Abdominal herniations may be congenital or acquired and come with varying eponyms. They are distinguished primarily based on location and content. 75-80% of all hernias occur in the inguinal region.
Content of the hernia is variable, and may include:
small bowel loops
mobile colon segments (s...
An opacity projecting over the abdomen has a broad differential. Possibilities to consider include:
ingested, e.g. coins, batteries, bones, etc.
artifacts, e.g. object attached to the cloth of the patient like a safety pin or button
iatrogenic, e.g. haemostatic clips, gastric ...
Abdominoschisis refers to a split or in the abdominal wall. Some authors use the term synonymously with a gastroschisis. When the defect continues into the thoracic region it is termed a thoraco-abdominoschisis. A large abdominoschisis is considered part of the limb body wall complex 2.
Abnormal bowel wall attenuation patterns on CT scan can be grouped under five categories:
water halo sign
fat halo sign
The first three patterns are seen on contrast studies.
It is defined as uniform enhancement of th...
Abnormally thickened endometrium on imaging may occur for a number of reasons which may be categorised based on whether or not they are related to pregnancy. Aetiologies may also be classified based on whether the patient is premenopausal or postmenopausal.
Abscesses are focal confined collections of suppurative inflammatory material and can be thought of as having three components 1:
central core comprised of necrotic inflammatory cells and local tissue
peripheral halo of viable neutrophils
surrounded by a 'capsule' with dilated blood vessels a...
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...
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:
There are many acquired aortic conditions. These include
aortic rupture / transection
ascending aortic aneurysm
thoracic aortic injury
abdominal aortic aneurysm
inflammatory abdominal aortic aneurysm
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...
Acute airspace opacification with lymphadenopathy is a subset of the differential diagnosis for generalised airspace opacification and includes:
post-obstructive causes (usually chronic, but 'new' changes can occur)
primary lung cancer
Acute aortic syndrome (AAS) describes the presentation of patients with one of a number of life threatening aortic pathologies that give rise to aortic symptoms.
The spectrum of these aortic emergencies include:
aortic intramural haematoma
penetrating atherosclerotic ulcer
Acute occlusion of the basilar artery may cause brainstem or thalamic ischaemia or infarction. It is a true neuro-interventional emergency and, if not treated early, brainstem infarction results in rapid deterioration in the level of consciousness and ultimately death.
Acute bilateral airspace opacification is a subset of the larger differential diagnosis for airspace opacification. An exhaustive list of all possible causes of acute bilateral airspace opacities is long, but a useful way to consider the huge list is via the material within the airways:
Acute gastritis is a broad term for myriad causes of gastric mucosal inflammation.
Depends on the aetiology (see below).
nausea and vomiting
loss of appetite
infection: H. pylori (most com...
Acute hepatitis occurs when the liver suffers an injury with a resulting inflammatory reaction. The cause of the injury can occur in multiple different ways, and imaging findings are often non-specific. Ultrasound and MRI may be useful imaging modalities to suggest the diagnosis, but often the d...
Acute sinusitis is an acute inflammation of the nasal and paranasal sinus mucosa that last less than four weeks and can occur in any of the paranasal sinuses.
Fever, headache, postnasal discharge of thick sputum, nasal congestion and abnormal smell.
Acute unilateral airspace opacification is a subset of the differential diagnosis for airspace opacification.
The exhaustive list of all possible causes would be huge, but a useful framework includes :
pus, i.e. infection
Differentiating between acute and chronic infarction on a CT brain is an important skill for many health professionals particularly in the emergency setting:
acute: cytotoxic oedema
chronic: encephalomalacia; Wallerian degeneration
acute: more dense than CSF
Adenosis of the breast is a benign lobulocentric proliferative process in which lobules are enlarged and increased in number in addition to an increased number of glands within each lobule.
Pathologically subclassified into three main subtypes which include:
sclerosing adenosis of the breast
Adrenal calcification is not a rare finding in healthy asymptomatic people and is usually the result of previous haemorrhage, or tuberculosis. Addison's disease patients only occasionally have calcification.
sepsis: Waterhouse-Friderichsen syndrome
Adrenal haemorrhage can result from a variety of traumatic and non-traumatic causes. When unilateral, it is often clinically silent. In contrast, bilateral adrenal haemorrhage can lead to catastrophic adrenal insufficiency.
The large majority of patients with unilateral a...
Adrenal lesions cover a broad spectrum from benign to neoplastic entities. Due to increased use of cross sectional imaging they are frequently detected as incidental lesions.
Radiology plays a significant role in differentiation. Cross sectional imaging is the mainstay of imaging for identifyin...
Cervical lymphadenopathy in an adult can result from a vast number of conditions. They include:
from head and neck tumours
other neoplastic lesions
Adult cystic renal disease comprises multiple distinct hereditary and non-hereditary disease processes.
adult polycystic kidney disease (APCKD), a.k.a. autosomal dominant polycystic kidney disease (ADPCKD)
medullary cystic kidney disease
von Hippel-Lindau di...
Human alpha fetoprotein (AFP) elevation may occur in a vast number of conditions:
liver tumours (hepatocellular carcinoma, hepatoblastoma)
<10 ng/ml is within normal limits
>20 ng/ml is above normal limits but has low specificity for tumor since it may occur in a setting of diffuse liver inju...
AIDS defining illnesses are conditions that in the setting of a HIV infection confirm the diagnosis of AIDS, and do not commonly occur in immunocompetent individuals 2. According to the CDC surveillance case definition 1, they are:
bacterial infections: multiple or recurrent
An air crescent sign describes the crescent of air that can be seen in invasive aspergillosis, semi-invasive aspergillosis or other processes that cause pulmonary necrosis. It usually heralds recovery and is the result of increased granulocyte activity.
In angioinvasive fungal infection, the no...
Air space opacification is a descriptive term that refers to filling of the pulmonary tree with material that attenuates x-rays more than the surrounding lung parenchyma. It is one of the many patterns of lung opacification and is equivalent to the pathological diagnosis of pulmonary consolidat...
The differential for air space opacities is extensive, and needs to be interpreted in context of chronicity (previous imaging) and clinical context. It is therefore useful to divide airspace opacities as follows:
acute airspace opacities with lymph node enlargement
acute airspace opacities: un...
Airway foreign bodies in children are potentially fatal and proper recognition is important because delayed diagnosis is common.
Children under the age of four years are at increased risk of foreign body (FB) aspiration with a slight male predominance 1.
Mammographic screening detects early breast cancers and thereby reduces potential mortality. However, its sensitivity is inversely related to breast density 1.
Altered density between two mammograms can arise in a number of situations:
Affecting both breasts:
interval commencement/cessation ...
Alternating radiolucent and radiodense metaphyseal lines can be seen with a number of conditions and the differential diagnosis is wide:
growth arrest lines
rickets: especially those on prolonged treatment, e.g. vitamin D dependent rickets
Amaurosis fugax is the transient mono-ocular loss of vision, normally lasting a few seconds to a few minutes, and is secondary to vascular ischaemia/insufficiency. Usually the cause is ascribed to occlusion of the central retinal artery there are a wide number of local and central causes.
Amorphous or indistinct calcifications are a morphological descriptive term for breast calcification and are defined as having small, hazy, faint calcifications with no clearly defined shape or form.
80-200 micrometer in diameter
small, hazy calcification
The term ampullary tumour generally refers to either benign or malignant neoplasms that arise from the glandular epithelium of the ampulla of Vater, including 1:
ampullary adenoma (adenoma of ampulla of Vater)
ampullary carcinoma (carcinoma of ampulla of Vater)
According to some authors, ampu...
The term amputation refers to the disconnection of all or part of a limb from the body. Specifically amputation it is defined as removal of the structure through a bone. This is in contrast to disarticulation, which is removal of the structure through a joint.
When due to trauma, t...
Angiosarcoma of bone is a malignant vascular tumour of bone. These are rare and account for less than 1% of malignant bone tumours. The majority of these tumours arising in bone are primary; however, a tiny percentage is either radiation-induced or associated with bone infarction
Ankle tear drop sign is one of the radiological signs of an ankle joint effusion. It represents the presence of fluid in the inferior part of anterior compartment of ankle.
Anoxic brain injury, also known as global hypoxic-ischaemic injury, is seen in all age groups (from antenatal to the elderly) as a result of numerous aetiologies. The pattern of injury depends on a number of factors including:
age of the patient (brain maturity)
neonatal hypoxic-ischaemic ence...
Antenatal screening of Down syndrome (and other less common aneuploidies) should be available as a routine component of antenatal care. It allows families to either adjust to the idea of having a child with the condition, or to consider termination of pregnancy.
For a general description of Dow...
Causes of anterior hip pain include:
pigmented villonodular synovitis (PVNS)
inflammatory arthropathy (e.g. rheumatoid arthritis)
Anterior inferior cerebellar artery (AICA) territory infarcts are much less common than posterior inferior cerebellar artery (PICA) infarcts.
AICA territory infarcts are rare, comprising ~1% of ischaemic cerebellar strokes 2.
AICA stroke syndrome presents ...
Anterior knee pain is common with a variety of causes including:
inflammatory and depositional arthritis
bursitis around the knee
excessive lateral pressure syndrome (ELPS)
patellar cartilage defect
Anterior superior iliac spine (ASIS) avulsion injuries typically occur in athletes during forceful muscular contraction. ASIS is the site of attachment for sartorius and tensor fascia latae muscles.
ASIS avulsion, like other pelvic avulsion injuries, is a stable fracture.
Anterior vertebral body beaking occurs in a number of conditions and may eminate from the central portion or the lower third of the vertebral body.
Morquio syndrome 1 (middle for Morquio)
Hurler syndrome 2
An aortic nipple is seen in about 10% of PA chest x-rays on the lateral surface of the aortic arch/aortic knob. It represents the left superior intercostal vein.
When prominent, superior vena cava obstruction should be considered (the left superior intercostal vein might be a collateral pathway).
The aortopulmonary (aortic-pulmonary or AP) window is a radiological mediastinal space seen on frontal chest x-rays.
The term "aortopulmonary window" can also refer to a rare form of congenital heart disease, where there is an opening between the aorta and the pulmonary trunk 4. It...
Aphthous ulcers are deep mucosal ulcers of the gastrointestinal mucosa.
infective inflammatory conditions
noninfective inflammatory conditions
idiopathic granulomatous gastritis
Apical pleural cap refers to a curved density at the lung apex seen on chest radiograph.
The frequency of apical pleural thickening increases with age 3.
It arises from a number of causes:
idiopathic: often a chronic ischaemic aetiology is...
Architectural distortion is a mammographic descriptive term in breast imaging. It may be visualised as tethering or indentation of breast tissue.
Architectural distortion per se is not a mass. It is often due to a desmoplastic reaction in which there is focal disruption of the norma...
Areae gastricae are a normal finding on double contrast images of the stomach.
fine reticular network of barium-coated grooves between 1-5 mm islands/areas of gastric mucosa
may be seen in ~70-80% of patients if there is adequate high-density barium coating of the stomac...
Arteriovenous malformations (AVMs) are characterised by an abnormal leash of vessels allowing for arteriovenous shunting. They can occur anywhere in the body but have a predilection towards the head and neck. There is a direct arteriovenous communication with no intervening capillary bed. They ...
Artery of Percheron territory infarct is rare, on account of the relative rarity of the artery of Percheron, and presents with a variety of signs and symptoms collectively termed the paramedian thalamic syndrome. It is a type of posterior circulation infarction.
On imaging, it is classically ch...
Arthrogryposis (multiplex congenita) is a clinical or imaging descriptor that denotes congenital non-progressive joint contractures involving two or more body regions.
It is thought to occur in approximately 1:3000-10,000 live births 6,8.
It can result from a number o...
Asbestos related disease, in particular affecting the lung, comprise of a broad spectrum of entities related to the inhalational exposure to asbestos fibres. They can be divided into benign and malignant changes 1-3.
Benign pleural and parenchymal lung disease
asbestos related benign pleural d...
Dilatation of the ascending aorta is a common finding in the elderly but unusual in younger patients.
In adults, an ascending aortic diameter greater than 4 cm is considered to indicate dilatation 4. Aneurysmal dilatation is considered when the ascending aortic diameter reaches or ex...
Aseptic loosening is considered relatively common complication of hip joint replacements. It is usually considered a long-term complication and is often considered as the most common complication 3.
Aseptic loosening can occur as a result of inadequate initial fixation, mechanical lo...
Aspiration pneumonia is caused by a direct chemical insult due to the entry of a foreign substance, solid or liquid, into the respiratory tract.
Aspiration may be clinically silent, or it may present with dyspnoea, cough or fever. The clinical and radiographic features de...
Asplenia syndrome (also known as right isomerism or Ivemark syndrome) is a type of heterotaxy syndrome.
There is an increased male predilection. Asplenia syndrome is usually diagnosed in neonates.4
In contrast to polysplenia syndrome, most patients die bef...
Asymmetrical mammographic density is a mammographic morphological descriptor. It is given when there is increased density in one of the breasts, on either one or both standard mammographic views but without evidence of a discrete mass. An asymmetrical density can be further characterised as:
Asymmetry in breast size can arise from a number of factors.
Breasts are rarely absolutely the same size or volume. Normal variation is common. Most females have slight discrepancies in breast size. Asymmetric progressive breast enlargement is unusual but known. The role of the breas...
Athletic pubalgia refers to pain around the pubic symphysis and can have different causes, including what has become known as sports hernia or sportman's hernia and osteitis pubis.
Athletic pubalgia is a clinical syndrome of chronic lower pelvic and groin pain, usually encountered in athletes. ...
The atlantodental interval (ADI), as the name suggests, is the horizontal distance between the anterior arch of the atlas and the dens of the axis, used in the diagnosis of atlanto-occipital dissociation injuries and injuries of the atlas and axis.
It is the distance (in mm) between the posteri...
Atresia refers to a situation where there is underdevelopment of a structure with very rudimentary remnant tissues. This contrasts with an agenesis meaning there is no development of the structure as all. The term atresia is often used with hollow structures such as a bronchus or intestine.
Autoimmune thyroiditises (AIT) refers to a group of conditions where there is inflammation involving the thyroid gland related to thyroid antibodies.
They are most common thyroid disease group in the paediatric population 5.
Entities that fall under this category inclu...
Avulsion fractures of the knee are numerous due to the many ligaments and tendons inserting around this joint. They include 1:
anterior cruciate ligament avulsion fracture
posterior cruciate ligament avulsion fracture
avulsion of the medial collateral ligament
origin of MCL avulsion fracture...
Avulsion injuries, where a portion of cortical bone is ripped from the rest of the bone by the attached tendon, are common among those who participate in sports, and there are numerous sites at which these occur. Being familiar with them is important as chronic injuries can appear aggressive.
Barium peritonitis is a rare complication of gastrointestinal fluoroscopy, and occurs when there is gastrointestinal tract perforation and spillage of barium into the peritoneal cavity.
Barium in the peritoneal cavity is treated as a foreign body with resultant immune response that ...
Bartholin gland tumours include:
squamous cell carcinoma of the Bartholin gland: tends to be the most common histological subtype
adenocarcinoma of the Bartholin gland
adenoid cystic carcinoma of the Bartholin gland
Barton fractures are fractures of the distal radius. It is also sometimes termed the dorsal type Barton fracture to distinguish it from the volar type or reverse Barton fracture.
Barton fractures extend through the dorsal aspect to the articular surface but not to the volar aspect. Therefore, i...
Basal ganglia calcification is common and is seen in approximately 1% of all CT scans of the brain, depending on the demographics of the scanned population. It is seen more frequently in older patients and is considered a normal incidental and idiopathic finding in an elderly patient but should ...
There are many causes of basal ganglia T1 hyperintensity, but the majority relate to deposition of T1-intense elements within the basal ganglia such as:
calcium and phosphate abnormalities
acquired non-wilsonian hepatocerebral degeneration
The causes of basal ganglia T2 hyperintensity can be remembered using the mnemonic LINT:
venous infarction (internal cerebral vein thrombosis)
neurodegenerative / metabolic
Huntington disease: especially caudate heads
Basal ganglia T2 hypointensities can be caused by any of the following and is commonly remembered using the mnemonic ChOMP.
Parkinson disease: more in globus pallidus
Parkinson-plus syndrome: more in putamen
deoxyhemoglobin of hemorrhage
Basilar invagination, also called basilar impression, is a congenital or acquired craniocervical junction abnormality where the tip of the odontoid process projects above the foramen magnum.
The terms basilar invagination and basilar impression are often used interchangeably becau...
The basion-axial interval (BAI), as the name suggests, is the horizontal distance between the basion and the posterior cortex of the axis, used in the diagnosis of atlanto-occipital dissociation injuries.
It is the distance (in mm) between the basion and the superior extension of the posterior ...
The basion-dens interval (BDI), as the name suggests, is the distance between the basion and the tip of the dens, used in the diagnosis of atlanto-occipital dissociation injuries.
It is the distance from the most inferior portion of the basion to the closest point of the superior aspect of the ...
Bat's wing or butterfly pulmonary opacities refer to a pattern of bilateral perihilar shadowing. It is classically described on a frontal chest radiograph but can also refer to appearances on chest CT 3-4.
Bat's wing pulmonary opacities can be caused by:
Benign and malignant characteristics of breast lesions at ultrasound allow the classification as either malignant, intermediate or benign based on work published by Stavros et al in 1995.
Malignant characteristics (with positive predictive values)
Paediatric benign liver tumours are a relatively rare, but important group of conditions. Importantly, the commonest cause of a benign liver tumour is specific to the paediatric population. The list in descending order of frequency is:
mesenchymal hamartoma of t...
Benign lytic bone lesions encompass a wide variety of entities. A useful starting point is the FEGNOMASHIC mnemonic.
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There are a number of benign metastasising tumours:
benign metastasising meningioma 1,2
benign metastasising leiomyoma 3
primary adenoma of thyroid 4
giant cell tumour of bone 5
Benign minor salivary gland pathology is a broad term that encompasses a number of relatively uncommon pathologies that affect the minor salivary glands of the head and neck:
salivary retention cysts
Benign oesophageal lesions are less symptomatic than malignant oesophageal lesions, making up for only 1% of clinically apparent oesophageal lesions.
oesophageal leiomyoma (>50%)
oesophageal fibrovascular polyp (~12.5%)
may contain fat
oesophageal duplication cyst (10...
The gallbladder and extrahepatic bile ducts play host to a surprisingly large number of benign tumours and tumour-like lesions which may be visible on imaging. In the gallbladder most of them are detected incidentally, whereas in the bile ducts they are usually found in symptomatic patients (obs...
Bent bone dysplasias are a class of dysplasia included in a 2010 classification of genetic skeletal disorders 1.
kyphomelic dysplasias, a diverse class, including
congenital bowing of the long bones
cartilage-hair hypoplasia (CHH; metaphyseal d...
Bentall procedure is performed for the repair of ascending aortic root lesions. Typically the native aortic root and aortic valve are replaced with a composite graft that comprises of both ascending aortic and aortic valve grafts, into which the coronary arteries are anastomosed.
History and et...
Beta-hCG is a hormone found in the mother's blood serum that can be used to help interpret ultrasound findings.
Beta-hCG levels may be used in three ways:
qualitatively, for presence/absence of fetal tissue
more often determined with a urine test than with a serum test
includes or excludes a...
The bicaudate index is the ratio of width of two lateral ventricles at the level of the head of the caudate nucleus to distance between outer tables of skull at the same level. It can be a useful marker of ventricular volume and in the diagnosis of hydrocephalus.
The differential for bilaterally enlarged adrenal glands is relatively limited:
micronodular adrenal hyperplasia
macronodular adrenal hyperplasia
adrenocorticotropin (ACTH)-independent macronodular adrenocortical hyperplasia (AIMAH) 2
Bilateral megalencephaly refers to megalencephaly affecting both cerebral hemispheres.
neurofibromatosis type 1 (NF1)
tuberous sclerosis (TS)
Involvement of both middle cerebellar peduncles is uncommon, but has a relatively long differential, including 1:
multiple systemic atrophy (MSA)