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.

48 results found
Article

Angiographic string sign

The angiographic string sign, also known as the carotid string sign, refers to the thin string of intravenous contrast material distal to a stenotic focus in the internal carotid artery (ICA).  Mechanism A thin stripe of flow is caused by decreased pressure and flow distal to the stenosis, whi...
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Beak sign of arterial dissection

The beak sign of arterial dissection represents a wedge of haematoma at the distal end of the false lumen. It is here that false lumen propagation is occurring. It manifests as an acute angle between the dissection flap and the outer wall. It may be filled with contrast enhanced blood (high atte...
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Capp triad

The Capp triad refers to the constellation of clinical and imaging findings in patients with spontaneous retropharyngeal haematomas, and consists of: tracheal and oesophageal compression anterior displacement of the trachea subcutaneous bruising over the neck and anterior chest
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Cobweb sign of arterial dissection

The cobweb sign is seen in cases of arterial dissection (usually aortic dissection) on CTA examinations and represents strands or ribbons of media crossing the false lumen, and appearing as thin filiform filling defects. Although it is a specific sign for the false lumen, it is infrequently see...
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Comet tail sign: Urology

Comet-tail sign (in urological imaging) is helpful in distinguishing a ureteric calculus from a phlebolith and strongly favours the later.  The sign refers to a tail of soft tissue extending from a calcification, representing the collapsed/scarred/thrombosed parent vein. When well seen it is sa...
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Concentric ring sign

The concentric ring sign is a pathognomonic sign for a subacute haematoma on MRI. A subacute haematoma may show 3 characteristic layers of  signal intensity: a thin peripheral rim of low signal intensity on all pulse sequences corresponding to haemosiderin. an inner peripheral high-signal int...
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Crescent sign of arterial dissection

The crescent sign refers to the high signal crescent seen in the wall of a vessel when dissected. This may be seen both on T1 or T2 sequences depending on the age of the blood (see ageing blood on MRI). It is classically referred to in internal carotid artery dissection. It should not be confus...
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Disappearing basal ganglia sign

The disappearing basal ganglia sign is one of the early signs of an MCA infarction. It is defined as the loss of delineation of the basal ganglia, due to blurring of their grey-white matter interface and hypoattenuation, consequent to cytotoxic oedema at the time of an ischaemic event. It is be...
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Dog leg sign

The "dog leg" sign is a secondary angiographic sign on popliteal angiography, which demonstrates an irregular lumen of popliteal artery with acute bend in the course of popliteal artery. It is characteristically seen in popliteal artery aneurysms with mural thrombus. It is important s...
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Double barrel sign

Double barrel sign is an imaging appearance of two lumens adjacent to each other. It can be seen in: dilated bile duct adjacent to portal vein double barrel aorta: aortic dissection double barrel oesophagus: oesophageal dissection
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Double density sign of berry aneurysms

Double density sign of berry aneurysms refers to the angiographic appearance of a small intracranial aneurysm projecting in front or behind a vessel of similar calibre. As such, the border of the aneurysm cannot easily be seen, but the extra contrast within it can be seen as a rounded area of in...
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Draped aorta sign

The draped aorta sign is an important imaging feature that can be seen in contained rupture of an abdominal aortic aneurysm. It is highly indicative of aortic wall deficiency.  This sign is considered present when the posterior wall of an aortic aneurysm drapes or moulds to the anterior surface...
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Empty delta sign

The empty delta sign is CT sign of dural venous sinus thrombosis of the superior sagittal sinus, where contrast outlines a triangular filling defect (clot). It is only described with CECT-scan or MRI, not with NECT nor non-contrast MRI. Pathology The exact mechanism for this appearance is unce...
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Figure 3 sign

The figure 3 sign is seen in aortic coarctation and is formed by prestenotic dilatation of the aortic arch and left subclavian artery, indentation at the coarctation site (also known as the "tuck"), and poststenotic dilatation of the descending aorta. On barium studies of the oesopha...
Article

Floating aorta sign

The floating aorta sign refers to displacement of the abdominal aorta away from the vertebral column. It is a radiographic/ CT sign of retroperitoneal masses. Radiographic findings On lateral lumbar spine radiographs, the expected location of posterior aortic wall is expected to be <= 10mm...
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Floating viscera sign

The floating viscera sign is an angiographic sign that occurs when there is visualisation of branches of the abdominal aorta (e.g. coeliac axis, superior mesenteric artery, and renal arteries) during aortography with little or no visualisation of the aortic lumen. it indicates the presence of a...
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Griesinger sign

Griesinger sign, named after Wilhelm Griesinger, a German psychiatrist and neurologist (1817-1868) refers to oedema of the postauricular soft tissues overlying the mastoid process as a result of thrombosis of the mastoid emissary vein. It is a complication of acute otomastoiditis and may be asso...
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High-attenuation crescent sign

The high attenuating crescent sign represents an acute haematoma within either the mural thrombus or the aneurysm wall, especially when detected on unenhanced CT scans. It is a specific sign of impending abdominal aortic aneurysm (AAA) rupture or so-called contained rupture. Pathology The hype...
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Hoffman-Rigler sign

The Hoffman-Rigler sign is a sign of left ventricular enlargement where an approximation of the distance between the inferior vena cava (IVC) and left ventricle is used.​ Radiographic features On a lateral chest radiograph, if the distance between the left ventricular border and the posterior ...
Article

Hyperdense MCA sign

The hyperdense MCA sign refers to the appearance of the middle cerebral artery (MCA) on CT. It has been associated with poor outcome, although this is by no means established 5. Radiographic features There is increased attenuation of the proximal portion of the MCA and it is often associated w...
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Ivy sign

The ivy sign refers to the MRI appearance of patients with moya moya disease or moya moya syndrome. Prominent leptomeningeal collaterals result in vivid contrast enhancement and high signal on FLAIR due to slow flow. The appearance is reminiscent of the brain having been covered with ivy. Diffe...
Article

Kissing carotids

The term kissing carotids refers to tortuous and elongated vessels which touch in the midline. They can be be found in:  retropharynx 2 intra-sphenoid 1 within the pituitary fossa within sphenoid sinuses within sphenoid bones The significance of kissing carotids is two-fold: may mimic int...
Article

Light bulb sign - adrenal pheochromocytoma

The light bulb sign of an adrenal pheochromocytoma is MRI feature of this tumour. This refers to marked hyperintensity seen on T2 weighted sequences however this finding is neither sensitive nor specific and pheochromocytomas are more often heterogeneous with intermediate or high T2 signal inten...
Article

Lyre sign

The lyre sign refers to the splaying of the internal and external carotid by a carotid body tumour. Classically described on angiography it is also visible on CT angiography.
Article

Macaroni sign

Macaroni sign is a sign seen in Takayasu arteritis on ultrasound. It represents smooth, homogeneous and moderately echogenic circumferential thickening of arterial wall that occurs in takayasu arteritis. The sign is highly specific for Takayasu arteritis, more commonly noted in the common caroti...
Article

Mercedes-Benz sign (aorta)

The Mercedes-Benz sign can be seen in the aorta in the context of aortic dissection on CT 1.  It is seen at three distinct intimal flaps that have a triradiate configuration similar to the Mercedes-Benz logo (Figure 1). Two of the three lumens outline by these intimal flaps belong to the false ...
Article

Pericardial calcification

Pericardial calcification (PC) usually occurs in patients with a history of pericarditis.  Pathology Causes uraemia previous trauma or prior pericarditis later sequelae of rheumatic heart disease malignant pericardial involvement (e.g. mediastinal teratoma) On chest radiography, location ...
Article

Pseudo vein sign

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 ...
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...
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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.
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 "...
Article

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...
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

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

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

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

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

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

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 sign

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

Threads and streaks sign

The threads and streaks sign refers to an angiographic appearance of a vascularised tumour thrombus extending into the ipsilateral renal vein or the inferior vena cava from a renal cell carcinoma. This gives an appearance of linear, thread like or string like appearance of the involved vessel.  ...
Article

Thrombus fissuration

Thrombus fissuration is a sign of impending rupture of an aortic aneurysm. It reflects blood dissecting into the intramural thrombus. This sign is observed on contrast-enhanced CT as linear contrast infiltrations from the aneurysm lumen through the intramural thrombus. Thrombus fissurations exte...
Article

Tulip bulb sign

Tulip bulb sign refers to characteristic appearance due to dilatation of sinuses of Valsalva slightly extending into the ascending aorta as seen on CT scan of chest.  It is seen especially in Marfan's syndrome. On CT angiography, aneurysm of the aortic root with effacement of sinotubular junct...
Article

Unfolded aorta

The term unfolded aorta refers to the widened and 'opened up' appearance of the aortic arch on a frontal chest radiograph. It is one of the more common causes for apparent mediastinal widening and is seen with increasing age. It occurs due to the discrepancy in the growth of the ascending aorta...
Article

Westermark sign

Westermark sign is a sign of pulmonary embolus (PE) seen on chest radiographs. Along with Fleishner sign and Hampton hump, it makes one of the one of the three described signs of pulmonary embolus on chest radiographs. Pathology In one study (PIOPED) this sign was present on ~10% of chest x-r...
Article

Windsock sign (aortic dissection)

The windsock sign refers to appearances seen in type A thoracic aortic dissections on contrast CT. It results from intimo-intimal intussussception between the true and false dissected lumens of the thoracic aorta. The altering density of contrast between the dissection lumens which taper distall...
Article

Yin-yang sign

The yin-yang sign is a radiological sign described in both true and false aneurysms on various imaging modalities.  Radiographic features Doppler sonography The yin-yang sign indicates bidirectional flow due to swirling of blood within the (true or false) aneurysm. Contrast enhanced CT The ...

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