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.

729 results found
Article

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 in ultrasound, multiphase CT/MRI or in...
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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 is seen in a patient with Paget disease.  This is a result of disorganised 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 indicating lunate dislocation or perilunate dislocation 1-2. A lateral image will help differentiate whether there is lunate or perilunate dislocation, with lunate dislocation demonstrating...
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Pine cone bladder

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

The pistol grip deformity is considered a typical radiographic sign of cam-type femoro-acetabular 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 Stulberg and co-workers in 1975 1.
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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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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 lipohaemarthrosis. 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 haemangioma)

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 haemangiomas 2. It is the axial equivalent of the corduroy sign seen on sagittal and coronal images. On CT the...
Article

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 mint sweet, the polo, also referre...
Article

Pooping duck sign

Pooping duck sign indicates the presence of a triquetral fracture, 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 the poop dorsal to the duck. The ...
Article

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 d...
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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...
Article

Porcelain gallbladder

Porcelain gallbladder refers to extensive calcium encrustation of the gallbladder wall. The term has been used to emphasise the blue discoloration and brittle consistency of the gallbladder wall at surgery. Often an incidental finding on multiple different modalities, CT can be used to confirm t...
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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...
Article

Positive carpal sign

The positive carpal sign is a useful radiographic sign for the diagnosis of Turner's syndrome in association with the other musculoskeletal manifestation. Radiographic features Abnormality in the shape of the proximal carpal row in the dorsopalmar radiographs of the wrist and hand (taken in th...
Article

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...
Article

Positive PCL line sign

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 medullary cavity of the distal femur, if it does not, it ...
Article

Posterior fat pad sign

The posterior fat pad sign is the visualisation of a lucent crescent of fat located in olecranon fossa on true lateral view of elbow joint with the elbow flexed at a right angle, and it indicates an elbow joint effusion. Normally, the posterior fat pad will not be seen on this view.  In an appr...
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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...
Article

Powers ratio

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 spinola...
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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...
Article

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. Radiographic appearance Plain radiograph On lateral wrist radiographs, the pronator fat pad normally appears a thin ra...
Article

Pseudocalculus sign (common bile duct)

A pseudocalculus sign is a term coined to describe a mimic of a distally impacted common bile duct stone on MRCP and CT cholangiography.  It results from the forceful contraction of ampulla of Vater with secondary pouting into the lower end of the CBD. This impression is superiorly rounded and ...
Article

Pseudocavitation (lung)

Pseudocavitation has been described as a well recognised 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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Pseudo gallbladder sign

Pseudo gallbladder 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 few cases of biliary atresia. In these patients it is an important f...
Article

Pseudogestational sac

A pseudogestational sac or pseudosac 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 originally reported before the use of endova...
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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, co...
Article

Pseudo-omphalocoele

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

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 bands superimpose...
Article

Pseudosubarachnoid haemorrhage

Pseudosubarachnoid haemorrhage is a sign related to apparent increased attenuation within the basal cisterns which simulates a true subarachnoid haemorrhage (SAH). Pathology Causes and associations The most common cause is cerebral oedema where there is a decrease in parenchymal attenuation a...
Article

Pseudo vein sign (bowel)

The pseudo vein 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 “pseudo-vein” persists b...
Article

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...
Article

Pulmonary plethora

Pulmonary plethora is a term used to describe the appearances of increased pulmonary perfusion on chest radiographs. It is commonly used in paediatric radiology.  Pathology Usually a left-to-right shunt of 2:1 is required for pulmonary plethora to occur 2,3. Increased pulmonary perfusion occur...
Article

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 (vCJD). It is also described in other neurological conditions: Fabry disease (although the hyperintense signal is seen on T1WI) ...
Article

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...
Article

Putaminal rim sign

The putaminal rim sign, also known as putaminal slit sign,  is a relatively specific sign of multiple system atrophy - parkinsonism (MSA-P), and refers to a linear region of high T2 signal surrounding the lateral aspect of the putamen at 1.5T MRI. Importantly this appearance can be seen in norma...
Article

Putty kidney

A putty kidney refers to a pattern of renal calcification associated with renal tuberculosis conventionally described on plain radiography. Calcification characteristically is very homogeneous and ground glass like, representing calcified caseous tissue 3-4. Premkumar et al labelled calcificatio...
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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 pleural, rib, fluid and lung. Similar to the sinusoid sign, this sign has a high sensitivity and specificity for pleural effusion, which is anechoic in itself.
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Raccoon eyes sign (base of skull fracture)

Raccoon eyes sign is periorbital ecchymosis and is indicative of base of skull fracture of the anterior cranial fossa.
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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 angula...
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Racing car sign (callosal dysgnesis)

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 tires represented by the widely spaced frontal horns, and the dilat...
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Radial bands sign

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 dysfuction of...
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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 paediatric 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 r...
Article

Radiological signs (gastrointestinal tract)

Radiological signs are described across the disciplines of imaging, including the gastrointestinal tract. Fruit-inspired, nature-related, and more feature in the list of signs described for a wide array of pathology. How fascinating are the minds of radiologists work in describing pathology?
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Raindrop skull

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

Ranke complex

Ranke complex is seen in 'healed' primary pulmonary tuberculosis comprised of two parts: Ghon lesion: calcified parenchymal tuberculoma ipsilateral calcified hilar node
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Rat bite erosions (gout)

Rat (a.k.a. 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 (oesophagus)

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

Renal arterial cut-off sign  as the name suggests is an abrupt termination of the vascular contrast opacified renal arterial lumen. It may be associated with or without any contrast extravasation It is seen in a vascular injury like segmental or main renal artery thrombosis or occlusion.
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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 cryptogenic organising pneumonia, formerly bronchiolitis obliterans with or...
Article

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 (forming more than three-fourths of a circle) or ring (forming a complete circle) shape of at least 2 mm in thickness. It was initially described on high-...
Article

Reverse figure 3 sign

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 CXR. It is formed by prestenotic dilatation of the ascending aorta, indentation of the coarctation site (or "tuck"...
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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-hyperechogenecity with surrounding hyperechoic rim .This sign is useful to differentiate metastases from cirrhotic nodules where target sign is seen in liver metastases.
Article

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 (NF1) due the presence of multiple neurofibromas of intercostal nerves.  This deformity is also described in osteogenesis imperfecta 1 Edward...
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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...
Article

Rigler notch sign

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 carcinoma1. However, this sign is also observed in other conditions, including granulomatous infections, and its differe...
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Rigler sign

The Rigler sign, also known as the double wall sign, is seen on a radiograph of the abdomen when the air is present on both sides of the intestine, i.e. when there is air on both the luminal and peritoneal side of the bowel wall. Pneumoperitoneum may be a result of perforation or, from recent i...
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Rigler triad

Rigler triad consists of three findings seen in gallstone ileus: pneumobilia small bowel obstruction ectopic gallstone, usually in the right iliac fossa Practical points Rigler triad should not be confused with Rigler sign, the Rigler notch sign or Hoffman-Rigler sign. History and etymolog...
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Rim sign in chronic hydronephrosis

The rim sign can be seen in association with chronic hydronephrosis.  In patient's 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 calices and...
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Rim sign in renal vascular compromise

Rim sign in renal vascular compromise is seen in major renal vascular compromise. It can be seen in: renal artery obstruction from embolism, thrombosis or dissection renal vein thrombosis acute tubular necrosis Radiographic features At contrast enhanced CT or MR imaging, a thin (1-3 mm) ri...
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Rim sign of avascular necrosis

The rim sign comprises a high T2 or intermediate T1 signal line sandwiched between two low signal lines, and represents fluid between sclerotic borders of an osteochondral fragment, and implies instability (stage III). The rim sign should not be confused with the double line sign of osteonecros...
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Rind sign (bones)

The rind sign indicates a lesion surrounded by a layer of thick, sclerotic reactive bone (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 colour 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 pregnan...
Article

Rings and arcs calcification

Rings and arcs calcification is characteristic of chondroid lesions, such as enchondromas and chondrosarcomas. It is due to endochondral mineralisation 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)
Article

Robert sign

Robert sign refers to the presence of a gas shadow within the heart or the greater vessels, in cases of fetal death in utero. It is a rare sign caused by postmortem blood degeneration, usually seen 1-2 days after death; and may be seen as early as 12 hours. Related articles fetal death in utero
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Rokitansky nodule

A Rokitansky nodule or dermoid plug refers to a solid protuberence projecting from an ovarian cyst in the context of a mature cystic teratoma. It often contains calcific, dental, adipose, hair and/or sebaceous components 1. 
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Rolling stone sign

The rolling stone sign refers to the presence of gallstones within the gallbladder that are mobile when the patient moves. Small gallstones can sometimes be difficult to diagnose due to the absence of posterior shadow artefact but the presence of a rolling stone sign increases the confidence of...
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Romana sign (Chagas disease)

Romana sign, also known as chagoma, refers to periorbital swelling, palpebral oedema and conjunctivitis seen 1-2 weeks following infection with Trypanosoma cruzi (causative agent in the Chagas disease).  Romana sign is associated with ipsilateral regional lymphadenopathy.  History and etymolog...
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Romanus lesion

The Romanus lesion represents an early finding in inflammatory spondyloarthropathies, such as ankylosing spondylitis and enteropathic arthritis, and appears as irregularity and erosion involving the anterior and posterior edges of the vertebral endplates 1. Healing response to these inflammatory...
Article

Rosary sign (gallbladder)

The rosary sign is a CT finding in adenomyomatosis of the gallbladder. It is formed by the enhanced proliferative mucosal epithelium, with the intramural diverticula surrounded by the unenhanced hypertrophied muscle coat of the gallbladder. The rosary sign is similar to the pearl necklace sign.
Article

Rose-thorn ulcers

Rose-thorn ulcers or rose-thorn appearance refers to deep penetrating linear ulcers or fissuring typically seen within stenosed terminal ileum with a thickened wall. They appear as thorn-like extraluminal projections on barium studies and this appearance is one of the typical signs of Crohn dise...
Article

Rugger-jersey spine

Rugger-jersey spine describes the prominent subendplate densities at multiple contiguous levels to produce an alternating sclerotic-lucent-sclerotic appearance. This simulates the transverse bands of a rugby jersey. This term and pattern are distinctive for hyperparathyroidism. Pathology In r...
Article

Saber sheath trachea

Saber-sheath trachea refers to diffuse coronal narrowing of the intrathoracic portion of the trachea with the concomitant widening of the sagittal diameter. It is not uncommon and is pathognomonic for chronic obstructive pulmonary disease (COPD) 1.  The sagittal:coronal diameter is over 2:1 2 a...
Article

Saber sign in pneumobilia

The saber sign refers to a pattern of gas distribution seen in supine radiographs of patients with pneumobilia.  A sword-shaped lucency is apparent in the right paraspinal region of the upper abdomen representing arching gas extending from the common bile duct into the left hepatic duct.  This i...
Article

Sack of marbles sign

The sack of marbles sign refers to aggregations of multiple small globules of fat within a cyst mimicking marble spheres within a sack. They appear hyperechoic on ultrasound, fat attenuation on CT, and high signal on T1WI and T2WI on MRI. It is considered highly suggestive of a dermoid cyst ​1.
Article

Saddle pulmonary embolism

Saddle pulmonary embolism commonly refers to a large pulmonary embolism that straddles the bifurcation of the pulmonary trunk, extending into the left and right pulmonary arteries. If large enough, it can completely obstruct both left and right pulmonary arteries resulting in right heart failur...
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Sail sign (elbow)

The sail sign on an elbow radiograph describes the elevation of the anterior fat pad to create a silhouette similar to a billowing spinnaker sail from a boat. It indicates the presence of an elbow joint effusion. The anterior fat pad is usually concealed within the coronoid fossa or seen parall...
Article

Sail signs

There are numerous sails signs in radiology, where a normal structure is displaced or a pathology creates the appearance of a sail: elbow sail sign: the raised anterior fat pad on an elbow radiograph thymic sail sign: normal thymus on a paediatric chest radiograph spinnaker-sail sign (angel w...
Article

Salad oil sign

Salad oil sign, also referred as droplet sign, is characterised by small rounded high T2 signal foci within a breast implant on MRI studies and represents water droplets or small amounts of air within the silicone. It also can be characterised as hypointense foci on the water-suppressed sequence...
Article

Salt and pepper sign

The salt and pepper sign is used to refer to a speckled appearance of tissue. It is used in many instances, but most commonly on MRI. Please note that pathologists also use the term. Differential diagnosis Vascular tumours Used to describe some highly vascular tumours which contain foci of ha...
Article

Salt and pepper sign (skull)

Salt and pepper sign or pepperpot skull of the calvarium refers to multiple tiny well-defined lucencies in the skull vault caused by resorption of trabecular bone in hyperparathyroidism. There is a loss of definition between the inner and outer tables of the skull and a ground-glass appearance ...
Article

Sandwich sign (Marchiafava-Bignami disease)

Sandwich sign of Marchiafava-Bignami disease is described as the appearance due to the involvement of central layers of the corpus callosum. T2 and FLAIR hyperintensities are seen in the central region of body and splenium of corpus callosum with sparing of peripheral dorsal and ventral layers ...
Article

Sandwich sign (mesentery)

A sandwich sign, sometimes known as a hamburger sign, refers to a mesenteric nodal mass, either para-aortic or not, giving an appearance of a hamburger. Confluent lymphadenopathy on both sides of the mesenteric vessels gives rise to an appearance described as the sandwich sign 2. The sign is sp...
Article

Sandwich vertebral body

Sandwich vertebral body is a radiologic appearance in which the endplates are densely sclerotic, giving the appearance of a sandwich. This term and pattern are distinctive for osteopetrosis. Differential diagnosis the sandwich vertebrae appearance resembles Rugger-jersey spine but can be diff...
Article

Scalpel sign (spinal cord)

The scalpel sign has been recently described in dorsal thoracic arachnoid web on sagittal MRI studies. It relates to focal distortion of the thoracic cord, appearing anteriorly displaced. The enlarged dorsal CSF space mimics the profile of a surgical scalpel. It is helpful in distinguishing cas...
Article

Scimitar sign of cystic adventitial disease

Scimitar sign traditionally referred a catheter angiographic appearance, although it can also be seen on MRA and CTA. It denotes lateral displacement and stenosis of the popliteal artery in patients with cystic adventitial disease. 
Article

Scottie dog sign (spine)

The Scottie dog sign refers to the normal appearance of the lumbar spine when seen on oblique radiographic projection. On oblique views, the posterior elements of the vertebra form the figure of a Scottie dog with: the transverse process being the nose the pedicle forming the eye the inferior...

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