K space is an abstract concept and refers to a data matrix containing the raw MRI data. This data is subjected to mathematical function or formula called a transform to generate the final image. A discrete Fourier or fast Fourier transform 1-3 is generally used though other transforms such as th...
K wires (Kirschner wires) are a type of stabilization wire/pin used in orthopaedic surgery. They are pointed stainless steel wires that can be used in multiple roles during internal fixation:
as a temporary measure before more definitive fixation
thin wires are especially useful for smaller bo...
K trans is a measure of capillary permeability obtained using dynamic contrast enhanced (DCE) MR perfusion. It is calculated by measuring the accumulation of gadolinium-based contrast agent in the extravascular-extracellular space.
Increased permeability of vessels in the brain is seen in a va...
Kabuki syndrome (Niikawa-Kuroki syndrome) is a rare polydysplasia that is thought to be more common in Japan.
Estimated incidence of 1:32,000 in Japan. Sporadically seen elsewhere in the world. The reason for the disparity in incidence is controversial.
The cause for t...
Kager fat pad (also known as the pre-calcaneal fat pad or pre-Achilles fat pad) refers to the fat within the Kager triangle, which normally appears lucent (fat density) on radiographs and has relatively well-defined margins. Pathologies affecting nearby structures result in loss of the normal ma...
Kager's triangle is a sharply marginated radiolucent triangle seen posteriorly on lateral radiographs of the ankle. It represents the Kager fat pad.
It is bordered anteriorly by the flexor hallucis longus (FHL) muscle and tendon, posteriorly by the Achilles tendon, and inferiorly by the calcane...
Kallmann syndrome (KS) is a rare genetic disorder characterised by hypogonadotropic hypogonadism associated with anosmia or hyposmia. When anosmia is absent it is simply referred to as idiopathic hypogonadotropic hypogonadism (IHH).
It is a rare disorder with an estimated prevale...
Kaposi sarcoma (KS) is a low-to-intermediate grade mesenchymal tumour that involves the lymphovascular system. The tumour can involve the pulmonary, gastrointestinal, cutaneous and musculoskeletal systems.
There are four recognised variants 1:
classic (chronic): multiple distal low...
Kappa is a nonparametric test that can be used to measure interobserver agreement on imaging studies.
If comparing two observers, the concept behind the test is similar to the chi-squared test. Two 2 x 2 tables are set up: one with the expected values if there were chance agreement, and one wit...
Kartagener syndrome is a subset of primary ciliary dyskinesia, an autosomal recessive condition characterised by abnormal ciliary structure and/or function, leading to impaired mucociliary clearance.
The prevalence of primary ciliary dyskinesia is approximately 1 in 12,000-60,000...
Kasabach-Merritt syndrome (also known as haemangioma thrombocytopaenia syndrome) is a rare life-threatening disease found in infant in which a rapidly growing vascular tumour is responsible for thrombocytopaenia, microangiopathic haemolytic anemia and consumptive coagulopathy.
Kasai classification is used to describe the three main anatomical types of biliary atresia.
type I: obliteration of common bile duct (patent cystic and common hepatic duct)
IIa: obliteration of common hepatic duct (patent cystic and common bile duct), sometimes with a...
Kawasaki disease (KD) is a small to medium vessel vasculitis predominantly affecting young children. It can affect any body organ but there is a predilection for the coronary vessels.
An autoimmune aetiology has been postulated. It is generally self limiting but acute fatalities are ...
Kawashima procedure is palliative surgical procedure performed in cases of:
left isomerism and azygos continuation of the inferior vena cava
single functional ventricle
single atrium and common atrioventricular valve with or without regurgitation
It is performed by creati...
Kearns-Sayre syndrome (KSS), also known as oculocraniosomatic disorder, is a rare multisystem mitochondrial disorder.
Patient often present with progressive external ophthalmoplegia 1. Neurologic symptoms develop in childhood or adolescence, usually before 20 years of ag...
The Kellgren and Lawrence system is a method of classifying the severity of knee osteoarthritis (OA) using five grades. This classification was proposed by Kellgren et al in 1957 2 and later accepted by WHO in 1961.
grade 0: no radiographic features of OA are present
grade 1: d...
Keratocystic odontogenic tumours (KCOT or KOT), previously known as odontogenic keratocysts, are benign cystic neoplasms involving the mandible or maxilla and believed to arise from dental lamina. They are locally aggressive and tend to recur after excision.
On imaging, they typically appear a...
Keratosis obturans (KO) is a rare external auditory canal disease characterised by abnormal accumulation and consequently occlusion and expansion of the bony portion of the EAC by a plug of desquamated keratin. It can be confused by EAC cholesteatoma but they are completely different entities re...
Getting a film with Kerley lines in the exam is one of the many exam set-pieces that can be prepared for.
The film goes up and after a couple of seconds pause, you need to start talking:
There are bilateral basal interstitial lines that extend to the pleural surface - these are Kerley B l...
Kerma is a measure of energy transferred from radiation to matter and stands for kinetic energy released to matter. It is related to, but not the same as absorbed dose.
Kerma measures the amount of energy that is transferred from photons to electrons per unit mass at a certain position. Absorbe...
The Kernohan grading system for diffuse astrocytomas is no longer used, superseded by the the WHO grading system.
It was first described in 1949 and divided astrocytomas into 4 grades (I - IV) on the basis of histological features 1.
Kernohan notch phenomenon is an imaging finding resulting from extensive midline shift due to mass effect, resulting in indentation in the contralateral cerebral crus by the tentorium cerebelli. This has also been referred to as Kernohan-Woltman notch phenomenon and false localising sign.
The Keros classification is a method of classifying the depth of the olfactory fossa.
The ethmoid labyrinth is covered by the fovea ethmoidalis of the frontal bone and separates the ethmoidal cells from the anterior cranial fossa.
The very thin, horizontal cribriform plate (lamina cribrosa) of...
Kerr Kink a sign of renal tuberculosis. Scarring leads to a sharp kink at the pelvi-ureteric junction.
The Royal Australian and New Zealand College of Radiologists (RANZCR) have published a curriculum of "Key Conditions in Year 1 of Training", which have been defined as those that may be life threatening if undiagnosed over a period of 12 hours.
Forty-six conditions are listed per the...
The key image is a property of a stack, and refers to the image which is most representative of the stack as a whole. This image will then be used as the thumbnail for the stack both in case view and when the stack is included in an article.
The key image icon is located in the top left hand c...
The keyhole sign is an ultrasonographic sign seen in boys with posterior urethral valves. It refers to the appearance of posterior urethra which is dilated, and associated thick walled distended bladder which on ultrasound may resemble a key hole.
The kidney sweat sign applies to the presence of thin, hypoechoic, extracapsular fluid collections around kidneys in renal failure patients. This fluid is assumed to represent perirenal oedema. It can be appreciated on ultrasound, CT and MR imaging.
The kidneys are paired retroperitoneal organs that lie at the level of the T12 to L3 vertebral bodies.
The kidneys are located on the posterior abdominal wall, with one on either side of the vertebral column, in the perirenal space. The long axis of the kidney is parall...
Kienböck disease is the eponymous name given to avascular necrosis (aseptic necrosis) involving the lunate.
The age distribution for Kienbock disease depends on gender. The condition is most common within the dominant wrist of young adult men where it appears to be due to repeate...
Kiesselbach's plexus (Kiesselbach's area or Little's area) is a vascular region of the anteroinferior nasal septum that comprises four arterial anastomoses:
anterior ethmoidal artery
a branch of the opthalmic artery
a branch of the maxillary artery
greater palatine art...
The Kikuchi level is a histopathological term used for describing the degree of infiltration of a sessile early invasive colorectal cancer1. Preoperative assessment of the level of invasion using this classification may decrease the incidence of unnecessary surgery for sessile polyps.
Kikuchi-Fujimoto disease (KFD) (also known as subacute necrotising lymphadenitis or subacute necrotising histiocytosis) is an idiopathic disease characterised usually by cervical lymph node enlargement (80%).
It typically affects young women.
It usually pre...
A Killian-Jamieson diverticulum is a true oesophageal diverticulum.
They are located just below the cricopharyngeal muscle, anteriorly and laterally, as a left sided or less commonly bilateral outpouchings from the cervical oesophagus.
It is infrequently encountered compared with Ze...
Kilovoltage peak (kVp) is the peak voltage applied to the X-ray tube. It determines the highest energy of X-ray photon. It is responsible for acceleration of electrons from cathode to anode. It also determines tube current in space charge region.
Increase in kVp shifts the X-ray spectrum to ri...
A Kim lesion is defined as a superficial tear between posterior labrum and glenoid articular cartilage without labral detachment .
Failure to identify and treat this lesion leads to permanent posterior instability .
flattening or incomplete...
Kimura disease is a rare benign inflammatory disease that characteristically manifests as enlargement of cervical lymph nodes and salivary glands.
Kimura disease typically affects males (80%) between 20 and 40 years of age (80% of cases) 1-2, and is most frequently seen in Asia. S...
The Kirklin complex is a combination of the Carman meniscus sign associated with a radiolucent semi-circular zone surrounding the elevated ridge of the ulcer. This complex is seen in cases of gastric adenocarcinoma on barium studies.
Carman meniscus sign
The Kirklin sign refers to a deformity of the normal gastric air bubble on an upright chest radiograph due to a mass lesion of the gastric cardia or fundus.
The differential for a Kirklin sign includes
gastrointestinal stromal tumour (G...
Kirner deformity is characterised by a curvature of the distal phalynx of the 5th digit in both a palmar and radial direction.
The deformity typically presents in late childhood to early adolescence, although a mild deformity may be present at birth. Both sexes are affected, altho...
The term kissing carotids refers to tortuous and elongated vessels which touch in the midline. They can be be found in:
within the pituitary fossa
within sphenoid sinuses
within sphenoid bones
The significance of kissing carotids is two-fold:
may mimic int...
Klatskin tumour is a term that was traditionally given to a hilar cholangiocarcinoma, occuring at the bifurcation of the common hepatic duct. Typically, these tumours are small, poorly differentiated, exhibit aggressive biologic behaviour, and tend to obstruct the intrahepatic bile ducts.
Klaus height index is the distance between tip of the dens and the tuberculum torcula line (Twining's line). A normal height is 40-41mm.
A decreased Klaus height index is seen in basilar invagination.
Klebsiella pneumonia is refers to a pneumonia resulting from an infection from the organism Klebsiella pneumoniae.
There tends to be a higher prevalance in older patients with alcoholism and debilitated hospitalised patients 3.
Klebsiella pneumoniae is amongst the mos...
Klinefelter syndrome (KS) is a chromosomal anomaly, which in most cases is characterised by 47 chromosomes instead of the usual 46.
The estimated incidence is 0.15-0.2% of live births.
the testes are normal prior to puberty and small in post pubertal testes...
Klippel-Feil syndrome (KFS) is a complex heterogeneous entity that results in cervical vertebral fusion. Two or more non-segmented cervical vertebrae are usually sufficient for diagnosis.
There is a recognised female predilection 1. KFS has an incidence of 1:40,000-42,000 2.
Klippel-Trénaunay-Weber syndrome (KTWS) is a syndrome combination of capillary malformations, soft-tissue or bone hypertrophy, and varicose veins or venous malformations. It is considered an angio-osteo-hypertrophic syndrome.
KTS classically comprises a triad of:
port wine nevi
bony or soft t...
Knee bursae are sacs surrounding the knee joint that are filled with synovial fluid. They facilitate movement and reduce friction where tendons or muscles pass over bony prominences. The knee bursae can be either communicating or non-communicating with the knee joint itself.
The knee capsule is a dual-layered structure that surrounds the knee joint. It is relatively thin anteriorly and posteriorly, thickened laterally by the collateral ligaments.
The outer layer of the knee capsule consists of fibrous connective tissue to hold the joint in place, wh...
Knee dislocations are rare but a significant number have serious associated vascular injury. They account for <0.5% of all joint dislocations.
This article discussed tibiofemoral joint dislocation. Please see separate articles for discussion of medial and lateral patellar dislocation.
The knee joint is a modified hinge joint between the femur, tibia and patella. It is the largest synovial joint in the body and allows flexion and extension of the leg as well as some rotation in the flexed position.
location: two condylar joints between femur and tibia; saddle joint b...
The knee menisci are fibrocartilaginous structures that sit within the knee joint, deepening the tibiofemoral articulation. They function to improve stability, shock absorption and load transmission of the knee.
There are two knee menisci in each joint: medial and lateral. The me...
Check for an effusion on the lateral:
peripatellar fat pads should sit next to each other
anterior suprapatellar fat pad
prefemoral fat pad
soft tissue density between them indicates an effusion
if simple effusion (haemarthrosis), think severe ligamentous, meni...
The knee series is comprised of an AP and lateral radiograph and is used to evaluate fractures and other bony pathologies.
knee AP view
knee lateral view
knee intercondylar view
knee patellofemoral joint view
knee AP weight-bearing ...
The synovial membrane of the knee is the inner aspect of the knee capsule, which produces synovial fluid to aid in the lubrication of the knee joint. It is also reflected on to the articular margins of the femur, tibia and patella. It does not cover the menisci or the cruciate ligaments posterio...
Knee AP view is a standard projection to assess the knee joint, distal femur, proximal tibia and fibula and the patella.
patient is supine on the table with the knee and ankle joint in contact with the table
leg is extended
ensure the knee is not rotated
X-ray beam featur...
Kniest dysplasia is rare type of short limbed skeletal dysplasia.
It is thought to carry an autosomal dominant inheritance. Kniest dysplasia is one of a spectrum of skeletal disorders caused by mutations in the COL2A1 gene. This gene provides instructions for making a prote...
The knot of Henry is the superficial (i.e. plantar) crossing of the flexor digitorum tendon obliquely over the flexor hallucis longus tendon in the midfoot, at the level of the navicular bone. Distally to the knot of Henry there are connections, sometimes multiple, between the two tendons.
Knuckle sign refers to the abrupt tapering or cutoff of a pulmonary artery secondary to embolus. It is better visualised on CT pulmonary angiography scan than chest x-ray. This is an important ancillary finding in pulmonary embolism (PE), and often associated with the Fleischner sign of dilated ...
Köhler disease is an eponymous term referring to chilhood onset avascular necrosis of the navicular bone in the foot. Mueller Weiss syndrome is the adult counterpart of navicular bone avascular necrosis. 4,5
It typically presents in the paediatric population (4-6 years age) and th...
Komi classification of bile duct cysts, as stated by Komi et al , divides anomalous union of the pancreatico-bile ducts (AUPBD) into 3 types based on the angle of union of the ducts 1.
type I: union of the ducts at a right angle to each other
type Ia: without dilatation or
Kommerell diverticula occur in some anomalies of the aortic arch system. It usually refers to the bulbous configuration of the origin of an aberrant left subclavian artery in the setting of a right sided aortic arch. However, it was originally described as a diverticular outpouching at the origi...
Krabbe disease, also known as globoid cell leukodystrophy, is an autosomal recessive leukodystrophy.
Can vary and depends on age of onset 5.
loss of developed milestones
Krukenberg tumour, also known as carcinoma mucocellulare, refers to the "signet ring" subtype of metastatic tumour to the ovary. The colon and stomach are the most common primary tumours to result in ovarian metastases, followed by the breast, lung, and contralateral ovary.
Kufor-Rakeb syndrome is a neurodegenerative disease, considered a form of Mendelian parkinsonism.
This syndrome has an autosomal recessive pattern of inheritance, and was first described in an Arab consanguineous kindred.
Kufor-Rakeb syndrome has a juveni...
Kummel disease is an eponymous name for avascular necrosis of the vertebrae.
Kummel disease represents delayed (usually two weeks) vertebral body collapse due to ischaemia and non-union of the anterior vertebral body wedge fractures after major trauma.
Risk factors inc...
Kump's bump is a superior convexity of the growth plate located in the anteromedial quadrant of the distal tibia physis, which is the first site of physeal fusion. Closure usually occurs at about 12-13 years of age. The Kump's bump should not to be mistaken for a fracture or abnormal physeal fus...
Küttner tumour (KT) refers to a chronic sclerosing sialadenitis of the salivary glands. Despite the term tumour, it is a non neoplastic condition. It is classically described in relation the submandibular gland but less commonly can also affect other salivary glands 9 and occassionally as well ...
This classification was proposed by Kuwada in 19904 and at the time of writing (July 2016) remains the most widely used system for describing achilles tendon rupture.
Achilles tendon tears may be grouped (according to severity of the tear and degree of retraction) into 4 types:
type I: partia...
The Kveim Stilzbach skin test is a sensitive and specific test for sarcoidosis, requiring the intradermal injection of homogenized spleen or liver material from a patient with known sarcoidosis. In patients with sarcoidosis, a typical sarcoid granuloma will develop at the injection site within 4...
Kyphomelic dysplasias (also known as "pseudocampomelia") is thought to be a heterogeneous class of "bent bone" skeletal dysplasias. Entities included in a differential for the class are:
congenital bowing of the long bones
cartilage-hair hypoplasia (CHH; metaphyseal dyspla...
Kyphosis is a term used to describe the sagittal curvature of the thoracic spine.
An increased kyphotic angle is seen in the following conditions:
vertebral body fracture
A decreased kyphotic an...
This originally French article needs further translation and merging with the existing English article on hydatid disease.
Le kyste hydatique est une affection parasitaire due au taenia granulosis, considérée comme une zoonose atteignant aussi bien l'homme que les animaux, notamment les carnivo...