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.

27 results found
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L sign (brain)

The L sign is one of the features useful in identifying the central sulcus on cross-sectional imaging. It relies on identifying the superior frontal sulcus which intersects the precentral sulcus in an "L" junction, thus defining the precentral gyrus. The central sulcus is the next posterior sul...
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Lambda sign

There are a number of lambda signs: lambda sign of twin pregnancy lambda sign of sarcoidosis
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Lambda sign (sarcoidosis)

The lambda sign is seen on gallium-67 scans in the setting of thoracic sarcoidosis. Bilateral hilar and right paratracheal lymph nodes are typically involved which can resemble the lambda symbol (λ). See also lambda sign of twin pregnancy
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Lateral crescent sign (inguinal hernia)

Lateral crescent sign is a useful diagnostic sign of a direct inguinal hernia on CT scan, the hernia causing compression and lateral displacement of the inguinal canal contents (ductus deferens, testicular vessels, fat, etc) to form a semicircle of tissue that resembles a moon crescent seen late...
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Lateral femoral notch sign (knee)

The (deep) lateral femoral notch sign describes a depression on the lateral femoral condyle at the terminal sulcus, a junction between the weight bearing tibial articular surface and the patellar articular surface of the femoral condyle. Pathology The likely mechanism is a hyperextension or im...
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Lead pipe sign

Lead pipe appearance of colon is the classical barium enema finding in chronic ulcerative colitis. There is complete loss of haustral markings in the diseased section of colon, and the organ appears smooth walled and cylindrical. 
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Lemon sign (cerebellum)

The lemon sign, noted on antenatal imaging, is one of the many notable fruit inspired signs. It is a feature when there appears to be an indentation of the frontal bone (depicting that of a lemon). It is classically seen as a sign of a Chiari II malformation and also seen in the majority (90-98%...
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Lentiform fork sign

The lentiform fork sign has been described on MRI seen as bilateral symmetrical hyperintensities in the basal ganglia surrounded by a more/brightly hyperintense rim delineating the lentiform nucleus. It has been postulated to result from metabolic acidosis due to any cause 1, e.g. end stage ren...
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Leontiasis ossea

Leontiasis ossea is largely a historical term used to describe a number of conditions that result in the affected patient's face resembling that of a lion. Although it is most frequently associated with craniofacial fibrous dysplasia, it has a broader meaning encompassing other lesions that have...
Article

Leopard skin sign (white matter)

The Leopard skin sign (also known as tigroid pattern or stripe sign) results from dark-spots or stripes (spared perivascular white matter) within bright demyelinated periventricular white matter on T2W images. It is characteristically seen in : metachromatic leukodystrophy Pelizaeus-Merzbacher...
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Lhermitte sign (spinal cord)

Lhermitte sign is a clinical finding that is typically seen with multiple sclerosis (MS) but can also be seen in other entities which affect the dorsal columns of the spinal cord: cervical cord tumours cervical spondylosis, e.g. after a fracture 3 vitamin B12 deficiency It is characterised b...
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Licked candy stick appearance (bones)

The term licked candy stick appearance refers to tapering of the tips of the metacarpal bones, metatarsal bones, phalanges or clavicles and is usually associated with: psoriatic arthropathy rheumatoid arthritis leprosy neuropathic joint
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Light bulb sign (hepatic haemangioma)

The light bulb sign of a hepatic haemangioma is a feature than can be seen on MRI imaging with a classic hepatic haemangioma. This refers to marked hyperintensity seen on heavily T2 weighted sequences that has been likened to a glowing light bulb. See also light bulb sign - shoulder light bul...
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Light bulb sign (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...
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Lightbulb sign (shoulder dislocation)

The lightbulb sign refers to the abnormal AP radiograph appearance of the humeral head in posterior shoulder dislocation. When the humerus dislocates it also internally rotates such that the head contour projects like a lightbulb when viewed from the front 1. See also light bulb sign (hepatic...
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Lincoln sign on bone scintigraphy

Lincoln sign on bone scintigraphy​ (also known as black beard sign) is one of the signs of Paget disease on the radionuclide bone scan when the disease involves the mandible. The sign might be seen when the extensive mandibular involvement with Paget disease results in the uptake of the radiotra...
Article

Linguine sign (breast)

Linguine sign is one of the imaging signs of intracapsular rupture of a breast implant. After implantation of a silicone or saline breast implant, a fibrous capsule (scar) forms around the implant shell. In an intracapsular rupture, the contents of the implant are contained by the fibrous scar,...
Article

Lipohaemarthrosis

Lipohaemarthrosis results from an intra-articular fracture with escape of fat and blood from the bone marrow into the joint, and is most frequently seen in the knee, associated with a tibial plateau fracture or distal femoral fracture. They have also been described in the hip, shoulder and elbow...
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Locked facet joint

Locked facet joint is a type of facet joint dislocation that results from jumping of the inferior articular process over the superior articular process of the vertebra below and becomes locked in the position. It can be unilateral or bilateral. Radiographic features Plain radiograph The tip ...
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Loss of normal half-moon overlap sign

Loss of half-moon overlap sign, which does not really roll off the tongue, is a sign of posterior shoulder dislocation on AP radiographs.  On a normal true anteroposterior image, there is a half-moon overlap between the humeral head and the glenoid. In a posteriorly dislocated shoulder, there i...
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Loss of the insular ribbon sign

The loss of the insular ribbon sign refers to a loss of definition of the gray-white interface in the lateral margin of the insular cortex ("insular ribbon") and is considered an early CT sign of MCA infarction. The insular cortex is more susceptible to ischaemia following MCA occlusion than ot...
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Low attenuation lymphadenopathy

Low attenuation lymphadenopathy suggests underlying necrosis and can be seen in: metastatic carcinoma (or lymphoma) infections (tuberculous or fungal) Whipple disease coeliac sprue See also lymphadenopathy low attenuation lymphadenopathy high attenuating lymphadenoapthy
Article

Lower T sign

The lower T sign is one of the features useful in identifying the central sulcus on cross-sectional imaging.  It relies on identifying the inferior frontal sulcus which intersects the precentral sulcus in a "T" junction, thus defining the precentral gyrus. The central sulcus is the next posteri...
Article

Lucent liver sign

The lucent liver sign is represented by a reduction of hepatic radiodensity on supine radiograph when there is a collection of free intraperitoneal air located anterior to the liver.
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Luftsichel sign (lungs)

The Luftsichel sign is seen in some cases of left upper lobe collapse and refers to the frontal chest radiographic appearance due to hyperinflation of the superior segment of the left lower lobe interposing itself between the mediastinum and the collapsed left upper lobe.   Radiographic feature...
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Lung hyperinflation

Lung hyperinflation is a common condition in patients with chronic obstructive pulmonary disease (COPD). It is also linked to ageing and other chronic diseases that cause airflow obstruction. Pathology The airflow limitation during expiration is produced by two factors: destruction of the lun...
Article

Lyre sign (carotid artery)

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.

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