An absent septum pellucidum may rarely be an isolated finding, or more commonly be seen in association with a variety of conditions.
The septum pellucidum is partly or entirely absent in 2 or 3 individuals per 100,000 in the general population.
An absent septum pelluc...
An absent thumb can have many associations. They include:
Fanconi anemia (pancytopenia-dysmelia syndrome)
phocomelia (e.g. thalidomide embryopathy)
Poland syndrome (pectoral muscle aplasia and syndactyly)
Seckel syndrome ...
Absent end-diastolic flow (AEDF) in an umbilical artery Doppler assessment is a useful feature which indicates underlying fetal vascular stress if detected in mid or late pregnancy. It is often classified as Class II in severity in abnormal umbilical arterial Dopplers 9.
Absence of the yolk sac in the presence of an embryo on a transvaginal ultrasound is considered abnormal, and in general is associated with subsequent embryonic death.
Absorbed dose is a measure of the energy deposited in a medium by ionising radiation. It is equal to the energy deposited per unit mass of a medium, and so has the unit joules (J) per kilogram (kg), with the adopted name of gray (Gy) where 1 Gy = 1 J.kg-1.
The absorbed dose is not a good indica...
In ultrasound, absorption is the reduction in intensity of the sound waves as it passes through tissue. Most of the energy lost is in the form of heat.
Acaeruloplasminaemia is an autosomal recessive type of neurodegeneration with brain iron accumulation and disorder of iron metabolism caused by a mutation in the caeruloplasmin (CP) gene resulting in the production of dysfunctional caeruloplasmin.
Acaeruloplasminaemia is a very ra...
An acardiac twin, also known a recipient twin, refers to the haemodynamically disadvantaged twin of a twin-pair in the setting of twin reversed arterial perfusion (TRAP) sequence. The acardiac twin undergoes secondary atrophy and is non-viable.
Acardiac twinning is thought to affe...
ACC/AHA classification of coronary lesions is a system use to classify coronary arterial calcific plaque burden. It is classified as
discrete (< 10 mm)
nonangulated segment < 45º
little or no calcification
less than totally occlusive
not ostial in locati...
There are a number of accepted abbreviations that we use on Radiopaedia.org. We would like the site to be as standardized as possible and we have therefore chosen our accepted abbreviations and would ask that where possible these are used:
a.k.a. not aka (short for "also known as")
cf. not c.f...
The accessory anterior inferior tibiofibular ligament (AITFL), also known as Bassett's ligament, can be a cause of anterior ankle impingement syndrome. The accessory AITFL is described as a separate thickened distal fascial of the AITFL with a far distal extension on the lateral malleolus.
The accessory appendicular artery, also known as the artery of Seshachalam, is a branch of the posterior cecal artery. It arises from the ileocolic artery, and runs in the mesoappendix.
The exact prevalence of this accessory artery and its impact upon the risk of appendicitis varies among studi...
Accessory breast tissue is a relatively common congenital condition in which abnormal accessory breast tissue is seen in addition to the presence of normal breast tissue. This normal variant can present as a mass anywhere along the course of the embryologic mammary streak (axilla to the inguinal...
Accessory fissures of the lung usually occur at the borders of bronchopulmonary segments. They are common normal variants but are less commonly seen on imaging.
Some of the more common accessory fissure include 1:
azygos fissure: most commonly seen accessory fissure
inferior accessory fissur...
The accessory flexor digitorum longus muscle is an accessory muscle in the deep posterior compartment of the leg with a reported prevalence of 6-8%. Unilateral muscles are more common although bilateral cases have been reported.
origin: variable; either the medial margin of the tibia a...
Accessory gallbladders are a rare anatomical variant occurring in 0.03% of cases (approximately 1 in 3000 people). They can arise from either the left or right hepatic ducts or both. Accessory gallbladders arise from a bifid diverticulum of the hepatic duct in the 5th or 6th week of development ...
The accessory (or superior) hemiazygos vein forms part of the azygos system and along with the hemiazygos vein, it is partially analogous to the right-sided azygos vein. It drains the left superior hemithorax.
Origin and course
The accessory hemiazygos vein is formed by the con...
An accessory left atrial appendage is a frequent fortuitous finding in cardiac imaging, encountered in ~10% of patients. They are more often seen as a small diverticular structure projecting from the right upper side of the left atrial wall.
it must not be confused with ...
The accessory meningeal artery is a branch of the maxillary artery but can also branch from the middle meningeal artery.
The artery passes upwards through the foramen ovale to supply the trigeminal ganglion and the dura mater of Meckel's cave and the middle cranial fossa. It also usually suppli...
The accessory middle cerebral artery is a variant of the middle cerebral artery (MCA) that arises from the anterior cerebral artery (ACA). It is different from a duplicated middle cerebral artery, in which the duplicated vessel originates also from the distal end of the internal carotid artery (...
Accessory navicular syndrome occurs when a type II accessory navicular (or "os tibiale externum") becomes painful due to movement across the pseudojoint between the ossicle and the navicular bone.
It can be inferred on musculoskeletal ultrasound if a patient's...
The accessory ossicle of the anterior arch of the atlas is a normal variant and is best appreciated on a lateral cervical/sagittal study. It is observed as a circular and corticated osseous density that articulates with the inferior aspect of the anterior arch of the atlas.
It is not associate...
Accessory ossicles are secondary ossification centers that remain separate from the adjacent bone. They are usually round or ovoid in shape, occur in typical locations and have well defined smooth cortical margins on all sides.
In most cases, they are congenital in origin, although they may occ...
Accessory ossicles of the feet are common developmental variants with almost 40 having been described. Some of the more common include 1-4:
os tibiale externum (accessory navicular)
os calcaneus secundaris
There are numerous named and unnamed accessory ossicles of the lower limb. These include:
ossicles of the hip
ossicles of the knee
ossicles of the foot
os tibiale externum
os calcaneus secundaris
Accessory ossicles of the wrist are commonly seen on plain radiographs of the wrist and associated cross-sectional imaging. Over 20 were originally described 2, although the more common include 1:
lunula: between TFCC and triquetrum
os styloideum (carpal boss): on dorsal surface of 2nd or 3rd ...
Accessory ossicles of the wrist can be easily recalled with the mnemonic:
O: os styloideum (carpal boss)
T: (os) triangulare
T: (os) trapezium secondarium
E: (os) epilunate
O: os hamuli propriu
Another useful mnemonic is HOTELS
H: (os) hamuli propr...
Accessory parotid glands are a normal variant and represent ectopic salivary tissue separate from, but usually in close proximity to, the main parotid glands.
Accessory parotid glands are commonly picked up incidentally on ultrasound; seen in ~20% of the general population 2.
Accessory peroneal muscles are a group of accessory muscles that can occur in the foot region as a normal variant in some individuals. The peroneal compartment is known as the lateral compartment of the leg.
Peroneus quartus muscle
Originally, several accessory muscles were distinguished in th...
The accessory phrenic nerve is an anatomical variant seen in a little over one third of patients (36%). It most commonly arises from the ansa cervicalis, or slightly less commonly, the subclavian nerve. It is unknown as to how much the accessory phrenic nerve contributes to diaphragmatic functio...
Accessory renal arteries are a common variant and are present in ~25% (range 20-30%) of the population. Their proper identification is of utmost importance for surgical planning prior to live donor transplantation 2,3 and renal artery embolization for various reasons 5.
The term extra renal art...
An accessory right inferior hepatic vein is the most common variation of the hepatic veins. It is present in up to 48% of the population and drains the posterior part of the right lobe (mainly segments 6 and 7) directly into the inferior vena cava.
Variations in hepatic vascular anatomy are pa...
Accessory sacroiliac joints are a common finding, present on ~15% (range 13-17.5%) of CT studies, and may be unilateral or bilateral. They are an articulation between the medial aspect of the posterior superior iliac spine and the sacrum just lateral to the second dorsal sacral foramen. They may...
The accessory semimembranosus muscle is a rare accessory muscle of the posterior compartment of the thigh. It arises from the distal aspect of the semimembranosus muscle belly and courses through the popliteal fossa between it and the semitendinosus muscle medially and the biceps femoris lateral...
The accessory soleus muscle is an anatomical variant characterized by an additional distinct muscle encountered along a normal soleus muscle. It is uncommon with a prevalence of ~3% (range 0.7-5.5%).
origin: fibula, soleal line of the tibia, or the anterior surface of the soleus muscle...
An accessory superior acetabular notch is a normal variant of the acetabulum, which can be seen on radiographs. It may lead to diagnostic confusion, especially in younger patients.
appear as bilateral symmetric fluid-filled pits in the roof of the acetabulum with sh...
The parietal and occipital bones in particular are common regions for accessory sutures because of their multiple ossification centers.
It is important to know these anatomic variations, mainly on the head trauma image studies in children, where it could be difficult to differentiate non-depres...
The accordion sign (also known as concertina sign) is seen on CT examinations of the abdomen and refers to the similarity between the thickened edematous wall of pseudomembranous colitis and the folds of an accordion. This appearance is the result of hyperaemic enhancing mucosa stretched over ma...
Ace-of-spades sign refers to the pathognomonic configuration of the left ventricle as seen in apical hypertrophic cardiomyopathy 1-3.
It consists of marked ventricular wall thickening at the apex resulting in cavity narrowing at the apex with a relatively normal appearance of the mid-ventricula...
The acetabular angle is a radiographic measurement used when evaluating potential developmental dysplasia of the hip (DDH). It is most useful in patients who have started to ossify the epiphysis since ossification diminishes the usefulness of ultrasound.
The angle is formed by a horizontal lin...
The acetabular foramen is formed by the bony margins of the acetabular notch and completed by the transverse ligament of the hip. From its margins (both transverse ligament and acetabular notch) arises the ligamentum teres. Through it pass nutrient vessels to the femoral head epiphysis.
Acetabular fractures are a pelvic fracture, which may also involve the ilium, ischium, and/or pubis depending on fracture configuration.
Acetabular fractures are uncommon. The reported incidence is approximately 3 per 100,000 per year. This study reported a 63% to 37% male to fema...
Acetabular labral tears, as the name implies, are tears involving the acetabular labrum of the hip.
With the increasing use of hip arthroscopy in orthopedic surgery since the 1970s pathologies of the acetabular labrum as a possible cause of chronic hip and groin pain have become more familiar...
Acetabular labrum acts to deepen the acetabulum and increase contact between the pelvis and the femoral head. Its exact biomechanical role remains to be fully elucidated.
The acetabular labrum is a C-shaped fibrocartilaginous structure with an opening anteroinferiorly at the site...
The acetablar notch is a depression in the margin of the acetabulum located anteroinferiorly. It is bridged by the transverse ligament, and thus forms the acteabular foramen. The ligamentum teres has part of its origin from the acetabular notch.
The acetabulum (plural: acetabula) is the large cup-shaped cavity on the anterolateral aspect of the pelvis that articulates with the femoral head to form the hip joint.
All three bones of the pelvis (the ilium, ischium, and pubis) together form the acetabulum. The three bones ar...
Achalasia (primary achalasia) is a failure of organised esophageal peristalsis causing impaired relaxation of the lower esophageal sphincter, and resulting in food stasis and often marked dilatation of the esophagus.
Obstruction of the distal esophagus from other non-functional etiologies, not...
Acheiria refers to absence of one or both hands and can occur in a number of situations, including:
amniotic band syndrome: particularly if unilateral
Cornelia de Lange syndrome 1
fetal hydantoin syndrome 2
Rare defect occurring in 1:65 000 live births.
Achievements are a recent feature of your public profile. They are a way of showcasing to the world some of the ways you have contributed to Radiopaedia.
There are 6 achievements currently, two of them representing 'current status' and representing the current level of a specific...
Achilles tendinopathy refers to a combination of pathological changes affecting the Achilles tendon usually due to overuse and excessive chronic stress upon the tendon. It can be seen both in athletes and non-athletes (weekend warriors). It is hard to differentiate clinically from a paratendinop...
Achilles tendon ossification is an uncommon condition that consists of characteristic bone formation within the substance of the Achilles tendon.
Achilles tendon ossification is more common in males 4.
The etiology is unknown but Achilles tendon ossification is seen ...
Achilles tendon tears are the most common ankle tendon injuries, and are most commonly seen secondary to sports-related injury, especially squash and basketball.
There is strong male over-representation presumably as a result of the predominantly sport related etiology. Patients a...
Achilles tendon thickening can occur for a number of reasons.
The Achilles tendon has an average AP diameter of 6 mm 1. Thickening of the tendon is when it exceeds 8 mm in AP diameter and can result from:
Achilles tendon xanthomas are painless soft tissue masses occurring most commonly at the distal one-third of the tendon and are usually bilateral and symmetrical.
It is characterized by localised accumulation of lipid-laden macrophages, inflammatory cells and giant cells secondary to...
Achondrogenesis refers to a group of rare and extreme skeletal dysplasias.
The estimated incidence is 1:40,000 with no recognised gender predilection.
It is classified as an osteochondrodysplasia, meaning deficiency of both bone and cartilage development.
Achondrogenesis type Ia, also known as the Houston-Harris subtype, is a subtype of achondrogenesis. It is an extremely rare lethal skeletal dysplasia (chondrodysplasia) with a characteristic severe disarrangement of endochondral ossification.
Some of the common clinical f...
Achondrogenesis type Ib, also known as Parenti-Fraccaro subtype, is a subtype of achondrogenesis and is an extremely rare skeletal dysplasia (chondrodysplasia).
Undersulphation has a pronounced effect on the composition of the extracellular matrix of cartilage, and this has been sh...
Achondroplasia is a congenital genetic disorder resulting in rhizomelic dwarfism and is the most common skeletal dysplasia. It has numerous distinctive radiographic features.
It occurs due to sporadic mutations in the majority of cases but can be inherited as an autosomal dominan...
Achondroplasia is the most common cause of short-limb dwarfism. (For a general discussion, see the generic article on achondroplasia.)
As the skull base forms by endochondral ossification whereas the skull vault by membranous ossification, there is a marked discrepancy in relative size as the s...
Acinar-predominant adenocarcinoma of the lung is a histological subtype of non-mucinous invasive adenocarcinoma of the lung.
In 2011, the International Association for the Study of Lung Cancer (IASLC), American Thoracic Society (ATS), and European Respiratory Society (ERS) 4 introd...
Acinic cell carcinoma of the lung (also known as a Fechner tumor) is a type of lung carcinoma of the salivary gland type. It is extremely rare, especially when it presents in the form of primary acinic cell carcinoma.
Histologically, they are comprised of clear cells with abundant gr...
Acinic cell carcinomas of the salivary glands are rare malignant neoplasms that account for 1-3% of all salivary gland tumors.
Pathology may superficially resemble normal serous (acinar) cells of the salivary glands. It is considered a low-grade, indolent malignancy, but with a tend...
Acoustic enhancement, also called posterior enhancement or enhanced through transmission, refers to the increased echoes deep to structures that transmit sound exceptionally well.
This is characteristic of fluid filled structures such as cysts, the urinary bladder and the gallbladder. The fluid...
Acoustic impedance (Z) is a physical property of tissue. It describes how much resistance an ultrasound beam encounters as it passes through a tissue.
Acoustic impedance depends on:
the density of the tissue (d, in kg/m3)
the speed of the sound wave (c, in m/s)
and they are related by:
Z = ...
Acoustic neuromas, also known as vestibular schwannomas, are relatively common tumors that arise from the vestibulocochlear nerve (CN VIII) and represent ~80% of cerebellopontine angle masses. Bilateral acoustic schwannomas are strongly suggestive of neurofibromatosis type 2 (NF2).
On imaging, ...
Acoustic shadowing on an ultrasound image is characterized by a signal void behind structures that strongly absorb or reflect ultrasonic waves. This happens most frequently with solid structures, as sound conducts most rapidly in areas where molecules are closely packed, such as in bone or stone...
There are many acquired aortic conditions. These include
aortic rupture / transection
ascending aortic aneurysm
thoracic aortic injury
abdominal aortic aneurysm
inflammatory abdominal aortic aneurysm
Acquired cholesteatomas make up 98% of all middle ear cholesteatomas and are almost always closely related to the tympanic membrane, from which most are thought to arise.
The vast majority of acquired cholesteatomas develop as a result of chronic middle ear infection and...
Acquired cystic kidney disease (ACKD) is a condition that occurs in patients with end-stage renal disease (ESRD), especially when on dialysis treatment. They do not have a history of other cystic renal disease.
Its incidence increases with the amount of time a patient is azotemic...
Acquired hepatocerebral degeneration is an uncommon irreversible extrapyramidal neurodegenerative condition encountered in patients with cirrhotic chronic liver disease, resulting in widespread cerebral, basal ganglia and cerebellar damage.
Acquired hepatocerebral degeneration is ...
Acquired tonsillar ectopia is usually thought of as a subgroup of cerebellar tonsillar ectopia in which downward displacement of the cerebellar tonsils is secondary to another well defined and distinct pathological process. This is to distinguish it from Chiari I malformations and low-lying tons...
An acquired tracheo-esophageal fistula refers to a pathological communication between the trachea and esophagus due to a secondary cause
Acquired causes of tracheo-oesophagal fistulae can be divided into those that are related to malignancy (common) and those from other causes (unco...
The time of acquisition for a conventional spin echo or gradient echo sequence is the product of the repetition time, phase encoding steps, and number of averages (TR x phase steps x NEX). For example, with a one second TR, 128 phase steps, and two averages we would get an acquisition time of ab...
Acrania is a rare lethal congenital anomaly characterized by an absence of the calvaria.
The estimated incidence is at ~1:1000 pregnancies 4.
The condition is thought to result from abnormal migration of mesenchymal tissue, which normally covers the cerebral hemisphe...
Acrania anencephaly sequence is the progression from a relatively normal-appearing exposed brain due to an absent cranium (acrania) to an amorphous brain mass (exencephaly) to no recognisable brain tissue (anencephaly) 1.
The acrania anencephaly sequence begins with acrania, which...
Acrocephalopolysyndactyly (ACPS) syndrome is comprised of a rare group of disorders collectively characterized by:
calvarial anomalies: e.g. craniosynostoses
digital anomalies: syndactyly and polydactyly
While there can be some overlap in features, they can be primarily classified into the fo...
Acrocephalosyndactyly syndromes (ACS) is a rare group of disorders collectively characterized by:
calvarial anomalies, e.g. craniosynostoses
digital anomalies, e.g. syndactyly
While there can be some overlap in features, they can be primarily classified into the following majo...
Acrodysostosis is a rare skeletal dysplasia characterized by growth retardation, nasal hypoplasia, brachydactyly, midfacial deficiency, mental retardation and deafness.
Most cases are sporadic. Few cases with autosomal dominant transmission have been reported. It is believed to occur...
Acromegaly is the result of excessive growth hormone production in skeletally mature patients, most commonly from a pituitary adenoma. The same excess of growth hormone in individuals whose epiphyses have not fused will result in gigantism (excessively tall stature).
Acromial apohysiolysis is a finding on shoulder MRI that may be encountered in patients with an unfused acromial apophysis. It is associated with athletes in throwing sports.
Presents with superior shoulder tenderness in a patient <25 years old, often in a young throwing ...
The shape of the acromion had been initially divided into three types (which was known as the Bigliani classification) 3, to which a fourth has been added 2. They are used as a standardized way of describing the acromion, as well as predicting to a degree the incidence of impingement.
Acromioclavicular joint injuries are common and range from a mild sprain to complete disruption of the acromioclavicular joint (ACJ) and injury to surrounding structures.
Acromioclavicular joint injuries usually occur from a direct blow or following a fall onto the shoul...
The acromioclavicular (AC) joint is a plane synovial joint of the pectoral girdle.
The acromioclavicular joint is between the small facets of the convex distal clavicle and flat medial acromion. The articular surfaces are lined with hyaline cartilage 4. A fibrocartilaginous wedge...
The acromioclavicular AP view is single projection assessing the patency of the acromioclavicular joint.
See also, acromioclavicular joint injuries.
patient is erect
midcoronal plane of the patient is parallel to the image receptor, in other words, the patient's back is agai...
The acromioclavicular AP weight-bearing view is and additional interjection often performed to rule out displacement when it is suspected yet not confirmed on the AP view
See also, acromioclavicular joint injuries.
the patient is erect holding a weight in the affected sides h...
There is much variation in acromioclavicular joint configuration, which may be confused with pathology. The relationship of the acromion to the distal clavicle at the AC joint can be described in the coronal plane as 1-3:
low-lying: associated with shoulder impingement (unfo...
The acromioclavicular (AC) joint radiographic series is a used to evaluate the acromioclavicular joint and the distal clavicle.
AC radiographs are performed for a variety of indications including:
direct blows to the should region
following a fall onto adducted ...
Acromiohumeral interval is a useful and reliable measurement on AP shoulder radiographs and when narrowed is indicative of rotator cuff tear or tendinopathy.
Measurements of the acromiohumeral interval in the following intervals are suggestive of pathology 1,2:
>12 mm: shoulder dis...
The acromion, also known as the acromial process, is a small section of the scapula that extends anteriorly from the spine of the scapula.
It forms the acromioclavicular joint with the lateral third of the clavicle, and also connects with the coracoid process via the coraco-acro...
Acro-osteolysis refers to resorption of the distal phalanx. The terminal tuft is most commonly affected but the shaft of the distal phalanx can also be affected in a few conditions. It is associated with a heterogeneous group of pathological entities and, some of which can be remembered by using...
The causes of acro-osteolysis can be remembered using the mnemonic:
I: injury, e.g. thermal burn, frost bite
N: neuropathy, e.g. diabetes, leprosy
C: collagen vascular disease, e.g. scleroderma, Raynaud disease
Acroparesthesia refers to tingling, pins-and-needles, burning or numbness or stiffness in the hands and feet, particularly the fingers and toes 1. Occasionally episodic pain is also present, which can be very severe 1.
Is one of the more common manifestations of Fabry disease (more common than...
ACR TI-RADS is a reporting system for thyroid nodules on ultrasound proposed by the American College of Radiology (ACR) 1.
This uses a standardized scoring system for reports providing users with recommendations for when to use fine needle aspiration (FNA) or ultrasound follow-up of suspicious ...