sensitivity and specificity for pleural effusion, which - when simple - is itself anechoic.
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Raccoon eyes sign (base of skull fracture)

Raccoon eyes sign (or panda eyes in the UK and Ireland) is due to periorbital ecchymosis and is specific for base of skull fracture of the anterior cranial fossa. However it is not pathognomonic for trauma, and there are several rare causes described, including metastatic neuroblastoma, Kaposi ...
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Rachitic rosary

Rachitic rosary refers to expansion of the anterior rib ends at the costochondral junctions and is most frequently seen in rickets as nodularity at the costochondral junctions. Differential diagnosis Other causes of this appearance include:  scurvy the costochondral junction is more angular ...
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Racing car sign (callosal dysgenesis)

The racing car sign refers to widely spaced lateral ventricles due to agenesis of the corpus callosum with intervening Probst bundles. Appearances on axial MRI or CT are reminiscent of a Formula One car seen from above, with the tyres represented by the widely-spaced frontal horns, and the dilat...
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Radial bands sign (tuberous sclerosis)

The radial bands sign refers to linear bands seen on MRI, radiating from the periventricular white matter to the subcortical region, thought to be specific for tuberous sclerosis 1,2. Pathology The exact pathogenesis of radial bands is uncertain, but they are thought to relate to dysfunction o...
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Radiocapitellar line

The radiocapitellar line is one of the key lines used to assess alignment on the elbow radiograph. It is particularly useful in the pediatric setting. The rule A line drawn down the neck of the radius should intersect the capitellum. It is important to ensure that you draw the line down the ra...
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Raindrop skull

The raindrop skull appearance of calvarial multiple myeloma is the presence of multiple, well-defined lytic lesions (punched out lesions) of various size scattered throughout the skull. This term is applied as an analogy to rain hitting a surface and splashing, where it leaves a random pattern o...
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Ranke complex (tuberculosis)

Ranke complex is seen in 'healed' primary pulmonary tuberculosis and is a later manifestation of the Ghon complex. It consists of two components: a Ghon lesion that has undergone calcification an ipsilateral calcified mediastinal node History and etymology Karl Ernest Ranke (1870-1926) was a...
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Rat bite erosions (gout)

Rat (or mouse) bite erosions are seen in gout and refer to punched out erosions with sclerotic and overhanging margins. 
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Rat-tail sign (esophagus)

The rat-tail sign is used to refer to the tapering of the inferior esophagus in achalasia. The same appearance (although it is difficult to see the similarity) is also referred to as the ​bird beak sign (esophagus). 
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Renal arterial cut-off sign

Renal arterial cut-off sign, as the name suggests, is an abrupt termination of the contrast-opacified lumen of the renal artery. It may or may not be associated with contrast extravasation. It is seen in a vascular injury, e.g. segmental or main renal artery thrombosis or occlusion.
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Retrocardiac sail sign

The retrocardiac sail sign represents the characteristic and highly specific appearance of left lower lobe collapse on a frontal chest x-ray. Radiographic appearance The collapsed, medially displaced left lower lobe is represented by a triangular area of increased density with sharp margins, s...
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Reverse bat wing pulmonary opacities

Reverse bat wing pulmonary opacities refer to peripheral opacities of the lungs, sparing the perihilar region. It is a relatively unusual appearance with a relatively narrow differential: chronic eosinophilic pneumonia organizing pneumonia (formerly bronchiolitis obliterans with organizing pne...
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Reversed halo sign (lungs)

Reversed halo sign, also known as the atoll sign, is defined as central ground-glass opacity surrounded by denser consolidation of crescentic shape (forming more than three-fourths of a circle) or complete ring of at least 2 mm in thickness 8. It was initially described on high-resolution CT. T...
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Reverse figure 3 sign (esophagus)

The reverse figure 3 sign (also known as the E sign) is seen on barium swallows in patients with a coarctation of the aorta and is the medial equivalent of the figure 3 sign seen on plain chest radiographs. It is formed by prestenotic dilatation of the ascending aorta, indentation of the coarcta...
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Reverse rim sign (kidney)

The reverse rim sign describes relative hypoenhancement of the renal cortex and normal enhancement of the renal medulla on contrast-enhanced CT and MRI. This enhancement pattern can also be visualized using CEUS 2. It is a typical finding of renal cortical necrosis that may occur in the setting...
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Reverse target sign (cirrhotic nodules)

A reverse target sign is a potential ultrasound marker for cirrhotic nodules on ultrasound.It represents central iso-hyperechogenicity with surrounding hyperechoic rim. This sign is useful to differentiate metastases from cirrhotic nodules, conversely the target sign is seen with liver metastases.
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Ribbon ribs deformity

Ribbon ribs deformity refers to the presence of thinned ribs on image studies. Such findings could be present in patients with neurofibromatosis type 1 due to the presence of multiple neurofibromas of intercostal nerves.  This deformity is also described in osteogenesis imperfecta 1 Edwards s...
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Rice grain calcification

Rice grain calcification is characteristic of infection with Taenia solium (cysticercosis); when the inflammatory response of the host kills the larval cysts (cysticerci), they undergo granulomatous change and become calcified. Radiographic features Ovoid flecks of calcification resembling gra...
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Right posterior hepatic notch sign

The right posterior hepatic notch sign is a sharp indentation of the normally smooth posterior right hepatic lobe margin. It is associated with cirrhosis, although the mechanism is not entirely clear. It has been suggested that this may be an indication of relative caudate lobe hypertrophy and d...
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Rigler notch sign (lungs)

The Rigler notch sign refers to an indentation in the border of a solid lung mass, which is thought to represents a feeding vessel, thus suggesting the presence of a bronchial carcinoma 1. However, this sign is also observed in other conditions, including granulomatous infections, and its differ...
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Rigler sign (bowel)

The Rigler sign, also known as the double-wall sign, is a sign of pneumoperitoneum seen on an abdominal radiograph when gas is outlining both sides of the bowel wall, i.e. gas within the bowel's lumen and gas within the peritoneal cavity. It is seen with large amounts of pneumoperitoneum (>1000 ...
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Rigler triad (gallstone ileus)

Rigler triad consists of three findings seen in gallstone ileus: pneumobilia small bowel obstruction ectopic gallstone, usually in the right iliac fossa History and etymology It is named after Leo George Rigler, American radiologist (1896-1979) 1. Practical points Rigler triad should not ...
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Rim sign (avascular necrosis)

A rim sign can be seen in avascular necrosis and comprises a high T2 or intermediate T1 signal line sandwiched between two low signal lines, and represents fluid between the sclerotic borders of an osteochondral fragment, and implies instability (stage III). This rim sign should not be confused...
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Rim sign (chronic hydronephrosis)

The rim sign can be seen in association with chronic hydronephrosis.  In patients with chronic hydronephrosis, in all forms of contrast-enhanced imaging of the obstructed kidney, enhancement may occur in the residual, but markedly atrophic, renal parenchyma, surrounding the dilated calyces and ...
Article

Rim sign (pulmonary infarction)

The rim sign can be seen in cases of pulmonary infarction on PET-CT with very mild peripheral continuous FDG uptake and the complete absence of central uptake. This is a different appearance to that seen in lung abscesses or necrotic tumors, whereby the peripheral FDG-avidity is marked. History...
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Rim sign (spinal cord metastasis)

The rim sign has been described as a helpful MRI sign of spinal cord metastases, enabling them to be distinguished from other enhancing spinal cord lesions (e.g. ependymoma and astrocytoma).  Radiographic features MRI The rim sign is seen on sagittal post contrast T1 weighted imaging of the s...
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Rind sign (bones)

The rind sign is used when a lesion is surrounded by a layer of thick, sclerotic reactive bone (i.e. a rind) and is suggestive of fibrous dysplasia. The classic rind sign is most commonly seen in the proximal femur.
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Ring of fire sign (adnexa)

The ring of fire sign, also known as ring of vascularity, signifies a hypervascular lesion with peripheral vascularity on color or pulsed Doppler examination of the adnexa due to low impedance high diastolic flow 1. This sign can be seen in: corpus luteum cyst (more commonly) ectopic pregnancy
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Rings and arcs calcification

Rings and arcs calcification is characteristic of chondroid lesions, such as enchondromas and chondrosarcomas. It is due to endochondral mineralization of multiple hyaline cartilage nodules and is similar to popcorn calcification, which has rings and arcs on the background of more amorphous calc...
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Ring shadow (disambiguation)

Ring shadows are radiographic signs seen on either chest x-rays or on upper gastrointestinal fluoroscopy: ring shadow (chest) ring shadow (abdomen)

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