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.

77 results found
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...
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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...
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Saddle pulmonary embolism

Saddle pulmonary embolism commonly refers to a large pulmonary embolism that straddles the bifurcation of the main pulmonary artery, 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 ...
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Sail sign

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...
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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...
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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 loss of definition between the inner and outer tables of the skull and a ground-glass appearance as...
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Sandwich sign

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...
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Sandwich sign of Marchiafava-Bignami disease

Sandwich sign of Marchiafava-Bignami disease is described as the appearance due to involvement of central layers of 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 of corpu...
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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 is distinctive for osteopetrosis. Differential diagnosis the sandwich vertebrae appearance resembles Rugger-jersey spine but can be diffe...
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Scalpel sign

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...
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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

Scotty dog sign

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

The seatbelt sign is both a clinical and radiological sign. It is simply the presence of bruising/abrasions in the distribution of a seatbelt (i.e. horizontal and/or diagonal) across the abdomen, chest and sometimes neck.  A positive seatbelt sign, in combination with abdominal pain or tenderne...
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Sentinel clot sign

The sentinel clot sign is a useful CT finding for the evaluation of probable anatomic sites of haemorrhage. On CT, acute clotted haemorrhage typically has high attenuation (45 to 80 HU), whereas surrounding areas of acute nonclotted haemorrhage or more chronic haemorrhage have either lower atte...
Article

Sentinel loop

A sentinel loop is a focal area of adynamic ileus close to an intra-abdominal inflammatory process. The sentinel loop sign may aid in localizing the source of inflammation. For example, a sentinel loop in the upper abdomen may indicate pancreatitis, while one in the right lower quadrant may be ...
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Septal bounce

Septal bounce is a sign of ventricular interdependence on echocardiography, cardiac CT, and cardiac MRI, manifested by reduced or paradoxical interventricular septal movement during diastole (i.e. initial septal movement towards and then away from the left ventricle) during early diastole second...
Article

Septal lines in lung

Septal lines, also known as Kerley lines, are seen when the interlobular septa in the pulmonary interstitium become prominent. This may be because of lymphatic engorgement or oedema of the connective tissues of the interlobular septa. They usually occur when pulmonary capillary wedge pressure re...
Article

Sergeant stripes sign

The sergeant stripes sign refers to the oblique direction of the cerebellar tonsillar folia; this is seen in Chiari 1 malformation.
Article

Seurat spleen

Seurat spleen is an angiographic appearance seen following blunt trauma to the spleen. Multiple small punctate regions of intraparenchymal contrast extravasation lead to a spotted appearance. History and etymology The term refers to a likeness between the angiographic appearance and the artwor...
Article

Shading sign

Shading sign is an MRI finding typically seen in an endometrioma. It may also be seen with some endometrioid tumours (e.g endometrioid carcinoma of the ovary) It helps to distinguish endometriomas from other blood containing lesions (e.g. haemorrhagic corpus luteum cysts), with a sensitivity of...
Article

Shepherd crook deformity

A shepherd crook deformity refers to a coxa varus angulation of the proximal femur, classically seen in femoral involvement by fibrous dysplasia, although may be seen in other disorders such as Paget disese of bone and osteogenesis imperfecta. The shape of the proximal femur resembels that of th...
Article

Shifting granuloma sign

Shifting granuloma sign refers to a shift in the location of a parenchymal lesion visible on prior films that may be seen in the presence of atelectasis. Such as when a calcified granuloma is present in a lung and a significant parenchymal collapse shifts it from one place to other.  
Article

Shiny corner sign

The shiny corner sign is a spinal finding in ankylosing spondylitis, representing reactive sclerosis secondary to inflammatory erosions at the superior and inferior endplates (corners on lateral radiograph) of the vertebral bodies which are known as Romanus lesions. Eventually, the vertebral bod...
Article

Shmoo sign

Shmoo sign refers to the appearance of a prominent, rounded left ventricle and dilated aorta on a plain AP chest radiograph giving the appearance of Shmoo, a fictional cartoon character in the comic strip Li'l  Abner in the 1940s. This sign is indicative of left ventricular hypertrophy.
Article

Shortening of the cervical canal

Shortening of the uterine cervical canal as the name implies refers to a abnormal shortening of the uterine cervical length. It is considered a sign of cervical incompetence in pregnancy and can lead to premature delivery. Pathology Aetiology primary (i.e. congenital/idiopathic) secondary m...
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Shoulder sign of pyloric stenosis

The shoulder sign of pyloric stenosis is seen during barium examination and refers to the bulging of the hypertrophied pyloric muscle into the lumen of the antrum. It is closely related to the cervix sign of pyloric stenosis.  See also cervix sign of pyloric stenosis target sign of pyloric ...
Article

Shred sign

Shred sign is a static sonographic sign observed in lung consolidation. The deeper border of consolidated lung tissue that makes contact with the aerated lung is shredded and irregular. This sign is not seen in massive translobar consolidation in which it is more difficult to appreciate the deep...
Article

Sigmoid kidney

A sigmoid kidney is an uncommon variant of the horseshoe kidney. Whereas the typical horseshoe kidney is fused only at the lower poles, in a sigmoid kidney both the upper and the lower poles are fused 1.
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Signal flare phenomenon

The signal flare phenomenon is a useful sign to identify active bleeding in a liquefied haematoma with haematocrit effect on dynamic CT scan images. When active arterial haemorrhage is present in a liquefied haematoma that has a haematocrit effect, a signal flare phenomenon may be seen as a lin...
Article

Signet ring sign

The signet ring sign is seen in bronchiectasis when the dilated bronchus and accompanying pulmonary artery branch are seen in cross-section. The bronchus and artery should be the same size, whereas in bronchiectasis, the bronchus is markedly dilated. The signet ring analogy has also been applie...
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Silhouette sign

Silhouette sign is somewhat of a misnomer and in the true sense actually denotes the loss of a silhouette, thus, it is sometimes also known as loss of silhouette sign or loss of outline sign 4.  The differential attenuation of x-ray photons by two adjacent structures defines the silhouette, e.g...
Article

Sinusoid sign

The sinusoid sign is a dynamic sonographic sign in M mode describing the movement line representing the lung towards the pleural line which is displayed as sinusoidal pattern. Similar to the quad sign, this sign has a high sensitivity and specificity for pleural effusion, which is anechoic in it...
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Sitting duck appearance

The sitting duck appearance denotes the normal anatomical configuration of the jugular foramen: the head of the duck (pointing backwards on the right side) represents the anteromedial pars nervosa the body of the duck representing the pars vascularis
Article

Small bowel faeces sign

The small bowel faeces sign (SBFS) can be observed on abdominal CT-scans. The sign has been described as a finding indicative of small bowel obstruction (SBO) or another severe small-bowel abnormality (i.e. metabolic or infectious disease). While the reported prevalence of the sign in SBO is low...
Article

Snowcap sign

Snowcap sign or snowcapping is defined as the appearance of dense sclerosis over the head of humerus or femur in cases of avascular necrosis as seen on plain radiographs, which resembels a snow capped mountain.
Article

Snowman sign: pituitary macroadenoma

Snowman sign in neuroimaging refers to the configuration of pituitary macroadenomas, which are soft tumours, due to indentation at the diaphragma sellar giving them a snowman configuration (or "number eight" or "dumbbell" configuration). This feature helps in differentiating ...
Article

Snowman sign: total anomalous pulmonary venous return

Snowman sign refers to the configuration of the heart and the superior mediastinal borders resembling a snowman. This is seen in total anomalous pulmonary venous return (TAPVR) type I (supracardiac type). It is an abnormality of the fetal circulation wherein the entire pulmonary venous flow is ...
Article

Snowstorm sign: complete hydatiform mole

Snowstorm sign in obstetric imaging is classically seen in complete hydatiform mole. It is characterised by the presence of multiple hydropic villi which gives the ultrasonographic appearance of a central heterogeneous mass having a solid, hyper echoic area and interspersed with multitude of cys...
Article

Soft tissue rim sign

The soft-tissue rim sign is used to distinguish a ureteric calculus from a phlebolith. The former appears as a calcific density with a surrounding rim of soft tissue which represents the oedematous ureteric wall. Phleboliths on the other hand usually have imperceptible walls (although up to 8% m...
Article

Sonographic halo sign

Sonographic halo sign is used in a number of situations. They include: hypoechoic halo sign in liver metastases: used in hepatobiliary imaging, is a concerning feature for malignant lesion if the lesion is a hyperechoic liver lesion 1,3 ultrasound halo in angiolymphoid hyperplasia with eosinop...
Article

Sonographic Murphy sign

Sonographic Murphy sign (SMS) is defined as maximal abdominal tenderness from pressure of the ultrasound probe over the visualised gallbladder 1,2. SMS is a sign of local inflammation around the gallbladder along with right upper quadrant pain, tenderness or mass 2. It is one of the most impor...
Article

Spade phalanx sign

Spade phalanx sign refers to a characteristic distal phalangeal shape in acromegaly. Radiographic features Plain radiographs The terminal phalangeal tufts become hypertrophied and have a "spade appearance". Other findings on hand radiography of acromegaly include joint spaces may ...
Article

Spaghetti sign in the bladder

The spaghetti sign refers to the presence of a linear worm like filling defect within a contrast opacified bladder. This linear filling defect is considered to represent blood clot extruded from the ureter and thereby moulded in the tubular shape. It is seen in patients with gross haematuria. Pr...
Article

Spalding sign

The Spalding sign refers the overlapping of the fetal skull bones caused by collapse of the fetal brain.  It appears usually a week or more after fetal death in utero.  This finding was originally described on abdominal radiographs and is indicative of fetal demise.
Article

Spilled teacup sign

The spilled teacup sign describes abnormal volar displacement and tilt of a dislocated lunate on lateral radiographs of the wrist 1-2. The convexity of the lunate is no longer in articulation with the distal radius while the concavity is no longer in articulation with the capitate. It is an impo...
Article

Spinnaker sign

The spinnaker sign (also known as the angel wing sign) is a sign of pneumomediastinum seen on neonatal chest radiographs. It refers to the thymus being outlined by air with each lobe displaced laterally and appearing like spinnaker sails. This is distinct from the sail sign appearance of the nor...
Article

Split pleura sign

The split pleura sign is seen with pleural empyemas and is considered the most reliable CT sign helping to distinguish an empyema from a peripheral pulmonary abscess (see empyema vs pulmonary abscess) 1-2.  The sign results from fibrin coating both the parietal and visceral surfaces of the pleu...
Article

Spoke wheel sign - meningioma

The spoke wheel sign refers to the pattern of vessels coursing through meningiomas, when seen in cross-section.  It is the result of the same phenomenon which results in the sunburst pattern (vessels seen from the side rather than in cross section). Terminology A similar appearance also referr...
Article

Stag's antler sign

The stag's antler sign refers to upper lobe pulmonary venous diversion (cephalisation) in pulmonary venous hypertension or pulmonary oedema as seen on frontal chest radiograph. The prominence of upper lobe pulmonary veins resemble stag's antler. It is the earliest sign of pulmonary venous hyper...
Article

Staghorn calculus

Staghorn calculi, also sometimes called coral calculi, are renal calculi that obtain their characteristic shape by forming a cast of the renal pelvis and calyces, thus resembling the horns of a stag. For a general discussion of renal calculi please refer to nephrolithiasis. Epidemiology Stagh...
Article

Starry sky appearance on ultrasound

A "starry sky appearance" refers to a sonographic appearance of the liver parenchyma in which there are bright echogenic dots throughout a background of decreased liver parenchymal echogenicity. Although usually associated with acute hepatitis, this sign has been found to have poor sen...
Article

Steeple sign

The steeple sign, also called wine bottle sign, refers to the tapering of the upper trachea on a frontal chest radiograph reminiscent of a church steeple. The appearance is suggestive of croup, which should be obvious clinically. A corresponding lateral x-ray would show narrowing of the subglott...
Article

Stener lesion

Stener lesions are seen in the context of a torn ulnar collateral ligament of the thumb's metacarpophalangeal joint (gamekeeper's thumb).  Pathology Normally, the ulnar collateral ligament lies deep to the adductor pollicis tendon. A Stener lesion is characterised by slippage of the torn end o...
Article

Stepladder sign

The stepladder sign is a sonographic sign indicating an intra-capsular breast implant rupture. It is considered the most reliable ultrasonographic finding in silicone gel breast implant intra-capsular rupture. It is identified as multiple, discontinuous, parallel, linear echoes in the lumen, and...
Article

Stierlin sign

The Stierlin sign refers to repeated emptying of the caecum, seen radiographically as barium remaining in the terminal part of the ileum and in the transverse colon. This occurs due to irritation of the caecum caused by M. tuberculosis.   See also gastrointestinal tuberculosis  Fleischner si...
Article

Stipple sign

The stipple sign refers to the pointillistic end-on appearance on intravenous pyelography or retrograde pyelography of contrast material tracking into the interstices of a papillary lesion. Because the majority of transitional cell carcinomas (TCC) have a papillary configuration, the presence of...
Article

Strawberry gallbladder

Strawberry gallbladder refers to the surface appearance (not shape) of the mucosa of the gallbladder due to multiple small collections of triglycerides and cholesterol esters within the lamina propria of the gallbladder wall.  Strawberry gallbladder represents diffuse cholesterolosis and is a c...
Article

Strawberry skull

Strawberry skull refers to the shape of the head on an antenatal ultrasound. Epidemiology Associations In general, strawberry skull is considered one of the nonspecific 'soft markers' for abnormal fetal development. It is considered more closely associated with trisomy 18 (Edward syndrome). ...
Article

Striated nephrogram

Striated nephrogram, originally described on plain film urography, but just as easily seen on CT urography represents linear bands of contrast extending from the medulla of the kidney towards the cortex. Pathology Striations result from stasis and concentration of contrast material in oedemato...
Article

String of beads sign

The string of beads sign is the description typically given to the appearance of the renal artery in fibromuscular dysplasia (FMD) but may also be used to describe the appearance of splanchnic arteries in segmental arterial mediolysis (SAM). It refers to the appearance arising from the stenoses ...
Article

String of pearls sign

String of pearls sign can refer to: string of pearls sign on an abdominal radiograph of fluid-filled dilated small-bowel loops string of pearls sign on ultrasound in polycystic ovarian syndrome string of pearls sign for angiographic appearances in fibromuscular dysplasia 
Article

String of pearls sign (gastrointestinal)

The string of pearls (or beads) sign can be seen on upright or decubitus abdominal radiographs as well as on CT in patients with small bowel obstruction, increased intraluminal fluid, and slow resorption of intraluminal gas. It consists of an obliquely or horizontally oriented row of small gas ...
Article

String sign

The string sign may refer to: angiographic string sign gastrointestinal string sign string sign of parosteal osteosarcoma
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String sign of parosteal osteosarcoma

The string sign of parosteal osteosarcoma refers to the plain radiographic and CT appearance a radiolucent cleavage plane between portions of the tumor and cortex of the affected bone. The tumour stalk becomes more broad-based with time, obliterating the string sign in later stages. The string ...
Article

Stuck temporomandibular joint disc

A stuck disc refers to a TMJ disc which does not translate anteriorly out of the mandibular fossa onto the articular eminence, but rather remains (thus "stuck") in the fossa. It is a form of TMJ dysfunction and is typically associated with restricted range of motion. Treatment is wit...
Article

Subcoracoid triangle sign

The subcoracoid triangle sign refers to obliteration of the fat triangle between the coracohumeral ligamant (CHL) and the coracoid process. It is considered a specific but not sensitive sign for adhesive capsulitis of the shoulder 1. 
Article

Subpleural line

Subpleural line refers to a thin curvilinear opacity, 1-3 mm in thickness, lying less than 1 cm from and parallel to the pleural surface. It corresponds to: atelectasis of normal lung if seen in the dependent posteroinferior portion of lung of a patient in the supine position (disappears if pro...
Article

Sugar coating

The so called "sugar coating" or zuckerguss (German for sugar icing) is seen in post contrast images of the brain and spinal cord in patients with leptomeningeal drop metastases or leptomeningeal carcinomatosis. It is seen both as a result of CNS involvement from distant primaries as w...
Article

Sulcal effacement

Sulcal effacement is a local secondary sign of mass effect in the cranium. Any lesion exerting mass effect on brain parenchyma can push adjacent gyri together, thereby displacing the CSF from the sulci. It is greatest at the site where the cause of the mass effect is located (e.g. tumour, haemo...
Article

Sunburst appearance - bone

Sunburst appearance is a type of periosteal reaction giving the appearance of a sunburst secondary to an aggressive periostitis. It should not be confused with the sunburst sign of meningioma vascularity.  The sunburst appearance occurs when the lesion grows too fast and the periosteum does not...
Article

Sunburst sign - meningioma

The sunburst sign refers to the characteristic vascular supply seen in some meningiomas when seen from the side (tangential to the dural attachment). It is the result of the same phenomenon which results in the spoke wheel pattern of vessels (viewed in cross section, parallel to dural attachment...
Article

Sunset eye sign

The sunset eye sign (also known as the setting sun phenomenon) is a clinical phenomenon encountered in infants and young children with raised intracranial pressures (seen in up to 40% of children with obstructive hydrocephalus and 13% of children with shunt dysfunction 1).  It consists of an up...
Article

Swallow tail sign

The swallow tail sign describes the normal axial imaging appearance of nigrosome-1 within the substantia nigra on high resolution T2*/SWI weighted MRI. Absence of the sign (absent swallow tail sign) is reported to have a diagnostic accuracy of greater than 90% for Parkinson disease 1.   Nigroso...
Article

Swan neck deformity

Swan neck deformity is a deformity of the digits that consists of: hyperextension of the proximal interphalangeal (PIP) joints compensatory flexion of the distal interphalangeal (DIP)  joints Pathology Swan neck deformity is seen in 3, 4: rheumatoid arthritis (classical association) post-t...
Article

Swirl sign

The swirl sign refers to the non-contrast CT appearance of acute extravasation of blood into a haematoma, for example an extradural haematoma or subdural hematoma. It represents unclotted fresh blood which is of lower attenuation than clotted blood which surrounds it 1. It is the corollary of t...
Article

Swischuk line

The Swischuk line is helpful in differentiating pathological anterior displacement of the cervical spine from physiological displacement, termed pseudosubluxation. Measurement the line is drawn from anterior aspect of posterior arch of C1 to anterior aspect of posterior arch of C3 the anterio...
Article

Swiss cheese sign

The Swiss cheese sign has been attributed to the appearances on CT of fluid containing pneumatoceles, that typically occur following pulmonary lacerations.1 The pneumatoceles appear as 'holes' in the lung parenchyma and hence the description with respect to Swiss style cheeses (e.g. emmental), ...

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